Untersuchung der druckinduzierten Kristallisation von Polyäthylen mit Hilfe einer neuen Raman-Hochdruckzelle

Abstract

A high pressure Raman cell is described which permits temperature dependent experiments an fluids and solids up to 7 kbar and 300 °C. Volume changes of samples can be measured simultaneously. The cell was used in a study of pressure induced crystallization of polyethylene. Under isothermal-isobaric conditions crystallization was followed by observation of the line shape changes in the CH₂-twisting and longitudinal acoustic mode (LAM) region and compared to the volume changes. The observed shift of theLAM frequency indicates a thickening of lamellae after formation. The measured pressure dependence of the crystallization rate and of the all-trans sequence length confirms the view that crystal growth is controlled by secondary nucleation.