Influence of molar mass and of nucleating agents on the orientation of polyethylene terephthalate

Abstract

If amorphous polyethylene terephthalate is drawn at temperatures of about 90 °C, this is slightly above the glass transition temperature, the material is deformed completely homogeneously without necking; the molecules become oriented. Which parameters influence the orientation obtained? In crystalline polymers the orientation is determined mainly by the drawing ratio. In amorphous polymers also the drawing temperature and the drawing rate are of great interest. This has been shown already some years ago for polystyrene by Berdelew et al. [1]. Measurements with polyethylene terephthalate have been performed in our laboratory [2]. Figure 1 shows some results. As a measure of orientation the birefringence ∆n ₀ is used. Complete orientation corresponds to a value of ∆n ₀ equal to 265 · 10⁻³. Similar results were obtained by De Vries et al. [4].