Pre-mix useful in the manufacture of a fiber based product

Abstract

The present invention relates to a process wherein microfibrillated cellulose (MFC) is mixed with at least two retention aids, selected from a cationic or amphoteric polymer and a microparticle or nanoparticle as a pre-mix before dosing it to the stock in a process for manufacture of a fiber based product.

Claims

1. A process for the production of a fiber based product comprising the steps of: preparing a pre-mix comprising: a) microfibrillated cellulose, wherein the amount of the microfibrillated cellulose is 0.1 kg to 50 kg per ton dry furnish; b) cationic or amphoteric polymer, wherein the amount of the cationic or amphoteric polymer is 0.01 kg to 10 kg per ton dry furnish; c) microparticles or nanoparticles, wherein the amount of microparticles or nanoparticles is 0.01 kg to 10 kg per ton dry furnish, wherein said microparticles or nanoparticles are silica, microsilica, bentonite or microbentonite particles; and, d) salt in an amount between 0.1 to 50% (wt/wt) based on a solids content of the pre-mix, wherein the salt is selected from a group consisting of sodium chloride, calcium chloride, magnesium chloride, and aluminum chloride; and, dosing said pre-mix to a stock for manufacturing a fiber based product with a furnish comprising the stock.

2. The process according to claim 1, wherein said microparticles or nanoparticles are anionic at neutral or alkaline pH.

3. The process according to claim 1, wherein the weight ratio of polymer to microparticles or nanoparticles is in the range of from 1:3 to 1:20.

4. The process according to claim 1, wherein said cationic or amphoteric polymer is a cationic polymer.

5. The process according to claim 4, wherein said cationic polymer is selected from starch, polyaminoamide-epichlorohydrin and cationic polyacryl amide or copolymer thereof.

6. The process for the production of a fiber based product as claimed in claim 1, wherein the pre-mix is prepared by co-refining or co-fluidizing the components of the pre-mix when manufacturing the microfibrillated cellulose.

7. The process according to claim 1, wherein the weight ratio of polymer to microparticles or nanoparticles is in the range of from 1:5 to 1:12.

Description

DETAILED DESCRIPTION

(1) 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.

(2) 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).

(3) 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 wt %) 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 300 m.sup.2/g, such as from 1 to 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.

(4) 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 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 (CM), 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 fibrils.

(5) 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.

(6) The above described definition of MFC includes, but is not limited to, the new proposed TAPPI standard W13021 on cellulose nanofibril (CMF) defining a cellulose nanofiber material containing multiple elementary fibrils with both crystalline and amorphous regions.

(7) The papermaking machine that may be used in the process according to the present invention may be any conventional type of machine known to the skilled person used for the production of paper, paperboard, tissue or similar products.

(8) 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.