To obtain an acetyl cellulose with a high degree of polymerization by using an extended dipping time and keeping a reaction temp. low and the reaction time short in an acetylating reaction wherein a cellulose is first dipped in acetic acid and then an acetylating agent consisting of acetic anhydride, acetic acid and a small amount of sulfuric acid are added to the mixture.
A cellulose with a degree of polymerization as high as possible is used. A bacterial cellulose with a high degree of polymerization is produced by cellulose-producing bacteria. For example, an aerated stirred culture yields a cellulose with a weight-average polymerization degree (in terms of polystyrene) of not less than 1.6×104 and a stationary culture yields a cellulose with a weight-average polymerization degree of not less than 2.0×104. The acetic acid dipping is made in such a way that 10-20 pts.wt. acetic acid is added to 1 pt.wt. cellulose and the mixture is kept for not less than 24hrs, preferably approx. 24hrs. After the dipping treatment, the cellulose is separated by means of a common solid-liquid separation operation and an acetylating agent (the amount of sulfuric acid is 4-7 pts.wt. per 100 pts.wt. cellulose) is added to it and the mixture is kept at 10-30°C for 0.5-1.5hrs, and subsequently cast in a large amount of water.
WATABE OTOHIKO
MORINAGA YASUSHI
HORII FUMITAKA
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