GB813838A - Polyvinyl alcohol fibres and method of manufacturing same - Google Patents

Abstract

An aqueous solution containing a polymer blend of from 99.5 per cent to 30 per cent by weight of polyvinyl alcohol and from 0.5 per cent to 70 per cent by weight of a polyvinyl amino-acetal which contains -CH2CHOH- units and <FORM:0813838/IV (a)/1> units, wherein R(N) is a monovalent radical having 1 to 3 basic nitrogen atoms and up to 20 carbon atoms and in which between 3 per cent and 80 per cent of the initial hydroxyl groups have been acetalized, the polymer blend being such that from 0.2 to 10 per cent of the initial total number of hydroxyl groups have been acetalized, is spun into filaments which are stretched at 15 DEG to 250 DEG C. for 0.5 second to 3 minutes to a draw ratio of 2/1 to 12/1 , heat treated at 140 DEG to 260 DEG C. for 0.2 second to 1 hour until they show not more than a 10 per cent shrinkage when immersed in water at 60 DEG C. for 30 minutes, and are treated with a mono-aldehyde (non-amino) of up to 20 carbon atoms until 5 to 60 per cent of the hydroxyl groups in the filament have reacted. R(N) may be -R3N(R1)(R2), where R1 and R2 ar hydrogen or alkyl groups of 1 to 8 carbon atoms and R3 is an aliphatic divalent radical of 1 to 4 carbon atoms; the group <FORM:0813838/IV (a)/2> where R3 has the meaning given above and R1 and R2 are hydrogen or alkyl groups of 1 to 5 carbon atoms; the group <FORM:0813838/IV (a)/3> R1 and R3 having the same meaning as in the previous group; pyridine, methyl- or ethyl-substituted pyridine or the group -R3-NH -NH2. The polymer blend may also contain polymers of ethylene; vinyl chloride, acetate or cyanide; methyl methacrylate, methacrylamide, acrylamide, formalized or acetalized vinyl alcohol or oxyacetalized (by oxy-acetaldehyde) vinyl alcohol to the extent that the ratio of the other various units to vinyl alcohol units is between 1 : 49 and 1 : 6. The composition may be dry-spun into a chamber at 40 DEG -180 DEG C. or, with or without the addition of sodium sulphate, potassium sulphate, ammonium sulphate or sodium dihydrogen phosphate, wet-spun into an aqueous bath at a temperature of 25 DEG to 60 DEG C. containing one of these salts. The spinning composition may also contain sodium hypophosphite to prevent yellowing or the treated filaments may be bleached with hydrogen peroxide, sodium hypochlorite or sodium chlorite and with a fluorescent bleaching compound. The heat-stretching is performed by means of guides or rollers in a salt bath or in a anhydrous medium such as air, nitrogen, carbon dioxide, oil or molten metal at a temperature which is at least 2 DEG C. below the softening temperature. In Example 3, the yarn is taken from the coagulating bath and stretched to a draw ratio of 3/1 between positively driven rolls, further stretched in a solution of sodium sulphate at 70 DEG C., wound on a bobbin and, before heat treatment, is drawn in air at 240 DEG C. to a further ratio of 3/1 . The heat-setting may be performed in a medium similar to that adopted for the stretching or in water vapour alone or in water vapour-air mixture at 10 kg./cm.2 above atmospheric pressure. In Example 6, the fibres are drawn to a ratio of 2.5/1 after coagulation and are stapled and crimped before heat treatment at 220 DEG C. and final aldehyde treatment. A number of aldehydes are specified for the final treatment, including formaldehyde and other aliphatic aldehydes, chloro- and bromo-acetaldehyde, benzaldehyde and chloro- and nitro-benzaldehyde, hexahydrobenzaldehyde, furfural and naphthaldehyde. Sulphuric, hydrochloric or phosphoric acid may be added, as a catalyst, to the aqueous solution of the aldehyde, which may also contain a surface-active agent and sodium, potassium or ammonium sulphate, sodium or potassium chloride or sodium nitrate and which may be at a temperature of 40 DEG to 95 DEG C. In Example 6 the aldehyde solution also contains methyl alcohol. The amino acetal is obtained by reacting polyvinyl alcohol with an amino aldehyde or an acetal, e.g. betacyclohexylamino-butyraldehyde dimethyl acetal, in aqueous solution containing sulphuric, hydrochloric or phosphoric acid, e.g. at 70 DEG C. The spinning solution may be obtained by dialysing the product with a semi-permeable membrane to remove acid and unreacted acetal and adding polyvinyl alcohol or, without dialysis, by neutralizing the acid with sodium hydroxide, concentrating the solution and adding polyvinyl alcohol.