SKIN SAPONIFICATION OF CELLULOSE ACETATE FIBER AND ITS ADAPTABILITIES FOR MODIFICATION

Abstract

Skin saponification of cellulose di-and tri-acetate fibers with alkali at relatively high temperature was examined and the adaptabilities of the saponified fibers for modification were estimated.I. By the treatment with 0.1_??_0.5M NaOH solution at 90°C, the triacetate was found to besaponified annulary from the outside of the fiber inward with slow velocity. In case of the diacetate, similar behavior was not observed because saponification proceeded very quickly. When the diacatate was treated with a weak base such as Na2CO3 (0.025_??_0.5M) at 90°C, the annular saponification was observed only at low concentration for short treating time.From these results, it is apparent that the diacetate is more susceptible to alkali than the triacetate; this may be mostly due to the interaction between alkali and cellulose hydroxyl groups left in the diacetate and not due to the difference in fine structure of fibers.It was found that the rate of saponification of the diacetate is delayed by the addition of a neutral salt such as NaCl into Na2CO3 solution. The retardation effect becomes more remarkable with the increase of NaCl. For example, the treatment with Na2CO3 (0.025_??_0.5M) solution which contains 20% NaCl at 95°C for 10_??_60min. showed that perfect annular saponification takes place in all cases. The saponified layer becomes thicker with the increase of treating time and the concentration of Na2CO3. This saponification behavior is mainly from the anti-swelling effect of NaCl on the fibers.2. Suitable skin saponification condition is as follows: for the triacetate, 0.05_??_0.1M NaOH solution at 85_??_95°C, saponify as not to let the acetic acid content drop below 58%; for the diacetate, Na2CO3-NaCl mix solution (0.03-0.07M Na2CO3 and 15_??_20% NaCl) at 85_??_95°C, saponify as not to let the acetic acid content drop below 50%.When the saponification is carried out under these conditions, uniform skin saponification will beobtained not only for yarns but also for fabrics. Strength loss due to the saponification was small and the luster of the fiber is almost the same as the original one. It is also free from static electrification. Crease recovery was improved by the treatment of the saponified fabric with dimethylolethyleneurea. Durable water repellency, remarkably high tear strength and improvement of crease recovery were obtained by the treatment with a reactive softening agent such as octadecylethleneurea.