  Polybutene-1 (PB-1), a typical semicrystalline polymer, in its stable form I
shows a peculiar temperature dependent strain-whitening behavior when being
stretched at different temperatures where the extent of strain-whitening
weakens with the increasing of stretching temperature reaching a minima value
followed by an increase at higher stretching temperatures. Correspondingly, a
stronger strain-hardening phenomenon was observed at higher stretching
temperatures. The strain-whitening phenomenon in semicrystalline polymers has
its origin of cavitation process during stretching. In this work, the effect of
crystalline lamellar thickness and stretching temperature on the cavitation
process in PB-1 has been investigated by means of combined synchrotron
ultrasmall-angle and wide-angle X-ray scattering techniques. It was found that,
with respect to the cavitation process, three modes of cavitation during the
stretching process can be identified, namely no cavitation for sample with the
thinnest lamellae where only shear yielding occurred, cavitation with
reorientation for the samples stretched at lower temperatures and samples with
thicker lamellae, and cavitation without reorientation for samples with thinner
lamellae stretched at higher temperatures. The mode cavitation with
reorientation occurs before yield point where the plate-like cavities start to
be generated within the lamellar stacks with normal perpendicular to the
stretching direction due to the blocky substructure of the crystalline lamellae
and reorient gradually to the stretching direction after strain-hardening. The
mode of cavitation without reorientation appears after yield point where
ellipsoidal shaped cavities are generated in those lamellae stacks with normal
parallel to the stretching direction followed by an improvement of their
orientation at larger strains.
