Internally coated hollow polyacrylonitrile fibres for membrane applications - by treating with cyclohexane, then with alcohol-contg. solns. of PVA and maleic anhydride-ceric salt, and heating to seal larger pores

摘要

A process is claimed for the prodn. of hollow polyacrylonitrile fibre (I) for membrane applications, using suitable coating materials. The novelty is that the pore on the inside of the capillaries are coated in several stages so as to seal the larger pores in a controlled manner. The coating process involves (a) 10 mins. immersion in a hydrocarbon, pref. cyclohexane, (b) removing the hydrocarbon and treating for 1-3 mins. with a PVA-contg. soln. (A), and (c) removing soln. (A), treating for 1-3 mins, with a soln. (B) which can react with (A) at a sufficiently high temp. and removing (B) before heating to reaction temp., or treating with a mixt. of (A) and (B); solns. (A) and (B) contain at least some monoalcohol, pref. ethanol. Also claimed are hollow polyacrylonitrile (PAN) fibres (I) in which the pores are coated by reaction of polyvinyl alcohol (PVA) with maleic anhydride/Ce (IV) sulphate inside the capillaries, with preferenial coating of the larger pores so as to improve the sepg. power and stabilise the pore structure. Pref. the PAN fibres used are PAN membrane capillaries with 'frozen-in' polymer and pore structure as described in DE4009865. Pref. the coating layer is produced by applying solns. of PVA (A) and Ce(IV) salt/maleic anhydride (B), one after the other or together, and heating to bring about the hardening reaction. The coated capillaries (capillary bundle) are dried evenly by holding them vertically for 1-3 mins. and reversing the fibres several times, and then cured by placing in a horizontal position and heating for 2-4 hrs. at 70-100 deg. C, pref. 3 hrs. at 80 deg. C. Pref. (A) is a soln. of PVA in water-ethanol and (B) consists of maleic anhydride, water, ethanol, polyethylene oxide-diol and Ce(SO4)2.4H2O. Pref., solns. (A) and (B) are applied together as a freshly-prepd. 1:1 mixt., and the solns. contain at least 50 wt.% mono-alcohol, e.g. ethanol. USE/ADVANTAGE - Provides a simple and repoducible process for the prodn. of PAN membrane capillaries with improved separating power, without collapsing the pore structure and polymer structure by using alcohol-contg. coating solns.