Shrinkage,shrinkage force and the structure of ultra high modulus polyethylenes

Measurements of shrinkage and shrinkage force have been undertaken on drawn polyethylenes over a wide range of temperatures. The behaviour has been studied as a function of draw ratio and molecular weight for several linear polyethylenes and polyethylene copolymers. Although complete retraction is observed on heating even the most highly drawn samples above the melting range, at lower temperatures the shrinkage is less than that of low draw material. This is attributed to the formation of a substantial degree of crystal continuity during drawing, so that shrinkage requires mobility in the crystalline phase. The shrinkage forces are very high, being comparable with the drawing stresses at corresponding temperatures, and are molecular weight dependent, increasing with increasing molecular weight. It is considered that the results presented here on shrinkage and shrinkage force provide further support for the proposition that the drawing process relates to the extension of a molecular network.