Linear low density polyethylene/cycloolefin copolymer blends

Linear low density polyethylene (LLDPE) was melt compounded with various amounts of a cycloolefin copolymer (COC). Scanning and transmission electron microscopy evidenced, at qualitative level, some interfacial adhesion between LLDPE and COC. Another indication of interactions between the components was the increase of crystallinity degree with rising COC content and the enhancement of COC glass transition temperature with the LLDPE fraction. In order to explain this behaviour, the incorporation of ethylene segments COC into LLDPE crystalline phase, leading to an increased number or norbornene units in the remaining COC component undergoing the glass transition, was hypothesized. The thermo-oxidative degradation stability of LLDPE was substantially enhanced by COC introduction for filler contents higher than 20 wt%, especially when an oxidative atmosphere was considered. An increasing fraction of COC in the blends was responsible for an enhancement of the elastic modulus and of a decrease in the strain at break, while tensile strength passed through a minimum, in agreement with the model predictions based on the equivalent box model and equations provided by the percolation theory. The introduction of a rising COC amount in the blends increased the maximum load sustained by the samples in impact tests but decreased the blends ductility. Concurrently a significant reduction of the creep compliance of LLDPE was observed for COC fractions higher than 20 wt%