HARD-ELASTIC FIBERS (A REVIEW OF A NOVEL STATE FOR CRYSTALLINE POLYMERS).

This bibliography-based review paper is concerned with some features of synthetic fibers, also known as springy fiber, which exhibit the rubber-like property of high elastic recovery from large deformations, yet with much higher modulus and tenacity than is typical for elastomers. This springy or ″hard″ elastic behavior of this highly crystalline and highly oriented fiber has been shown to stem from a row nucleated morphology which results upon stress crystallization. However, the exact morphology which results in ″springiness″ is extremely sensitive to such processing parameters as spinning temperature, quench temperature, shear rate, draw down ratio, and annealing temperature. This results in the same polymer behaving in a springy or nonspringy manner depending upon the exact processing conditions. In spite of the great interest in energy mechanisms for the large elastic recovery of springy materials, there is also evidence for entropic contributions to the retractive forces. Thus, heat absorption decreases upon extension after about 5% and internal energy begins to increase at the same extension level. Many polymers have been shown to exhibit springy behavior under the proper conditions: PP, polyoxymethylene, polypivalolactone, poly(3-methylbutene-1), poly(4-methylpentene), PE, and 66 nylon. The major requirement for producing the proper row crystallized morphology for springy behavior is a rapid rate of crystallization. Refs.