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Lamellar Thickness and Stretching Temperature Dependency of Cavitation in Semicrysta line Polymers
Lamellar Thickness and Stretching Temperature Dependency of Cavitation in Semicrysta line Polymers
Polybutene-l (PB-1), a tWical semicrystalline polymer, in its stable form I shows a peculiar temperature dependent strain-whitening behaviorl. The strain-whitening phenomenon has its origin of cavitation process during stretching. The effect of crystalline lamellar thickness and stretching temperature on the cavitation process in PB-1 was investigated by synchrotron ultrasmall-angle (USAXS) and wide-angle X-ray scattering (WAXS) techniques2. Three modes of cavitation during the stretching process can be identified, namely "no cavitation" for the quenched 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.
