STUDIES ON THE POLYVINYL ALCOHOL FIBERS

Abstract

The polyvinyl alcohol made by convenional saponification method of polyvinyl acetate contains generally approximately 0.5mol. % of unsaponified acetyl groups. The properties of thh polyvinyl alcohol fibers depend on the amount of such unsaponified acetyl groups. In wet spinning process of the polyvinyl alcohol fibers, such unsaponified acetyl group can be removed by adding alkali to the spinning solution. The remaining alkali in spinning solution then is neutralized by controlling the pH of the coagulation bath in order to prevent discoloration of the fibers during the heattreatment process.When polyvinyl alcohol is to be spun by a dry spinning process, the raw material must be highly purified to remove all traces of impurities such as alkali and sodium acetate, otherwise the fiber product will tend to discolor during the heat-treatment process. The content of unsaponified acetyl groups could be decreased from 0.6mol. % to 0.05mol. % by means of re-saponifying the polyvinyl alcohol powder (ordinary saponified and then heat-treated) with an aqueous alkaline solution in suspension state. After re-saponification, the sample was washed and then submitted to the dry spinning.As the results, the fibers thus obtained have higher softening temperature and higher hot water resistance than the fibers made of the conventional polyvinyl alcohol. Furtheromore by increasing draw ratio and heat-treatment temperature of such re-saponified polyvinyl alcohol fibers, the fibers having boiling water resistance without acetalization could be obtained.