HIGH-PRESSURE DSC INVESTIGATIONS ON N-ALKANES, N-ALKANE MIXTURES AND POLYETHYLENE

A high pressure cell for a power-compensated DSC is presented, allowin g measurements at pressures up to 500 MPa. With the aid of this appara tus, n-alkanes, binary n-alkane mixtures, and two linear polyethylenes have been investigated. The fusion temperature and the heat of fusion have been measured for different n-alkanes in the pressure region bet ween normal pressure and up to 500 MPa. For five eutectic and non-eute ctic binary mixtures, the liquidus and solidus temperatures were deter mined. It is possible to describe the mixing behaviour of n-alkanes wi th the one-parameter approximation derived by Porter. The increase of the Porter parameter with pressure implies decreasing miscibility at h igher pressures. From the Porter parameter the critical point can be c alculated. Thus, it can be seen that n-alkanes which build mixed cryst als at normal pressure demix at higher pressures. From these results, it can be concluded that the same is true for polyethylene.