LAMELLAR THICKENING GROWTH OF AN EXTENDED-CHAIN SINGLE-CRYSTAL OF POLYETHYLENE .1. POINTERS TO A NEW CRYSTALLIZATION MECHANISM OF POLYMERS

Crystallization and growth of an isolated extended chain single crysta l (ECSC) of polyethylene (PE) under high pressure from the melt into t he mobile phase, such as hexagonal phase, was studied by in-situ optic al microscopy and transmission electron microscopy. Direct evidence is obtained that an isolated ECSC was formed from a folded chain single crystal through the combination of newly recognized ''lamellar thicken ing growth'' and the long familiar lateral growth. This confirmed the prediction of chain sliding diffusion theory that the lamellar thicken ing growth takes place the important role in the origin of folded chai n and extended chain crystals (FCCs and ECCs) presented by one of auth ors (M.H.) previously. The lamellar thickness (I) inceased linearly wi th time (l), indicating that the lamellar thickening growth rate is co nstant as long as the crystal is in isolation, i.e., it does not impin ge on others, directly reflected also by the straightened taper of the cross-sectional shape. This is quite different from the well-known la mellar thickening of stacked-lamellar system where l increases linearl y with logarithm of time (log t). It is shown that the difference is d ue to the difference between the primary and the secondary crystalliza tion processes. The lamellar thickening growth rate (U), defined by (d l/dt)/2, was measured for the first time by developing two methods, '' direct method'' and ''mapping method''.