Time-temperature superposition and dynamic mechanical properties of metallocene polyethylene

This paper is devoted to the study of dynamic mechanical behaviour of two metallocene polyethylenes (m-PE). For this purpose two metallocene linear low density polyethylene (m-LLDPE) and very low density polyethylene (m-VLDPE) were used consisting of 3.3 mol% butyl and 6 mol% ethyl branches, respectively. The m-LLDPE showed three transitions at 31, -8 and -115degreesC attributed to the alpha, beta and gamma-transitions, respectively. The beta-relaxation was observed as a shoulder on the alpha-relaxation peak. Studies on the m-VLDPE revealed no appreciable alpha-relaxation but an increased beta-relaxation than that of the m-LLDPE. The effects of cooling rate and annealing were also investigated for the m-LLDPE. Slow cooled sample showed a higher alpha-relaxation temperature and was appreciably greater in breadth and area than that of the sample cooled in water. No appreciable shift in either the alpha or beta-relaxation temperature were found by comparing loss modulus of quenched and annealed sample of the m-LLDPE. The time-temperature superposition principle was also found to be applicable to the alpha-relaxation process of the m-LLDPE and master curve was obtained at 80degreesC.