Modelling of the melting point shift in semi-crystalline thermoplastics dependent on prior cooling rate and heating rate

The different local properties of plastic parts are highly dependent on local thermal histories. In DSC measurements a shift in peak melting temperature was detected in semi-crystalline thermoplastics (Polypropylene and Polyamide) dependent on the heating rate and prior treatment conditions of the samples. To investigate such phenomena, the shift in peak melting temperature depending on a prior cooling and subsequent heating for polyamide 6.6 and isotactic polypropylene is examined using Flash-DSC measurements. Due to crystallisation and heat conduction effects the temperature shows a dependence on the cooling and heating rate. From the observations, a model was developed that is able to predict the measured peak melting temperature as a function of the cooling and heating rate. A phenomenological model is developed uniting the effect of cooling rate prior and the melting rate in order to predict the main melting point.