Plastic deformation and solid-phase transformation in polybutene-1

Abstract

The stress-strain behaviour under uniaxial tension was investigated for polybutene-1 specimens crystallized in Modification II with various types of spherulitic microstructure and degrees of crystallinity. As for Modification I, the tensile properties were found to depend greatly on the initial microstructure, but Modification II specimens exhibit a much more pronounced plastic behaviour than specimens fully transformed into Modification I prior to deformation. The deformation of spherulites within the samples was followed either by direct microscopic observation or by means of small-angle light scattering patterns. In situ microscopic observations of individual spherulites showed that the characteristic dark band, which appeared in the early stages of the deformation of Modification I spherulites and which corresponds to the whitening of the strained samples when observed with reflected light, occurred for much larger strains in the case of specimens initially crystallized in Modification II. Differential scanning calorimetry and wide-angle X-ray scattering experiments performed before and after the tensile tests ensured that the unstable tetragonal Modification II was transformed into the stable hexagonal Modification I during the plastic deformation. Eventually, the evolution of this phase transformation was determined as a function of the applied tensile strain by use of X-ray diffractometry.