Effects of carbon particles on the structure and properties of immiscible polymer blends

• Main Author: Manzoor, Muhammad Bilal
• Other Authors: Wilkinson, Arthur
• Published: University of Manchester 2013
• Subjects: 620.1
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607380

Two types of binary immiscible polymer blend and composite systems, based on polypropylene (PP)/ polystyrene (PS) and PP/Poly(methyl methacrylate) (PMMA), and a ternary polymer blend system of PP/PS/PMMA was prepared via melt compounding. Matrix/minor phase concentration was kept to 80/20 vol % for all the blends prepared. Structural changes upon the addition of minor phase were observed using SEM and TEM. Both of the PP/PS and PP/PMMA binary blends studied in this work show continuous-discontinuous (matrix-droplet) type morphologies. The coarse particle morphology of the dispersed phases suggested high interfacial tensions, and ease of pull-out of dispersed droplets indicates poor adhesion between the phases. Both of these proposals were supported by the results of DMTA and dynamic shear rheometry. The values of Tg of the dispersed phase components remained the same in the blends, again indicative of immiscibility. Morphologies of the ternary polymer blends were predicted using the spreading coefficient model, which predicted encapsulation of PMMA by PS. SEM of solvent-etched surfaces and TEM results were in agreement with this prediction. The addition of CB to the blends caused micro-structural changes in the blends and produced electrically conductive composites. CB acted differently towards the PS and PMMA phases. Higher loadings of CB (10 wt. %) in the PP/PS blend increased its electrical conductivity and dynamic moduli more than in PP/PMMA blends due to the formation of a co-continuous morphology and to strong PS-CB interactions. Whereas at lower CB loadings (2 and 5 wt. % CB) the rise in mechanical moduli and electrical conductivities was comparable to that in PP/PMMA–CB. The less significant increase in electrical conductivity of PP/PMMA-CB composites compared to PP/PS-CB composites was due to the absence of a co-continuous morphology, which can impart a double percolation effect. Based on this behaviour, and the morphological results of the ternary polymer blends, a ternary polymer-CB composite was formulated which showed both higher mechanical and electrical properties than those of binary blend-CB composites and of the neat binary polymer blends. The concentration ratios of the dispersed phase were found to be very important in determining the structure and properties of the ternary blend-CB composites. Functionalised CNT behaved differently than CB towards these binary blend systems. Instead of PS, CNT preferred to reside in the PMMA phase of the binary blend composite systems, which led at higher CNT loadings to the formation of a co-continuous PMMA phase. This morphological change significantly improved the dynamic moduli and electrical conductivity of the PP/PMMA-CNT composites. GNP based binary blend composites exhibited morphological changes similar to the CB based composites but at lower GNP loadings than for CB and CNT. As with the CB and CNT based systems; GNP blend composites forming a co-continuous morphology (PP/PS-GNP) exhibited superior moduli and electrical conductivity. Binary GNP blend composites exhibited moduli and electrical conductivities superior to CB and CNT binary blend composites. A general trend of a rise in Tc of PP was seen with addition of all of these carbon particles. WAXRD measurements confirmed the presence of smaller crystals in the composites as a result of fast crystallisation caused by the rise in PP matrix Tc.