The Use of Etching Techniques to Investigate the Morphology of Mechanically Induced Transformations in an Aliphatic Polyketone

摘要

Existing permanganic etching techniques have been adapted for an aliphatic polyketone terpolymer to examine its spherulitic and lamellar morphology by Scanning Electron Microscopy(SEM) and Transmission Electron Microscopy (TEM). A spherulitic morphology was observed consisting of irregularly shaped spherulites with an average diameter of 5-7 #mu#m and poorly defined spherulite boundaries. Crystalline lamellae were found to be oriented radially within the spherulites. The morphology associated with mechanically induced transformations in a number of deformation systems has been studied and compared to that arising in other common polymeric systems. Changes in morpholgy through the neck region of drawn samples revealed the elongation of the spherulites as the morphology is transformed from a spherulitic to a fibrillar structure. In samples tested between 23degC, and 120degC, radial flaws were observed within the spherulites prior to and within the neck transformation zone. These radial flaws were not observed for samples tested at higher temperature. Four-point bend tests were conducted on double notched and pre-cracked aliphatic polyketone samples. Examination of the process zone around the crack at the core of the sample revealed crazes characteristic of semicrystalline polymers subjected to a highly constrained stress state. However, the process zone around the crack at the surface of the sample was found to consist of shear bands, suggesting a less constrained damage regime. High cycle fatiguo loading also induced flaws oriented radially within the spherulties. Examination of the region around the failure surface in samples fatigue cycled until failure revealed a process consisting of an array of craxes reminiscent to that found in the four-point bend tests.