Process for making composition for conversion to lyocell fiber from sawdust
A process for making a composition for conversion to lyocell fiber where the process comprises pulping a raw material in a digester to provide an alkaline pulp, wherein the raw material comprises sawdust in an amount greater than 0 % up to 100 %; and contacting the alkaline pulp comprising cellulose and at least about 7 % hemicellulose under alkaline conditions with an amount of an oxidant sufficient to reduce the average degree of polymerization of the cellulose to within the range of from about 200 to about 1100, without substantially reducing the hemicellulose content of the pulp or substantially increasing the copper number.
1. A process for making a composition for conversion to lyocell fiber, said process comprising:
pulping a raw material in a digester to provide an alkaline pulp, wherein the raw material comprises sawdust in an amount greater than 25% up to 100%; and
contacting the alkaline pulp comprising cellulose and at least about 7% hemicellulose under alkaline conditions with an amount of an oxidant sufficient to reduce the average degree of polymerization of the cellulose to within the range of from about 200 to about 1100, without substantially reducing the hemicellulose content of the pulp or substantially increasing the copper number.
2. The process of claim 1 , wherein said oxidant comprises at least one member of the group consisting of a chemical with a peroxide group, hydrogen peroxide, oxygen, chlorine dioxide, ozone and combinations thereof.
3. The process of claim 1 , wherein the reduction in the average degree of polymerization of the cellulose occurs in the presence of a ratio of magnesium to transition metals of less than about 50%.
4. The process of claim 1 , wherein the hemicellulose content of the pulp is reduced less than about 50%.
5. The process of claim 4 , wherein the hemicellulose content of the pulp is reduced less than about 15%.
6. The process of claim 5 , wherein the hemicellulose content of the pulp is reduced less than about 5%.
7. The process of claim 1 , wherein the copper number increases less than about 50%.
8. The process of claim 7 , wherein the copper number increases less than about 25%.
9. The process of claim 1 , wherein the contacting step further comprises contacting the pulp with an alkali source selected from the group consisting of sodium hydroxide, oxidized white liquor, and unoxidized white liquor.
10. The process of claim 9 , wherein the alkaline pulp and oxidant are contacted at a pH greater than about 8.
11. The process of claim 1 , further comprising a step for dissolving the composition in a solvent, after the step of contacting the alkaline pulp with an oxidant, wherein the composition is readily dissolved in NMMO monohydrate within 5 minutes for forming into a spinnable dope.
12. The process of claim 1 , wherein the digester is a continuous digester.
13. The process of claim 12 , wherein the digester is an M&D or Pandia-type digester.
14. The process of claim 1 , wherein the sawdust comprises less than or about 50% of fibers retained on a one-quarter inch screen by TAPPI standard 233.
15. The process of claim 14 , wherein the sawdust comprises less than about 30% of fibers retained on a one-quarter inch screen by TAPPI standard 233.
16. The process of cLaim 15 , wherein the sawdust comprises less than about 15% of fibers retained on a one-quarter inch screen by TAPPI standard 233.
17. The process of claim 1 , wherein said raw material comprises about 50% up to 100% sawdust.