Structural Changes and Thermo-Shrinking Properties in Secondarily Dry Heat-Stretched Acrylic Fibers

Abstract

Acrylonitrile (AN) /methylacrylate (MA) copolymer having AN/MA ratio of 90/10 by weight was wet-spun and drawn 12 times in hot water. The original sample was then subjected to the steam treatment at various temperatures under unconstrained length. This sample is called with symbol SH. SH was then drawn in dry state under various temperatures and stretch-ratios (named with the symbol ST). The practically important thermoelastic behavior of these acrylic fibers above the glass transition temperatures was studied from shrinkage, stress-strain curve and dye diffusion measurement. An inherent stretch ratio named rubbery elongation limit (REL) is defined to each of SH by the initial straight line part of the stress-strain curve obtained in hot water. ST obtained by drawing SH within REL, were found almost completely recoverable to the original length when subjected to hot water shrinkage treatment. For these fibers, the diffusion coefficient, D, of basic dye (C. I. Basic Red 18) showed no appreciable change by stretching. When SH was drawn above REL, the unrecoverable fraction of the length in the hot water shrinkage treatment of ST gradually increased and D clearly decreased with increasing stretch ratio. Based on the more detailed analysis of the quantitative thermoelastic data, structural models for the SH and ST were proposed which are applicable characteristically to acrylic fiber.