11-05-1960 дата публикации
Номер: GB0000834612A
Partially acetalated polyvinyl alcohol fibres are made by heat-treating polyvinyl alcohol (containing not more than 0.5 mol. per cent of unsaponified acetyl groups) in solid form until it is insoluble in cold water but soluble in hot water, partially acetalating the heat-treated polyvinyl alcohol in a heterogeneous system with an aldehyde, or an acetal thereof, to such a degree that the product is still hot-water soluble, preparing a spinning solution from the partially acetalated polyvinyl alcohol, extruding fibres by wet or dry spinning the solution and subjecting the extruded fibres to stretching, heat treatment and further acetalation. Preferably, the first acetalation step is effected with an aldehyde containing a basic group, e.g. amino-, dimethylamino-, ethylamino-, diethylamino-, dipropylamino-, benzylamino-, dibenzylamino-, dibutylamino-, pyrrolidino-, phthalimido-, or piperidino-acetaldehyde, dimethylamino-, diethylamino-, dipropylamino-, dibenzylamino- or piperidino-propionaldehyde, dimethylamino-, diethylamino-, dipropylamino-, dibutylamino-, dibenzylamino-, or piperidino-butyl aldehyde, dimethylamino hydroxy-butylaldehyde or dimethylaminobenzaldehyde or the acetals thereof. The further acetalation is preferably effected with formaldehyde, but an aldehyde having a large lattice may be used, e.g. benzaldehyde. Addition of reducing agents, e.g. urea, formamide, formic acid, ammonium formate, formaldehyde or a derivative thereof, or dicyandiamide, to the spinning solution or to a treatment bath through which the partially acetalated polyvinyl alcohol fibres are passed prevents discoloration of the fibres during heat treatment. Alternatively, discoloration of the fibres may be obviated by neutralization of the spinning solution with a base, e.g. sodium hydroxide, carbonate or bicarbonate, or by immersion of the fibres in an alkaline solution. Discoloration of the fibres does not occur when the heat treatment is at a low temperature or is a wet heat treatment ...
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