SOLID-STATE RELAXATIONS IN LINEAR LOW-DENSITY (1-OCTENE COMONOMER), LOW-DENSITY, AND HIGH-DENSITY POLYETHYLENE BLENDS

Extensive thermal and relaxational behavior in the blends of linear lo w-density polyethylene (LLDPE) (1-octene comonomer) with low-density p olyethylene (LDPE) and high-density polyethylene (HDPE) have been inve stigated to elucidate miscibility and molecular relaxations in the cry stalline and amorphous phases by using a differential scanning calorim eter (DSC) and a dynamic mechanical thermal analyzer (DMTA). In the LL DPE/LDPE blends, two distinct endotherms during melting and crystalliz ation by DSC were observed supporting the belief that LLDPE and LDPE e xclude one another during crystallization. However, the dynamic mechan ical beta and gamma relaxations of the blends indicate that the two co nstituents are miscible in the amorphous phase, while LLDPE dominates alpha relaxation. In the LLDPE/HDPE system, there was a single composi tion-dependent peak during melting and crystallization, and the heat o f fusion varied linearly with composition supporting the incorporation of HDPE into the LLDPE crystals. The dynamic mechanical alpha, beta, and gamma relaxations of the blends display an intermediate behavior t hat indicates miscibility in both the crystalline and amorphous phases . In the LDPE/HDPE blend, the melting or crystallization peaks of LDPE were strongly influenced by HDPE. The behavior of the a relaxation wa s dominated by HDPE, while those of beta and gamma relaxations were in termediate of the constituents, which were similar to those of the LLD PE/HDPE blends. (C) 1997 John Wiley & Sons, Inc.