SOME MECHANICAL PROPERTIES OF POLYETHYLENE-POLYPROPYLENE BLEND FIBERS

Abstract

Polyethylene-polypropylene blend fibers were prepared from the melt-blended mixtures of lowpressure polyethylene and isotactic polypropylene at the weight ratios of (100/0), (95/5), (90/10), (80/20), (60/40), (40/60), (20/80), and (0/100). The spinnability and drawability of the blend polymers are nearly the same as those of polyethylene or polypropylene alone. Orientation of polyethylene or polypropylene molecules during drawing seems to be scarecely inhibited by blending. Some mechanical properties of undrawn and drawn fibers were investigated in terms of the composition. Undrawn fibers: The blend fibers show slightly lower yield stress, lower elongation, and higher tensile strength in comparison with polyethylene or polypropylene fibers. These effects can be elucidated by the decrease in crystallinity, and by the difficulty in slippage of molecules in the boundary layer of polyethylene and polypropylene phases in the blend fibers.Drawn fibers: The tensile strength, elongation, and Young's modulus of the blend fibers are, in most cases, between those of polyethylene and polypropylene fibers in the same drawing condition, and increase or decrease monotonically with the composition. Knot strength-composition curve has a maximum at the polypropylene content of 50_??_80%. At the maximum, the ratio of knot strength to tensile strength exceeds 90%. Elastic recovery of the blended fibers containing more than 40% of polypropylene is nearly the same as that of polypropylene which is much better than polyethylene in elastic properties. These anomalous, but favorable properties in the blend fibers are supposed to be derived from the fact that the blend polymer does not form so-called the “sea-island” structure, but forms the “network” structure which consists of isolated continuous phases of polyethylene and polypropylene.