DIFFERENTIAL MELTING IN COMPACTED HIGH-MODULUS MELT-SPUN POLYETHYLENEFIBERS

The compaction of high-modulus melt-spun polyethylene fibres has been investigated for compaction temperatures above the optimum. After such treatment the specimens are liable to be non-uniform because of diffe rential melting. Individual compacted fibres are observed to melt not only from the outside inwards, but also in certain internal regions, d epending upon the availability of local free volume. The regions of di fferent stability have been identified and inferences drawn concerning the structure of the initial fibres. It is suggested in particular th at the longitudinal regions of deficit density (which exhibit craterin g in transverse sections and melt before their surroundings) are a res ult of initial crystallization occurring within a rigid framework insi de the fibre, possibly nucleated on a strained molecular network. The presence of banded recrystallization around residual fibres demonstrat es that this phenomenon develops via interaction of neighbouring lamel lae as they grow.