Paper filler composition
A method for preparing an aqueous suspension may include providing a fibrous substrate comprising cellulose having a Canadian Standard freeness equal to or less than 450 cm 3 , and microfibrillating the fibrous substrate in an aqueous environment by grinding in the presence of a grinding medium consisting essentially of mullite. The grinding may be carried out in the absence of grindable inorganic particulate material. The grinding medium may be present in an amount of at least about 10% by volume of the aqueous environment. The microfibrillated cellulose may have a fibre steepness of from about 20 to about 50.
1. A method of preparing a partially dried composition comprising microfibrillated cellulose and water, the method comprising the steps of: (a) microfibrillating a fibrous substrate comprising cellulose in an aqueous environment by grinding in the presence of grinding medium which is to be removed after completion of grinding, wherein the fibrous substrate comprising cellulose has a Canadian Standard freeness equal to or less than 450 cm 3 ; wherein the grinding medium is present in an amount of at least about 10% by volume of the aqueous environment, to form an aqueous composition comprising microfibrillated cellulose and water, wherein the microfibrillated cellulose has a d 50 by laser light scattering of from about 5 μm to about 500 μm and a fibre steepness of from about 20 to about 50; and (b) treating the aqueous composition comprising microfibrillated cellulose and water to remove at least about 50% by volume of the water to form a partially dried composition comprising microfibrillated cellulose and water.
2. The method according to claim 1 , wherein the treating step (b) comprises gravity or vacuum-assisted drainage, with or without pressing, or by evaporation, or by filtration, or by a combination of these techniques to obtain a partially dried composition comprising microfibrillated cellulose and water.
3. The method according to claim 1 , wherein the composition of step (a) further comprises one or more additives.
4. The method according to claim 3 , wherein the additive is selected from the group consisting of retention aid, dispersant, biocide, suspending agent, salts, carboxymethyl cellulose, amphoteric carboxymethyl cellulose, starch, oxidising agents, 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO), TEMPO derivatives, and wood degrading enzymes.
5. The method according to claim 1 , wherein the grinding is performed in a grinding vessel.
6. The method according to claim 5 , wherein the grinding vessel is a stirred media detritor.
7. The method according to claim 6 , wherein the stirred media detritor comprises one or more screens having a nominal aperture size of at least about 250 μm.
8. The method according to claim 5 , wherein the grinding vessel is a tower mill.
9. The method according to claim 1 , wherein water is added proximate to one or more quiescent zones or a classifier.
10. The method according to claim 1 , further comprising the step of rehydrating the partially dried composition and incorporating the composition into a papermaking composition.
11. The method according to claim 1 , wherein the grinding media has a specific gravity of at least 2.5.
12. The method according to claim 1 , wherein the grinding media has an average diameter in a range of from about 0.5 mm to about 6 mm.
13. The method according to claim 1 , wherein the fibrous substrate comprising cellulose is in the form of a recycled pulp, a papermill waste stream, waste from a papermill, or combinations thereof.
14. The method according to claim 1 , wherein the grinding medium is present in an amount up to about 70% by volume of the aqueous environment.
15. The method according to claim 1 , wherein the fibrous substrate comprising cellulose is present in the aqueous environment at an initial solids content of at least about 5 wt %.
16. The method according to claim 1 , wherein the initial solids content is at least about 0.5 wt %.
17. The method according to claim 1 , wherein the grinding is performed in a cascade of grinding vessels.
18. The method according to claim 1 , wherein the fibrous substrate comprising cellulose is a pulp selected from the group consisting of a chemical pulp, a chemithermomechanical pulp, a mechanical pulp, a recycled pulp, and a paper broke pulp.
19. The method according to claim 1 , wherein the total amount of energy used in the method is less than about 10,000 kWh per tonne of dry fibre in the fibrous substrate comprising cellulose.
20. The method according to claim 1 , wherein the aqueous composition may be dewatered to obtain a wet sheet comprising about 10% solids.
21. The method according to claim 1 , wherein the aqueous composition may be dewatered to obtain a wet sheet comprising about 20% solids.
22. The method according to claim 1 , wherein the aqueous composition may be dewatered to obtain a wet sheet comprising about 30% solids.
23. The method according to claim 1 , wherein the aqueous composition may be dewatered to obtain a wet sheet comprising about 40% solids.
24. The method according to claim 1 , wherein the aqueous composition may be dewatered to obtain a wet sheet comprising about 50% solids.
25. The method according to claim 1 , wherein the aqueous composition may be dewatered to obtain a wet sheet comprising about 60% solids.
26. The method according to claim 1 , wherein the aqueous composition may be dewatered to obtain a wet sheet comprising about 70% solids.
27. The method according to claim 1 , wherein the aqueous composition may be dewatered to obtain a wet sheet comprising about 80% solids.
28. The method according to claim 1 , wherein the aqueous composition may be dewatered to obtain a wet sheet comprising about 90% solids.
29. A method of preparing a papermaking composition comprising rehydrating the partially dried product of claim 1 and incorporating the rehydrated product in a papermaking composition.
30. A method of preparing a paper product prepared from or comprising the papermaking composition of claim 1 .