| 摘要 |
Filaments and fibres of cellulose acetate having a combined acetic acid content of 45-62,5%, insoluble in acetone, having a transverse section similar to that of regenerated cellulose filaments of the polynosic type from which they are made, and of oriented fibrillar micro-structure, are made by acetylating regenerated cellulose filaments or fibres of polynosic type in an acetylating bath containing acetic anhydride and an inert organic liquid diluent which is a non-solvent for cellulose acetate and of potential miscibility with acetic anhydride, at a temperature at which the anhydride and diluent are completely miscible, using as catalyst an alkali metal acetate in amount such that at the end of the acetylation the bath contains at most 2% by weight of free acetic acid. A "potentially miscible" diluent is immiscible with acetic anhydride at room temperature but miscible at higher temperatures. The diluent may be decahydronaphthalene, white spirit, carbon disulphide or cyclohexane. The weight ratio acetylation bath: cellulose is preferably at least 10:1 and the weight ratio diluent: acetic anhydride between 2:3 and 3:2. After acetylation the bath is cooled whereupon it separates into two layers, and the diluent layer can be stripped of the small proportion of acetic anhydride it contains by distillation, fortified with additional acetic anhydride and used again. |
