ES348215A1 - Method for treating acrylic composite fiber - Google Patents

Abstract

A process for heat-relaxing and simultaneously producing a coiled crimp in a spun and stretched conjugate acrylonitrile polymer fibre formed from at least two different acrylonitrile polymers each containing at least 80% by weight of acrylonitrile, possessing dissimilar thermal behaviour and arranged in eccentric or longitudinal lamellar relationship, said fibre containing at least 20% by weight of water based upon the dry weight of the fibre, comprises immersing said fibre in a water-immiscible liquid organic medium in which the fibre is insoluble at a temperature of at least 105 C. for a time sufficient to develop a threedimensional coiled crimp. Blends of the specified polymers may be used, and a list of comonomers which may be co-polymerized with acrylonitrile is given. There is no critical upper limit of water content, but it is usually up to 400% by weight based upon the dry weight of the fibre. Preferably, the temperature of the liquid organic medium is from 105 C. to 150 C., the fibre being immersed therein for from 30 seconds to 3 minutes. Suitably, the liquid organic medium is a mineral oil, especially liquid paraffin B.P., kerosene or spindle oil, or a vegetable oil, suitably cotton-seed oil, coconut oil, soya bean oil or peanut oil, or a silicone oil, provided said media have boiling points of at least 105 C. at atmospheric pressure. By using a water immiscible organic heating medium the water contained in the fibre is rapidly converted to water vapour upon treatment, which causes thermal shrinkage of the fibre while plasticizing the fibre. As water is evaporated, the fibre bundle is caused to unravel into individual filaments, thus weakening the bond between the individual filaments and accordingly, facilitating the development of the desired 3-dimensionally coiled crimp. The conjugate filaments may be made by dry-spinning or wet-spinning, and the process may be carried out using filaments which have been stretched under hot humid conditions and accordingly contain at least 20% by weight of water relative to the dry weight of the fibre and unrelaxed conjugate fibres which have been provided with at least 20% of water by sprinkling with water or by passage through a water bath. The heat-relaxation treatment of the invention is conducted after the conjugate fibre has been spun and stretched, stretching being effected in known manner. Thus, the swollen gel conjugate fibre emerging from the coagulating bath may be washed with water, and then stretched to 3 to 20 times its initial length, whereby the fibre acquires a practical degree of strength and elongation. Stretching may be carried out in one step, but by taking advantage of the cold-stretchability of the unstretched fibre, it is possible to stretch the fibre 1À1 to 4 times in the washing water bath at room temperature and then hot stretch the " pre-stretched " fibre so that the total stretch ratio would be 3 to 20 times its initial length. It is also possible to carry out the hot-stretching in several steps. Hot-stretching may also be carried out in steam at a temperature of 100 to 140 C. Examples are given.