Tensile properties of the gamma phase of isotactic polypropylene with small particles

Mechanical properties of the pure γ-form of iPP have never been conducted at any level mainly due to difficulties in producing pure γ specimens. The mechanical properties of γ structure are very important because most processes are conducted at high pressures. This study provides an opportunity to investigate the effect of different crystal forms of iPP on the mechanical response. Wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), static tensile tests, were employed to characterize and compare the physical and mechanical properties of α and γ phases. Several specimens of the pure γ-form were successfully prepared at 200 MPa and 177.5°C and a number of the pure α-form specimens were prepared at low pressure and 120°C. The WAXD patterns confirmed that pure forms were produced. The average degree of crystallinity, as determined by DSC, was 41% and 43% for the α- and γ- forms, respectively. The tensile results showed that the γ-form exhibits considerably higher elongation at break and small reduction in stiffness as compared to that of the α-form. The average measured yield strength of the γ phase is higher than that of the α phase by 8%.