A multi-technique and multi-scale analysis of the thermal degradation of PEEK in laser heating

The present work studies the thermal degradation of laser-heated poly-ether-ether-ketone (PEEK) as the heating duration increases. Its damage morphology, chemical composition, crystallinity content, and mechanical properties are examined with optical microscopy, attenuated total reflection-Fourier transform infrared spectroscopy, differential scanning calorimetry, Raman spectroscopy, and continuous stiffness measurement nanoindentation. The applicability of those methods in detecting the thermal degradation of laser-heated PEEK and assessing the induced thermal damage is highlighted. Results show that short-time laser heating acts as an annealing process that improves the crystallinity and hardness on the affected surface of PEEK by up to 5.1% and 10.8% respectively. With a further increase in the heating duration, surface carbonisation occurs and a char layer is formed. Surface carbonisation is associated with the thermal limits of PEEK in laser heating decreasing by up to 50% its hardness and by 45% its indentation modulus. Finally, the char layer is found to act as a shielding mechanism that protects the bulk PEEK from the applied thermal load, resulting in mostly superficial thermally induced damage.

Automated summary

The present work investigates the thermal degradation of laser-heated PEEK and its effects on morphology, composition, crystallinity, and mechanical properties. Various methods including microscopy, spectroscopy, and nanoindentation are employed to examine the thermal damage. The results demonstrate that short-time laser heating can improve the crystallinity and hardness of PEEK, while prolonged heating leads to surface carbonisation and the formation of a char layer. The char layer acts as a protective mechanism, resulting in mainly superficial thermally induced damage.