| 摘要 |
PROBLEM TO BE SOLVED: To stably obtain a low-viscosity cellulose acetate by preparing two catalyst solutions prepared by diluting sulfuric acid with acetic acid and having the same or different concentrations, adding the first portion to the reaction system at the start of an acetylation reaction and adding the second portion to the system when the degree of substitution of a cellulose acetate as the reaction intermediate exceeds a specified value. SOLUTION: The second portion is added to the reaction system when the degree of substitution of a cellulose acetate as the reaction intermediate exceeds 1.8. The amounts of sulfuric acid added in the first and second stages are desirably 0.5-5 pts.wt. and 0.01-2.0 pts.wt., respectively per 100 pts.wt. starting cellulose. The ratio between the first and second portions added is desirably 80/20 to 50/50 in terms of a ratio between the weights of the sulfuric acid added. It is desirable that sulfuric acid used in the first and second addition is in the form of a 1-5 wt.% acetic acid solution. It is desirable that the amounts of acetic anhydride and acetic acid added in the acetylation step are 200-400 pts.wt. and 300-600 pts.wt. per 100 pts.wt. cellulose. It is desirable that the acetylation reaction is performed in a vacuum.
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