| 摘要 |
The colour stability under heat of acrylonitrile polymers which are free from aldehyde groups and which contain at least 35 per cent of combined acrylonitrile is improved by contacting the polymer with an aqueous medium in which the polymer is insoluble, at a pH of not more than 5.8 and a temperature between 50 DEG and 150 DEG C., this treatment also resulting in a whitening of the polymer. Acrylonitrile polymers specified are polyacrylonitrile and copolymers with vinyl acetate, propionate, and butyrate, allyl and methallyl alcohols, allyl and methallyl acetates, laurates, and cyanides, isobutylene, acrylic, methacrylic, and ethacrylic acids, methyl, ethyl, propyl, and butyl acrylates and methacrylates, acrylamide, methacrylamide and the N-methyl, N-ethyl, N-propyl, and N-butyl substitution products thereof, methacrylonitrile, ethacrylonitrile, the methyl, ethyl, propyl and butyl diesters of maleic, fumaric, and citraconic acids, and vinyl and vinylidene fluorides and chlorides. The pH of the aqueous medium may be adjusted by means of organic and inorganic acids and anhydrides, of which several are specified; the aqueous medium may also contain other substances such as alcohol, acetone, or formaldehyde. Prior to treatment in the acid medium the polymers may be immersed in acidified sodium hypochlorite. The process is preferably applied to gelled fibres of the polymer. Specifications 594,999, 672,775 and 735,208 are referred to. |
