BARRIER LAYERS COMPRISING NANOCELLULOSE ONTO THE SURFACE OF PAPER OR PAPERBOARD SUBSTRATES AT THE WET END OF A PAPERMAKING PROCESS

Abstract

Methods of sequentially applying nanocellulose(s) onto the surface of paper and paperboard substrates, paper or paperboard prepared using said methods, and systems for producing paper or paperboard having sequentially applied nanocellulose(s).

Claims

1. A method of applying a nanocellulose-containing composition onto a surface of a paper or paperboard substrate, the method comprising: applying a first layer of a first nanocellulose-containing composition to a first surface of a consolidating base sheet of paper or paperboard comprising cellulose fibres after the consolidating base sheet leaves a headbox of a paper machine, thereby forming a consolidating substrate comprising a first layer of nanocellulose on the first surface of the paper or paperboard; wherein the first nanocellulose-containing composition comprises nanocellulose in a range of about 0.2 wt % to about 6 wt %, preferably about 0.5 to about 3 wt. %, based on the total weight of the first nanocellulose-containing composition; wherein the nanocellulose has a d.sub.50 (by Malvern) of about 50 to about 400 m, a Lc(l) of about 0.1-1 mm, a Lc(w) of about 0.1 to about 1.5 mm by fibre analyzer, a fibre steepness of about 20 to about 50, an FLT between 4 and 17 N m g.sup.1; and a Fines B content by fibre analyzer between about 1% and about 80% as a percentage of total measured particle length by fibre analyzer.

2. The method according to claim 1, further comprising applying a second layer of a second nanocellulose-containing composition to the first layer of nanocellulose of the consolidating substrate thereby forming a three layer paper or paperboard; wherein the first nanocellulose-containing composition comprises nanocellulose in a range of about 0.2 wt % to about 6 wt %, preferably about 0.5 to about 3 wt. %, based on the total weight of the first nanocellulose-containing composition; wherein the nanocellulose of the second nanocellulose-containing has a d.sub.50 (by Malvern) of about 50 to about 400 m, a Lc(l) of about 0.1-1 mm, a Lc(w) of about 0.1 to about 1.5 mm by fibre analyzer, a fibre steepness of about 20 to about 50, an FLT between 4 and 17 N m g.sup.1; and a Fines B content by fibre analyzer between about 1% and about 80% as a percentage of total measured particle length by fibre analyzer; and wherein the first nanocellulose-containing composition has a first particle size distribution, and the second nanocellulose-containing composition has a second particle size distribution, and the mean size, of the first particle size distribution, is greater than the mean size of the second particle size distribution.

3-7. (canceled)

8. The method according to any one of claim 1, wherein the first nanocellulose-containing composition comprises one or more of: one or more inorganic particulate material; one or more starches; one or more sizing agents; one or more polyacrylamides; and one or more copolymers.

9-20. (canceled)

21. The method according to claim 1, wherein the layer of the first nanocellulose-containing composition is applied using a slotted applicator or by spraying.

22-24. (canceled)

25. The method according to claim 1, wherein applying the layer of the first nanocellulose-containing composition causes the consolidating substrate to have a heptane vapor transmission rate of about 0 g m.sup.2 day.sup.1 to about 2,500 g m.sup.2 day.sup.1.

26-27. (canceled)

28. The method according to claim 1, wherein the first nanocellulose-containing composition comprises at least about 0.2 wt % nanocellulose based on the total weight of the first nanocellulose-containing composition.

29. The method according to claim 1, wherein the first nanocellulose-containing composition comprises at most about 6 wt %, at most about 5.5 wt. %, at most about 5 wt. %, at most about 4.5 wt %, at most about 4 wt. %, at most about 3.5 wt. %, or at most about 3 wt. % nanocellulose based on the total weight of the first nanocellulose-containing composition.

30-32. (canceled)

33. The method according to claim 2, wherein the mean size, of the first particle size distribution of the first nanocellulose-containing composition, is from about 50 m to about 400 m as measured by Malvern.

34-36. (canceled)

37. The method according to claim 2, wherein the second nanocellulose-containing composition comprises one or more of: one or more inorganic particulate material; one or more starches; one or more sizing agents; one or more polyacrylamides; and one or more copolymers.

38-49. (canceled)

50. The method according to claim 2, wherein the layer of the second nanocellulose-containing composition is applied using a slotted applicator.

51-52. (canceled)

53. The method according to claim 2, wherein the second nanocellulose-containing composition is applied by spraying.

54. The method according to claim 2, wherein applying the second layer of the second nanocellulose-containing composition causes the consolidating substrate to have a heptane vapor transmission rate of about 0 g m.sup.2 day.sup.1 to about 2,500 g m.sup.2 day.sup.1.

55-56. (canceled)

57. The method according to claim 2, wherein the second nanocellulose-containing composition comprises at least about 0.2 wt % nanocellulose based on the total weight of the second nanocellulose-containing composition.

58. The method according to claim 2, wherein the first nanocellulose-containing composition comprises at most about 6 wt %, at most about 5.5 wt. %, at most about 5 wt. %, at most about 4.5 wt %, at most about 4 wt. %, at most about 3.5 wt. %, or at most about 3 wt. % nanocellulose based on the total weight of the second nanocellulose-containing composition.

59. (canceled)

60. The method according to claim 2, wherein: the layer of the first nanocellulose-containing composition is applied using a first slotted applicator; and the layer of the second nanocellulose-containing composition is applied using a second slotted applicator.

61-64. (canceled)

65. The method according to claim 2, wherein the first layer of the first nanocellulose-containing composition, and the second layer of the second nanocellulose containing composition, are both applied via spraying.

66. The method according to claim 2, wherein: the first layer of the first nanocellulose-containing composition is applied using a slotted applicator; and the second layer of the second nanocellulose-containing composition is applied via spraying.

67-86. (canceled)

87. The method according to claim 2, wherein the mean size, of the first particle size distribution of the first nanocellulose-containing composition and/or the second particle size distribution of the second nanocellulose-containing composition is from about 50 m to about 400 m.

88-89. (canceled)

90. The method according to claim 1, wherein the dry solids of the first nanocellulose-containing composition are about 5% to about 100% nanocellulose.

91-93. (canceled)

94. A paper or paperboard prepared using the method according to claim 1.

95-120. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0145] FIG. 1 is a top view of a paper or paperboard machine forming section equipped with a surface applicator and spray booms capable of sequentially applying a single nanocellulose-containing composition.

[0146] FIG. 2 is a top view of a paper or paperboard machine forming section equipped with spray booms capable of sequentially applying a single nanocellulose-containing composition.

[0147] FIG. 3 is a top view of a paper or paperboard machine forming section equipped with a surface applicator and spray booms capable of applying different nanocellulose-containing compositions.

[0148] FIG. 4 is a top view of a paper or paperboard machine forming section equipped with spray booms capable of applying different nanocellulose-containing compositions.

[0149] FIG. 5 is a photograph compilation of coated paper surfaces achieved with sequential spraying of a microfibrillated cellulose/ground calcium carbonate (1:1) composition applied onto an unbleached Kraft base paper.

[0150] FIG. 6 is a photograph compilation of coated paper surfaces achieved with sequential spraying of a microfibrillated cellulose/ground calcium carbonate (1:1) composition applied onto an unbleached Kraft base paper.

[0151] FIG. 7 is a plot illustrating the Gurley porosity of microfibrillated cellulose coated sheets.

[0152] FIG. 8 is a plot illustrating the heptane vapor transmission rate of microfibrillated cellulose coated sheets.

DETAILED DESCRIPTION

Application of Nanocellulose-Containing Composition(s)

[0153] The following is a description of different techniques for applying two or more nanocellulose-containing compositions onto the surface of a paper or paperboard substrate. It will be appreciated that the following are illustrative examples of the broader scope of the present disclosure.

[0154] FIG. 1 illustrates a paper or paperboard machine forming section equipped with a surface applicator and spray booms for sequential addition of nanocellulose-containing composition. In some embodiments, the paper or paperboard machine may be a Fourdrinier.

[0155] As illustrated, the paper or paperboard machine forming section is configured with a headbox 102 that distributes a continuous flow of stock at constant velocity, both across the width of the screen of the paper machine, as well as lengthwise.

[0156] The stock may be derived from cellulose-containing pulp, which may have been prepared by any suitable chemical or mechanical treatment, or combination thereof, which is well known in the art. The pulp may be derived from any suitable source, such as wood, grasses (e.g., sugarcane and bamboo), or rags (e.g., textile waste, cotton, hemp, or flax). The pulp may be bleached in accordance with processes that are well known to those skilled in the art. Those processes, suitable for use in the present disclosure, will be readily evident. In certain embodiments, the pulp may be unbleached. The bleached or unbleached pulp may be beaten, refined, or both, to a predetermined freeness (reported in the art as Canadian standard freeness (CSF) in cm.sup.3 or Schopper Riegler Freeness). The stock is then prepared from the bleached or unbleached and beaten pulp.

[0157] The stock may comprise or be derived from a Kraft pulp, which is naturally colored (i.e., unbleached). In certain embodiments, the stock may comprise or be derived from unbleached Kraft pulp, recycled pulp, or combinations thereof. In certain embodiments, the stock may comprise or be derived from recycled pulp.

[0158] In some embodiments, the pulp may be obtained from chemical pulp, chemithermomechanical pulp, mechanical pulp, thermomechanical pulp (including, for example, Northern Bleached Softwood Kraft pulp (NBSK), Bleached hardwood pulp, and Bleached Chemi-Thermo Mechanical Pulp (BCTMP)), recycled pulp, paper broke pulp, papermill waste stream, waste from a papermill, or combinations thereof.

[0159] The stock may contain other additives known in the art. For example, the stock may contain a non-ionic, cationic, or anionic retention aid or microparticle retention system. The stock may also or alternatively contain a sizing agent that may be, for example, a long chain alkylketene dimer (AKD), a wax emulsion or a succinic acid derivative (e.g., alkenylsuccinic anhydride (ASA)), and rosin plus alum or cationic rosin emulsions. The stock may also or alternatively contain dye and/or an optical brightening agent. The stock may also or alternatively comprise dry and/or wet strength aids such as, for example, starch or epichlorohydrin copolymer.

[0160] In some embodiments, the stock may be a thick stock, meaning it includes about 4 w % solids. It may be mixed with recirculated whitewater from the machine before pumping to the headbox. Headbox solids are machine dependent. In some embodiments, the stock of the present disclosure may be from about 0.1 wt % to about 1 wt % solids. Sizing chemicals may be in the range of about 0.05 wt % to about 0.5 wt %, with retention aids being rather lower. Starch may be up to a few wt % of the stock.

[0161] The stock is output from the headbox 102 as a consolidating base sheet 104 (an example of a paper or paperboard substrate). Upon exiting the headbox 102, the consolidating base sheet 104 is transported through a water removal stage of the paper or paperboard machine forming section. Within the water removal stage, the consolidating base sheet 104 may be transported over one or more dewatering elements 106 configured to remove water from the consolidating base sheet via suction.

[0162] A wet/dry line 108 is formed in the consolidating base sheet 104. In some embodiments, the consolidating base sheet 104 may be about 5 wt % to about 10 wt % solids at the wet/dry line 108. In some embodiments, the dewatering elements 106 may be one or more dewatering foils upstream of the wet/dry line 108 with respect to movement of the consolidating base sheet 104, and/or one or more vacuum boxes downstream of the wet/dry line 108 with respect to movement of the consolidating base sheet 104. Example dewatering foils include, but are not limited to, silicon nitride foils and sialon ceramic foils.

[0163] The paper or paperboard machine forming section may include a slotted applicator 110, a first spray boom 114a, and a second spray boom 114b all in fluidic communication with a nanocellulose-containing composition delivery system. As used herein, a slotted applicator refers to an applicator configured to provide a layer of nanocellulose-containing composition to the surface of a consolidating base sheet. Example slotted applicators include slot coaters and curtain coaters, which are each described in detailed herein below.

[0164] Each of the first spray boom 114a and the second spray boom 114b may include one or more spray nozzles 116. The first spray boom 114a and the second spray boom 114b may have the same or differing numbers of spray nozzles 116. The first spray boom 114a and the second spray boom 114b are not limited to have the number of spray nozzles 116 illustrated.

[0165] The slotted applicator 110, first spray boom 114a, and second spray boom 114b may each be in fluidic communication (via one or more delivery lines 118) with a nanocellulose-containing composition delivery system 120. For example, and as illustrated in FIG. 1, the slotted applicator 110, first spray boom 114a, and second spray boom 114b may all be in fluidic communication with the nanocellulose-containing composition delivery system 120 via a single delivery line 118. Alternatively, and as illustrated in FIG. 3, the slotted applicator 110 may be in fluidic communication with the nanocellulose-containing composition delivery system 120 via a first delivery line 118a, and the first spray boom 114a and second spray boom 114b may both be in fluidic communication with the nanocellulose-containing composition delivery system 120 via a second delivery line 118b. As a further alternative, the slotted applicator 110 may be in fluidic communication with the nanocellulose-containing composition delivery system 120 via a first delivery line 118a, the first spray boom 114a may be in fluidic communication with the nanocellulose-containing composition delivery system 120 via a second delivery line 118b, and the second spray boom 114b may be in fluidic communication with the nanocellulose-containing composition delivery system 120 via a third delivery line 118c.

[0166] In the example of FIG. 1, nanocellulose-containing composition is first applied to the consolidating base sheet 104 using the slotted applicator 110. In other words, the nanocellulose-containing composition may first be applied to the consolidating base sheet 104 using curtain coating, in the situation where the slotted applicator 110 is a curtain coater, or slot coating in the situation where the slotted applicator 110 is a slot coater.

[0167] The nanocellulose-containing composition may be applied to the top of the consolidating base sheet 104 (subsequent to the wet/dry line) via a non-pressurized or pressurized slot opening in the slotted applicator 110. The slotted applicator 110 may be a slot die coater.

[0168] The consolidating base sheet 104, having the first layer of the nanocellulose-containing composition applied thereto, may be passed over one or more dewatering elements 106 prior to at least a second layer of the nanocellulose-containing composition being applied to the top surface of the consolidating base sheet 104. The consolidating base sheet 104, having the first layer of the nanocellulose-containing composition applied thereto, may be passed over one or more dewatering elements 106 prior to a second layer of the nanocellulose-containing composition being applied to the top surface of the consolidating base sheet 104.

[0169] One skilled in the art will appreciate that while the figures illustrate certain numbers of dewatering elements 106, the present disclosure is not limited to a system having any particular number of dewatering elements 106.

[0170] In the example of FIG. 1, the first layer of the nanocellulose-containing composition may be applied via curtain or slot coating (i.e., via the slotted applicator 110), and a second layer of nanocellulose-containing composition may be applied, optionally, via spraying. In particular, the second layer of the nanocellulose-containing composition may be applied via the first spray boom 114a having one or more spray nozzles 116. The number and configuration of the spray nozzle(s) 116, of the first spray boom 114a, may be configured to apply the second layer of the nanocellulose-containing composition to the entire (or substantially the entire) width of the consolidating base sheet 104 having the first layer of the nanocellulose-containing composition already applied thereto.

[0171] The spray nozzles 116 may cause the nanocellulose-containing composition to exhibit a particular spray profile 122. In some embodiments, the spray profile 122 may be conical. In some embodiments, the spray profile 122 may be linear.

[0172] The consolidating base sheet 104, having the first and second layers of the nanocellulose-containing composition applied thereto, may be passed over one or more dewatering elements 106 (e.g., vacuum boxes) prior to at least a third layer of the nanocellulose-containing composition being applied to the top surface of the consolidating base sheet 104. The consolidating base sheet 104, having the first and second layers of the nanocellulose-containing composition applied thereto, may be passed over one or more dewatering elements 106 (e.g., vacuum boxes) prior to a third layer of the nanocellulose-containing composition being applied to the top surface of the consolidating base sheet 104.

[0173] In the example of FIG. 1, the first layer of the nanocellulose-containing composition may be applied via curtain or slot coating (i.e., via the slotted applicator 110), and second and third layers of nanocellulose-containing compositions may be applied via spraying. In particular, a third layer of the nanocellulose-containing composition may be applied via the second spray boom 114b having one or more spray nozzles 116. The number and configuration of the spray nozzle(s) 116, of the second spray boom 114b, may be configured to apply a third layer of the nanocellulose-containing composition to the entire (or substantially the entire) width of the consolidating base sheet 104 having first and second layers of the nanocellulose-containing composition already applied thereto.

[0174] One skilled in the art will appreciate that the present disclosure is not limited to the specific number of spray booms illustrated in FIG. 1. Rather, one skilled in the art will appreciate that FIG. 1 is to be interpreted as teaching application of a (single) nanocellulose-containing composition to a consolidating base sheet, where a first application of the nanocellulose-containing composition involves curtain or slot coating, and one or more subsequent applications (e.g., just a second application; a second and third application; a second, third, and fourth application, etc.) of the nanocellulose-containing composition involves spraying.

[0175] In embodiments where the paper or paperboard machine forming section includes two or more spray booms, the spray nozzles of the different booms may be aligned with respect to movement of the consolidating base sheet. Alternatively, as illustrated in FIG. 1, in embodiments where the paper or paperboard machine forming section includes two or more spray booms, the spray nozzles of one boom may be offset (along a direction of movement of the consolidating base sheet) with respect to spray nozzles of a different boom. In some instances, this offset configuration of spray nozzles may achieve a more uniform coverage of the nanocellulose-containing composition along the width of the consolidating base sheet.

[0176] After the last application of the nanocellulose-containing composition is finished, the consolidating base sheet 104 may be transported over one or more additional dewatering elements 106 (e.g., vacuum boxes) to achieve a paper or paperboard having a sufficient dryness. In the example of FIG. 1, the consolidating base sheet 104 may be transported over three additional dewatering elements 106.

[0177] Sometime after the last application of the nanocellulose-containing composition is finished, the consolidating base sheet 104 may undergo edge trimming 124 to trim the consolidating base sheet 104 to a desired width. In some embodiments, the edge trimming 124 may be water jet edge trimming.

[0178] The consolidating base sheet 104 may be transported over one or more dewatering elements 106 (e.g., vacuum boxes) after the consolidating base sheet 104 undergoes edge trimming 124. In the example of FIG. 1, the consolidating base sheet 104 may be transported over two and a half dewatering elements 106 following edge trimming 124.

[0179] Once the consolidating base sheet 104 is sufficiently dewatered, resulting in the consolidating base sheet 104 becoming paper or paperboard (corresponding to a complex of dewatered stock and two or more layers of a nanocellulose-containing composition), the paper or paperboard may undergo sheet transfer 126 to a couch roll 128.

[0180] FIG. 2 provides an alternative configuration of the paper or paperboard machine forming section. The above disclosure of FIG. 1 is applicable to FIG. 2, except for the following differences.

[0181] As noted above, FIG. 1 relates to a paper or paperboard machine forming section configured for sequential application of a nanocellulose-containing composition to a consolidating base sheet 104, where a first application of the nanocellulose-containing composition involves curtain or slot coating, and one or more subsequent applications (e.g., just a second application; a second and third application; a second, third, and fourth application, etc.) of the nanocellulose-containing composition involves spraying. In contrast, FIG. 2 illustrates a paper or paperboard machine forming section configured for sequential application of a nanocellulose-containing composition to a consolidating base sheet 104, where all applications of the nanocellulose-containing composition occur via spraying.

[0182] While FIG. 2 shows use of a first spray boom 114a, a second spray boom 114b, a third spray boom 114c, and a fourth spray boom 114d, the disclosure is not limited thereto. Rather, one skilled in the art will appreciate that FIG. 2 is to be interpreted as teaching sequential application of two or more layers of a nanocellulose-containing composition to a consolidating base sheet, where each of the two or more application layers occur via spraying.

[0183] FIG. 3 provides yet another alternative configuration of the paper or paperboard machine forming section. The above disclosure of FIG. 1 is applicable to FIG. 3, except for the following differences.

[0184] As noted above, FIG. 1 relates to a paper or paperboard machine forming section configured for sequential application of two or more layers (the first being via curtain or slot coating, and the at least second being via spraying), of a single nanocellulose-containing composition, are applied to the consolidating base sheet 104. In contrast, FIG. 3 illustrates a paper or paperboard machine forming section configured for sequential application of two or more nanocellulose-containing compositions to the consolidating base sheet 104.

[0185] As illustrated in FIG. 3, the slotted applicator 110 may be in fluidic communication with a first nanocellulose-containing composition delivery system 120a (configured to deliver a first nanocellulose-containing composition), and the first spray boom 114a and the second spray boom 114b may be in communication with a second nanocellulose-containing composition delivery system 120b (configured to deliver a second nanocellulose-containing composition). For example, the slotted applicator 110 may be in fluidic communication with the first nanocellulose-containing composition delivery system 120a via a first delivery line 118a, and the first spray boom 114a and the second spray boom 114b may both be in fluidic communication with the second nanocellulose-containing composition delivery system 120b via a second delivery line 118b. Alternatively, the first spray boom 114a may be in fluidic communication with the second nanocellulose-containing composition delivery system 120b via the second delivery line 118b, and the second spray boom 114b may be in fluidic communication with the second nanocellulose-containing composition delivery system 120b via a third delivery line 118c.

[0186] While FIG. 3 illustrates the slotted applicator 110 being in fluidic communication with the first nanocellulose-containing composition delivery system 120a, and the first spray boom 114a and the second spray boom 114b being in fluidic communication with the second nanocellulose-containing composition delivery system 120b, the present disclosure is not limited thereto. For example, at least one spray boom (e.g., at least one of the first spray boom 114a or the second spray boom 114b, or a non-illustrated spray boom) may be in fluidic communication (along with the slotted applicator 110) with the first nanocellulose-containing composition delivery system 120a via the first delivery line 118a or a different delivery line.

[0187] FIG. 4 provides yet a further configuration of the paper or paperboard machine forming section. The above disclosure of FIG. 2 is applicable to FIG. 4, except for the following differences.

[0188] As noted above, FIG. 2 relates to a paper or paperboard machine forming section configured for sequential application of a single nanocellulose-containing composition to a consolidating base sheet, where all applications of the nanocellulose-containing composition occur via spraying. In contrast, FIG. 4 illustrates a paper or paperboard machine forming section configured for sequential application of two or more nanocellulose-containing compositions to the consolidating base sheet 104.

[0189] As illustrated in FIG. 4, the first spray boom 114a and the second spray boom 114b may be in fluidic communication with the first nanocellulose-containing composition delivery system 120a, and the third spray boom 114c and the fourth spray boom 114d may be in communication with the second nanocellulose-containing composition delivery system 120b. For example, the first spray boom 114 and the second spray boom 114b may be in fluidic communication with the first nanocellulose-containing composition delivery system 120a via the first delivery line 118a, and the third spray boom 114c and the fourth spray boom 114d may both be in fluidic communication with the second nanocellulose-containing composition delivery system 120b via the second delivery line 118b. Alternatively, the first spray boom 114a and the second spray boom 114b may be in fluidic communication with the first nanocellulose-containing composition delivery system 120a via different delivery lines, and/or the third spray boom 114c and the fourth spray boom 114d may be in fluidic communication with the second nanocellulose-containing composition delivery system 120b via different delivery lines.

[0190] However, the present disclosure is not limited to the illustration of FIG. 4. Rather, one skilled in the art will appreciate that FIG. 4 is to be interpreted to cover a paper or paperboard machine forming section in which at least one spray boom is configured to apply at least one layer of a first nanocellulose-containing composition to the consolidating base sheet 104, and at least one other spray boom is configured to apply at least one layer of a second nanocellulose-containing composition to the consolidating base sheet 104.

[0191] As illustrated in FIGS. 1 and 3, a slotted applicator 110 is used to apply nanocellulose-containing composition prior to spraying. One skilled in the art will appreciate that, in some embodiments, spraying may be used to apply nanocellulose-containing composition(s) prior to curtain or slot coating using the slotted applicator 110. Moreover, in some embodiments one or more instances of curtain or slot coating, using slotted applicators 110 may be used in between two instances of spraying. In addition, in some embodiments one or more instances of spraying may be used in between two instances of curtain or slot coating using slotted applicators 110. The exact configuration, in which nanocellulose-containing composition(s) is applied, is configurable.

Slot Coaters

[0192] Slot coating apparatuses, systems, and techniques are known to those skilled in the art. The present disclosure envisions use of art- and industry-known slot coating apparatuses, systems, and techniques, as well as those not yet known or discovered. An example slot coating technique that may be used in accordance with the present disclosure is that described in U.S. Pat. No. 10,550,520, issued on Feb. 4, 2020, and entitled Method with a Horizontal Jet Applicator for a Paper Machine Wet End, the entirety of which is hereby incorporated by reference.

[0193] Generally, the slotted applicator 110 may have a channel in fluidic communication with a horizontal slot having a vertical gap height (in some instances less than 0.100 inch). Nanocellulose-containing composition is pumped through the channel and to the horizontal slot. In some instances, the nanocellulose-containing composition is pumped at a rate of less than 5 US gallons per minute per inch of the slot.

[0194] The additive leaves the slot in a substantially horizontal direction above the consolidating base sheet 104 traveling in a substantially horizontal direction. This vertical gap height should be set to get the required flow at a speed needed to maintain a good formation.

[0195] The nanocellulose-containing composition is forced out of the narrow slot in the slotted applicator 110 as a full-width, essentially horizontal jet and lands on the consolidating base sheet 104 of the paper machine.

[0196] Commercial machines run production web speeds of about 500-3000 feet per minute. A vertical layer of nanocellulose-containing composition, falling by gravity, has a much lower machine direction velocity than the consolidating base sheet 104 on which it lands, which may cause significant extension of the nanocellulose-containing composition layer, as well as stresses and disruptions both in this layer and in the top surface of the consolidating base sheet 104. Pressurizing the slotted applicator 110 to increase the velocity of the vertically falling nanocellulose-containing composition may cause the nanocellulose-containing composition to partially penetrate and disrupt the forming consolidating base sheet 104 as it lands. Thus, a slot coater, having a pressurized slot for dispensing of nanocellulose-containing composition, is angled away from true vertical.

[0197] The slot coater may be configured such that the flow of the nanocellulose-containing composition, from an expansion chamber, passes through a narrow, essentially parallel slot that is oriented in a horizontal, or nearly horizontal, direction to the consolidating base sheet 104, and forms a full width jet which then lands on the consolidating base sheet 104. By adjusting the pressure in the slot coater and the slot gap height, it is possible to adjust the velocity of the essentially horizontal jet relative to the velocity of the consolidating base sheet 104, and therefore to land the jet of nanocellulose-containing composition on the consolidating base sheet 104 without disruption.

[0198] The slot coater may have long, essentially parallel lips that form the slot and have an angle between the top and bottom surfaces of less than 3 degrees.

[0199] The slot coater may include a knuckle and jack mechanism, allowing for opening and closing of a lip holder to assist in maintenance of the slot coater.

[0200] The nanocellulose-containing composition may enter a distribution chamber, where it then passes through spaced apart tubes into an expansion chamber. From there, the nanocellulose-containing composition may accumulate to ensure even distribution through a channel into a nozzle chamber. From the nozzle chamber, the nanocellulose-containing composition may get distributed evenly across and through a slot formed by the substantially parallel lips, so the nanocellulose-containing composition falls evenly onto the mobile consolidating base sheet 104.

Curtain Coaters

[0201] Curtain coating apparatuses, systems, and techniques are known to those skilled in the art. The present disclosure envisions use of art- and industry-known curtain coating apparatuses, systems, and techniques, as well as those not yet known or discovered.

[0202] Generally, a curtain coater includes the same components as the slot coater described above, except a curtain coater's slot (which may nor may not be pressurized) is oriented vertically with respect to the consolidating base sheet 104 (as compared to horizontally or nearly horizontally oriented as is a slot coater's slot).

[0203] While it is noted herein that curtain coating may have some drawbacks, curtain coating may nonetheless be sufficient in at least some contexts to apply a layer of nanocellulose-containing composition as described herein.

Spraying

[0204] Various nozzle configurations may be utilized to achieve the effects and benefits set forth in the present disclosure. In some embodiments, the nozzles, used to spray nanocellulose-containing composition, may produce a flat fan spray. In such embodiments, the orifice of a spray nozzle may be roughly elliptical but having sharp edges.

[0205] Various pressures may also be utilized to achieve the effects and benefits set forth in the present disclosure. In some embodiments, a pressure between about 10 psi and about 50 psi may be utilized. One skilled in the art will appreciate that the pressure utilized may depend, at least in part, on the nozzle configuration utilized.

[0206] Some nozzles have codes, such as 95-30, where the first number refers to the angle of the spray at 40 psi and the second refers to the US gallons per minute at 40 psi (multiplied by 10). So, for example, the code 95-30 has a wide, 95 spray angle and delivers 3 gallons/min at 40 psi.

[0207] The flowrate/pressure figures are all based on water. But it has been found that, despite its very different rheology, nanocellulose-containing composition at around 1.5% solids nanocellulose gives the same flowrate/pressure relationship.

Nanocellulose

[0208] As its name implies, as used herein a nanocellulose-containing composition comprises nanocellulose. As used herein, nanocellulose refers to cellulose structures with one dimension (e.g., diameter) in the sub-micron region (i.e., <1 m).

[0209] In some embodiments, the nanocellulose may include cellulose nanofibre (CNF). CNF refers to cellulose structures having a diameter of about 5 nm to about 10 nm, and an average length of about 50 nm to about 100 nm. To produce CNF, wood may be crushed into woodchips of about 5 cm in width and 1 cm in thickness. At a paper mill, fibres are extracted from the woodchips and pulped. The pulp is then chemically processed to produce fibres, which may then be further chemically or enzymatically treated to make them easier to separate into their constituent fibrils.

[0210] In some embodiments, the nanocellulose may include nanofibrillated cellulose (NFC). NFC refers to cellulose fibres that have been fibrillated (via mechanical disintegration) to achieve agglomerates of cellulose microfibril units. NFC has nanoscale (e.g., <100 nm) diameter, and a typical length of several micrometers. NFC may be produced from various cellulosic sources including, but not limited to, wood, bleached kraft pulp, bleached sulfite pulp, sugar beet pulp, wheat straw and soy hulls, sisal, bagasse, palm trees, ramie, carrots, and luffa cylindrica. NFC may be produced using various mechanical disintegration processes and systems such as, but not limited to, a homogenizer system, a microfluidizer, and a grinder.

[0211] In some embodiments, the nanocellulose may include cellulose nanocrystals (CNCs). CNCs are a derivative of cellulose, which can be obtained through acid hydrolysis of cellulose, where the cellulose is exposed to (e.g., sulfuric) acid under controlled temperature for a time. The acid hydrolysis dissolves the amorphous regions of cellulose, but leaves the crystalline regions largely intact, hence the production of nanocrystals. CNCs can be isolated from various renewable resources such as plants (e.g., cotton and wood), bacteria, and sea animals. Depending on the isolation method utilized and the source of the cellulose, CNCs can range from 5 nm to 30 nm in diameter and have aspect ratios up to about 100. CNCs can have high specific strength and Young's modulus. Moreover, the active hydroxyl surface groups of CNCs enable chemical functionalization.

[0212] In some embodiments, the nanocellulose may include microfibrillated cellulose (MFC). As used herein, microfibrillated cellulose and MFC both refer to a material containing nanoscale fibrils that have been partially or completely separated from their parent fibres. In some embodiments, microfibrillated cellulose may have at least one dimension less than about 100 nm. MFC comprises partly or totally fibrillated cellulose or lignocellulose fibres. The liberated fibrils have a diameter less than about 100 nm, whereas the actual fibril diameter or particle size distribution and/or aspect ratio (length/width) depends on the source and the manufacturing methods.

[0213] The smallest fibril is called elementary fibril and has a diameter of approximately 2 nm to 4 nm (see, e.g., Chinga-Carrasco, G., Cellulose fibres, nanofibrils and microfibrils: The morphological sequence of MFC components from a plant physiology and fibre technology point of view, Nanoscale Research Letters 2011, 6:417), while it is common that the aggregated form of the elementary fibrils, also defined as microfibril (see, e.g., Fengel, D., Ultrastructural behavior of cell wall polysaccharides, Tappi J., March 1970, Vol 53, No. 3.), is the main product that is obtained when making MFC (e.g., by using an extended refining process or pressure-drop disintegration process). Depending on the source and the manufacturing process, the length of the fibrils can vary from around 1 m to more than 10 m. A coarse MFC grade might contain a substantial fraction of fibrillated fibres (i.e., protruding fibrils from the tracheid (cellulose fibre)), and with a certain amount of fibrils liberated from the tracheid (cellulose fibre).

[0214] MFC can also be characterized by various physico-chemical properties, such as large surface area or its ability to form a gel-like material at low solid contents (e.g., 1 wt % to 5 wt %) when dispersed in water. The cellulose fibre is preferably fibrillated to such an extent that the final specific surface area of the formed MFC is from about 1 m.sup.2/g to about 300 m.sup.2/g, such as from about 1 m.sup.2/g to about 200 m.sup.2/g, or more preferably about 50 m.sup.2/g to about 200 m.sup.2/g, when determined for a freeze-dried material with the Brunauer, Emmett, and Teller (BET) method.

[0215] In some embodiments, the MFC may have a Schopper Riegler value (SR.degree.) of more than about 85 SR.degree, more than about 90 SR.degree, or more than about 92 SR.degree. The Schopper-Riegler value can be determined through the standard method defined in EN ISO 5267-1.

[0216] MFC may be characterized by its mean particle size. One technique for measuring the mean particle size of MFC involves laser light scattering, using a Malvern Insitec machine as supplied by Malvern Instruments Ltd (or other methods that give essentially the same result). In the laser light scattering technique, the size of particles in powders, suspensions, and emulsions may be measured using the diffraction of a laser beam, based on an application of Mie theory. Such a machine provides measurements and a plot of the cumulative percentage by volume of particles having an equivalent spherical diameter (e.s.d.), less than given e.s.d. values. The mean particle size d.sub.50 is the value determined in this way of the particle e.s.d. at which there are 50% by volume of the particles which have an equivalent spherical diameter less than that d.sub.50 value.

[0217] The following is an example procedure for determining particle size distribution of MFC as measured by a Malvern Insitec L light scattering device. To start, it is beneficial to ensure that the MFC slurry is homogeneous by shaking the container contents vigorously. If grinding media is present in the sample, a 850 micron screen may be used to remove the grinding media before running the Malvern analysis. If no grinding medium is present, the slurry may be pipetted from the sample. Turn on the Malvern Insitec unit and start the pump by pressing the pump speed on/off button on top of the Malvern unit and set the speed at 2500 rpm and ensure that the ultrasonic is off. Ensure that the Malvern Insitec is clean by flushing the unit 2-3 times with clean, room temperature water+5 C. Raise the stirrer to the marked drain position and remove the outlet hose and syphon the solution from the system ensuring that the inlet hose is lifted to drain any trapped solution. Replace water with clean room temperature tap water+5 C. (800 ml to 900 ml). Fully push down the Malvern stirrer and the pump will start automatically. If the water is very turbulent turn the pump off and on again to help settle the water. Lift the outlet hose to remove any trapped air.

[0218] The MFC may have a d.sub.50 value ranging from about 1 m to about 500 m, as measured by laser light scattering. The MFC may have a d.sub.50 value equal to or less than about 400 m, equal to or less than about 300 m, equal to or less than about 200 m, equal to or less than about 150 m, equal to or less than about 125 m, equal to or less than about 100 m, equal to or less than about 90 m, equal to or less than about 80 m, equal to or less than about 70 m, equal to or less than about 60 m, equal to or less than about 50 m, equal to or less than about 40 m, equal to or less than about 30 m, equal to or less than about 20 m, or equal to or less than about 10 m.

[0219] The MFC may have a modal fibre particle size ranging from about 0.1 m to about 500 m, and a modal inorganic particulate material particle size ranging from about 0.25 m to about 20 m. The MFC may have a modal fibre particle size of at least about 0.5 m, at least about 10 m, at least about 50 m, at least about 100 m, at least about 150 m, at least about 200 m, at least about 300 m, or at least about 400 m.

[0220] The MFC may additionally or alternatively be characterized in terms of fibre steepness. Fibre steepness (i.e., the steepness of the particle size distribution of the fibres in the MFC) may be determined by the following formula:

Steepness=100(d.sub.30/d.sub.70)

[0221] The MFC may have a fibre steepness equal to or less than about 100, equal to or less than about 75, equal to or less than about 50, equal to or less than about 40, or equal to or less than about 30. In some embodiments, the MFC may have a fibre steepness of about 20 to about 50.

[0222] In situations where the MFC includes inorganic particulate material, the fibre steepness may be calculated by mathematically subtracting the inorganic particulate material.

[0223] MFC may be characterized by fibre length (Lc(w) ISO). The MFC may have a fibre length of less than about 0.7 mm, less than about 0.6 mm, less than about 0.5 mm, less than about 0.4 mm, less than about 0.3 mm, less than about 0.2 mm, or less than about 0.1 mm as measured by a fibre image analyzer. In some embodiments, the MFC may have a fibre length of less than about 0.7 mm.

[0224] Nanocellulose may contain some hemicelluloses, of which the amount is dependent on the plant source. Mechanical disintegration of the pre-treated fibres (e.g. hydrolysed, pre-swelled, or oxidized cellulose raw material) is carried out with suitable equipment such as a refiner, grinder, homogenizer, colloider, friction grinder, ultrasound sonicator, fluidizer such as microfluidizer, macrofluidizer or fluidizer-type homogenizer.

[0225] Depending on the manufacturing method utilized, nanocellulose might also contain fines or other chemicals present in wood fibres or in papermaking process. Nanocellulose might also contain various amounts of micron size fibre particles that have not been efficiently fibrillated.

[0226] Fines A is a measure of the fine fibres and fragments that are not well fibrillated, and Fines B is a measure of highly fibrillated fragments. Fines A are low aspect ratio fibers and fragments less than 200 m in length. Fines B are fibrillated fragments greater than 200 m in length, but less than 10 m and width. The MFC made from Northern Softwood has longer fibres and an elevated level of Fines B, whilst keeping fibrillation high and the overall level of fines low. This is beneficial because it limits the effect of the MFC on sheet drainage. In contrast, the MFC made from birch in this case is highly fibrillated, yielding a product with high strength potential but which is significantly more detrimental to drainage rate.

[0227] Nanocellulose may be produced from wood cellulose fibres, both from hardwood or softwood fibres. Nanocellulose can also be made from microbial sources, agricultural fibres such as wheat straw pulp, bamboo, bagasse, or other non-wood fibre sources. Nanocellulose may also be made from pulp including pulp from virgin fibre (e.g., mechanical, chemical, and/or thermomechanical pulps). In some embodiments, the nanocellulose may be obtained from a chemical pulp, or a chemithermomechanical pulp, or a mechanical pulp, or thermomechanical pulp, including, for example, Northern Bleached Softwood Kraft pulp (NBSK), Bleached Chemi-Thermo Mechanical Pulp (BCTMP), a recycled pulp, a paper broke pulp, a paper mill waste stream, or a combination thereof. In some embodiments, the pulp source may be kraft pulp, or bleached long fibre kraft pulp. In some embodiments, the pulp source may be softwood pulp selected from spruce, pine, fir, larch and hemlock or mixed softwood pulp. In some embodiments, the pulp source may be hardwood pulp selected from eucalyptus, aspen and birch, or mixed hardwood pulps. In some embodiments, the pulp source may be eucalyptus pulp, spruce pulp, pine pulp, beech pulp, hemp pulp, acacia cotton pulp, and mixtures thereof.

[0228] Nanocellulose may be derived from recycled pulp or a papermill broke and/or industrial waste, or a paper stream rich in mineral fillers and cellulosic materials from a papermill. The recycled cellulose pulp may be beaten (e.g., in a Valley beater) and/or otherwise refined (e.g., processing in a conical or plate refiner) to any predetermined freeness, reported in the art as Canadian standard freeness (CSF) in cm.sup.3 or Schopper Riegler Freeness. CSF means a value for the freeness or drainage rate of pulp measured by the rate that a suspension of pulp may be drained, and this test is carried out according to the T 227 cm-09 TAPPI standard. For example, the cellulose pulp may have a CSF of about 10 cm.sup.3 or greater prior to undergoing processing into nanocellulose. The recycled cellulose pulp may have a CSF of about 700 cm.sup.3 or less, for example, equal to or less than about 650 cm.sup.3, equal to or less than about 600 cm.sup.3, equal to or less than about 550 cm.sup.3, equal to or less than about 500 cm.sup.3, equal to or less than about 450 cm.sup.3, equal to or less than about 400 cm.sup.3, equal to or less than about 350 cm.sup.3, o equal to or less than about 300 cm.sup.3, equal to or less than about 250 cm.sup.3, equal to or less than about 200 cm.sup.3, equal to or less than about 150 cm.sup.3, equal to or less than about 100 cm.sup.3, or equal to or less than about 50 cm.sup.3. The recycled cellulose pulp may have a CSF of about 20 to about 700. The recycled cellulose pulp may then be dewatered by methods well known in the art, for example, the pulp may be filtered through a screen in order to obtain a wet sheet comprising at least about 10% solids, for example at least about 15% solids, at least about 20% solids, at least about 30% solids, or at least about 40% solids.

Production of MFC

[0229] Methods of manufacturing MFC include mechanical disintegration by refining, milling, beating and homogenizing, and refining, for example, by an extruder. These mechanical measures may be enhanced by chemical or chemo-enzymatic treatments as a preliminary step. Various known methods of microfibrillation of cellulosic fibres are summarized in U.S. Pat. No. 6,602,994 B1 as including, for example, homogenization, steam explosion, pressurization-depressurization, impact, grinding, ultrasound, microwave explosion, milling and combinations of these. WO 2007/001229 discloses enzyme treatment and, as a method of choice, oxidation in the presence of a transition metal for turning cellulosic fibres to MFC. After the oxidation step, the material is disintegrated by mechanical means. A combination of mechanical and chemical treatment can also be used. Examples of chemicals that can be used are those that either modify the cellulose fibres through a chemical reaction or those that modify the cellulose fibres via, for example, grafting or sorption of chemicals onto/into the fibres.

[0230] Various methods of producing MFC are known in the art. Certain methods and compositions comprising MFC produced by grinding procedures are described in WO-A-2010/131016. Husband, J. C., Svending, P., Skuse, D. R., Motsi, T., Likitalo, M., Coles, A., FiberLean Technologies Ltd., 2015, Paper filler composition, PCT International Application No. WO-A-2010/131016. Paper products comprising such MFC have been shown to exhibit excellent paper properties, such as paper burst and tensile strength. The methods described in WO-A-2010/131016 also enable the production of MFC economically.

[0231] WO 2007/091942 A1 describes a process in which chemical pulp is first refined, then treated with one or more wood degrading enzymes, and finally homogenized to produce MFC as the final product. The consistency of the pulp is described to be preferably from about 0.4% to about 10%. The advantage is said to be avoidance of clogging in the high-pressure fluidizer or homogenizer.

[0232] WO2010/131016 describes a grinding procedure for production of MFC with or without inorganic particulate material. Such a grinding procedure is described below. In an embodiment of the process set forth in WO-A-2010/131016, the contents of which is hereby incorporated by reference in its entirety, the process utilizes mechanical disintegration of cellulose fibres to produce MFC cost-effectively and at large scale, without requiring cellulose pre-treatment. An embodiment of the method uses stirred media detritor grinding technology, which disintegrates fibres into MFC by agitating grinding media beads. In this process, an inorganic particulate material, such as calcium carbonate or kaolin, is added as a grinding aid, greatly reducing the energy required. Husband, J. C., Svending, P., Skuse, D. R., Motsi, T., Likitalo, M., Coles, A., FiberLean Technologies Ltd., 2015, Paper filler composition, U.S. Pat. No. 9,127,405B2.

[0233] A stirred media mill consists of a rotating impeller that transfers kinetic energy to small grinding media beads, which grind down the charge via a combination of shear, compressive, and impact forces. A variety of grinding apparatus may be used to produce MFC by the disclosed methods herein, including, for example, a tower mill, a screened grinding mill, or a stirred media detritor.

Homogenization Preparation of MFC

[0234] In some embodiments, microfibrillation of a fibrous substrate comprising cellulose may be effected under wet conditions in the presence of the inorganic particulate material by a method in which the mixture of cellulose pulp and inorganic particulate material is pressurized (for example, to a pressure of about 500 bar) and then passed to a zone of lower pressure. The rate at which the mixture is passed to the low-pressure zone is sufficiently high and the pressure of the low pressure zone is sufficiently low to cause microfibrillation of the cellulose fibres. For example, the pressure drop may be affected by forcing the mixture through an annular opening that has a narrow entrance orifice with a much larger exit orifice. The drastic decrease in pressure as the mixture accelerates into a larger volume (i.e., a lower pressure zone) induces cavitation which causes microfibrillation. In an embodiment, microfibrillation of the fibrous substrate comprising cellulose may be affected in a homogenizer under wet conditions in the presence of the inorganic particulate material. In the homogenizer, the cellulose pulp-inorganic particulate material mixture is pressurized (for example, to a pressure of about 500 bar), and forced through a small nozzle or orifice. The mixture may be pressurized to a pressure of from about 100 to about 1000 bar, for example to a pressure equal to or greater than 200 bar, equal to or greater than about 300 bar, equal to or greater than about 500, or equal to or greater than about 700 bar. The homogenization subjects the fibres to high shear forces such that as the pressurized cellulose pulp exits the nozzle or orifice, cavitation causes microfibrillation of the cellulose fibres in the pulp.

[0235] Water may be added to improve flowability of the suspension through the homogenizer. The resulting aqueous suspension comprising MFC and inorganic particulate material may be fed back into the inlet of the homogenizer for multiple passes through the homogenizer. In some embodiments, the inorganic particulate material is a naturally platy mineral, such as kaolin. As such, homogenization not only facilitates microfibrillation of the cellulose pulp, but also facilitates delamination of the platy inorganic particulate material.

[0236] A platy inorganic particulate material, such as kaolin, is understood to have a shape factor of at least about 10, at least about 15, at least about 20, at least about 30, at least about 40, at least about 50, at least about 60, at least about 70, at least about 80, at least about 90, or at least about 100. Shape factor, as used herein, is a measure of the ratio of particle diameter to particle thickness for a population of particles of varying size and shape as measured using the electrical conductivity methods, apparatuses, and equations described in U.S. Pat. No. 5,576,617, which is incorporated herein by reference.

Production of NFC

[0237] Methods of manufacturing NFC are known in the art/industry. One or more art-/industry-known techniques may be used to produce NFC of the present disclosure. Example NFC production techniques are disclosed in U.S. patent application Ser. No. 17/193,376, entitled Process for the Production of Nano-Fibrillar Cellulose Gels, to Gane et al.; U.S. Pat. No. 10,975,242, Process for the Production of Nano-Fibrillar Cellulose Gels, to Gane et al.; U.S. Pat. No. 10,294,371, Process for the Production of Nano-Fibrillar Cellulose Gels, to Gane et al.; U.S. Pat. No. 8,871,056, Process for the Production of Nano-Fibrillar Cellulose Gels, to Gane et al.; U.S. patent application Ser. No. 17/193,338, entitled Process for the Production of Nano-Fibrillar Cellulose Suspensions, to Gane et al.; U.S. Pat. No. 10,982,387, Process for the Production of Nano-Fibrillar Cellulose Suspensions, to Gane et al.; U.S. Pat. No. 10,301,774, Process for the Production of Nano-Fibrillar Cellulose Suspensions, to Gane et al.; U.S. Pat. No. 8,871,057, Process for the Production of Nano-Fibrillar Cellulose Suspensions, to Gane et al.; all of which are incorporated herein by reference in their entireties.

Nanocellulose-Containing Compositions

[0238] A nanocellulose-containing composition of the present disclosure may include nanocellulose in varying amounts. As used herein, reference to the total weight of the nanocellulose-containing composition includes all components of the nanocellulose-containing composition including the weight of all liquids present, unless otherwise stated.

[0239] Nanocellulose may be present in an amount of at least about 0.01 wt %, 0.05 wt %, 0.1 wt %, 0.15 wt %, 0.2 wt %, 0.25 wt %, 0.3 wt %, 0.35 wt %, 0.4 wt %, 0.45 wt %, or 0.5 wt %, of the total weight of the nanocellulose-containing composition. In some embodiments, the nanocellulose may be present in an amount of at least about 0.2 wt % of the total weight of the nanocellulose-containing composition. In some embodiments, the nanocellulose may be present in an amount of at least about 0.5 wt % of the total weight of the nanocellulose-containing composition.

[0240] Nanocellulose may be at most about 1 wt %, 1.05 wt %, 1.10 wt %, 1.15 wt %, 1.20 wt %, 1.25 wt %, 1.30 wt %, 1.35 wt %, 1.40 wt %, 1.45 wt %, 1.50 wt %, 1.55 wt %, 1.60 wt %, 1.65 wt %, 1.70 wt %, 1.75 wt %, 1.80 wt %, 1.85 wt %, 1.90 wt %, 1.95 wt %, 2.0 wt %, 2.05 wt %, 2.10 wt %, 2.15 wt %, 2.20 wt %, 2.25 wt %, 2.30 wt %, 2.35 wt %, 2.40 wt %, 2.45 wt %, 2.50 wt %, 2.55 wt %, 2.60 wt %, 2.65 wt %, 2.70 wt %, 2.75 wt %, 2.80 wt %, 2.85 wt %, 2.90 wt %, 2.95 wt %, 3.0 wt %, 3.05 wt %, 3.10 wt %, 3.15 wt %, 3.20 wt %, 3.25 wt %, 3.30 wt %, 3.35 wt %, 3.40 wt %, 3.45 wt %, 3.50 wt %, 3.55 wt %, 3.60 wt %, 3.65 wt %, 3.70 wt %, 3.75 wt %, 3.80 wt %, 3.85 wt %, 3.90 wt %, 3.95 wt %, 4.0 wt %, 4.05 wt %, 4.10 wt %, 4.15 wt %, 4.20 wt %, 4.25 wt %, 4.30 wt %, 4.35 wt %, 4.40 wt %, 4.45 wt %, 4.50 wt %, 4.55 wt %, 4.60 wt %, 4.65 wt %, 4.70 wt %, 4.75 wt %, 4.80 wt %, 4.85 wt %, 4.90 wt %, 4.95 wt %, 5.0 wt %, 5.05 wt %, 5.10 wt %, 5.15 wt %, 5.20 wt %, 5.25 wt %, 5.30 wt %, 5.35 wt %, 5.40 wt %, 5.45 wt %, 5.50 wt %, 5.55 wt %, 5.60 wt %, 5.65 wt %, 5.70 wt %, 5.75 wt %, 5.80 wt %, 5.85 wt %, 5.90 wt %, 5.95 wt %, 6.0 wt % of the total weight of the nanocellulose-containing composition. Any two of the above listed values may be combined to create a range of nanocellulose of the total weight of the nanocellulose-containing composition. In some embodiments, the nanocellullose may be present in an amount of at most about 6 wt % of the total weight of the nanocellulose-containing composition. In some embodiments, the nanocellullose may be present in an amount of at most about 5 wt % of the total weight of the nanocellulose-containing composition. In some embodiments, the nanocellullose may be present in an amount of at most about 4 wt % of the total weight of the nanocellulose-containing composition. In some embodiments, the nanocellullose may be present in an amount of at most about 3 wt % of the total weight of the nanocellulose-containing composition. In some embodiments, the nanocellullose may be present in an amount of at most about 2 wt % of the total weight of the nanocellulose-containing composition.

[0241] In some embodiments, the nanocellulose may be about 0.5% wt % to about 6 wt % of the total weight of the nanocellulose-containing composition.

[0242] In some embodiments, the nanocellulose may be about 1 wt % to about 2 wt % of the total weight of the nanocellulose-containing composition.

[0243] Nanocellulose may be present in an amount of at least about 0.01 wt %, 0.05 wt %, 0.1 wt %, 0.15 wt %, 0.2 wt %, 0.5 wt %, 0.7 wt %, or 1.0 wt %, 1.5 wt %, 2.5 wt %, 5 wt %, 10 wt %, 15 wt %, 20 wt %, 25 wt %, 30 wt %, 35 wt %, 40 wt %, 45 wt %, or 50 wt %, of the total solid content of the nanocellulose-containing composition. In some embodiments, the nanocellulose may be present in an amount of at least about 40 wt % of the total solid content of the nanocellulose-containing composition. In some embodiments, the nanocellulose may be present in an amount of at least about 50 wt % of the total solid content of the nanocellulose-containing composition.

[0244] In some embodiments, the dry solids of a nanocellulose-containing composition may be about 100% nanocellulose. In some embodiments, the dry solids of a nanocellulose-containing composition may be about 5% to about 100% nanocellulose. In some embodiments, the dry solids of a nanocellulose-containing composition may be about 5% to about 95% nanocellulose. In some embodiments, the dry solids of a nanocellulose-containing composition may be about 30% to about 100% nanocellulose. In some embodiments, the dry solids of a nanocellulose-containing composition may be about 30% to about 95% nanocellulose. In some embodiments where nanocellulose is less than 100% of the dry solids of the nanocellulose-containing composition, the remaining dry solids of the composition may be mineral.

[0245] In some embodiments, a nanocellulose-containing composition of the present disclosure may include one or more inorganic particulate materials. The inorganic particulate material, when present, may, for example, be an alkaline earth metal carbonate or sulphate, such as calcium carbonate, magnesium carbonate, dolomite, gypsum, a clay such as hydrous kandite clay such as kaolin, halloysite or ball clay, bentonite, an anhydrous (calcined) kandite clay such as metakaolin or fully calcined kaolin, talc, mica, perlite or diatomaceous earth, or magnesium hydroxide, or aluminum trihydrate, or combination thereof. In some embodiments, the nanocellulose-containing composition may include calcium carbonate, clay, aluminum trihydrate, or a combination thereof.

[0246] In some instances, the calcium carbonate may be ground calcium carbonate (GCC). GCC is typically obtained by crushing and then grinding an inorganic particulate material source such as chalk, marble, or limestone, which may be followed by a particle size classification step, to obtain a product having the desired degree of fineness. Other techniques such as bleaching, flotation, and magnetic separation may also be used to obtain a product having the desired degree of fineness and/or color. The particulate solid material may be ground autogenously (i.e., by attrition between the particles of the solid material themselves, or, alternatively, in the presence of a particulate grinding medium comprising particles of a different material from the calcium carbonate to be ground). These processes may be carried out with or without the presence of a dispersant and biocides, which may be added at any stage of the process.

[0247] In some instances, the calcium carbonate may be precipitated calcium carbonate (PCC). PCC may be used as the source of particulate calcium carbonate in the nanocellulose disclosed herein and may be produced by any of the known methods available in the art. TAPPI Monograph Series No 30, Paper Coating Pigments, pages 34-35 describes the three main commercial processes for preparing precipitated calcium carbonate which is suitable for use in preparing products for use in the paper industry, but may also be used in the practice of the present disclosure. In all three processes, a calcium carbonate feed material, such as limestone, is first calcined to produce quicklime, and the quicklime is then soaked in water to yield calcium hydroxide or milk of lime. In the first process, the milk of lime is directly carbonated with carbon dioxide gas. This process has the advantage that no by-product is formed, and it is relatively easy to control the properties and purity of the calcium carbonate product. In the second process the milk of lime is contacted with soda ash to produce, by double decomposition, a precipitate of calcium carbonate and a solution of sodium hydroxide. The sodium hydroxide may be substantially completely separated from the calcium carbonate if this process is used commercially. In the third main commercial process, the milk of lime is first contacted with ammonium chloride to give a calcium chloride solution and ammonia gas. The calcium chloride solution is then contacted with soda ash to produce by double decomposition precipitated calcium carbonate and a solution of sodium chloride. The crystals can be produced in a variety of different shapes and sizes, depending on the specific reaction process that is used. The three main forms of PCC crystals are aragonite, rhombohedral, and scalenohedral, all of which are suitable for use in the herein disclosed nanocellulose, including mixtures thereof.

[0248] Wet grinding of calcium carbonate involves the formation of an aqueous suspension of the calcium carbonate which may then be ground, optionally in the presence of a suitable dispersing agent. Reference may be made to, for example, EP-A-614948 (the contents of which are incorporated by reference in their entirety) for more information regarding the wet grinding of calcium carbonate.

[0249] As noted above, in some embodiments the nanocellulose may include kaolin clay. The kaolin clay may be a processed material derived from a natural source, namely raw natural kaolin clay mineral. The processed kaolin clay may typically contain at least about 50% by weight kaolinite. For example, most commercially processed kaolin clays contain greater than about 75% by weight kaolinite and may contain greater than about 90%, in some cases greater than about 95% by weight of kaolinite.

[0250] The kaolin may be prepared from the raw natural kaolin clay mineral by one or more other processes which are well known to those skilled in the art, for example by known refining or beneficiation steps. For example, the clay mineral may be bleached with a reductive bleaching agent, such as sodium hydrosulfite. If sodium hydrosulfite is used, the bleached clay mineral may optionally be dewatered, and optionally washed and again optionally dewatered, after the sodium hydrosulfite bleaching step.

[0251] The clay mineral may be treated to remove impurities, for example, by flocculation, flotation, or magnetic separation techniques well known in the art. Alternatively, the clay mineral may be untreated in the form of a solid or as an aqueous suspension.

[0252] The process for preparing the particulate kaolin clay may also include one or more comminution steps (e.g., grinding or milling). The comminution may be carried out by use of beads or granules of a plastic (e.g. nylon), sand or ceramic grinding or milling aid. The coarse kaolin may be refined to remove impurities and improve physical properties using well known procedures. The kaolin clay may be treated by a known particle size classification procedure (e.g., screening and centrifuging (or both)), to obtain particles having a desired d.sub.50 value or particle size distribution.

[0253] When the inorganic particulate material is obtained from naturally occurring sources, it may be that some mineral impurities will contaminate the ground material. For example, naturally occurring calcium carbonate can be present in association with other minerals (i.e., inorganic particulate material). Thus, in some embodiments, the inorganic particulate material includes some extent of impurities. In general, however, the inorganic particulate material may contain less than about 5% by weight, preferably less than about 1% by weight, of other mineral impurities.

[0254] In some embodiments, a nanocellulose-containing composition may comprise two or more of bentonite, GCC, PCC, and kaolin.

[0255] In some circumstances, one or more other minerals (i.e., inorganic particulate material) may be included in the nanocellulose of the present disclosure. Such one or more other minerals include, for example, kaolin, calcined kaolin, wollastonite, bauxite, talc, and mica.

[0256] The inorganic particulate material may have a particle size distribution in which at least about 10% by weight of the particles have an equivalent spherical diameter (e.s.d.) of less than 2 m, for example, at least about 20% by weight, at least about 30% by weight, at least about 40% by weight, at least about 50% by weight, at least about 60% by weight, at least about 70% by weight, at least about 80% by weight, at least about 90% by weight, at least about 95% by weight, or about 100% of the particles have an e.s.d. of less than 2 m.

[0257] Particle size properties, referred to herein for the inorganic particulate materials, may be measured in a well-known manner. For example, the particle size properties of the inorganic particulate materials may be measured by sedimentation of the particulate material in a fully dispersed condition in an aqueous medium using a Sedigraph 5100 machine as supplied by Micromeritics Instruments Corporation, Norcross, Ga., USA. Such a machine provides measurements and a plot of the cumulative percentage by weight of particles having a size, referred to in the art as the equivalent spherical diameter (e.s.d), less than given e.s.d. values. The mean particle size d.sub.50 is the value determined in this way of the particle e.s.d. at which there are 50% by weight of the particles which have an equivalent spherical diameter less than that d.sub.50 value.

[0258] Alternatively, where stated, the particle size properties referred to herein for the inorganic particulate materials are as measured by the well-known conventional method employed in the art of laser light scattering, using a Malvern Mastersizer 3000 or Malvern Insitec, as supplied by Malvern Instruments Ltd (or equivalent laser light scattering device or by other methods which give essentially the same result). In the laser light scattering technique, the size of particles in powders, suspensions and emulsions may be measured using the diffraction of a laser beam, based on an application of Mie theory. Such a machine provides measurements and a plot of the cumulative percentage by volume of particles having a size, referred to in the art as the equivalent spherical diameter (e.s.d), less than given e.s.d values. The mean particle size d.sub.50 is the value determined in this way of the particle e.s.d at which there are 50% by volume of the particles which have an equivalent spherical diameter less than that do value.

[0259] In some embodiments, a nanocellulose-containing composition of the present disclosure may include one or more additives. For example, the nanocellulose-containing composition may include one or more emulsions, one or more fire retardants, and combinations thereof.

[0260] Unless stated otherwise, reference to an emulsion herein means a compound or composition configured to reduce water absorption of a paper or paperboard of which the emulsion is a component. An emulsion may sometimes be referred to as a wax. Example emulsions include, but are not limited to, polyvinyl acetate emulsion and paraffin emulsion. In some embodiments, a nanocellulose-containing composition of the present disclosure may include polyvinyl acetate emulsion and/or paraffin emulsion.

[0261] Unless stated otherwise, reference to a fire retardant herein means a compound or composition configured to provide fire retardant properties to a paper or paperboard of which the fire retardant is a component. Example fire retardants include, but are not limited to, zinc oxide, aluminum hydroxide, and ammonium polyphosphate. In some embodiments, a nanocellulose-containing composition of the present disclosure may include zinc oxide, aluminum hydroxide, and/or ammonium polyphosphate.

[0262] In some embodiments, a nanocellulose-containing composition of the present disclosure may include a solvent. In some embodiments, the solvent may be water, alcohol, toluene, or a combination thereof. In some embodiments, the alcohol may comprise one or more of ethanol, glycerol, and polyvinyl alcohol.

Application of Two or More Nanocellulose-Containing Compositions

[0263] As described above with respect to FIGS. 3 and 4, more than one nanocellulose-containing composition may be applied to the same consolidating base sheet (an example of a paper or paperboard substrate) in a sequential manner.

[0264] In some embodiments, a first nanocellulose-containing composition may have a first particle size distribution with a first mean size, and a subsequently-applied second nanocellulose containing composition may have a second particle size distribution with a second mean size. In some embodiments, the first and second mean sizes may be different. In some embodiments, the first mean size (of the first particle size distribution) may be greater than the second mean size (of the second particle size distribution. Having the first mean size be greater than the second mean size may result in cheaper manufacturing of, and a better draining paper or paper board, as compared to one in which the first and second mean sizes are the same.

[0265] The first mean size (d.sub.50), of the first particle size distribution of the first nanocellulose-containing composition, may be 5 m, 10 m, 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, 45 m, 50 m, 55 m, 60 m, 65 m, 70 m, 75 m, 80 m, 85 m, 90 m, 95 m, 100 m, 105 m, 110 m, 115 m, 120 m, 125 m, 130 m, 135 m, 140 m, 145 m, 150 m, 155 m, 160 m, 165 m, 170 m, 175 m, 180 m, 185 m, 190 m, 195 m, 200 m, 205 m, 210 m, 215 m, 220 m, 225 m, 230 m, 235 m, 240 m, 245 m, 250 m, 255 m, 260 m, 265 m, 270 m, 275 m, 280 m, 285 m, 290 m, 295 m, 300 m, 305 m, 310 m, 315 m, 320 m, 325 m, 330 m, 335 m, 340 m, 345 m, 350 m, 355 m, 360 m, 365 m, 370 m, 375 m, 380 m, 385 m, 390 m, 395 m, 400 m, 405 m, 410 m, 415 m, 420 m, 425 m, 430 m, 435 m, 440 m, 445 m, 450 m, 455 m, 460 m, 465 m, 470 m, 475 m, 480 m, 485 m, 490 m, 495 m, 500 m, or any value there between (e.g., 5.1 m, 5.2 m, 6 m, 7 m, etc.).

[0266] Moreover, the first mean size (d.sub.50) of the first particle size distribution of the first nanocellulose-containing composition, may fall within a range of any of the foregoing-listing particle size distributions. For example, in some embodiments the first mean size (d.sub.50) of the first particle size distribution of the first nanocellulose-containing composition, may be from 5 m to 500 m, or some other range therein.

[0267] In some embodiments, the first particle size distribution, of the first nanocellulose-containing composition, may have a steepness of 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or any value there between (e.g., 20.1, 20.2, etc.).

[0268] Moreover, the steepness, of the first particle size distribution of the first nanocellulose-containing composition, may fall within a range of any of the foregoing-listed steepnesses. For example, in some embodiments, the steepness, of the first particle size distribution of the first nanocellulose-containing composition, may be from 20 to 50, or some other range therein.

[0269] The second mean size (d.sub.50), of the second particle size distribution of the second nanocellulose-containing composition, may be 5 m, 10 m, 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, 45 m, 50 m, 55 m, 60 m, 65 m, 70 m, 75 m, 80 m, 85 m, 90 m, 95 m, 100 m, 105 m, 110 m, 115 m, 120 m, 125 m, 130 m, 135 m, 140 m, 145 m, 150 m, 155 m, 160 m, 165 m, 170 m, 175 m, 180 m, 185 m, 190 m, 195 m, 200 m, 205 m, 210 m, 215 m, 220 m, 225 m, 230 m, 235 m, 240 m, 245 m, 250 m, 255 m, 260 m, 265 m, 270 m, 275 m, 280 m, 285 m, 290 m, 295 m, 300 m, 305 m, 310 m, 315 m, 320 m, 325 m, 330 m, 335 m, 340 m, 345 m, 350 m, 355 m, 360 m, 365 m, 370 m, 375 m, 380 m, 385 m, 390 m, 395 m, 400 m, 405 m, 410 m, 415 m, 420 m, 425 m, 430 m, 435 m, 440 m, 445 m, 450 m, 455 m, 460 m, 465 m, 470 m, 475 m, 480 m, 485 m, 490 m, 495 m, 500 m, or any value there between (e.g., 5.1 m, 5.2 m, 6 m, 7 m, etc.).

[0270] Moreover, the second mean size (d.sub.50) of the second particle size distribution of the second nanocellulose-containing composition, may fall within a range of any of the foregoing-listing particle size distributions. For example, in some embodiments the second mean size (d.sub.50) of the second particle size distribution of the second nanocellulose-containing composition, may be from 5 m to 500 m, or some other range therein.

[0271] In some embodiments, the second particle size distribution, of the second nanocellulose-containing composition, may have a steepness of 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or any value there between (e.g., 20.1, 20.2, etc.).

[0272] Moreover, the steepness, of the second particle size distribution of the second nanocellulose-containing composition, may fall within a range of any of the foregoing-listed steepnesses. For example, in some embodiments, the steepness, of the second particle size distribution of the second nanocellulose-containing composition, may be from 20 to 50, or some other range therein.

[0273] In some embodiments, the first mean size (of the first particle size distribution) may be less than the second mean size (of the second particle size distribution).

[0274] In some embodiments, the first and second nanocellulose-containing compositions may comprise different nanocellulose.

[0275] In some embodiments, the first and second nanocellulose-containing compositions may comprise different amounts of nanocellulose.

[0276] In some embodiments, at least one nanocellulose-containing composition may include one or more inorganic particulate material, and at least one other nanocellulose-containing composition may be free of inorganic particulate material, or inorganic particulate material free. In some embodiments, the first nanocellulose-containing composition may include one or more inorganic particulate material, and the second nanocellulose-containing composition may be free of inorganic particulate material, or inorganic particulate material free.

Paper and Paperboard

[0277] There are numerous types of paper or paperboard possible to be made with the disclosed nanocellulose-containing compositions and by the manufacturing processes described herein. There is no clear demarcation between paper and paperboard products. The latter tend to be thicker paper-based materials with increased grammages. Paperboard may be a single ply or multi-ply. The present disclosure is directed to numerous forms of paperboard, including, by way of example and not limitation, boxboard or cartonboard, including folding cartons and rigid set-up boxes and folding boxboard; e.g. a liquid packaging board. The paperboard may be chipboard or white lined chipboard. The paperboard may be a Kraft board, laminated board. The paperboard may be a solid bleached board or a solid unbleached board. Various forms of containerboard are subsumed within the paperboard products of the present disclosure such as corrugated fibreboard (which is a building material and not a paper or paperboard product per se), linerboard or a binder's board. The paperboard described herein may be suitable for wrapping and packaging a variety of end-products, including for example foods.

[0278] In certain embodiments, the paperboard is or comprises linerboard. In certain embodiments, the linerboard is or comprises one of brown Kraft liner, white top Kraft liner, test liner, white top test liner, brown light weight recycled liner, mottled test liner, and white top recycled liner.

[0279] In certain embodiments, the paper is or comprises Kraft paper.

[0280] In certain embodiments, the paper or paperboard substrate of the present disclosure has a grammage of from about 75 g/m.sup.2 to about 400 g/m.sup.2, for example, from about 100 g/m.sup.2 to about 375 g/m.sup.2, about 100 g/m.sup.2 to about 350 g/m.sup.2, about 100 g/m.sup.2 to about 300 g/m.sup.2, about 100 g/m.sup.2 to about 275 g/m.sup.2, about 100 g/m.sup.2 to about 250 g/m.sup.2, about 100 g/m.sup.2 to about 225 g/m.sup.2, or from about 100 g/m.sup.2 to about 200 g/m.sup.2. In some embodiments, the paper or paperboard substrate of the present disclosure comprises a base layer having a grammage ranging from about 25 g/m.sup.2 to about 500 g/m.sup.2.

[0281] Advantageously, when the last-applied nanocellulose-containing composition of the present disclosure comprises inorganic particulate material, the resulting paper or paperboard may have a combination of desirable optical, surface, and mechanical properties, which are obtainable while utilizing relatively low amounts of a top ply having a high filler content, thereby offering light-weighting of the paper or paperboard compared to conventional top ply/substrate configurations. Another benefit is that application of one or more nanocellulose-containing compositions in accordance with the present disclosure can result in a substantial reduction in the amount of fibre raw material required to produce the paper or paperboard. Further, any reduction in mechanical properties which may occur following application of a nanocellulose-containing composition may be offset by increasing the grammage of the paper or paperboard substrate, which is a relatively cheaper material, thereby recovering strength properties.

[0282] In certain embodiments, the paper or paperboard may comprise a further layer, or further layers, on the top layer of nanocellulose-containing composition. For example, one or more layers or plies, or at least two further layers or plies, or up to about five further layers or plies, or up to about four further layers or plies, or up to about three further layers or plies.

[0283] In certain embodiments, one of, or at least one of, the further layers or plies is a barrier layer or ply, or wax layer or ply, or silicon layer or ply, or a combination of two or three of such layers.

[0284] Another advantageous feature of the present disclosure is improved printing on the paper or paperboard. A conventional white top liner typically has a white surface consisting of a white paper with relatively low filler content, typically in the 5-15% filler range. As a result, such white top liners tend to be quite rough and open with a coarse pore structure. This is not ideal for receiving printing ink.

Methods for Sequentially Applying Nanocellulose(s) onto the Surface of Paper and Paperboard Substrates

[0285] The present disclosure also relates to methods for sequentially applying nanocellulose(s) onto the surface of paper or paperboard substrates.

[0286] A first method of the present disclosure relates to sequentially applying nanocellulose onto the surface of a paper and paperboard substrate, where the method comprises sequentially applying at least first and second layers of a (single) nanocellulose-containing composition to a consolidating base sheet after the consolidating base sheet leaves a headbox of a paper or paperboard machine, and where at least one of the first or second layers is applied via spraying.

[0287] In some embodiments of the first method, both the first and second layers are applied via spraying.

[0288] In some embodiments of the first method, the first layer is applied via curtain or slot coating, and the second layer is applied via spraying.

[0289] In some embodiments of the first method, the method comprises applying the final (e.g., second, third, fourth, etc.) layer to cause the consolidating base sheet to have a heptane vapor transmission rate of about 0 g m.sup.2 day.sup.1 to about 100 g m.sup.2 day.sup.1.

[0290] In some embodiments of the first method, at least one of the first layer and the second layer is applied across substantially the entire width of the consolidating base sheet.

[0291] In some embodiments of the first method, at least one of the first layer and the second layer is applied across the entire width of the consolidating base sheet.

[0292] In some embodiments of the first method, the nanocellulose-containing composition comprises nanofibrillated cellulose, microfibrillated cellulose, or a combination thereof.

[0293] In some embodiments of the first method, the nanocellulose-containing composition comprises microcrystalline cellulose, nanocrystalline cellulose, cellulose nanocrystals (CNCs), or a combination thereof.

[0294] In some embodiments of the first method, the nanocellulose-containing composition comprises nanocellulose in a range of about 0.5 wt % to about 6 wt % based on the total weight of the nanocellulose-containing composition.

[0295] In some embodiments of the first method, the nanocellulose-containing composition comprises nanocellulose in a range of about 1 wt % to about 2 wt % based on the total weight of the nanocellulose-containing composition.

[0296] In some embodiments of the first method, the nanocellulose-containing composition comprises at least about 0.5 wt % nanocellulose based on the total weight of the nanocellulose-containing composition.

[0297] In some embodiments of the first method, the nanocellulose-containing composition comprises at least about 1 wt % nanocellulose based on the total weight of the nanocellulose-containing composition.

[0298] In some embodiments of the first method, the nanocellulose-containing composition comprises at least about 1.5 wt % nanocellulose based on the total weight of the nanocellulose-containing composition.

[0299] In some embodiments of the first method, the nanocellulose-containing composition comprises at least about 2.5 wt % nanocellulose based on the total weight of the nanocellulose-containing composition.

[0300] In some embodiments of the first method, the nanocellulose-containing composition comprises at most about 6 wt % nanocellulose based on the total weight of the nanocellulose-containing composition.

[0301] In some embodiments of the first method, the nanocellulose-containing composition comprises at most about 5 wt % nanocellulose based on the total weight of the nanocellulose-containing composition.

[0302] In some embodiments of the first method, the nanocellulose-containing composition comprises at most about 4 wt % nanocellulose based on the total weight of the nanocellulose-containing composition.

[0303] In some embodiments of the first method, the nanocellulose-containing composition comprises at most about 3 wt % nanocellulose based on the total weight of the nanocellulose-containing composition.

[0304] In some embodiments of the first method, the nanocellulose-containing composition comprises at most about 2 wt % nanocellulose based on the total weight of the nanocellulose-containing composition.

[0305] In some embodiments of the first method, the nanocellulose-containing composition comprises one or more inorganic particulate material. In some embodiments of the first method, the one or more inorganic particulate material comprises bentonite, alkaline earth metal carbonate, alkaline earth metal sulphate, dolomite, gypsum, hydrous kandite clay, anhydrous calcined kandite clay, talc, mica, perlite, diatomaceous earth, magnesium hydroxide, aluminum trihydrate, or a combination thereof. In some embodiments of the first method, the one or more inorganic particulate material in bentonite.

[0306] In some embodiments of the first method, the nanocellulose-containing composition comprises one or more starches. In some embodiments of the first method, the one or more starches comprise one or more cationic starches. As used herein, a cationic starch is a starch that is first cooked to dissolve the starch in water.

[0307] In some embodiments of the first method, the nanocellulose-containing composition comprises one or more sizing agents. In some embodiments of the first method, the one or more sizing agents comprise rosin, rosin/aluminum emulsion, cationic rosin emulsion, alkylketene dimer, wax emulsion, succinic acid derivative, or a combination thereof. In some embodiments of the first method, the succinic acid derivative is alkenylsuccinic anhydride.

[0308] In some embodiments of the first method, the nanocellulose-containing composition comprises one or more polyacrylamides. The one or more polyacrylamides may aid in drainage of the paper or paperboard.

[0309] In some embodiments of the first method, the nanocellulose-containing composition comprises polydiallyldimethylammonium chloride (polyDADMAC).

[0310] In some embodiments of the first method, the nanocellulose-containing composition comprises one or more copolymers.

[0311] In some embodiments of the first method, the one or more copolymers comprise ethylene vinyl alcohol (EVOH), polyvinyl alcohol (PVOH), or a combination thereof.

[0312] In some embodiments of the first method, the one or more copolymers may be applied to a top of the last nanocellulose-containing layer applied to the consolidating base sheet.

[0313] A second method of the present disclosure relates to sequentially applying nanocellulose onto the surface of a paper or paperboard substrate, where the method comprises sequentially applying at least a first nanocellulose-containing composition and a second nanocellulose-containing composition to a consolidating base sheet after the consolidating base sheet leaves a headbox of a paper machine, and where at least one of the first nanocellulose-containing composition and the second nanocellulose containing composition is applied via spraying.

[0314] In some embodiments of the second method, both the first nanocellulose-containing composition and the second nanocellulose containing composition are applied via spraying.

[0315] In some embodiments of the second method, the first nanocellulose-containing composition is applied via curtain or slot coating, and the second nanocellulose-containing composition is applied via spraying.

[0316] In some embodiments of the second method, the first nanocellulose-containing composition has a first particle size distribution, the second nanocellulose-containing composition has a second particle size distribution, and the mean size, of the first particle size distribution, is greater than the mean size of the second particle size distribution.

[0317] The mean size (d.sub.50), of the first particle size distribution of the first nanocellulose-containing composition, may be 5 m, 10 m, 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, 45 m, 50 m, 55 m, 60 m, 65 m, 70 m, 75 m, 80 m, 85 m, 90 m, 95 m, 100 m, 105 m, 110 m, 115 m, 120 m, 125 m, 130 m, 135 m, 140 m, 145 m, 150 m, 155 m, 160 m, 165 m, 170 m, 175 m, 180 m, 185 m, 190 m, 195 m, 200 m, 205 m, 210 m, 215 m, 220 m, 225 m, 230 m, 235 m, 240 m, 245 m, 250 m, 255 m, 260 m, 265 m, 270 m, 275 m, 280 m, 285 m, 290 m, 295 m, 300 m, 305 m, 310 m, 315 m, 320 m, 325 m, 330 m, 335 m, 340 m, 345 m, 350 m, 355 m, 360 m, 365 m, 370 m, 375 m, 380 m, 385 m, 390 m, 395 m, 400 m, 405 m, 410 m, 415 m, 420 m, 425 m, 430 m, 435 m, 440 m, 445 m, 450 m, 455 m, 460 m, 465 m, 470 m, 475 m, 480 m, 485 m, 490 m, 495 m, 500 m, or any value there between (e.g., 5.1 m, 5.2 m, 6 m, 7 m, etc.).

[0318] Moreover, the mean size (d.sub.50), of the first particle size distribution of the first nanocellulose-containing composition, may fall within a range of any of the foregoing-listing particle size distributions. For example, in some embodiments the mean size (d.sub.50), of the first particle size distribution of the first nanocellulose-containing composition, may be from 5 m to 500 m, or some other range therein.

[0319] In some embodiments, the first particle size distribution, of the first nanocellulose-containing composition, may have a steepness of 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or any value there between (e.g., 20.1, 20.2, etc.).

[0320] Moreover, the steepness, of the first particle size distribution of the first nanocellulose-containing composition, may fall within a range of any of the foregoing-listed steepnesses. For example, in some embodiments, the steepness, of the first particle size distribution of the first nanocellulose-containing composition, may be from 20 to 50, or some other range therein.

[0321] The mean size (d.sub.50), of the second particle size distribution of the second nanocellulose-containing composition, may be 5 m, 10 m, 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, 45 m, 50 m, 55 m, 60 m, 65 m, 70 m, 75 m, 80 m, 85 m, 90 m, 95 m, 100 m, 105 m, 110 m, 115 m, 120 m, 125 m, 130 m, 135 m, 140 m, 145 m, 150 m, 155 m, 160 m, 165 m, 170 m, 175 m, 180 m, 185 m, 190 m, 195 m, 200 m, 205 m, 210 m, 215 m, 220 m, 225 m, 230 m, 235 m, 240 m, 245 m, 250 m, 255 m, 260 m, 265 m, 270 m, 275 m, 280 m, 285 m, 290 m, 295 m, 300 m, 305 m, 310 m, 315 m, 320 m, 325 m, 330 m, 335 m, 340 m, 345 m, 350 m, 355 m, 360 m, 365 m, 370 m, 375 m, 380 m, 385 m, 390 m, 395 m, 400 m, 405 m, 410 m, 415 m, 420 m, 425 m, 430 m, 435 m, 440 m, 445 m, 450 m, 455 m, 460 m, 465 m, 470 m, 475 m, 480 m, 485 m, 490 m, 495 m, 500 m, or any value there between (e.g., 5.1 m, 5.2 m, 6 m, 7 m, etc.).

[0322] Moreover, the mean size (d.sub.50), of the second particle size distribution of the second nanocellulose-containing composition, may fall within a range of any of the foregoing-listing particle size distributions. For example, in some embodiments the mean size (d.sub.50), of the second particle size distribution of the second nanocellulose-containing composition, may be from 5 m to 500 m, or some other range therein.

[0323] In some embodiments, the second particle size distribution, of the second nanocellulose-containing composition, may have a steepness of 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or any value there between (e.g., 20.1, 20.2, etc.).

[0324] Moreover, the steepness, of the second particle size distribution of the second nanocellulose-containing composition, may fall within a range of any of the foregoing-listed steepnesses. For example, in some embodiments, the steepness, of the second particle size distribution of the second nanocellulose-containing composition, may be from 20 to 50, or some other range therein.

[0325] In some embodiments, the second method comprises applying the final (e.g., second, third, fourth, etc.) nanocellulose-containing composition to cause the consolidating base sheet to have a heptane vapor transmission rate of about 0 g m.sup.2 day.sup.1 to about 100 g m.sup.2 day.sup.1.

[0326] In some embodiments of the second method, at least one of the first nanocellulose-containing composition and the second nanocellulose-containing composition is applied across substantially the entire width of the consolidating base sheet.

[0327] In some embodiments of the second method, at least one of the first nanocellulose-containing composition and the second nanocellulose-containing composition is applied across the entire width of the consolidating base sheet.

[0328] In some embodiments of the second method, the first nanocellulose-containing composition comprises nanofibrillated cellulose, microfibrillated cellulose, or a combination thereof.

[0329] In some embodiments of the second method, the first nanocellulose-containing composition comprises microcrystalline cellulose, nanocrystalline cellulose, cellulose nanocrystals (CNCs), or a combination thereof.

[0330] In some embodiments of the second method, the first nanocellulose-containing composition comprises nanocellulose in a range of about 0.5 wt % to about 6 wt % based on the total weight of the first nanocellulose-containing composition.

[0331] In some embodiments of the second method, the first nanocellulose-containing composition comprises nanocellulose in a range of about 1 wt % to about 2 wt % based on the total weight of the first nanocellulose-containing composition.

[0332] In some embodiments of the second method, the first nanocellulose-containing composition comprises at least about 0.5 wt % nanocellulose based on the total weight of the first nanocellulose-containing composition.

[0333] In some embodiments of the second method, the first nanocellulose-containing composition comprises at least about 1 wt % nanocellulose based on the total weight of the first nanocellulose-containing composition.

[0334] In some embodiments of the second method, the first nanocellulose-containing composition comprises at least about 1.5 wt % nanocellulose based on the total weight of the first nanocellulose-containing composition.

[0335] In some embodiments of the second method, the first nanocellulose-containing composition comprises at least about 2.5 wt % nanocellulose based on the total weight of the first nanocellulose-containing composition.

[0336] In some embodiments of the second method, the first nanocellulose-containing composition comprises at most about 6 wt % nanocellulose based on the total weight of the first nanocellulose-containing composition.

[0337] In some embodiments of the second method, the first nanocellulose-containing composition comprises at most about 3 wt % nanocellulose based on the total weight of the first nanocellulose-containing composition.

[0338] In some embodiments of the second method, the first nanocellulose-containing composition comprises at most about 2 wt % nanocellulose based on the total weight of the first nanocellulose-containing composition.

[0339] In some embodiments of the second method, the second nanocellulose-containing composition comprises nanofibrillated cellulose, microfibrillated cellulose, or a combination thereof.

[0340] In some embodiments of the second method, the second nanocellulose-containing composition comprises microcrystalline cellulose, nanocrystalline cellulose, cellulose nanocrystals (CNCs), or a combination thereof.

[0341] In some embodiments of the second method, the second nanocellulose-containing composition comprises nanocellulose in a range of about 0.5 wt % to about 6 wt % based on the total weight of the second nanocellulose-containing composition.

[0342] In some embodiments of the second method, the second nanocellulose-containing composition comprises nanocellulose in a range of about 1 wt % to about 2 wt % based on the total weight of the second nanocellulose-containing composition.

[0343] In some embodiments of the second method, the second nanocellulose-containing composition comprises at least about 0.5 wt % nanocellulose based on the total weight of the second nanocellulose-containing composition.

[0344] In some embodiments of the second method, the second nanocellulose-containing composition comprises at least about 1 wt % nanocellulose based on the total weight of the second nanocellulose-containing composition.

[0345] In some embodiments of the second method, the second nanocellulose-containing composition comprises at least about 1.5 wt % nanocellulose based on the total weight of the second nanocellulose-containing composition.

[0346] In some embodiments of the second method, the second nanocellulose-containing composition comprises at least about 2.5 wt % nanocellulose based on the total weight of the second nanocellulose-containing composition.

[0347] In some embodiments of the second method, the second nanocellulose-containing composition comprises at most about 6 wt % nanocellulose based on the total weight of the second nanocellulose-containing composition.

[0348] In some embodiments of the second method, the second nanocellulose-containing composition comprises at most about 3 wt % nanocellulose based on the total weight of the second nanocellulose-containing composition.

[0349] In some embodiments of the second method, the second nanocellulose-containing composition comprises at most about 2 wt % nanocellulose based on the total weight of the second nanocellulose-containing composition.

[0350] In some embodiments of the second method, at least one of the first nanocellulose-containing composition and the second nanocellulose containing composition comprises one or more inorganic particulate material. In some embodiments of the second method, the first nanocellulose-containing composition may comprise one or more inorganic particulate material, but the second nanocellulose-containing composition may be free of inorganic particulate material. In some embodiments of the second method, the one or more inorganic particulate material comprises bentonite, alkaline earth metal carbonate, alkaline earth metal sulphate, dolomite, gypsum, hydrous kandite clay, anhydrous calcined kandite clay, talc, mica, perlite, diatomaceous earth, magnesium hydroxide, aluminum trihydrate, or a combination thereof. In some embodiments of the second method, the one or more inorganic particulate material is bentonite.

[0351] In some embodiments of the second method, at least one of the first nanocellulose-containing composition and the second nanocellulose containing composition comprises one or more starches.

[0352] In some embodiments of the second method, the one or more starches comprise one or more cationic starches.

[0353] In some embodiments of the second method, at least one of the first nanocellulose-containing composition and the second nanocellulose containing composition comprises one or more sizing agents.

[0354] In some embodiments of the second method, the one or more sizing agents comprise rosin, rosin/aluminum emulsion, cationic rosin emulsion, alkylketene dimer, wax emulsion, succinic acid derivative, or a combination thereof. In some embodiments of the second method, the succinic acid derivative is alkenylsuccinic anhydride.

[0355] In some embodiments of the second method, at least one of the first nanocellulose-containing composition and the second nanocellulose containing composition comprises one or more polyacrylamides. The one or more polyacrylamides may aid in drainage of the paper or paperboard.

[0356] In some embodiments of the second method, the nanocellulose-containing composition comprises polydiallyldimethylammonium chloride (polyDADMAC).

[0357] In some embodiments of the second method, at least one of the first nanocellulose-containing composition and the second nanocellulose containing composition comprises one or more copolymers. In some embodiments of the second method, the one or more copolymers comprise ethylene vinyl alcohol (EVOH), polyvinyl alcohol (PVOH), or a combination thereof.

[0358] In some embodiments of the second method, the one or more copolymers may be applied to a top of the last nanocellulose-containing layer applied to the consolidating base sheet.

Method of Manufacturing a Multi-Ply Paper or Paperboard Product

[0359] An aspect of the present disclosure relates to a method of manufacturing a multi-ply paper or paperboard product. The method includes providing a consolidating base sheet of pulp following a headbox of a paper or paperboard machine, applying two or more layers of one or more nanocellulose-containing compositions onto the consolidating base sheet to form a consolidating multi-layer paper or paperboard structured material, and dewatering the multi-layer paper or paperboard structured material to produce the multi-ply paper or paperboard product. According to the method, a first layer of nanocellulose-containing composition is applied to the consolidating base sheet in an amount ranging from about 0.1 g/m.sup.2 to about 20 g/m.sup.2, a second layer of nanocellulose-containing composition is applied to the consolidating base sheet in an amount ranging from about 1 g/m.sup.2 to about 20 g/m.sup.2, and at least one of the first or second layers of nanocellulose-containing composition is applied by spraying.

[0360] Example pulps include, but are not limited to, recycled pulp, papermill broke, paper streams rich in mineral fillers, cellulosic materials from a papermill, chemical pulp, thermomechanical pulp, chemi-thermomechanical pulp, mechanical pulp, or a combination thereof. In some embodiments, the pulp comprises recycled paperboard. In some embodiments, the recycled paperboard is recycled corrugated containers.

[0361] The nanocellulose may include nanofibrillated cellulose, microfibrillated cellulose, or a combination thereof. The nanocellulose may additionally or alternatively include microcrystalline cellulose, nanocrystalline cellulose, cellulose nanocrystals (CNCs), or a combination thereof.

[0362] In some embodiments, the nanocellulose may be produced from hardwood pulp, softwood pulp, wheat straw pulp, bamboo, bagasse, virgin fibre, chemical pulp, chemithermomechanical pulp, mechanical pulp, thermomechanical pulp, kraft pulp, bleached long fibre kraft pulp, eucalyptus pulp, spruce pulp, pine pulp, beech pulp, hemp pulp, acacia cotton pulp, recycled pulp, papermill broke, paper steam rich in mineral fillers, or a combination thereof.

[0363] In some embodiments, the hardwood pulp may be selected from the group consisting of eucalyptus, aspen, birch, and mixed hardwood pulps. In some embodiments, the hardwood pulp may include at least one of eucalyptus, aspen, birch, and mixed hardwood pulp.

[0364] In some embodiments, the softwood pulp may be selected from the group consisting of spruce, pine, fir, larch, hemlock, and mixed softwood pulp. In some embodiments, the softwood pulp may include at least one of spruce, pine, fir, larch, hemlock, and mixed softwood pulp.

[0365] The method, of manufacturing a multi-ply paper or paperboard product, may include applying one or more additional layers atop the two or more layers of one or more nanocellulose-containing compositions. In some embodiments, the one or more additional layers may include one or more of a barrier layer, a wax layer, and a silicon layer.

[0366] The method, of manufacturing a multi-ply paper or paperboard product, may include applying an additional layer atop the two or more layers of one or more nanocellulose-containing compositions. In some embodiments, the additional layer may consist essentially of inorganic particulate material and nanocellulose. In some embodiments, the additional layer may consist essentially of inorganic particulate material and microfibrillated cellulose.

[0367] Examples of inorganic particulate material include calcium carbonate, ground calcium carbonate, precipitated calcium carbonate, magnesium carbonate, dolomite, gypsum, an anhydrous kandite clay, kaolin, perlite, bentonite, diatomaceous earth, wollastonite, talc, magnesium hydroxide, titanium dioxide, or aluminium trihydrate, or a combination thereof. In some embodiments, the inorganic particulate material comprises ground calcium carbonate and precipitated calcium carbonate.

[0368] The present disclosure also envisions a paper or paperboard manufacturing using the foregoing method. The paper or paperboard may, in some embodiments, include a base layer having a grammage ranging from about 25 g/m.sup.2 to about 500 g/m.sup.2. In some embodiments the paper or paperboard may be a white top containerboard.

EXAMPLES

Example 1. Paper Machine Trial

[0369] During a pilot paper machine trial, MFC surface application techniques based on curtain coating and spraying (up to 3 nozzles in sequence) were evaluated onto surfaces of bleached (80% UPM Eucalyptus, 20% St. Felecien softwood co-refined to 350 CSF) and unbleached (100% softwood Kraft 450 CSF) pulp furnishes. In the case of the bleached furnish, the MFC applied to the surface was prepared from bleached Eucalyptus pulp, and in the case of the unbleached furnish, the MFC applied to the surface was prepared from unbleached softwood Kraft pulp.

[0370] Trial points 2-7 were prepared using the bleached pulp furnish and bleached pulp MFC. Trial points 10 and 12-17 were prepared using unbleached pulp furnish and unbleached pulp MFC. Trial points 18-21 were prepared using unbleached pulp furnish and unbleached pulp MFC that had been mixed with ground calcium carbonate (GCC) in a ratio of 1:1 (based on dry mass) to improve the visibility of the homogeneity/uniformity of coated surfaces. The results are summarized in Table 1 below.

TABLE-US-00001 TABLE 1 Summary of trial conditions and results evaluating curtain and spraying surface application techniques at the wet end of a paper machine. Est. HVTR Tensile Actual Suspension Gurley (23 C., Index Trial MFC Coat Composition Surface Bendtsen Porosity 50% R.H.) (Machine Burst Point Weight (based on dry App. Porosity sec/ g/m.sup.2/ Direction) Index ID g/m.sup.2 matter) Method ml/min 100 ml day N .Math. m/g kN/g 2 0 N/A Uncoated 1408 9 2388 79.8 3.7 3 10 100% MFC Curtain 0 172059 22 94.2 4.4 4 12 (Bleached) Curtain 0 101682 24 98.8 4.6 5 2.5 1 spray 107 112 1704 98.8 4.4 nozzle 6 2.5 2 spray 42 288 1204 109.2 5.0 nozzles 7 2.5 3 spray 39 280 1081 99.6 4.9 nozzles 12 0 N/A Uncoated 290 43 1861 99.7 4.5 10 12 100% MFC Curtain 0 106890 28 107.0 4.7 13 2.5 (Unbleached) 1 spray 31 397 1073 93.8 3.8 nozzle 14 2.5 2 spray 11 1044 686 103.7 4.3 nozzles 15 2.5 3 spray 4 2615 216 108.2 4.4 nozzles 16 3 3 spray 4 3716 183 109.3 4.6 nozzles 17 4 3 spray 3 4501 121 109.1 4.3 nozzles 20 2.5 50% MFC 3 spray 43 259 1244 82.9 3.4 (Unbleached)/ nozzles 19 25 50% GCC 3 spray 19 607 1087 88.8 3.4 nozzles 18 2.5 3 spray 8 1411 908 95.2 4.0 nozzles 21 2.25 3 spray 4 2935 652 97.4 3.6 nozzles HVTR = n-Heptane Vapour Transmission Rate.

The Results Indicated:

[0371] MFC applied by curtain surface application technique provided the greatest improvements to sheet properties (as indicated by low Bendtsen Porosity and HVTR, and high Gurley Porosity, Tensile Index and Burst Index values).

[0372] Applying the MFC via spraying led to disruption of the sheet web when using 1 nozzle. As the number of nozzles were increased, and the same coat weight was applied sequentially, the sheet properties were improved.

[0373] Visual analysis of the resultant sheets of paper coated with spraying indicated that utilizing more nozzles in sequence improved the uniformity and homogeneity of the coating and led to less disruption of the base substrate (see FIGS. 5 and 6).

Example 2. Sequentially-Applied Layers of Two Types of Microfibrillated Cellulose

[0374] Two types of MFC samples were prepared from softwood and hardwood pulps, respectively, by grinding in a stirred media mill.

TABLE-US-00002 TABLE 2 Valmet Fibre Analyser parameters for MFC products. % fines B Fibre (high Lc(l)/ Lc(w)/ width/ aspect % Sample mm mm m % fines ratio) fibrillation MFC A 0.21 0.311 17.8 92.1 49.9 6.18 (softwood) MFC B 0.42 0.618 20.9 85.02 15.61 4.97 (hardwood)

TABLE-US-00003 TABLE 3 Malvern Insitec parameters for MFC products. Steepness Sample D30/m D50/m D70/m factor MFC A (softwood) 54 103 176 31 MFC B (hardwood) 75 146 277 27

[0375] MFC A was made by a batch grinding process. MFC B was made by a continuous grinding process. Both were ground with about 3,000 kWh/t.

[0376] MFC was applied as one or more surface layers to freshly-formed base sheets by filtration using the laboratory method described below.

[0377] An 80 g m.sup.2 base sheet, made from a blend of 70/30 Eucalyptus/Pine bleached Kraft pulp refined to CSF 450 ml, was formed in a standard Messmer handsheet former (TAPPI T205) but not pressed or dried.

[0378] Once the base sheet was formed, some of the retained water was removed by manually pressing the sheet with three blotting papers. No adhesion was observed between the blotters and the sheet.

[0379] The base sheet was then turned upside down for its smoother side to be on top, and transferred to a second, vacuum-assisted handsheet former.

[0380] A specific amount of microfibrillated cellulose at a total solids content of 1.5% was measured out to achieve the desired grammage of the applied first layer on top of the base sheet. This was then diluted to a final volume of 400 ml with water.

[0381] The dilute suspension of microfibrillated cellulose was then carefully poured over the base sheet in the second former so that the formation of the base sheet was not disturbed. Vacuum was then applied to the underside of the sheet to drain the water through it and form a layer of the microfibrillated cellulose on top of the base sheet.

[0382] Once drainage was complete, the vacuum was released. A further diluted suspension of a second microfibrillated cellulose product was then applied in the same way to the sheet to form a second layer of microfibrillated cellulose on top of the first.

[0383] After formation of the layers of microfibrillated cellulose on the surface of the sheet, it was transferred to a Rapid Kthen handsheet dryer (90 C., 1 bar pressure) for simultaneous pressing and drying for a period of 6 minutes.

[0384] On completion of the drying step, the sheet was left overnight in a laboratory with a conditioned atmosphere of 23 C. and 50% RH.

[0385] After conditioning, the Gurley porosity of each sheet was measured according to TAPPI T460. The heptane vapour transmission rate of each sheet was also measured using the following procedure.

[0386] 10 ml of heptane liquid was placed in a permeability cup (ASTM E96).

[0387] A circle of diameter 7.46 cm was cut from the sheet and placed over the cup with the MFC coated side facing downwards towards the heptane liquid. The cup was then sealed so that vapour could only escape by passing through the sheet.

[0388] The initial weight of the cup with the heptane and sample in place was recorded, then the cup was left in a conditioned laboratory at 23 C. and 50% RH.

[0389] The cup was re-weighed periodically over a 24 hr. period. The weight of the cup as a function of time was plotted and fitted to a simple linear function.

[0390] Weight loss was attributed to passage of heptane vapor through the sample, and the heptane vapor transmission rate was calculated from the gradient of the plot of weight in grams vs. time in hours according to Formula 1.

[00001]$\begin{array}{cc}HVTR\left({\mathrm{gm}}^{-2}{\mathrm{day}}^{-1}\right)=\frac{24\mathrm{gradient}}{\mathrm{Area}\left(m^2\right)}& \mathrm{Formula}1\end{array}$

[0391] Table 4 shows the measured values of Gurley porosity and heptane vapor transmission rate of samples coated with MFC as described above. Where one type of MFC only is used, MFC B gives a higher value for Gurley porosity and a lower value for HVTR than MFC A. However, when two layers are used, equivalent performance to MFC B is obtained even when the lower layer of MFC A comprises of the total. These data are represented graphically in FIGS. 7 and 8.

TABLE-US-00004 TABLE 4 Gurley porosity and heptane vapour transmission rate of MFC coated paper samples MFC A MFC B Trial (softwood)/ (hardwood)/ Total Gurley HVTR/g point gsm gsm MFC/gsm porosity/s m.sup.2 day.sup.1 1 0 0 0 6 2443 2 2 0 2 12 2371 3 4 0 4 91 1675 4 6 0 6 587 1351 5 0 2 2 33 2194 6 0 4 4 2618 417 7 0 6 6 21071 25 8 2 2 4 2905 222 9 2 4 6 21283 28 10 4 2 6 18871 34

Example 3

[0392] The samples for Example 3 were prepared and tested in the following manner.

Experimental Procedure

[0393] The solids content of MFC measured before coating by drying a suspension of MFC in the oven and recording mass of dry and wet sample. The mass of MFC required to make a 6 gsm coating on the base paper was calculated. A circle of the base paper was cut out around the filtration mesh part of an FLT former. The required mass of MFC to coat 6 gsm on the paper was diluted to 250 ML with water. The base paper was wetted under a tap and attached to the FLT former mesh with vacuum filtration. The vacuum was then turned off and the dilute MFC suspension was poured over the sheet. The vacuum was then turned on until all visible water had drained. At this point, the coated paper was removed from the filtration mesh and dried in Rapid Kothen driers for 7 minutes. The sheets were conditioned at 50% relative humidity and 23 degrees Celsius for a minimum of 15 hours before testing. The Kit test was performed according to the TAPPI standard with the modification that only two sheets were tested per sample. Bendtsen porosity is a measure of air permeability-measured using Twinhead PPS Parker Print Surf machine at a clamping pressure of 2000 kPa with air blast off and hard backing. 7 measurements were made across 2 sheets for each MFC sample. Heptane vapour transmission rate is measured by putting 8 mL of heptane in a metal pot and clamping a circle cut out from the centre of an MFC coated sheet over the pot and weighing every 2 hours for 6 hours. The rate of heptane loss over time is measured and the area of the exposed paper is used to calculate the rate of heptane vapour transmission per area. This was measured in triplicate.

Interpretation of Results

[0394] For birch, acacia and unbleached eucalyptus, when the FLT of the material increases, the HVTR decreases, Kit increases and air permeability decreases. For eucalyptus, at high FLT, there is a decrease in HVTR and Kit test, suggesting some of the material is lost into the base sheet. The results show that the FLT test is a useful indication of barrier performance across multiple pulp types. The sequential layer application method of MPC may help to prevent the loss of MPC material into the sheet when high FLT materials are used.

TABLE-US-00005 Bendtsen porosity HVTR FLT Bendtsen standard standard index/ porosity error HVTR error Fines Sample Pulp N ml ml Kit g m.sup.2 g m.sup.2 Malvern B name Type mg1 min1 min1 number day.sup.1 day.sup.1 Steepness % B1 Birch 6.9 66 3 0 1761.9 27.4 28.5 6.1 B2 Birch 8.2 19 1 0 1013.4 46.2 27.5 9.09 B3 Birch 11.4 2 0 4 186.6 40.2 30.3 14.6 B4 Birch 14.3 1 0 5 34.1 2.9 35.7 24.19 A2 Acacia 5.7 249 9 0 2038.9 131.6 23.0 7.88 A3 Acacia 8.2 6 1 2 566.0 37.8 26.0 9.06 A4 Acacia 9.2 7 1 2 736.8 28.9 27.3 9.16 A5 Acacia 10.7 1 0 7 83.1 7.5 32.0 29.02 N1 Botnia 8.6 8 2 2 873.8 151.7 25.8 20.66 RMA90 N2 Botnia 8.6 12 1 1 1090.1 15.0 24.1 28.01 RMA90 N3 Botnia 14.1 4 1 4 443.9 62.4 29.8 74.26 RMA90 N4 Botnia 14.7 4 1 1 352.1 34.0 40.5 68.35 RMA90 E5 Eucalyptus 7.1 29 1 1 1540.9 240.7 27.1 5.31 E4 Eucalyptus 9.0 5 1 3 449.2 102.3 25.6 7.68 E1 Eucalyptus 10.7 1 0 5 60.1 8.1 26.9 15.61 E3 Eucalyptus 11.2 1 0 7 27.5 1.8 28.8 10.94 E7 Eucalyptus 14.6 0 0 6 22.6 19.4 34.2 35.76 E6 Eucalyptus 16.6 4 1 1 294.4 54.0 39.2 70.93 X1 Unbleached 9.2 18 1 2 957.1 283.2 26.0 4.73 Eucalyptus X2 Unbleached 10.6 5 0 5 876.6 218.3 29.0 8.8 Eucalyptus X3 Unbleached 12.7 0 0 6 27.7 8.5 29.0 13.79 Eucalyptus R None- N/A 782 10 0 2216.9 5.9 reference sheet. Base with water filtered through

Further Definitions

[0395] The titles, headings and subheadings provided herein should not be interpreted as limiting the various aspects of the disclosure. Accordingly, the terms defined below are more fully defined by reference to the specification in its entirety. All references cited herein are incorporated by reference in their entirety.

[0396] Unless otherwise defined, scientific and technical terms used herein shall have the meanings that are commonly understood by those of ordinary skill in the art. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

[0397] In this application, the use of or means and/or unless stated otherwise. In the context of a multiple dependent claim, the use of or refers to more than one preceding independent or dependent claim in the alternative only.

[0398] It is further noted that, as used in this specification and the appended claims, the singular forms a, an, and the, and any singular use of any word, include plural referents unless expressly and unequivocally limited to one referent.

[0399] The instant disclosure is most clearly understood with reference to the following definitions.

[0400] The term about is used herein to mean approximately, in the region of, roughly, or around. When the term about is used in conjunction with a numerical range, it modifies that range by extending the boundaries above and below the numerical values set forth. In general, the term about is used herein to modify a numerical value above and below the stated value by a variance of 10%.

[0401] As used herein, the terms comprising (and any form of comprising, such as comprise, comprises, and comprised), having (and any form of having, such as have and has), including (and any form of including, such as includes and include), or containing (and any form of containing, such as contains and contain), are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. Additionally, a term that is used in conjunction with the term comprising is also understood to be able to be used in conjunction with the term consisting of or consisting essentially of.

[0402] The term dry weight is intended to mean the weight of the composition free of liquid, in particular free of water.

[0403] As used herein, the term includes and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.

[0404] As used herein, the phrase integer from X to Y means any integer that includes the endpoints. For example, the phrase integer from 1 to 5 means 1, 2, 3, 4, or 5.

[0405] The term recycled cellulose-containing materials means recycled pulp or a papermill broke and/or industrial waste, or paper streams rich in mineral fillers and cellulosic materials from a papermill.

[0406] For the avoidance of doubt, insofar as is practicable any embodiment of a given aspect of the present disclosure may occur in combination with any other embodiment of the same aspect of the present disclosure. In addition, insofar as is practicable it is to be understood that any preferred or optional embodiment of any aspect of the present disclosure should also be considered as a preferred or optional embodiment of any other aspect of the present disclosure.

[0407] The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present disclosure. Also, the description of the embodiments of the present disclosure is intended to be illustrative and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.

[0408] It is to be understood that while the disclosure has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the disclosure, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.

[0409] The various embodiments described in this specification can be combined to provide further embodiments. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications, and publications to provide yet further embodiments.

[0410] The disclosures of each patent, patent application, publication, and accession number cited herein are hereby incorporated herein by reference in their entirety.

[0411] While the present disclosure has been disclosed with reference to various embodiments, it is apparent that other embodiments and variations of these may be devised by others skilled in the art without departing from the true spirit and scope of the disclosure. The appended claims are intended to be construed to include all such embodiments and equivalent variations. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.

[0412] The foregoing written specification is sufficient to enable one skilled in the art to practice the embodiments. The foregoing description and Examples detail certain embodiments and describes the best mode contemplated by the inventors. It will be appreciated, however, that no matter how detailed the foregoing may appear in text, the embodiment may be practiced in many ways and should be construed in accordance with the appended claims and any equivalents thereof.