Melting point of polymers under high pressure: Part I: Influence of the polymer properties

The pressure dependence of the melting point of various polymers including homo- and copolymers (HDPE, LDPE, PP and ethylene vinyl acetate copolymers (EVA)) was investigated under nitrogen atmosphere up to 330 MPa within a high pressure differential thermal analysis cell designed by our group. The properties of the polymers (vinylacetate content, melt flow index, molecular weight, isotactic index, crystallinity, density, and frequency of branching) have been correlated with the change of the melting point under pressure (dTm/dp). It could be shown that the melting point always increases linearly with pressure up to 330 MPa. The pressure dependence was found to be in the range of 11–17 K/(100 MPa). From these results it is possible to approximate dTm/dp using the enthalpy of fusion of the polymers at ambient pressure.