Process for the manufacture of structured materials using nano-fibrillar cellulose gels
A process for manufacturing structured material by providing cellulose fibres and at least one filler and/or pigment, combining the cellulose fibres and the at least one filler and/or pigment, fibrillating the cellulose fibres in the presence of the at least one filler and/or pigment until a gel is formed, subsequently providing additional non-fibrillated fibres, and combining the gel with the additional non-fibrillated fibres.
1. A process for manufacturing a structured material, comprising the steps of:
(a) providing cellulose fibres;
(b) providing at least one filler and/or pigment selected from the group consisting of precipitated calcium carbonate (PCC), natural ground calcium carbonate (GCC), surface modified calcium carbonate, dolomite, and mixtures thereof;
(c) combining the cellulose fibres of step (a) and the at least one filler and/or pigment of step (b) at a weight ratio of fibres to filler on a dry weight basis of from 1:33 to 10:1;
(d) fibrillating the cellulose fibres in an aqueous environment in the presence of the at least one filler and/or pigment from step (c) until a nano-fibrillar cellulose gel is formed, wherein the formation of the gel is verified by monitoring the viscosity of the mixture in dependence of the shearing rate, wherein the viscosity decrease of the mixture upon step-wise increase of the shearing rate is larger than the corresponding viscosity increase upon subsequent step-wise reduction of the shearing rate over at least part of the shear rate range as shearing approaches zero;
(e) providing additional non-fibrillated fibres in the form of a preformed fibre web, wherein the non-fibrillated fibres are from recycled pulp, deinked pulp, or any mixture thereof;
(f) combining the nano-fibrillar cellulose gel of step (d) with the non-fibrillated fibres of step (e) so that the combination of the nano-fibrillar cellulose gel and the non-fibrillated fibres in the form of a preformed fibre web comprises 0.5 to 20 wt. % of the nano-fibrillar cellulose gel, as expressed by the cellulosic content of the nano-fibrillar cellulose gel, on a dry/dry basis; and
(g) dewatering the combination of step (f) to form a base structure.
2. The process according to claim 1 , wherein the cellulose fibres of steps (a) and/or (e) are recycled pulp.
3. The process according to claim 1 , wherein the cellulose fibres of step (a) may be issued from a step of recycling a material comprising cellulose fibres.
4. The process according to claim 1 , wherein the non-fibrillated fibres of step (e) are recycled pulp.
5. The process according to claim 1 , wherein the base structure is paper.
6. The process according to claim 1 , wherein the structured material is a material composite.
7. The process according to claim 1 , wherein before, during or after the addition of non-fibrillated fibres in step (e), but after step (d) and (f), at least one further filler and/or pigment is added.
8. The process according to claim 7 , wherein the at least one further filler and/or pigment particles have a median particle size of from 0.01 to 5 μm.
9. The process according to claim 1 , wherein the cellulose fibres of step (a) are provided in the form of a suspension.
10. The process according to claim 9 , wherein the suspension has a solids content of from 0.2 to 35 wt. %.
11. The process according to claim 1 , wherein the filler of step (b) and/or the at least one further filler of step (e) is associated with a dispersing agent selected from the group consisting of homopolymers or copolymers of polycarboxylic acids and/or their salts or derivatives or esters thereof; esters based on acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid; acryl amide or acrylic esters, methylmethacrylate, or any mixture thereof; and alkali polyphosphates, phosphonic-, citric- and tartaric acids and the salts or esters thereof; or any mixture thereof.
12. The process according to claim 1 , wherein the step (c) is carried out by adding the filler to the fibres, or the fibres to the filler in one or several steps.
13. The process according to claim 1 , wherein the filler of step (b) and/or the fibres of step (a) are added entirely or in portions before or during the fibrillating step (d).
14. The process according to claim 1 , wherein the weight ratio of fibres to filler of step (b) on a dry weight basis is from 1:5 to 5:1.
15. The process according to claim 1 , wherein the fibrillating in step (d) is carried out with a homogenizer or a friction grinder.
16. The process according to claim 1 , wherein the total content of filler on a dry weight basis of the structured material is from 1 wt. % to 60 wt. %.
17. The process according to claim 1 , wherein the base structure is a board.
18. The process according to claim 1 , wherein the base structure is a compact block.