Fibers From Crystalline Hydrocarbon Polymers1

Abstract

Properties of fibers derived from crystalline polymers of ethylene, propylene, 4-methyl- 1-pentene, and styrene are presented and contrasted. Polyethylene fiber properties depend markedly on the crystallinity or density of the polymer; although high-strength fibers can be made from linear polyethylene, resiliency properties are poor, tensile properties are highly time-dependent, and endurance under sustained loading is very poor. On the other hand, polypropylene fibers have good stress-endurance properties, excellent recovery from high extensions, and fair-to-good recovery properties at low strains; recovery at 'low strains is shown to depend on the extent of fiber orientation and annealing. Anoma lies in the change of the sonic modulus of polypropylene yarns during extension and relaxation are noted and interpreted in terms of structure changes in the crystalline phase. The high melting temperature of 235°C for poly(4-methyl-1-pentene) appears to be due to its low entropy of melting, and fibers from this polymer are characterized by low tenacity when tested at elevated temperatures. Crystalline polystyrene fibers have relatively good retention of tenacity at elevated temperatures and are characterized by excellent resiliency at low strains, good wash-wear characteristics in cotton blends, and low abrasion resistance.