Structural Change during Uniaxial Drawing of Unoriented Poly (tetramethylene succinate) Films.

Abstract

Unoriented films of poly (tetramethylene succinate) [PTMS] were uniaxially drawn at a given temperature (basically at room temperature and occasionally at elevated temperatures). In their drawing process, stress-strain measurements and time-resolved wide-angle X-ray diffraction [WAXD] experiments were carried out.In the drawing process, at first the chain axes (c-axes) of α-form crystallites were gradually oriented in the drawing direction via necking, and then the solid-state phase transformation from α- to β-form crystals occurred increasingly by further drawing. The stress at which the transformation took place was always greater than the yielding stress that was recorded just before the onset of necking. Even at diffrent drawing temperatures ranging from room temperature to 110°C, the transformation occurred at the approximately same strain (or draw ratio), but the stress at which the tranformation took place decreased with increasing temperature.After a run of uniaxial drawing, the sample strip was held still at the final length for more than 120min, but its WAXD pattern displayed only the β-form reflections during such a holding process. In the case of the strip held at a constant strain of 640% for 120min, the stress thereby decreased by 25%, but no α-form reflections were observed in the WAXD pattern. When the stress was fully released, the reflections of β-form disappeared completely and those of α-form appeared again: Finally the uniaxially oriented film of PTMS consisting of α-form crystals was obtained.