A study of crystallisation behaviour and compatibility of high-density polyethylene/linear low-density polyethylene blends

Blends of high-density polyethylene (HDPE) with a linear low-density polyethylene (LLDPE) (ethylene-but-1-ene copolymer) at various compositions were examined by optical microscopy and differential scanning calorimetry in order to study their crystallisation processes and compatibility. The thermal behaviour of blend samples cooled from the melt under various conditions pointed to the presence of co-crystallisation phenomena. Microscopic observations of blend films isothermally crystallised from melt did not reveal any phase segregation of LLDPE in the spherulitic regions of HDPE. Analysis of the isothermal crystallisation kinetics (in the range 392-400 K) indicated that the crystallisation rate of HDPE is largely depressed in the blends, suggesting that the nucleation and growth rate of the crystals are affected by the presence of melted LLDPE. The melting behaviour of isothermally crystallised samples can be mainly attributed to morphological effects relevant to crystal size and perfection. No depression of the equilibrium melting temperature of HDPE was observed in the blends. © 1990.