Process for the production of gel-based composite materials
A process for the production of composite materials comprising nano-fibrillar cellulose gels, 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 at least one further filler and/or pigment and combining the gel with the at least one further filler and/or pigment.
1. A process for producing a composite material comprising the steps of:
(a) providing cellulose fibres, wherein the cellulose fibres of step (a) are selected from eucalyptus pulp, spruce pulp, pine pulp, beech pulp, hemp pulp, cotton pulp, bamboo pulp, bagasse, recycled pulp, deinked pulp, or any mixture thereof;
(b) providing at least one filler comprising calcium carbonate, wherein the filler of step (b) consists of particles having a median particle size of from 0.5 to 4 μm;
(c) combining the cellulose fibres of step (a) and the at least one filler of step (b) at a weight ratio of fibres to filler on a dry weight basis of from 1:33 to 10:1 by adding the fibres and at least one filler entirely or in portions before or during the fibrillating step (d);
(d) fibrillating the cellulose fibres in an aqueous environment in the presence of the at least one filler from step (c) until a nano-fibrillar 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 stronger 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 at least one further filler, wherein the at least one further filler of step (e) consists of particles having a median particle size of from 0.01 to 15 μm; and
(f) combining the nano-fibrillar gel obtained in step (d) with the at least one further filler from of step (e), wherein the combination of the gel and the at least one further filler from step (f) is subjected to dewatering to obtain a compacted composite material.
2. The process according to claim 1 , wherein the cellulose fibres of step (a) are provided in the form of a suspension.
3. The process according to claim 1 , wherein the cellulose fibres of step (a) are provided in the form of a suspension at a solids content of from 0.2 to 35 wt %.
4. The process according to claim 1 , wherein the cellulose fibres of step (a) are provided in the form of a suspension at a solids content of from 1 to 4 wt %.
5. The process according to claim 1 , wherein the filler of step (e) is precipitated calcium carbonate (PCC), natural ground calcium carbonate (GCC), surface modified calcium carbonate, dolomite, talc, bentonite, clay, magnesite, satin white, sepiolite, huntite, diatomite, a silicate, or any mixture thereof.
6. The process according to claim 1 , wherein the filler of steps (b) and (e) are independently selected from precipitated calcium carbonate having vateritic, calcitic or aragonitic crystal structure, ultrafine discrete prismatic, scalenohedral or rhombohedral precipitated calcium carbonate, natural ground calcium carbonate, marble, limestone, chalk, or any mixture thereof.
7. The process according to claim 1 , wherein the at least one further filler of step (e) consists of particles having a median particle size of from 0.01 to 5 μm.
8. The process according to claim 1 , wherein the at least one further filler of step (e) consists of particles having a median particle size of from 0.05 to 1.5 μm.
9. The process according to claim 1 , wherein the at least one further filler of step (e) consists of particles having a median particle size of from 0.1 to 0.8 μm.
10. The process according to claim 1 , wherein the filler of steps (b) and/or (e) is associated with a dispersing agent selected from 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; alkali polyphosphates, phosphonic-, citric- and tartaric acids and the salts or esters thereof; or any mixture thereof.
11. The process according to claim 1 , wherein the combination of fibres and of at least one filler of step (b) is carried out by adding the filler to the fibres, or the fibres to the filler, in one or several steps.
12. The process according to claim 1 , wherein the weight ratio of fibres to filler in step (c) on a dry weight basis is from 1:10 to 7:1.
13. The process according to claim 1 , wherein the weight ratio of fibres to filler in (step c) on a dry weight basis is from 1:2 to 2:1.
14. The process according to claim 1 , wherein the fibrillating is carried out with a homogenizer or a friction grinder.
15. The process according to claim 1 , wherein the weight ratio of fibres from step (a) to filler of step (e) on a dry weight basis is from 1:9 to 99:1.
16. The process according to claim 1 , wherein the weight ratio of fibres from step (a) to filler of step (e) on a dry weight basis is from 1:3 to 9:1.
17. The process according to claim 1 , wherein the weight ratio of fibres from step (a) to filler of step (e) on a dry weight basis is from 1:2 to 3:1.
18. The process according to claim 1 , wherein the total content of filler of steps (b) and (e) on a dry weight basis of the composite material is from 10 wt-% to 95 wt-%.
19. The process according to claim 1 , wherein the total content of filler of steps (b) and (e) on a dry weight basis of the composite material is from 20 wt-% to 75 wt-%.
20. The process according to claim 1 , wherein the total content of filler of steps (b) and (e) on a dry weight basis of the composite material is from 25 wt-% to 67 wt-%.
21. The process according to claim 1 , wherein the total content of filler of steps (b) and (e) on a dry weight basis of the composite material is from 33 wt-% to 50 wt-%.
22. A process for producing a composite material comprising the steps of:
(a) providing cellulose fibres;
(b) providing at least one filler comprising calcium carbonate and one or more of dolomite, talc, bentonite, clay, magnesite, satin white, sepiolite, huntite, diatomite, and a silicate;
(c) combining the cellulose fibres of step (a) and the at least one filler of step (b) at a weight ratio of fibres to filler on a dry weight basis of from 1:33 to 10:1 by adding the fibres and at least one filler entirely or in portions before or during the fibrillating step (d);
(d) fibrillating the cellulose fibres in an aqueous environment in the presence of the at least one filler from step (c) until there are no fibres left and a nano-fibrillar gel is formed in an aqueous environment to obtain a fibrillation product;
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 stronger 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 at least one further filler, wherein the at least one further filler consists of particles having a median particle size of from 0.01 to 15 μm; and
(f) combining the nano-fibrillar gel in step (d) with the at least one further filler of step (e), wherein the combination of the gel and the at least one further filler from step (f) is subjected to dewatering to obtain a compacted composite material.