CS210220B1 - A method of preparing hemicellulate acetate - Google Patents

Abstract

The invention relates to a method of preparing hemicellulose acetate soluble in organic solvents. The essence of the invention is that activated hemicelluloses are treated with ethanol and acetic acid and then acetylated with a mixture of acetic anhydride and perchloric acid in an organic solvent environment, and after the end of the reaction the solvent is vacuum distilled off and hemicellulose acetate is isolated by a known method. The invention is used in the production of quick-drying varnishes and covering coatings, known under the name of the foreign product "Liquid Paper".

Description

1

The present invention relates to a process for the preparation of hemicelluate acetate soluble in organic solvents.

Hemicelluloses are found in fibrous portions of single and multi-annual plants at an average of 20-30%. I call it! in contrast to cellulose, non-fibrous amorphous character.

The average degree of polymerization of native hemicellulase from xylan and glucomannan typus ranges from 300 to 400, while hemicellulose, isolated from various wood processing wastes, accompanied by depolymerized, partially naoxidized cellulose, has a value of 20-200. while they have not found industrial uses in the true sense of the word because they are not widely commercially available. Exceptions are lambinogalactan made from larch wood from which xylan has also been produced. Today, however, inventions are increasingly exploring the protection of hemicellulase acquisition techniques.

Chemical modification changes the physicochemical properties of hemicellulose, extending the scope of their practical application. Acidated hemicelluloses have the ability to form films, the strength of which depends on the degree of substitution and polymerization. The solubility of native acetylated hemicellulose in organic solvents is low (TE Timell, Adv. Carbohyd. Chem. 19, 295, 1964), which has been found to be related to the problem of incomplete solubility of cellulose acetates prepared from wood pulps with higher hemicellulose content like cotton. The isolated hemicelluloses are poorly reactive in acetylation, which usually starts in heterogeneous reaction conditions. The increase in reactivity is achieved by swelling of hemicellulose in 1-acetic acid, pyridine, dimethylformamide, which also has the ability to dissolve the acetylated product, similar to the addition of dichloromethane (RL Whistler, Adv. Carbohyd. Chem. 5, 286, 1950, Koshijima T., Timell TE, Zinbo M., J. Polymer Sci Cil, 265, 1965, M. Kaustinen, D. A, Kaustinen, HA Swenson, Carbohyd Res., 11, 267, 1969). Said processes requiring high temperatures or long acetylation times to achieve complete solubility of the derivative, associated with degradation and depolymerization of the product. The high consumption of acetylating agent and solvents, their cost, makes these procedures uneconomical for practical use.

These drawbacks are solved by the proposed hemicellulose acetylation process by rapidly reacting the reaction under conditions of limited hemicellulose degradation, with minimal consumption of reagents.

SUMMARY OF THE INVENTION The invention is based on the fact that the initial air-dry hemicellulose is activated by swelling in water or dilute alkali with pre-acetylation, water, optionally with alkali neutralization, is displaced with ethanol, ethanol with acetic acid and after washing off the reagents 3 to 5 times the weight of the hemicellulose feed. without drying, transfer to a reaction vessel equipped with a stirrer and heating, respectively. cooling. After addition of a solvent, preferably chloroform, dichloromethane or trichlorethylene in an amount of 8 to 15 ml per 1 g of air hemicellulose, an acetylation mixture consisting of 5 to 10 ml of acetic anhydride and 0.005 to 0.05 g of perchloric acid is added dropwise over 5 to 15 minutes. for 1 g of air-dry chemical. at a temperature of 10 to 30 ° C, with stirring and acetylation, the dissolution of the micelle is continued until δο lasts 10 minutes to 5 hours. Isolation of the hemicellulose acetate from the reaction medium by neutralization of the catalyst with an equivalent amount of sodium bicarbonate and vacuum distillation of the solvent that can be used in the 3-way acetylation, either by precipitation into a de-water volume of water followed by filtration of the precipitate which is washed with water and dried, or by extracting the residue after repeatedly distilling off the reagents with water with 30 to 50 ml of chloroform, a solution of the acetate is obtained which, after drying with anhydrous sodium sulfate, is evaporated to dryness or precipitated into petroleum ether. White, hemicellulose acetate is obtained in yields above 90%, completely dissolved in chlorinated solvents (chloroform, dichloromethane, trichloride, etc.), suitable for the preparation of fast-drying lacquer coatings. The advantage of the proposed process for the preparation of hemicellulose acetate is that: - the consumption of acetylating agent and acetic acid is low, - the solvent that substitutes acetic acid for dissolution of the acetate in the reaction mixture can be regenerated by distillation and reused, - the hemicelluloses of the various solid wastes are used ( wood sawdust, flour, bark, straw, corn cobs and others) and waste extracts of chemical wood and pulp processing, - by utilizing waste it contributes to environmental protection as well as to the comprehensive use of wood and other plant materials. Example 1 1 g of hemicellulose composed of 85% D-xylose, 12% uronic acids and 3% of a mixture of D-galactose, D-glucose and L-arabinose, freshly precipitated from the alkaline extract of holocelluloid wood by triple volume ethanol, after aspirating the ethanol, neutralizes it with acetic acid in 75% ethanol, washing with 100 ml of 75% ethanol, 20 ml of 96% ethanol, twice with 5 ml of 1-acetic acid and transferring it to a 5-fold weight into the reaction vessel where it is stirred with 15 ml of dichloromethane. The mixture was added dropwise over 15 min. acetylation mixture consisting of 5 ml of acetic anhydride and 0.01 ml of perchloric acid (70%) at 15 to 16 ° C with stirring. After raising the temperature to 30 ° C, the reaction mixture clears after 10 minutes. After the solvent was distilled off in vacuo, the acetate was precipitated from the reaction mixture by the addition of 200 mL of cold water, filtered and washed with water and dried under vacuum at 60 ° C to give 1.65 g of acetate. (97% yield) soluble in chloroform EXAMPLE 2 1 g of hemicellulose containing 80% of D-xylose, 15% of L-arabinose and 5% of uronic acids isolated from corn cobs are swelled in water (3 ml). After 2 hours, 9 ml of 96% ethanol was added, the hemicelluloses were filtered off, washed twice with 3 ml of glacial acetic acid and sucked off to a 3-fold aqueous weight. 0.005 ml perchlorate in 10 ml of chloroform at 20 DEG C. After the reaction is complete, the mixture is neutralized as in Example 1, chloroform is distilled off under vacuum, and after addition of 25 ml of water, the acetylation mixture is distilled off, which is repeated twice. Extract the acetate from the residue with chloroform, eluting the chloroform extract

Claims (1)

OBJECT OF THE INVENTION A process for the preparation of hemicellulose acetate, characterized in that the water or diluted alkali-activated hemicellulosic solutions are treated successively with 75 to 96% ethanol and Tedic Acetic Acid and after aspirating to 3-5 times the weight of hemicellulose partially in an organic solvent type chlorinated hydrocarbons, preferably chloroform, dichloromethane and trichlorethylene, acetylated with a mixture of 5 to 10 ml of acetic anhydride and 0.005 to 0.05 g of perchloric acid per g of air-dry hemicelluloses at 10 to 30 ° C for 10 minutes to 5 hours and after completion of the reaction by neutralizing the catalyst, the solvent is distilled off in vacuo and the hemicellulose acetate is isolated from the reaction medium by any of the known methods.