Method of making bleached microcrystalline cellulose
A method of producing bleached microcrystalline cellulose which method comprises neutralizing or alkalizing an acidic microcrystalline production reaction mixture slurry, typically produced by acid hydrolysis or by electronic beam irradiation, followed by adding an oxidant to such reaction mixture. This practice of this method permits the production of microcrystalline cellulose having desirable color stability as well as compression characteristics suitable for pharmaceutical binder use from paper grade and other low purity pulps.
1. A method of making microcrystalline cellulose comprising the steps of:
a) Providing a cellulosic pulp and subjecting such pulp to an acid hydrolysis process to create an acidic product reaction mixture slurry comprising microcrystalline cellulose and a hydrolysate liquor;
b) Adding a sufficient amount of an alkaline material to the acidic product reaction mixture slurry to produce a neutralized product reaction mixture having a pH of between 7 and 12, wherein the neutralized product reaction mixture comprises microcrystalline cellulose and a neutralized hydrolysate liquor;
c) Adding oxidant to the neutralized product reaction mixture to form a bleached product reaction mixture comprising bleached microcrystalline cellulose and a bleached hydrolysate liquor, wherein the bleached product reaction mixture becomes acidic; and
d) Isolating the bleached microcrystalline cellulose from the bleached product reaction mixture.
2. The method of claim 1 wherein the pulp possesses an alpha cellulose content of less than 92 weight percent.
3. The method of claim 2 wherein the pulp possesses an alpha cellulose content of less than 90 weight percent.
4. The method of claim 3 wherein the alkaline material is sodium hydroxide.
5. The method of claim 1 wherein the pulp is selected from the group consisting of bleached, semi-bleached, or unbleached Kraft pulps, high kappa Kraft pulp, bleached or unbleached sulfite pulps, soda cooking pulps, (organic) solvent pulping pulps, semi-chemical pulping pulps, fluff pulps, softwood pulps, hardwood pulps, Eucalyptus pulps, sawdust pulps, non-wood pulps, old corrugated container pulps, recycled paper pulps and mixtures thereof.
6. The method of claim 1 wherein the alkaline material is selected from the group consisting of sodium hydroxide, ammonia, potassium hydroxide, sodium carbonate, and calcium hydroxide, calcium oxide and mixtures thereof.
7. The method of claim 1 wherein the oxidant is selected from the group consisting of hydrogen peroxide, peroxy acids, peroxy esters, hydroperoxides, inorganic peroxides and organic peroxides, and mixtures thereof.
8. The method of claim 7 wherein the oxidant is hydrogen peroxide.
9. The method of claim 1 wherein step b is conducted at between 50° C. and 120° C.
10. The method of claim 9 wherein step b is conducted at between 60° C. and 105° C.
11. The method of claim 1 wherein step c is conducted at between 50° C. and 120° C.
12. The method of claim 11 wherein step c is conducted at between 60° C. and 105° C.
13. The method of claim 1 wherein step c is conducted for between 1 and 180 minutes.
14. The method of claim 13 wherein step c is conducted for between 5 and 60 minutes.