Accelerated artificial ageing of new dimer fatty acid-based polyamides

摘要

Replacing petroleum-based raw materials with renewable resources is now a major challenge in terms of economical and environmental viewpoints. Vegetable oils are expected to be an interesting alternative to produce a new generation of bio-based polymers. Due to the possible outdoor exposure in diverse applications, knowledge of the resistance to weather of these new materials is an important issue, not only for aesthetic aspects as in rapid yellowing, but also for changes in their properties. New innovative dimer acid-based bio-polyamides (DAPA) were exposed to an artificial ageing environment produced by a UV/condensation weathering device for different times. To follow and to evaluate this material ageing, several techniques were employed to correlate the chemical modifications, with the morphology and the mechanical properties. The formation of peroxide was found to be very rapid and accompanied by high gel fraction formation and chain breaking. Infrared spectroscopy showed a build-up of carbonyl absorption in the range 1700-1780 cm"1, due to primary and secondary photo-oxidation products. In correlation with these morphological evolutions and in agreement with the high decrease of fusion enthalpy by differential scanning calorimetry, X-Ray diffraction showed an amorphous solid state after ageing. Strain-stress measurements revealed a change in DAPA behaviour, varying from a ductile to an elastomeric material, before and after ageing, respectively.