Mechanical grafting and morphology characterization in immiscible polymer blends
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Mechanical grafting and morphology characterization in immiscible polymer blends Jayant Joshi, Richard L. Lehman, Thomas J. Nosker AMIPP Advanced Polymer Center Rutgers University, Piscataway, New Jersey 08854 Corresponding Author: Jayant Joshi, email: [email protected] ABSTRACT Blends of PS/HDPE and PS/PP were investigated for synergism in flexural modulus with varying composition. The evolution of blend morphology was studied and related to the improvement in flexural modulus around the co-continuous composition. DSC studies were conducted to study crystallinity variations in the semi-crystalline component of the blend. We found that co-continuous morphologies help in developing strong mechanical bonds between the components. Crystallization is inhibited in the co-continuous region and is related to the spatial constraints during the solidification process. INTRODUCTION Synergism in mechanical properties of immiscible polymer blends can be an efficient way of obtaining superior properties from otherwise mismatched polymers. Immiscible polymers characteristically lack structural integrity and consequently exhibit poor mechanical performance when blended. However, previous research in our laboratory and elsewhere has shown that synergism can exist in certain polymer pairs which leads to enhanced physical properties[1-4]. Hara and Sauer[1] describe the various kinds of synergisms in mechanical properties which can exist between polymer pairs. They treat various cases of compatible polymer pairs (PS/PPO, PP/PB, PVC-copolymer-SAN etc), incompatible polymer pairs (PC/PMMA, PC/SAN, PE/PP, PC/PET etc) and ionomer pairs (SPS Ionomer/PS, PMMA Ionomer/PMMA etc) and analyze the mechanisms by which synergism might be occurring in these blends. Synergism arising out of purely mechanical bonds is of critical importance as it covers the majority of polymer pairs. This kind of synergism which has been described by us, recently as mechanical grafting[4], and earlier in pioneering work[3] in immiscible blends of recycled PS and HDPE, occurs only in the co-continuous region of the blends. A concurrent dip in crystallinity values is also associated with this phenomenon and has been attributed by the authors to stresses developed during contraction which inhibit growth of crystallites in the semicrystalline polymer. Co-continuous morphologies also have been extensively analyzed for their improved mechanical properties[5, 6]. Willemse et al [2] reported improved tensile moduli of PS/PP and PS/PE blends. Their study emphasized the importance of co-continuous morphologies[7] to mechanical performance of blends. Recent work in our laboratory has confirmed the existence of synergism in flexural modulus in co-continuous compositions of virgin PS/HDPE blends, and also in PS/PP blends. We have attempted to understand the nature of the synergism which causes the co-continuous morphologies to have superior properties. In this paper, we report some of those results, and also try to analyze the exact nature of the synergism by DS
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