Dielectric properties of PA6 — Montmorillonite nanocomposites under moderate electric field

Abstract

Polyamide 6 (PA6) nanocomposite samples were prepared by in-situ polymerisation. A neat PA6 sample and samples containing 2 and 4% of Montmorillonite were obtained. The samples were studied by Differential Scanning Calorimetry and Broadband Dielectric Spectroscopy. Glass transition temperature was found to increase of 4K for the sample containing 4% of nanofiller whereas the sample containing 2% showed no variation. The heat capacity step is strongly modified by the addition of 2% of Montmorillonite but not by 4%. This suggests that in the sample with 4% of Montmorillonite the molecule movements are impeded by the Montmorillonite sheets. The DSC curves also exhibit a secondary glass transition for the nanocomposites, related to the molecules intercalated between MMT sheets. Broadband dielectric spectroscopy experiments were conducted on all samples at electrical fields around 100 V/mm. The α relaxation process, related to glass transition molecular movements, is observable. The dielectric spectra were studied on as-received and dried samples. The variations of the relaxation times with temperature were extracted from the spectra by fitting with Havriliak-Negami equation. The influence of water and electric field were put in evidence. The presence of nanoclay was found to impede the molecular movements whereas water had a plasticizing effect. The superimposition of these two influences was observable on “as received” samples.