TEMPERATURE MODULATED DIFFERENTIAL SCANNING CALORIMETRY OF BRANCHED POLYETHYLENE BLENDS

摘要

Temperature modulated differential scanning calorimetry (TMDSC) has been established as an alternative technique to produce new and different quantitative information on melting and crystallisation of polymers relative to standard DSC. It provides a means of separating different kinetics of the sample with an oscillation heating rate superimposed upon a linear heating rate. The typical periodic oscillations can be sinusoidal or sawtooth, and the kinetics of transformations can be obtained by Fourier analysis of the modulated heat flow. Recently, TMDSC has been used for the analysis of the melting of many polymers, including high molar mass poly(ethylene terephthalate), poly(oxyethylene), and polyethylenes. Very low density polyethylenes (VLDPE), produced by metallocene or single-site catalysts, have a narrower distribution of comonomers than conventional linear low density polyethylenes. VLDPE1, a butene copolymer, contains only short branches. Conversely, VLDPE2, which is an octene copolymer, has both short and long chain branching. Thus, blending of these two polymers provides the possibility to prepare blends with very similar short branch content and distribution, while introducing the advantages of long branches. We have previously reported the morphology, crystallization and miscibility of these blends. The aim of this work is to investigate the melting behaviour including recrystallisation and reversible melting phenomena of VLDPE1-VLDPE2 blends by TMDSC after crystallising at different conditions.