Effect of sisal and hydrothermal ageing on the dielectric behaviour of polylactide/sisal biocomposites

[EN] The dielectric properties of virgin polylactide (PLA) and its reinforced composites with different weight amounts of sisal fibres were assessed at broad temperature (from - 130 degrees C to 130 degrees C) and frequency ranges (from 10(-2)-10(7) Hz), before and after being subjected to accelerated hydrothermal ageing. The synergetic effects of both the loading of sisal and hydrothermal ageing were analysed by means of dielectric relaxation spectra. The relaxation time functions were evaluated by the Havriliak-Negami model, substracting the ohmic contribution of conductivity. The intramolecular and intermolecular relaxations were respectively analysed by means of Arrhenius and Vogel-Fulcher-Tammann-Hesse thermal activation models. The addition of fibre increased the number of hydrogen bonds, which incremented the dielectric permittivity and mainly hindered the non-cooperative relaxations of the biocomposites by increasing the activation energy. Hydrothermal ageing enhanced the formation of the crystalline phase at the so-called transcrystalline region along sisal. This fact hindered the movement of the amorphous PLA fraction, and consequently decreased the dielectric permittivity and increased the dynamic fragility. (C) 2017 Elsevier Ltd. All rights reserved. The authors acknowledge the European Regional Development Fund and the Spanish Ministry of Economy and Competitiveness, through the Research Projects ENE2014-53734-C2-1-R and UPOV13-3E-1947. The Regional Valencian Government is thanked for the APOSTD14/041 program for J.D. Badia. The financial support given by the Prince of Songkla University and KTH Royal Institute of Technology is gratefully acknowledged. Badia, J.; Reig-Rodrigo, P.; Teruel Juanes, R.; Kittikorn, T.; Strömberg, E.; Ek, M.; Karlsson, S... (2017). Effect of sisal and hydrothermal ageing on the dielectric behaviour of polylactide/sisal biocomposites. Composites Science and Technology. 149:1-10. https://doi.org/10.1016/j.compscitech.2017.05.026