CORE SHELL POLY (DIMETHYLSILOXANE) - EPOXY MICROSPHERE AS IMPACT MODIFIER FOR EPOXY THERMOSETES

Abstract

We report a two-step method for preparation of core shell elastomeric microspheres (CSR) by suspension polymerisation route and demonstrate its potential as an effective impact modifier for thermosetting epoxy resin. The first step involves suspension addition curing of siloxane macromonomer in the presence of platinum based hydrosilylation catalyst. The effect of reaction parameters on the particle size distribution was determined and the elastomeric microspheres were subsequently coated to prepare core-shell (PDMS-epoxy) microspheres. Epoxy composites containing varying amounts of microspheres (3-10 %w/w) were prepared and the effect of coating on the mechanical properties, both in terms of quasi-static as well as dynamic properties were evaluated. The mechanical properties were found to improve at low loadings (≤ 5 % w/w), and the presence of an epoxy coating on the PDMS in the CSR led to improved dispersion, which was evident from its improved mechanical properties. The charpy impact strength increased by 148 % on introduction of core shell PDMS - epoxy (5% w/w). Morphological studies revealed that the roughness of the fractured surface increased due to introduction of microspheres. In contrast to the PDMS containing composites, where the microspheres were removed entirely due to impact loading, the fractured surface of CSR containing composites revealed the presence of broken microspheres, which is a direct evidence of improved adhesion between the elastomeric phase and the epoxy matrix. A representative schematic of the entire process is shown in figure below.