Method to produce a fibrous product comprising microfibrillated cellulose

Abstract

A method for the production of a fibrous product from a fibrous web, wherein the method comprises the steps of: —providing a fibrous suspension comprising a microfibrillated cellulose, wherein the content of the microfibrillated cellulose of said suspension is in the range of 60 to 99.9 weight-% based on total dry solid content, —adding an uncharged, amphoteric or weakly cationic polymer having a molecular weight of at least 50000 g/mol to said suspension, —adding an anionic polymer having a molecular weight of at least 00000 g/mol to said suspension to provide a mixture of said microfibrillated cellulose, said uncharged, amphoteric or weakly cationic polymer and said anionic polymer, 1—providing said mixture to a substrate to form a fibrous web, wherein the amount of uncharged, amphoteric or weakly cationic polymer in said mixture is in the range of 0.1 to 20 kg/metric ton based on total dry solid content and wherein the amount of anionic polymer in said mixture is in the range of 0.01 to 10 kg/metric ton based on total dry 20 solid content; and—dewatering said fibrous web to form a fibrous product.

Claims

1. A method for the production of a fibrous product from a fibrous suspension, wherein the method comprises the steps of: providing a fibrous suspension comprising a microfibrillated cellulose, wherein a content of the microfibrillated cellulose of said suspension is in a range of 60 to 99.9 weight-% based on total dry solid content, adding an uncharged, amphoteric or weakly cationic polymer having a molecular weight of at least 50,000 g/mol to said suspension, adding an anionic polymer having a molecular weight of at least 100,000 g/mol to said suspension to provide a mixture of said microfibrillated cellulose, said uncharged, amphoteric or weakly cationic polymer and said anionic polymer, providing said mixture to a substrate to form a fibrous web, wherein an amount of uncharged, amphoteric or weakly cationic polymer in said mixture is in a range of 0.1 to 20 kg/metric ton based on a total dry solid content and wherein an amount of anionic polymer in said mixture is in the range of 0.01 to 10 kg/metric ton based on the total dry solid content; and dewatering said fibrous web to form a fibrous product, wherein the fibrous product is a film.

2. The method as claimed in claim 1, wherein the production of the fibrous product is done in a paper making machine and wherein the substrate is a porous wire on which the mixture forms a fibrous web.

3. The method as claimed in claim 2, wherein a production speed of said paper making machine is in a range of 20 to 1200 m/min.

4. The method as claimed in claim 1 wherein the substrate is a paper, a paperboard, a polymer, or a metal substrate.

5. The method as claimed in claim 1, wherein the film has a basis weight of less than 40 g/m.sup.2 and a density in a range of from 700 to 1000 kg/m.sup.3.

6. The method as claimed in claim 1, wherein the uncharged, amphoteric or weakly cationic polymer is amphoteric guar gum.

7. The method as claimed in claim 6, wherein the uncharged, amphoteric or weakly cationic polymer is guar gum and a content of said guar gum in the web is in a range of 0.1 to 20 kg/metric ton based on a total dry solid content.

8. The method as claimed in claim 1, wherein the uncharged, amphoteric or weakly cationic polymer is uncharged guar gum.

9. The method as claimed in claim 1, wherein the anionic polymer is selected from the group consisting of: superfine MFC, anionic carboxymethylcellulose, synthetic polymers, or anionic guar gum.

10. The method as claimed in claim 9, wherein the anionic polymer is anionic polyacrylamide.

Description

DETAILED DESCRIPTION

(1) According to the inventive method a fibrous product such as a film is formed, by providing a fibrous suspension onto a substrate and dewatering the web to form said fibrous product such as film.

(2) According to one embodiment a suspension comprising a microfibrillated cellulose is provided to form said fibrous product.

(3) The fibrous content of the fibrous suspension may, according to one embodiment be in the range of from 60 to 99.9 weight-% based on total dry solid content. According to an alternative embodiment the fibrous content may be in the range of 70 to 95 weight-% based on total dry solid content, or in the range of from 75 to 90 weight-% based on total dry solid content.

(4) According to one embodiment the fibrous content is exclusively formed by the microfibrillated cellulose.

(5) Microfibrillated cellulose (MFC) shall in the context of the patent application mean a nano scale cellulose particle fiber or fibril with at least one dimension less than 100 nm. MFC comprises partly or totally fibrillated cellulose or lignocellulose fibers. The liberated fibrils have a diameter less than 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. The smallest fibril is called elementary fibril and has a diameter of approximately 2-4 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 (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 to more than 10 micrometers. A coarse MFC grade might contain a substantial fraction of fibrillated fibers, i.e. protruding fibrils from the tracheid (cellulose fiber), and with a certain amount of fibrils liberated from the tracheid (cellulose fiber).

(6) There are different acronyms for MFC such as cellulose microfibrils, fibrillated cellulose, nanofibrillated cellulose, fibril aggregates, nanoscale cellulose fibrils, cellulose nanofibers, cellulose nanofibrils, cellulose microfibers, cellulose fibrils, microfibrillar cellulose, microfibril aggregrates and cellulose microfibril aggregates. MFC can also be characterized by various physical or physical-chemical properties such as large surface area or its ability to form a gel-like material at low solids (1-5 weight-%) when dispersed in water. The cellulose fiber is preferably fibrillated to such an extent that the final specific surface area of the formed MFC is from about 1 to about 200 m.sup.2/g, or more preferably 50-200 m.sup.2/g when determined for a freeze-dried material with the BET method.

(7) Various methods exist to make MFC, such as single or multiple pass refining, pre-hydrolysis followed by refining or high shear disintegration or liberation of fibrils. One or several pre-treatment step is usually required in order to make MFC manufacturing both energy efficient and sustainable. The cellulose fibers of the pulp to be supplied may thus be pre-treated enzymatically or chemically, for example to hydrolyse or swell fiber or reduce the quantity of hemicellulose or lignin. The cellulose fibers may be chemically modified before fibrillation, wherein the cellulose molecules contain functional groups other (or more) than found in the original cellulose. Such groups include, among others, carboxymethyl (CMC), aldehyde and/or carboxyl groups (cellulose obtained by N-oxyl mediated oxydation, for example “TEMPO”), or quaternary ammonium (cationic cellulose). After being modified or oxidized in one of the above-described methods, it is easier to disintegrate the fibers into MFC or nanofibrillar size or NFC.

(8) The nanofibrillar cellulose may contain some hemicelluloses; the amount is dependent on the plant source. Mechanical disintegration of the pre-treated fibers, 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. Depending on the MFC manufacturing method, the product might also contain fines, or nanocrystalline cellulose or e.g. other chemicals present in wood fibers or in papermaking process. The product might also contain various amounts of micron size fiber particles that have not been efficiently fibrillated. MFC is produced from wood cellulose fibers, both from hardwood or softwood fibers. It can also be made from microbial sources, agricultural fibers such as wheat straw pulp, bamboo, bagasse, or other non-wood fiber sources. It is preferably made from pulp including pulp from virgin fiber, e.g. mechanical, chemical and/or thermomechanical pulps. It can also be made from broke or recycled paper. Preferably, the MFC is made from softwood fibers.

(9) The above described definition of MFC includes, but is not limited to, the new proposed TAPPI standard W13021 on cellulose nanofibril (CNF) defining a cellulose nanofiber material containing multiple elementary fibrils with both crystalline and amorphous regions, having a high aspect ratio with width of 5-30 nm and aspect ratio usually greater than 50.

(10) According to one embodiment the MFC may have a Schopper Riegler value (SR.sup.o) of more than 90. According to another embodiment the MFC may have a Schopper Riegler value (SR.sup.o) of more than 93. According to yet another embodiment the MFC may have a Schopper Riegler value (SR.sup.o) of more than 95. The Schopper-Riegler value can be obtained through the standard method defined in EN ISO 5267-1. This high SR value is determined for a re-pulped wet web, with or without additional chemicals, thus the fibers have not consolidated into a film or started e.g. hornification.

(11) The dry solid content of this kind of web, before disintegrated and measuring SR, is less than 50% (w/w). To determine the Schopper Riegler value it is preferable to take a sample just after the wire section where the wet web consistency is relatively low. The skilled person understands that paper making chemicals, such as retention agents or dewatering agents, have an impact on the SR value.

(12) The SR value specified herein, is to be understood as an indication but not a limitation, to reflect the characteristics of the MFC material itself. However, the sampling point of MFC might also influence the measured SR value. For example, the furnish could be either a fractionated or an unfractionated suspension and these might have different SR values. Therefore, the specified SR values given herein, are thus either a mixture of coarse and fine fractions, or a single fraction comprising an MFC grade providing the desired SR value.

(13) According to another embodiment the fibrous content is formed by a mixture of different types of fibers, such as microfibrillated cellulose, and a smaller amount of other types of fiber, such as short fibers, fine fibers, long fibers etc. By smaller amount is meant around 10% of the total fibrous content in the suspension, i.e. the main part of the fibrous content is a microfibrillated cellulose.

(14) The MFC used in the context of the present invention is preferably non-chemically modified MFC, such as native MFC or hydrophobized MFC. However, the MFC used in the context of the present invention may also be a mixture of non-chemically modified and chemically modified MFC.

(15) Preferably, the MFC has a high aspect ratio, i.e. length/diameter in the range of at least 100:1, preferably at least 500:1 or more preferably at least 1000:1. Preferably, the MFC is never-dried MFC or MFC that has been subjected to drying or MFC that has been concentrated to a dryness of at least 20%.

(16) The fibrous suspension may also comprise other additives, such as fillers, pigments, retention chemicals, cross-linkers, optical dyes, fluorescent whitening agents, de-foaming chemicals, salts, pH adjustment chemicals, surfactants, biocides, optical chemicals, pigments, nanopigments (spacers) etc.

(17) According to another embodiment the amphoteric polymer may be any one of an amphoteric hydrocolloid, such as scleroglucan, alginate, carrageenans, pectins, xanthan, hemicelluloses and amphoteric glucomannan, such as galactoglucomannan or a combination of such polymers. The hydrocolloid grade may be of both technical and high purity.

(18) The amphoteric properties can be either naturally derived or achieved by chemical modification by adsorbing e.g. multivalent metal salts or polyelectrolytes.

(19) According to an alternative embodiment the amphoteric polymer may be a starch.

(20) The mixture of the microfibrillated cellulose, the uncharged, amphoteric or weakly cationic polymer and the anionic polymer is then provided onto a substrate to form a wet web.

(21) The substrate may be a porous wire of a paper making machine.

(22) The paper making machine may be any conventional type of machine known to the skilled person used for the production of paper, paperboard, tissue or similar products.

(23) According to one embodiment the production speed of the paper making machine may be in the range of 30 to 1200 m/min.

(24) The substrate may be a paper or paperboard substrate onto which the web is formed. The substrate may also be a polymer or metal substrate.

(25) Subsequent to the wet web being placed onto the substrate, it is dewatered to form a fibrous product.

(26) The dewatering may, according to one embodiment be performed by vacuum, hot air, hot calenders etc.

(27) According to one embodiment the wet web is dewatered by vacuum, i.e. water, and other liquids, is sucked from the web when it is placed on the substrate.

(28) According to one embodiment the basis weight of the fibrous product such as a film is in the range of from 10 to 40 g/m.sup.2. According to an alternative embodiment the basis weight of the fibrous product such as a film is in the range of from 12 to 35 g/m.sup.2

(29) According to one embodiment the density of the fibrous product such as film is in the range of from 700 to 1600 g/m.sup.3. According to one alternative embodiment the density of the fibrous product such as film is in the range of from 700 to 1400 g/m.sup.3. According to yet one alternative embodiment the density of the fibrous product such as film is in the range of from 700 to 1200 g/m.sup.3. According to one embodiment the density of the fibrous product such as film is in the range of from 800 to 920 g/m.sup.3.

(30) The density of the fibrous product such as film may vary depending on several factors; one of them is the filler content. If the filler content is in the range of 10-20% the density of the fibrous product such as film may be in the upper part of the range, i.e. around 1400-1600 kg/m.sup.3.

(31) According to one embodiment, for a fibrous product such as film having a grammage of 30 gsm and at a relative humidity of 50%, the fibrous product such as film may have an oxygen transmission rate (OTR) below 30 cc/m.sup.2/24 h, or below 10 cc/m.sup.2/24 h, or below 5 cc/m.sup.2/24 h measured according to the standard ASTM D-3985.

(32) According to one embodiment the fibrous product such as film comprising the microfibrillated cellulose may be laminated to or with a thermoplastic polymer. The thermoplastic polymer may be any one of a polyethylene (PE), a polyethylene terephthalate (PET) and a polylactic acid (PLA). The polyethylene may be any one of a high density polyethylene (HDPE) and a low density polyethylene (LDPE), or various combinations thereof. By using for instance PLA as the thermoplastic polymer the product may be formed completely from biodegradable materials.

(33) The film or the laminate may also be applied to other paper products, such as food containers, paper sheets, paper boards or boards or other structures that need to be protected by a barrier film.

Examples

(34) The effect of mixing fiber suspensions in a Diaf-mixer on fibril aggregation was studied in the presence of various additives. Prior to mixing, the suspensions were diluted to 1.5 wt-% consistency using RO (reverse osmosis) water. The initial dispersing was typically done by dispersing a set amount of fiber suspension in a dilute solution of chemical additive using a rod mixer for 30 seconds (=standard mode of addition). In a reverse addition mode, the dilute solution of chemical additive was applied into the fibril suspension. In standard dual additive systems, the first chemical was applied using the standard mode of addition, i.e. fibrils introduced into the additive solution, and the second additive was dosed into the formed mixture. In the reversed dual mode, both chemical solutions were introduced into the fibril suspension. In premixing mode, the chemical additives were mixed together prior introducing the fibrils into the formed solution using the standard mode of addition. The contact time between additives and fibrils was kept short.

(35) The obtained suspensions were then mixed in a Diaf-mixer for 10 minutes. Samples were taken after 0 min (=mixed with rod mixer), and after mixing the suspension in a Diaf-mixer for 2 min and 10 min. The samples were diluted to 0.01% consistency and visually evaluated to evaluate the effect of different additives to aggregate formation during mixing.

(36) The visual evaluation was done in following basis: 0=heavy aggregation observed as a result of mixing 1=amount of aggregates was clearly increased in mixing, possibly some yarn formed in the blade 2=some loose clusters in blade, amount of aggregates was not significantly increased in mixing 3=loose clusters in blade, amount of aggregates was reduced to some extent as a result of mixing 4=clear dispersing effect, formation of aggregates clearly reduced

(37) TABLE-US-00001 Mode of Additive 1, Additive 2, chemical wt % of o.d. wt % of o.d. Sample addition fiber fiber Evaluation Reference — — — 1 Native guar gum Standard 0.1  — 2.5 (GG) High Mw A-PAM Standard 0.05 3 (H-APAM) Low Mw A-PAM Standard 0.05 1.5 (L-APAM) C-PAM Standard 0.05 1 Low-foam Standard 0.05 1 nonionic surfactant GG + H-APAM Standard GG 0.1 H-APam 4 dual 0.05 H-APAM + GG Standard H-APam GG 0.1 4− dual 0.05 GG + L-APAM Standard GG 0.1 L-APam 3+ dual 0.05 L-APAM + GG Standard L-APam GG 0.1 3+ dual 0.05 L-APAM + GG Premixing L-APam GG 0.1 1.5 0.05 GG + C-PAM Standard GG 0.1 C-PAM 3.5 dual 0.05 GG + L-APAM Reversed GG 0.1 L-APam 3+ dual 0.05 APAM = anionic polyacrylamide C-PAM = cationic polyacrylamide GG = guar gum

(38) In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.