Study on the microstructure of poly(amide 6-ether) copolymers and their application in elastic fibers

Abstract

Fiber elasticity is an important property for achieving clothing comfort. The excellent resilience of poly(amide 6-ether) copolymers makes them popular candidate materials for preparing PA6-based elastic fibers. However, the low reactivity between the PA6 segments and the traditional polyether diol soft segments makes it difficult to achieve high molecular weights, hampering its application in fibers. Herein, a series of poly(amide 6-ether) copolymers (PA6-PEA copolymers) bonded by amide bonds were prepared using polyether diamine (PEA) as the soft segment. The PA6 segment and the PEA segment exhibited high reactivity and good compatibility, endowing the copolymer microstructure with a crystalline phase of PA6, an amorphous phase of PEA, and a mixed amorphous phase of both PA6 and PEA. The improved compatibility of both the soft and hard segments in the amorphous region of the copolymer and the formation of a soft continuous phase effectively improved the elastic properties of the copolymers. The elastic recovery rate of copolymers at 100% constant elongation increased from 14.61% for PA6 to 59.02% for PA6-PEA-45. The elastic recovery rate of the PA6-PEA elastic fiber at a constant elongation of 20% was 93.00%, which was 18.67% higher than that of the fPA6 fiber and also higher than that of the poly(trimethylene terephthalate) (PTT) fiber (86%). The elastic recovery rate after 5 cycles of stretching and rebounding was 92.50%, and the stress relaxation rate was 13.24%, showing good tensile fatigue resistance. At the same time, the fiber can maintain outstanding mechanical properties (breaking strength exceeded 2.18 cN per dtex). The initial modulus of the PA6-PEA elastic fiber decreased from 15.83 cN per dtex to 5.35 cN per dtex. In addition, the introduction of hydrophilic PEA segments increased the moisture regain of the fiber to 7.23%, improving the softness, comfort and skin-friendliness of the fiber. This work provides a new idea for the preparation of PA6-based elastic fibers with both elastic and mechanical properties.