Die orientierung der kristallinen und der nichtkristallinen bereiche in verstreckten polyethylenterephthalat‐folien

Films of poly(ethylene terephthalate) were stretched at 100°C with different stretching rates. By this, oriented films with birefringences between 3.10 −3 and 100.10 −3 were produced. After a crystallization with fixed ends at 150°C, 200°C and 240°C, the orientation function of the crystalline regions, the density, and the birefringence were measured. From this data, the orientation function of the noncrystalline regions was computed. The results obtained show, that only a qualitative but not a quantitative computation of the orientation function is possible. With increasing birefringence of the material before crystallization, the orientation of the crystalline and the noncrystalline regions increases. Up to birefringences of Δ n 0 =40.10 −3 in both regions a strong increase of the orientation function is observed. At higher birefringences Δ n 0 , the increase diminishes and depends strongly on the crystallization temperature. The orientation of the crystals after crystallization is better than the initial average orientation of the sample before crystallization. Further the orientation function of former reported structure models for the crystalline regions were computed in dependence of the structure parameters. Comparing the computed and experimental results one finds, that the change from structures consisting of twisted lamellae into such of bended lamellae occurs at a birefringence Δ n 0 =20.10 −3 .