Colloquia

Summary

A new low melting PAEK polymer (Victrex AE 250) is investigated for its competitive advantage over commercially available high-performance thermoplastic polymers due to its lower melting temperature while maintaining exceptional mechanical properties and chemical resistance. A lower melting temperature is favoured to ease processing and reduce processing costs.

The non-isothermal and isothermal crystallization behaviour of LM-PAEK is investigated using conventional and flash DSC. For low cooling rates, a degree of crystallinity up to 25% is observed. The crystallization rate of LM-PAEK is slower than PEEK which is attributed to the less regular polymer backbone.

For LM-PAEK, and other high-performance thermoplastics in general, high processing temperatures above the melting temperature are required at which thermal degradation might take place. The thermal degradation of LM-PAEK is investigated in both an inert and oxidizing atmosphere. In both atmospheres, a decrease in the peak crystallization temperature is observed for temperatures above 345 °C, while for all investigated temperatures the degree of crystallinity remained constant. The decrease in crystallization rate was modelled with a Nakamura based model.

Additionally, melt processes, such as injection molding and extrusion, exert intense external flow and shear to the material before crystallization causing the polymer chains to be aligned and stretched along the flow direction. Flow-induced crystallization at 285 °C is investigated with a rotational rheometer. Specific work is used as a parameter to quantify flow-induced crystallization and evaluate the combined effects of shear rate and shear time. An acceleration of crystallization kinetics is observed for specific work above 10^6 Pa. Wide-angle X-ray scattering is used to investigate the crystal structures of a sheared sample at a shear rate of 10 s-1 for 40 seconds, corresponding to 5.6x10^6 Pa. These shear conditions proved to be insufficient to induce flow-oriented anisotropic structures though an acceleration of the crystallization rates is expected.