Paper filler method
A method for preparing an aqueous suspension comprising microfibrillated cellulose and inorganic particulate material, the method comprising a step of microfibrillating a fibrous substrate comprising cellulose in an aqueous environment in the presence of an inorganic particulate material.
1. A method for preparing an aqueous suspension comprising microfibrillated cellulose and inorganic particulate material, the method comprising:
a step of microfibrillating a fibrous substrate comprising cellulose in an aqueous environment in the presence of an inorganic particulate material,
wherein the fibrous substrate to the inorganic particulate material are in a ratio of about 99.5:0.5 to about 0.5:99.5,
wherein the microfibrillating is performed in the presence of a grinding medium, and
wherein the microfibrillated cellulose has a fibre steepness of from about 20 to about 50.
2. A method according to claim 1 , wherein the microfibrillating step comprises grinding the fibrous substrate comprising cellulose in the presence of the inorganic particulate material.
3. A method according to claim 1 , wherein the fibrous substrate comprising cellulose is in the form of a pulp, a papermill waste stream, waste from a papermill, or combinations thereof.
4. A method according to claim 1 , wherein the microfibrillating is performed in a tower mill comprising a quiescent zone above one or more grinding zones.
5. A method according to claim 2 , wherein the grinding is performed under plug flow conditions.
6. A method according to claim 4 , wherein water is added proximate to the quiescent zone at the top of the mill to reduce the viscosity of the aqueous suspension comprising microfibrillated cellulose and inorganic particulate material.
7. A method according to claim 4 , wherein water is added to one or more grinding zones via one or more water injection points located along the length of the tower mill.
8. A method according to claim 1 , wherein the microfibrillating is performed in a screened grinder comprising one or more screens having a nominal aperture size of at least about 250 μm.
9. A method according to claim 1 , wherein the grinding medium comprises particles having an average diameter in the range of from about 0.5 mm to about 6 mm.
10. A method according to claim 9 , wherein the grinding medium has a specific gravity of at least about 2.5.
11. A 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.
12. A method according to claim 1 , wherein the aqueous suspension is treated to remove at least a portion of the water to form a partially dried product.
13. A method according to claim 1 , wherein the inorganic particulate material has a particle size distribution, as measured by a method employing laser light scattering, such that at least about 10% by volume of the particles have an e.s.d. of less than 2 μm based on the dry weight of the inorganic particulate material.
14. A method according to claim 1 , wherein the microfibrillated cellulose has a d 50 of from about 5 to μm about 500 μm.
15. A method according to claim 3 , 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.
16. A method according to claim 11 , wherein the total amount of energy used in the method is less than about 5,000 kWh per tonne of dry fibre in the fibrous substrate comprising cellulose.
17. A method according to claim 1 , wherein the aqueous suspension is treated to remove about 100% by volume of the water to form an essentially completely dried product.