Rheological and thermal properties of m-LLDPE blends with m-HDPE and LDPE

The dynamic and steady state behavior of metallocene linear low density polyethylene (m-LLDPE) blended with metallocene high density polyethylene (m-HDPE) and with low density polyethylene (LDPE) were measured in parallel plate rheometer at 160, 180, and 200 degreesC. The composition dependence of zero shear viscosity eta(0), the characteristic relaxation time tau(0) and the characteristic frequency coo of m-LLDPE/m-HDPE blends show a linear variation in the whole range of weight fraction, which indicates that m-LLDPE/m-HDPE blends are miscible blend. At the same time, m-HDPE showing a 'dissident' theological behavior should possess a certain very low degree of LCB. Two calculation methods of LCB verify this point. In contrast, the composition dependence of zero shear viscosity eta(0) of m-LLDPE/LDPE blends shows a positive deviation from the log-additivity rule, which can be well fitted by using the immiscible blend equation of Utracki. The characteristic relaxation time tau(0) and the characteristic frequency coo have a sharp variation with the small amounts of LDPE in the blends, which also indicates a phase separation in the system. The thermal properties of m-LLDPE/m-HDPE blends are very similar to a single-component system. However, m-LLDPE/LDPE blends are immiscible in both melt and crystal states. DSC results are consistent with the rheological properties of these two series of blends. (C) 2002 Elsevier Science Ltd. All rights reserved.