Fast limiting behavior of the melting kinetics of polyethylene crystals examined by fast-scan calorimetry

Abstract

Melting behaviors of polyethylene (PE) crystals on heating were examined in terms of the heating rate β dependence by fast-scan chip-sensor calorimetry. PE crystals were prepared under broad ranges of crystallization temperature Tc and isothermal holding time Δt, including Δt shorter than completion time of primary crystallization. On the basis of a modeling of melting kinetics with a rate coefficient determined by the degree of superheating ΔT and the careful examination of the influence of thermal lags, the detailed analysis confirmed a systematic change in the melting kinetics depending on the crystal stability; i.e. less stable crystals, which were formed at low Tc with short Δt, experience lower kinetic barrier for melting. Melting peak of those less stable PE crystals showed linear β dependence, which exceeds the acceptable limit of the β dependence predicted from ΔT dependent melting rate in the modeling. The melting behavior approaches to that of indium, a standard material for melting, and suggests that the melting of those less stable PE crystals is nearly instantaneous without appreciable superheating, the confirmation of which becomes realized only by utilizing fast-scan calorimetry.