On cellulation and banding during crystallization of a linear-low-density polyethylene from linear nuclei

Linear-low-density polyethylene shows novel features, in addition to those found for the linear polymer, when crystallized as row structures from linear nuclei. There is the same division between disordered and ordered (inclined) fold surfaces for faster and slower crystallization, respectively, with the changeover occurring at a lower temperature and for a longer time than the linear polymer. The first new feature is that the kinetics of slower crystallization, with inclined fold surfaces, are non-linear, slowing as segregation proceeds, then recovering approximately to the initial value as cellulation sets in. Two patterns of cellulation, with associated kinks in the kinetic curves, have been observed. At all temperatures, a morphology similar to that encountered in linear polyethylene occurs when lamellae have become normal to the nucleating fibre. Beyond this, at 123 degreesC, is a coarser cellulation related to the onset of banding. This banding, the second new feature, contrasts with that in linear polyethylene which only occurs for faster crystallization, when the driving fold-surface stress is caused by the initial disordered packing itself. For slower crystallization in the linear-low-density material, fold-surface packing was initially ordered but surface stress is created, which banding helps relieve, when isothermal lamellar thickening is restricted by branches brought into the fold surfaces. (C) 2002 Published by Elsevier Science Ltd.