A 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 native microfibrillated cellulose, wherein the content of the microfibrillated cellulose of said suspension is in the range of 40 to 99.9 weight-% based on total dry solid content, said fibrous suspension further comprising organic acid, a metal salt or a mixture thereof, wherein the amount of organic acid, metal salt or mixture thereof is at least 2 weight-% based on total dry solid content of the suspension, —said fibrous suspension also comprising an uncharged, amphoteric or weakly cationic polymer having a molecular weight of at least 50000 g/mol, —said fibrous suspension also comprising an anionic polymer having a molecular weight of at least 10000 g/mol to said suspension, —providing said suspension to a substrate to form a fibrous web, wherein the amount of uncharged, amphoteric or weakly cationic polymer in said suspension 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 suspension is in the range of 0.01 to 10 kg/metric ton based on total dry solid content; and —dewatering said fibrous web to form a fibrous product.

Claims

1. A method to reduce or prevent agglomeration of fibers or fibrils in an aqueous suspension comprising native microfibrillated cellulose, wherein the suspension contains 0.3-20 weight-% solids, and wherein the method comprises: providing a fibrous suspension comprising native microfibrillated cellulose, wherein a content of the microfibrillated cellulose of said suspension is in a range of 40 to 99.9 weight-% based on a total dry solid content of the fibrous suspension, said fibrous suspension further comprising an organic acid, or a metal salt, or a mixture thereof, wherein an amount of the organic acid, the metal salt or the mixture thereof is at least 2 weight-% based on the total dry solid content of the fibrous suspension, said fibrous suspension also comprising an uncharged, amphoteric, or weakly cationic polymer having a molecular weight of at least 50,000 g/mol, and, said fibrous suspension also comprising an anionic polymer having a molecular weight of at least 10,000 g/mol.

2. 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 native microfibrillated cellulose, wherein a content of the microfibrillated cellulose of said suspension is in a range of 40 to 99.9 weight-% based on a total dry solid content of the fibrous suspension, said fibrous suspension further comprising an organic acid, or a metal salt, or a mixture thereof, wherein an amount of the organic acid, the metal salt or the mixture thereof is at least 2 weight-% based on the total dry solid content of the fibrous suspension, said fibrous suspension also comprising an uncharged, amphoteric, or weakly cationic polymer having a molecular weight of at least 50.000 g/mol, and, said fibrous suspension also comprising an anionic polymer having a molecular weight of at least 10000 g/mol; providing said suspension to a substrate to form a fibrous web, film, or coating, wherein the amount of uncharged, amphoteric or weakly cationic polymer in said suspension is in a range of 0.1 to 20 kg/metric ton based on a total dry solid content of said fibrous web, film, or coating and wherein the amount of anionic polymer in said suspension is in the range of 0.01 to 10 kg/metric ton based on a total dry solid content of said fibrous web, film, or coating; and dewatering said fibrous web, film, or coating to form a fibrous product.

3. The method as claimed in claim 2, wherein the method is performed in a paper making machine in which the substrate is a porous wire on which the suspension forms a fibrous web.

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

5. The method as claimed in claim 2, wherein the substrate is a paper, a paperboard, a polymer, or a metal substrate.

6. The method as claimed in claim 2, wherein the fibrous product is a film or a coating.

7. The method as claimed in claim 6, 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 1,200 kg/m.sup.3.

8. The method as claimed in claim 2, wherein the uncharged, amphoteric or weakly cationic polymer is amphoteric guar gum.

9. The method as claimed in claim 2, wherein the uncharged, amphoteric or weakly cationic polymer comprises uncharged guar gum.

10. The method as claimed in claim 9, wherein an amount of said guar gum in the web is in a range of 0.1 to 20 kg/metric ton based on the total dry solid content.

11. The method as claimed in claim 2, wherein the anionic polymer comprises superfine MFC, anionic carboxymethylcellulose, synthetic polymers, or anionic guar gum.

12. The method as claimed in claim 11, wherein the anionic polymer comprises anionic polyacrylamide.

13. The method as claimed in claim 12, wherein an amount of the anionic polymer in the web is in a range of 0.02 to 5 kg/metric ton based on the total dry solid content.

14. The method as claimed in claim 2, wherein the organic acid comprises citric acid or the metal salt comprises sodium citrate.

15. The method as claimed in claim 2, wherein the microfibrillated cellulose comprises never-dried microfibrillated cellulose or microfibrillated cellulose that has been subjected to drying or microfibrillated cellulose that has been concentrated to a dryness of at least 20%.

16. A film comprising obtained by the method of claim 2, wherein said film has a basis weight of less than 40 g/m.sup.2 and a density in the range of 700 to 1,000 kg/m.sup.3.

17. A laminate comprising: the film as claimed in claim 16, and a thermoplastic polymer.

18. The laminate as claimed in claim 17, wherein the thermoplastic polymer comprises one or more of a high density polyethylene and a low density polyethylene.

19. The laminate as claimed in claim 17, wherein said laminate is applied to a surface of a paper or board product.

20. (canceled)

21. An aqueous suspension, wherein the suspension contains 0.3-20 weight-% solids, and wherein the suspension comprises: native microfibrillated cellulose, wherein a content of the microfibrillated cellulose of said suspension is in a range of 40 to 99.9 weight-% based on a total dry solid content of the suspension; an organic acid, or a metal salt, or a mixture thereof, wherein an amount of the organic acid, the metal salt, or the mixture thereof is at least 2 weight-% based on the total dry solid content of the suspension, an uncharged, amphoteric, or weakly cationic polymer having a molecular weight of at least 50,000 g/mol, wherein a content of the uncharged, amphoteric, or weakly cationic polymer is 0.1 to 20 kg/metric ton based on the total dry solid content of the suspension; and, an anionic polymer having a molecular weight of at least 10,000 g/mol, wherein a content of the anionic polymer is 0.02 to 5 kg/metric ton based on total dry solid content of the suspension.

22. (canceled)

23. (canceled)

Description

DETAILED DESCRIPTION

[0053] 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.

[0054] According to one embodiment a suspension comprising a microfibrillated cellulose is provided to form said fibrous product.

[0055] The fibrous content of the fibrous suspension may, according to one embodiment be in the range of from 40 to 99.9 weight-% based on total dry solid content. According to one 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. Preferably, the solid content of the suspension is at least 1.6%, i.e. 1 kg of the suspension contains at least 16 grams of suspended in material in solid form. More preferably, the solid content of the suspension is at least 2%, such as 5%, such as at least 8% or at least 10% or at least 15%.

[0056] According to one embodiment the fibrous content is exclusively formed by the native microfibrillated cellulose, i.e the suspension comprises less than 1 chemically modified microfibrillated cellulose. Preferably, the suspension does not comprise any chemically modified microfibrillated cellulose.

[0057] 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).

[0058] 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 400 m.sup.2/g, or more preferably 50-200 m.sup.2/g when determined for a freeze-dried material with the BET method.

[0059] 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.

[0060] The nanofibrillar cellulose may contain some hemicelluloses; the amount is dependent on the plant source but may typically be in the range of 1-30 wt-%. 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.

[0061] 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, sugar beet, 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 or hard wood fibers.

[0062] According to one embodiment the MFC may have a Schopper Riegler value) (SR°) of more than 70. According to another embodiment the MFC may have a Schopper Riegler value (SR°) of more than 80, such as more than 90 or more than 93. According to yet another embodiment the MFC may have a Schopper Riegler value (SR°) of more than 95. The Schopper-Riegler value can be obtained through the standard method defined in EN ISO 5267-1.

[0063] 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.

[0064] 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.

[0065] 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%.

[0066] 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 or fillers) etc.

[0067] 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.

[0068] The amphoteric properties can be either naturally derived or achieved by chemical modification by adsorbing e.g. multivalent metal salts or polyelectrolytes.

[0069] According to one embodiment the amphoteric polymer may be a starch.

[0070] 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, film or coating.

[0071] The substrate may be a porous wire of a paper making machine. Alternatively, a cast forming process may be used. Coatings can be prepared using methods known in the art e.g. printing or papermaking surface treatment technologies such as blade coater, film press, surface sizing, spray, curtain coater etc.

[0072] 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.

[0073] According to one embodiment the production speed of the paper making machine may be in the range of 30 to 1200 m/min.

[0074] 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.

[0075] Subsequent to the wet web being placed onto the substrate, it is dewatered to form a fibrous product.

[0076] The dewatering is performed according to methods known in the art and may, according to one embodiment be performed by vacuum, hot air, hot calenders, wet pressing, acoustic, UV or radiation curing or a combination thereof.

[0077] 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.

[0078] 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 one 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

[0079] 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 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 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.

[0080] 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.

[0081] 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.2/24h, or below 10 cc/m.sup.2/24h, or below 5 cc/m.sup.2/24h measured according to the standard ASTM D-3985.

[0082] 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 a water vapor transmission rate (WVTR) below 80 cc/m.sup.2/24h, or below 50 cc/m.sup.2/24h, or below 25 cc/m.sup.2/24h measured according to ASTM F-1249.

[0083] 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. As an alternative to lamination, a dispersion coating may be provided on one or on both sides, such as using acrylic latexes or PE dispersions or PVdC dispersion.

[0084] 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.

[0085] 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.