Patent GB-1455667-A (GB)
Title: Insoluble and infusible cured phenol-aldehyde resin fibres and  production thereof
IPC: D01F6/94
Filed: 1974-05-29
Abstract: 1455667 Phenol-aldehyde resin fibres JAPAN EXLAN CO Ltd 29 May 1974 [29 May 1973 22 Nov 1973 26 Nov 1973 (2) 11 Dec 1973 (2)] 23872/74 Heading B5B [Also in Division C3] Insoluble and infusible, flame retardant phenol-aldehyde resin fibres are produced by curing fibres comprising 30-98% wt. of a crosslinkable phenol-aldehyde resin and 70-2% wt. of a water-soluble polymer (PVA) containing at least 50 mol. per cent of vinyl alcohol units. The phenol-aldehyde resin may be a resol or a mixture of a resol and a novolac resin. The PVA polymer preferably has a degree of polymerization of 500-2500 and may be prepared by hydrolysis of polyvinyl acetate or a copolymer of vinyl acetate, or by etherification, esterification or formalization of a part of the hydroxyl groups of the vinyl alcohol polymer thus obtained. The fibres are produced by first preparing an aqueous solution consisting of the cross-linkable phenol-aldehyde resin and PVA in the above percentage amounts, wet-spinning the aqueous solution and then curing the wetspun fibres, generally by heating above 60‹ C. and/or by acid treatment and/or by treatment with an acid and aldehyde. The aqueous solution is spun into an aqueous coagulating bath preferably containing at least one of the following coagulants: (NH 4 ) 2 SO 4 , Na 2 SO 4 , K 2 SO 4 , ZnSO 4 , CuSO 4 , FeSO 4 , MgSO 4 , (Al) 2 (SO 4 ) 3 , NH 4 NO 3 , NaNO 3 , KNO 3 , Al(NO 3 ) 3 , NaCl, KCl, Na 3 PO 4 , aluminium potassium sulphate, potassium bichromate and potassium citrate; and optionally at least one boron compound capable of forming boric ester bonds with the hydroxyl groups of the phenol/aldehyde resin and/or PVA, e.g. boric acid, metaboric acid, boron oxide, borates and metaborates; and optionally at least one reducing compound, e.g. sulphites, bisulphites, hydrosulphite, thiosulphate, bisulphite addition compounds of HCHO, hydroxylamine and stannous chloride. The coagulating bath is preferably made acid by addition of an inorganic and/or organic acid. In general the wet-spun fibres may be treated before or after curing with an inorganic and/or organic acid, or with an aqueous acidic solution containing either a boron compound or a reducing compound, which improves the colour of the fibres. In Examples 1-7 aqueous solutions of PVA having a degree of saponification of 78-99À9 mol. per cent and a degree of polymerization of 1750 and phenol-HCHO resol resin alone or in admixture with a phenol- HCHO novolac are wet-spun into aqueous coagulating baths containing Na 2 SO 4  and either boric acid or borax or potassium metaborate and optionally H 2 SO 4 . The fibres obtained are cold-drawn, heat-treated, washed and dried, and then cured by heating. In Examples 8, 9 aqueous solutions of the resol and PVA are wet spun into aqueous baths containing Na 2 SO 4 , H 2 SO 4  and either sodium hydrogen sulphite or hydrosulphite. In Examples 10, 11 and 14 aqueous solutions of the resol resin and PVA are wet spun into aqueous baths of NaS 2 O 4 , H 2 SO 4  and boric acid and the resulting fibres are cold-drawn and then crosslinked by heating. The cured fibres are then either treated with any of the following acids: H 2 SO 4 , benzoic, acetic, succinic, lactic, oxalic, maleic, malonic, H 3 PO 4 , or HCl, or are treated with an aqueous solution of boric acid or sodium borate. In Examples 12, 13 the uncured fibres of Example 10 are either treated with an aqueous solution of Na 2 SO 4  and H 2 SO 4  and then cured or are first cured by heating and then treated with aqueous p-toluene sulphonic acid. In Example 17 the crosslinked fibres of Example 10 are treated with aqueous solutions of any of the following reducing compounds: NaHSO 3 , Na 2 S 2 O 4 , SnCl 2  or with aqueous HCl alone and together with NaHSO 3 .