GB1111880A - Acrylic fibers and process for obtaining them - Google Patents

Abstract

1,111,880. Acrylic fibres. E. I. DU PONT DE NEMOURS & CO. 22 Feb., 1967, No. 8387/67. Heading B5B. Acrylic fibres having upon boil-off a " straightness factor " of 0À07 to 1À5, an " initial shrinkage temperature " of at least 145‹ C. and a " maximum shrinkage force factor " of no more than 0À9 may be produced by washing and drawing freshly spun acrylic filaments to 120 to 450% of their as-spun length, heat-softening the drawn filaments for at least 0À5 second while under restraint of at least 5 mgms/denier to relax the filaments 2 to 40% of their as-drawn length, if desired mechanically crimping the relaxed filaments and converting them into staple fibres. The filaments may be mechanically crimped to such an extent that 1À2 to 6 crimps per inch is imparted to them. A yarn may be prepared by blending at least 25% by weight of the acrylic fibres of the invention with synthetic fibres which shrink to a greater degree in heating than those of the invention. The filaments or fibres having the higher shrinkage may be conjugate consisting of two or more components bonded together in side-by-side arrangement along their lengths. The conjugate filament components may consist of (a) a polyacrylonitrile and (b) a copolymer of acrylonitrile and sodium styrene-sulphonate. The terms " acrylonitrile fibre " or "acrylic fibres" are defined as meaning fibres at least 85% by weight of which consists of polymerized acrylonitrile. The properties of the filaments of the invention are determined on filaments that are drawn thereafter relaxed in the manner specified, and mechanically crimped to the extent that the filaments have 1À2 to 6 crimps per cm. The straightness factor, SF is determined as follows: staple fibres to be tested, having a cut length of about 7À6 cm. are hand-carded, 0-5 gram if the carded fibre is dropped on to the surface of about 250 ml. of distilled water in a 400 ml. beaker, the covered beaker is immersed completely in a steam bath for 40 minutes, removed from the steam bath and allowed to cool to 30‹ C. or lower. The sample is then removed from the beaker with a glass rod and allowed to dry on a paper towel. Eight clumps of filaments are selected at random from the dried 0À5 gram sample of fibres find their mean curvature R and the mean frequency, f, of curvatures per inch of filaments is determined. The straightness factor, SF is then calculated by means of the formula The initial shrinkage temperature, IS, is determined by mounting a bundle of fibres of about 100 denier between the jaws of an Instron tester and separating the jaws until a tension of about 0À3 gram is indicated. With the jaws held at this position, the temperature of the air surrounding the fibre bundle is raised about 10‹ C. per minute. The stress and temperature are recorded and a plot of temperature, t, versus stress is prepared. The temperature, T, at which additional stress first appears is noted on the plot. The initial shrinkage temperature is calculated by means of the formula The Maximum Shrinkage Force Factor is calculated by means of the formula The fibres of the invention have a high resistance to development of crimp on heating and do not, like conventional acrylic fibres, exhibit surface distortion (e.g. develop pills) as the result of abrasive action encountered during wear of knitted fabrics consisting of the acrylic fibres. In the production of the fibres of the invention, by allowing shrinkage to occur render a restraint of at least 5 mg/denier, typically 5-30 mg/ denier, and under heat softening conditions, such as heated rolls, hot air, steam, or refluxing hot organic vapours, the fibres are caused to assume a straight configuration and acquire a low shrinkage tendency, preferably below 5%.