Nanostructured polymers: morphology and properties

Description/Abstract

This study is aimed to investigate the relationship between morphology and properties of non polar polymers in the presence of polar additives of different nature. The addi-
tion of the physical gel dibenzylidene sorbitol (DBS) in a polyethylene (PE) blend has shown to act as a nucleation site on the polymer. Electron microscopy was used to reveal the fibrillar network formed by the DBS and its interaction with the PE. Moreover, the nucleation density in each material was obtained as a function of the crystallization temperature, which showed an increase in the number of nuclei in the clarified system compared to the unclarified one. However, this was found to be temperature dependent. The nucleation of PE on DBS was also studied through the induction time, which
revealed a reduced surface energy of the polymer nucleus in the presence of the DBS. Space charge measurements were taken to investigate the charge transport in PE/DBS blends and the space charge at low concentration of the gelator was found to improve the space charge distribution. The same polyethylene blend has then been studied also upon addition of relatively polar ethylene/ vinyl acetate copolymers (EVA), with a VA content varying from 9 % to 40 %. Morphology studies showed that three main factors control the phase separation, namely the the time the blend is kept in the melt, the PE:EVA ratio and also the EVA molecular weight. However, breakdown testing demonstrated that the polarity of EVA decreased the breakdown strength of the blends, independently on the morphology. Finally, a preliminary study was conducted with EVA based nanocomposites to determine the effect of filler on the dielectric properties of the nanocomposite. Two relatively polar copolymers, EVA9 and EVA18, were processed by solution blending together with 5 % of o-MMT ( I30P and I44PA), and the time of solution blending was varied from 10 min to 100 min. X-ray scattering data
showed intercalation in the case of EVA9 based anocomposites and potential exfoliation for EVA18 based nanocomposites. However, X-ray results suggest that the solution blending could extract a fraction of the organo-modified ions from in between the MMT galleries, leading to shrinkage of the clay spacing. The nanocomposite was also analysed from the point of view of its breakdown properties, which were shown to be unaffected by the presence of fillers.