Non-isothermal crystallization of high density polyethylene

The quiescent non-isothermal crystallization kinetics of two polyethylene resins were investigated by the modified light depolarizing microscopy (LDM) technique developed by Ding and Spruiell (1994). The cooling rates studied were in the range of 5-5,000°C/min. Small angle light scattering (SALS), density gradient column (DGC), and differential scanning calorimetry (DSC) were used to determine the average spherulitic size, thermal properties, density, and the degree of crystallinity. The overall crystallization kinetics were analyzed by applying the Avrami analysis to the experimental data. It was found that the crystallization kinetics were strongly dependent on the cooling rate. According to the Avrami analysis, it is found that the growth mechanism was spherical and the nucleation was instantaneous for both resins. As the cooling rate increases, the average spherulitic size, the density, and the degree of crystallinity were all found to decrease. The half-time data which were obtained from the overall crystallization kinetics were also used to investigate possible regime existence and its transition according to the secondary nucleation crystallization theory introduced by Lauritzen and Hoffman (1961). The results were interpreted to indicate the presence of regime II and regime III in the crystallization temperature range studied; the regime Il-regime III transition was found to occur at approximately 115°C.