Morphology of binary blends of linear and branched polyethylene: composition and crystallization-temperature dependence

Abstract

The morphology of binary mixtures of low-molar-mass linear polyethylene (L2.5: M w = 2500, M w M n = 1.15 ) and higher-molar-mass branched polyethylenes, with 0.5 mol% of butyl branches (BB0.5) or 1.5 mol% of ethyl branches (BE1.5), has been studied by differential scanning calorimetry, polarized light microscopy and transmission electron microscopy. A progressive change from curved to straight lamellae and a strong decrease in average amorphous thickness is observed with increasing content of the linear polymer. Data obtained by model calculations of the average amorphous thickness assuming complete co-crystallization of the linear and branched polymers show good correspondence with the experimental data obtained for blends of L2.5 and BE1.5 except for the blend consisting of 80% of L2.5 but a pronounced deviation for blends of L2.5 and BB0.5. For the majority of the blends of L2.5 and BE1.5 there is a good agreement between calorimetric crystallinity and crystallinity determined by transmission electron microscopy, which indicates co-crystallization of the components. There is, however, significant deviation between the two crystallinity values for all blends of L2.5 and BB0.5, and for the blend of L2.5 and BE1.5 with 80% of L2.5, which can be explained by partial segregation of L2.5.