Method for the preparation of micro or nano crystalline cellulose
The invention relates to a method for the preparation of micro- or nano crystalline cellulosic compositions from virgin cellulose containing amorphous and crystalline cellulose phases comprising the following steps: (A) contacting virgin cellulose with a first solvent, characterized in that the first solvent is an aqueous solution comprising 40-65 wt. % ZnCl 2 in water, relative to the total weight of the of ZnCl 2 and water, (B) dissolving the amorphous cellulosic phase, whereby the amorphous cellulosic phase is preferentially dissolved over the crystalline cellulosic phase, (C) separating the dissolved amorphous cellulose from the crystalline cellulose and preferably step C wherein the obtained micro- or nanocellulose has XRD type I structure, which then can be contacted with a second solvent comprising between 65 and 90 wt. % ZnCl 2 in water to produce delaminated cellulose having XRD type II structure. The invention also relates to micro- or nano crystalline cellulose having an XRD type I structure and nano crystalline cellulose having an XRD type II structure or mixtures thereof of high crystallinity and purity and the uses thereof.
1. A method for the preparation of micro- or nano crystalline cellulose from a virgin cellulose containing an amorphous cellulose phase and a crystalline cellulose phase, the method comprising the steps of:
(A) contacting virgin cellulose with a first solvent, characterized in that the first solvent is an aqueous solution comprising 40-65 wt. % ZnCl 2 in water, relative to the total weight of the ZnCl 2 and water,
(B) dissolving the amorphous cellulosic phase, whereby the amorphous cellulose phase is preferentially dissolved over the crystalline cellulose phase, wherein the temperature in step A and B is below 80° C. and,
(C) separating the dissolved amorphous cellulose from the crystalline cellulose, wherein the crystalline cellulose obtained in step B comprises cellulose having an XRD type I structure.
2. The method according to claim 1 , wherein the temperature in step A and B is below 70° C.
3. The method according to claim 1 wherein the first solvent is free of a proton acid.
4. The method according to claim 1 , wherein the first solvent is free of a proton acid and comprises as proton scavenger ZnO or Zn(OH) 2 .
5. The method according to claim 1 , wherein the crystalline cellulose obtained in step B or C has a higher XRD crystallinity then the virgin cellulose material.
6. The method according to claim 1 , further comprising a step E wherein a coagulation agent is added to the dissolved amorphous cellulose obtained in step C to precipitate the amorphous cellulose.
7. The method according to claim 1 further comprising a step D wherein the crystalline cellulose obtained in step C is contacted with a second solvent to produce delaminated cellulose, wherein the second solvent comprises between 65 and 90 wt. %, ZnCl 2 in water.
8. The method according to claim 7 , wherein the delaminated cellulose obtained in step D comprises cellulose having an XRD type II structure.
9. The method according to claim 1 , wherein the virgin cellulose is in a biomass which contains virgin cellulose and lignin and optionally hemi-cellulose and
a) in step B the amorphous cellulose and optional hemicellulose is dissolved in the first solvent, wherein
b) in separation step C the dissolved amorphous cellulose and optional hemicellulose is separated from the crystalline cellulose and lignin and wherein
c) optionally in a step H the crystalline cellulose and lignin is treated with a solvent, wherein lignin is dissolved and wherein the crystalline cellulose phase is not dissolved and the dissolved lignin is separated from the crystalline cellulose.
10. The method according to claim 7 , wherein the virgin cellulose is in a biomass which contains virgin cellulose and lignin and optional hemi-cellulose, wherein
in step B amorphous cellulose and optional hemicellulose is dissolved in the first solvent, wherein
in separation step C the dissolved amorphous cellulose and optional hemicellulose is separated from the crystalline cellulose and lignin and wherein
in a step D the crystalline cellulose and lignin are contacted with the second solvent to produce delaminated crystalline cellulose and wherein
optionally in a step G the lignin is separated from the delaminated crystalline cellulose.
11. A micro- or nanocrystalline cellulose containing product P1 obtained by the method of claim 1 having an XRD type I structure, an XRD crystallinity of at least 85%, and a (poly-) sugar content less than 10 wt. %; or containing product P2 obtained by the method of claim 7 having an XRD type II structure, an XRD crystallinity of at least 80%, and a (poly-) sugar content less than 15 wt. %; or a mixture of product P1 and P2.
12. The cellulose composition of claim 11 , further comprising lignin.
13. A method for the preparation of a coating material, filler, or as a material for the manufacture of cellulose shaped products using the micro- or nanocellulose having XRD type I structure of claim 11 or of the nano cellulose having XRD type II structure of claim 11 or of the cellulose composition of claim 12 .
14. The method according claim 5 , wherein the crystalline cellulose obtained in step B or C has a higher XRD crystallinity then the virgin cellulose material, wherein the XRD crystallinity of the obtained crystalline cellulose is at least 10% higher than of the virgin cellulose and the XRD crystallinity of the obtained crystalline cellulose is at least 85%.
15. The method according to claim 6 , wherein the coagulation agent of Step E is an anti-solvent being one or more chosen from the group consisting of C1 to C8 alcohol, ketones, or water.
16. The method according to claim 7 , wherein the second solvent comprises a proton scavenger.
17. The method according to claim 7 , wherein the proton scavenger is ZnO or Zn(OH) 2 .
18. Nano-crystalline cellulose containing product P2 of claim 11 having a (poly-) sugar content less than 5 wt. %.
19. The method according to claim 13 wherein the cellulose shaped products are cellulose shaped fibers or films.