Determination of Limiting Physical and Mechanical Properties of Semi-Crystalline Polymers

přednáška

angličtina

The relationship between solid-phase content and structure and properties of different polypropylene grades was studied. The absolute value of solid-phase content and its time dependence was determined by the pulsed 1H-NMR method at temperature 23C. The solid-phase content values were correlated with absolute values of degree of crystallinity, evaluated by standard methods: density, DSC, and X-ray diffraction. Measurement temperature of 23C was applied, because this temperature is generally used as standard for conditioning and measurement of standard physical and mechanical properties. The absolute value of solid-phase content was compared with a long-term time-dependent measurement of crystallinity on different morphological forms of polypropylene (pellets, powder, injection-moulded specimens, and hot pressed films). Polypropylene samples with different molecular weight and stereoregularity were prepared, including totally atactic and highly isotactic materials. The atactic PP of low molecular weight was used as a totally liquid polymer phase. The measurement was performed on a broad variety of materials; such as on commercial PP products and polymers synthesised in laboratory reactors. Evaluation of tensile and flexural properties of selected materials confirmed a linear correlation between the modulus of elasticity and the solid-phase content with the ageing time. The values of physical and mechanical properties extrapolated to 100 % solid-phase content were defined as the limiting physical and mechanical properties. These limiting physical and mechanical properties were specified as material parameters of semi-crystalline polymers. The results were interpreted in terms of secondary crystallization of polypropylene.

semi-crystalline polymers, solid phase content, limiting properties

KRATOCHVÍLA, J.; VILČ, L.; KUČERA, J.; HAVLÍČKOVÁ, D.

26. 6. 2005

Praha