Reversed Annealing of Thermal Fractionated Polyethylenes by TMDSC

Abstract

Polyethylene samples prepared by thermal fractionation (TF) were annealed in several consecutive cycles in a temperature modulated DSC (TMDSC) at a temperatures one °C below the peak temperatures, increased from cycle to cycle relative to these peaks. The transition enthalpy of each cooling cycle was greater or equal to that of the preceding heating cycle. The total heat-flows of each heating cycle corresponded to those of the samples in the reference state up until the vicinity of the annealing temperature. During the annealing, the heat capacities decreased to a lower value over a one minute period. The thermal memory effect caused by the thermal fractionation was eliminated by a small overheating of the material for a short time. The fast disappearance of the thermal memory by a relatively very small degree of heating above their melting temperature denies a long range physical separation of macromolecules by TF.