POLYMER MELTING - HEATING RATE EFFECTS ON DSC MELTING PEAKS

The effect of heating rate on DSC peak shape has been investigated using Gray's model. Theoretical DSC melting curves for small samples with sharp transition temperatures were created and compared with DSC melting curves from pure indium samples. Good agreement was found between theoretical curves and experimental indium DSC peaks. As heating rate increases, there is an increase in both peak height and the time necessary for the sample to catch up with the programmed temperature. For pure indium samples the slope of the leading edge of the first half-peak shows no variation with increase in heating rate when plotted versus temperature. With increasing heating rate the melting peak appears narrower when heat flow is plotted versus time, and broader when plotted against temperature. Peak height dependence on heating rate was found to be somewhat more noticeable at lower heating rates than at higher rates. However, samples formed from a mixture of polyethylene (PE) and indium powder had melting curves that are quite different from those of pure indium. Significant variation in the slope of the first half-peak with heating rate results from changes in thermal resistance from sample surface to the interior. This information helps develop our understanding of, and aids in interpreting, ordinary DSC results.