Photo-oxidative degradation of injection molded sepiolite/polyamide66 nanocomposites

Abstract

Every day clay/polymer nanocomposites are included in more industrial applications, due to its high performance. Because of this, nanocomposites may be submitted to extreme conditions of work, which could degrade it. Exposure to solar radiation in the presence of oxygen (photo-degradation) represents one of the major problems of the Clay/Polymer anocomposites. In this study, samples of neat polyamide 66 (PA66-S-0) and reinforced nanocomposites with 1, 3, 5, 7 and 9 wt% organophilized sepiolite (PA66-S-1, PA66-S-3, PA66-S-5, PA66-S-7 and PA66-S-9 samples) are analysed after UV exposure, following the standard accelerated degradation method UNE-EN-ISO 4892-2. The aim of this study is to establish the effect of UV exposure on the mechanical, optical and crystallographic properties of the new material. Tensile tests show a reduction in the ductility and an embrittlement after degradation process. In addition, an increase of transparency is confirmed with the UV exposure. The carbonyl index in the samples containing sepiolite is lower than in neat PA66 whereas the yellowness index is not affected by degradation. Sepiolite has an inhibitor effect on the formation of C=O bonds. These results indicate that breaking of chains of PA66 starts in the amorphous region and that it is lower in the nanocomposites due to the low diffusion of oxygen induced by the sepiolite. This affirmation is corroborated by the obtained diffraction patterns.