| 摘要 |
Polyvinyl alcohol in fully crystalline form is prepared by dissolving polyvinyl alcohol in a polyhydric alcohol or carboxylic acid amide and recovering polyvinyl alcohol from the solution. The polyvinyl alcohol may be recovered by cooling the solution, extracting the solvent with a non-solvent for the polymer, e.g. methanol, ethanol or propanol, or distilling off the solvent under reduced pressure. Recovery may be effected during shaping operations, e.g. the solutions may be spun into fibres and filaments in coagulating baths. Specified polyhydric alcohols are ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, glycerol, triethylene glycol, 1,2,3 - butanetriol, 1,2,4 - butanetriol, 1,2,6 - hexanetriol and trimethylolpropane. Specified amides are dimethyl formamide, diethyl formamide, methylethyl formamide, dipropyl formamide, acetamide and methyl acetamide. The polyvinyl alcohol may be prepared by the alkaline saponification of polyvinyl acetate, polyvinyl formate or polyvinyl trifluoroacetate. The crystalline products may be easily pulverized by conventional mechanical means, and may be used in cosmetic compositions, e.g. together with zinc oxide, starch and boric acid, in low calorie foodstuffs, as filtration aids and catalyst supports, and in paints and coating materials for paper and textiles. In examples crystalline polyvinyl alcohols are prepared by cooling solutions of alkali saponified polyvinyl acetate in (1) pentanediol, (4) dimethyl formamide, (5) diethyl formamide, (6) triethylene glycol, (8) mixtures of diethylene glycol and triethylene glycol and (11) triethylene glycol; by cooling a solution of polyvinyl alcohol in (2) a mixture of diethylene glycol and triethylene glycol; by cooling solutions of alkali saponified polyvinyl trifluoro-acetate in (3) triethylene glycol, (7) pentanediol, and (10) mixtures of diethylene glycol and triethylene glycol; by precipitating with isopropanol a solution of alkali saponified polyvinyl acetate in (9) glycerol; and by spinning solutions of alkali saponified polyvinyl acetate in (12) diethylene glycol into a bath of ethanol.ALSO:Foodstuffs may be prepared from a mixture of fully crystalline polyvinyl alcohol and wheat flour. The crystalline polyvinyl alcohol may be prepared by recrystallization from solution in a polyhydric alcohol or carboxylic acid amide. In Example 2 a low calorie bread type material is made from a mixture of wheat flour and crystalline polyvinyl alcohol precipitated from a solution in triethylene glycol.ALSO:Cosmetic materials may comprise a finely ground fully crystalline polyvinyl alcohol. The crystalline polyvinyl alcohol may be prepared by recrystallisation from solution in a polyhydric alcohol or carboxylic acid amide. In Example 1 a cosmetic powder is prepared by grinding polyvinyl alcohol recrystallised from 1,5-pentanediol and mixing the product with zinc oxide, starch and boric acid powder. |
