SU440373A1 - The method of producing cellulose acetate - Google Patents

Description

(54) METHOD FOR OBTAINING CELLULOSE ACETATES

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In the absence of acetic acid, the most complete binding of sulfuric acid occurs in the sulfuric acid-acetic anhydride complex. The effect of exposure is well reproduced in laboratory and industrial production.

When using a catalyst that has been pretreated, the esterification process proceeds smoothly, as a result of which the temperature leap is reduced during the supply of the acetylating mixture, which facilitates temperature control and allows to obtain a product with a more uniform structure, giving homogeneous transparent solutions. A more complete binding of sulfuric acid to the complex allows one to obtain cellulose a1 acetate with a reduced (by a factor of two) bound sulfur content, which increases its thermostability.

Since the catalyst in the bound form is soft acting, it is possible to increase its dosage and thereby intensify the acetylation process, while retaining the full range of improved properties of the final product.

The activated cellulose is acetylated in the medium of acetic acid or methylene chloride with a catalyst — sulfuric acid, which is kept with acetic anhydride at the rate of 1–3 wt. including sulfuric acid per 100 weight. part of the anhydride at 20-25 ° C for 20-60 minutes The aged mixture can be served in one or two doses, depending on the weight of the batch and the conditions of heat removal. For exposure to acetic anhydride, the whole amount of sulfuric acid required for the reaction, or a part of it, preferably 80% of the total weight, can be supplied. According to this mode, the acetylation process can be carried out by batch and continuous methods.

Example 1. 100 wt. including cellulose activate 40 weight. including acetic acid at 45 ° C for 2.5 hours, 108 weight. including acetic anhydriCharacteristics of the finished product

yes soak with 2.4 weight. including sulfuric acid for 40 min at 20-25 ° C. A mixture of 664 wt. including methylene chloride, 166 weight. including acetic anhydride and 0.6 wt. including sulfuric acid and treated with this mixture of cellulose for 40 minutes at 18-20 ° C. Then the aged mixture of anhydride with sulfuric acid is added and acetylation is carried out with a gradual rise of 20-40 ° C until the unreacted fibers disappear. The hydrolysis and precipitation are carried out in the usual manner. Characteristics of the finished product in the table.

Example 2. 100 weight. the celluloses are activated as indicated in Example 1. A mixture of 664 wt. is added to the activated cellulose. including methylene chloride, 196 weight. including acetic anhydride and 0.30 wt. including sulfuric acid and treated with this mixture of cellulose for 40 minutes at 18-20 ° C. A mixture of 78 wt. h anhydride and 1.2 wt. of sulfuric acid, aged as indicated in Example 1, and acetylation was carried out in the same manner. Characteristics of the finished product are shown in the table.

Example 3. 100 weight. including cellulose soaked in 1300 weight. including 80% acetic acid and incubated for several hours at room temperature. The excess acetic acid is then squeezed until the pulp is as dry as possible and the remaining acid is displaced with glacial acetic acid. The pulp is squeezed from an excess of glacial acetic acid to three times its weight. 230 weight. am acetic anhydride incubated with 6 wt. including sulfuric acid at 20-25 ° C for 20 minutes. 400 wt. Is added to the activated pulp. including glacial acetic acid, and seasoned mixture of anhydride with sulfuric acid. Acetylation is carried out with a gradual rise in temperature from 20 to 55 ° C until the unreacted cellulose fibers disappear. Characteristics of the finished product are shown in the table.