AN EFFICIENT GREEN PROCESS FOR THE PREPARATION OF NANOCELLULOSES, NOVEL MODIFIED NANOCELLULOSES AND THEIR APPLICATION

Abstract

The present invention relates to an efficient process for the preparation of nanocelluloses using mixtures of ammonium formate and at least one acid as reactant and solvent as well as to novel modified nanocelluloses and their applications.

Claims

1. A process for the preparation of nanocellulose comprising at least the steps of a) providing a mixture comprising i) ammonium formate ii) at least one acid and iii) at least one cellulose containing feedstock b) heating the mixture provided in step a) at a reaction temperature of 100° C. or more.

2. The process according to claim 1, wherein the nanocellulose represents polymer particles comprising β(1,4) linked D-glucose units having an average degree of polymerization of at least 50 D-glucose units with at least one dimension being smaller than 1000 nm and being chemically derivatized or not.

3. The process according to claim 1, wherein the at least one acid comprises organic compounds bearing one, two or three carboxylic acid (—COOH) or sulfonic acid groups and inorganic acids selected from the group consisting of sulfuric acid, hydrohalic acids, perhalic acids and phosphoric acid.

4. The process according to claim 1, wherein at least one acid is a mono- and dicarboxylic acid selected from the group consisting of formic acid, acetic acid, propionic acid, glycolic acid, lactic acid, oxalic acid, levulinic acid, malonic acid, succinic acid, malic acid, maleic acid and adipic acid.

5. The process according to claim 1, wherein the molar ratio between ammonium formate and the sum of acids is from 0.2 to 1000.

6. The process according to claim 1, wherein the cellulose containing feedstock is selected from the group consisting of microcrystalline cellulose, microbial cellulose, cellulose derived from marine or other invertebrates, recycling or waste paper such as office waste paper and municipal waste paper, wood pulp such as softwood and hardwood pulp whether bleached or not, chemical (dissolving) pulp, delignified pulp, pulp rejects, native biomass in the form of plant fibres, wood chips, saw dust, straw, leaves, stems or husks and cellulosic synthetic fibres such as tyre cord and other cellulose sources such as mercerised cellulose, bagasse, miscanthus and bamboo.

7. The process according to claim 1, wherein the cellulose containing feedstock is chemically derivatized by carboxymethylation, carboxylation, oxidation, sulphation or esterification or not chemically derivatized.

8. The process according to claim 1, wherein the cellulose containing feedstock is mechanically pretreated by cutting, delamination, high pressure homogenization, sonication or other known methods or not or is pretreated by enzymatic hydrolysis or not mechanically pretreated.

9. (canceled)

10. The process according to claim 1, wherein the weight ratio between the cellulose containing feedstock calculated on its dry weight and the sum of ammonium formate and the at least one acid is from 0.001 to 1.

11. The process according to claim 1, wherein the sum of ammonium formate, the at least one acid, the cellulose containing feedstock and water is from 80 to 100 wt-% with regard to the total weight of the mixture provided in step a).

12. The process according to claim 1, wherein in step b) the reaction temperature is in the range of 100° C. to 190° C.

13-15. (canceled)

16. The process according to claim 1, wherein the nanocelluloses are isolated from the reaction mixture obtained in step b) by washing with water and/or alcohols or by removal of volatiles by distillation, fractionation or in vacuo.

17. The process according to claim 1, wherein formic and other acids and excess ammonium formate, where present are recycled into step a).

18. Nanocellulose obtainable by a process according to claim 1.

19. Nanocellulose comprising at least some cellulose polymers comprising repeating units of formula (I) ##STR00003## and terminal units of formula (II) ##STR00004##

20. Nanocellulose according to claim 19, comprising further amino groups obtained via reductive amination of aldehyde groups already present or produced by partial oxidation of the cellulose polymer.

21. Nanocellulose according to claim 18 having a zeta potential of 2.0 to 50.0 mV.

22. Nanocellulose according to claim 18 having a nitrogen content of 0.2 and 2.0 wt.-%.

23. Nanocellulose according to claim 18 having a crystallinity index as measured by X-ray diffraction in the range of 70% to 100%.

24. Nanocellulose according to claim 18 having a degree of polymerization of 100 to 15,000 glucose units or 500 to 5,000 glucose units.

25. (canceled)

26. (canceled)

27. Food, beverages, membranes, films, packaging materials, water absorption or purification materials, heavy metal sensors, aerogels, flocculants, reinforced synthetic polymers, paper, board, paints, adhesives, latexes, cements, stimulation fluids, drilling fluids, completion fluids, spacer fluids, cosmetic or pharmaceutical compositions, tissue and bone recovery materials, biosensors and bioadhesives comprising nanocellulose according to claim 18.

28. (canceled)

Description

[0093] FIGS. 1 and 2 show TEM images of nanocellulose prepared from microcrystalline cellulose according to above example 1. Whiskers with dimensions of 10 to 20 nm in diameter and up to 200 nm length are obtained thereby.

[0094] FIGS. 3 and 4 show TEM images of nanocellulose prepared from softwood pulp according to above example 6.

[0095] FIGS. 5 and 6 show TEM images of nanocellulose prepared from delignified pulp according to above example 11.

[0096] All nanocelluloses obtained according to the invention show high stability of their aqueous colloids for at least two weeks clearly indicating additional stabilization through the formation of amino groups at the reducing ends of the cellulose chains which causes increased nitrogen levels in the nanocelluloses according to the invention.