Effect of drawing on the melting point and heat of fusion of polyethylene

Abstract

AbstractThe melting point and the heat of fusion were measured by differential scanning calorimetry (DSC) as a function of draw ratio for linear polyethylene. Both the melting point and the heat of fusion increased with an increase in draw ratio. The plot of the heat of fusion against the melting point was approximately linear. The linear relation is explained theoretically using the assumption that the increases in the melting point and the heat of fusion are due to the orientation of the amorphous phase caused by drawing. The excess free energy of the amorphous phase derived from the orientation increases the melting point, and the amorphous phase absorbs heat for its randomization at the melting point. Hence for drawn samples having an oriented amorphous phase not only the crystal phase but also the amorphous phase contribute to the heat of fusion.