Micro/Nano Structure and Morphology of Multi-Phase Polymer/Oxide Composites Prepared by Powder Melt Processing
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Micro/Nano Structure and Morphology of Multi-Phase Polymer/Oxide Composites Prepared by Powder Melt Processing
Giorgiana Giancola and Richard Lehman Materials Science and Engineering, Rutgers University, Piscataway, New Jersey 08854.
ABSTRACT Powder polymer processing techniques were evaluated as a means to generate homogeneous immiscible polymer blends without the high residence times at elevated temperature and high shear rates required by extrusion. Using emulsion polymerized and cryogenically jet pulverized PMMA and HDPE powder precursors, blends were prepared with morphologies comparable to extruded blends. Advanced EDS imaging methods combined with SiO2 marker spheres enhanced electron imaging and analysis of all blend phases. These processing methods will be useful in producing polymer blends from fragile polymers, such as those used in biomedical applications, that cannot tolerate the temperature or shear rates of conventional melt processing. INTRODUCTION Blending immiscible polymers is a useful way of producing novel materials with enhanced properties that exceed the rule of mixtures of the constituents. Typically, polymer blends are not thermodynamically compatible due to entropy constraints resulting from high molecular weight of the polymers, [2] and immiscible structures result. Three general types of blends are observed when polymers “A” and “B” are combined: phase “A” dispersed in a continuous matrix of “B”, “B” dispersed in “A”, and a co-continuous blend in which both polymers are intertwined in a complex morphology.[1,3] Fine micro-to-nano morphologies are preferred in such blends to produce optimum mechanical properties via efficient load transfer mechanisms. From a polymer physics perspective, these fine structures have a strong affect on the glass transition and crystallization behavior of the components even though no chemical interactions exist. [2,4] Extrusion is an ideal method for processing thermoplastic immiscible polymer blends, although temperatures and shear rates must be controlled to avoid degradation of the polymers. [5] Compression molding minimizes such degradation since dwell time and shear are low, although little mixing occurs since the flow path is short.[6] For preblended micron sized polymer powder precursors, compression molding offers the ability to preserve the integrity of the materials while achieving a homogeneous morphology. In this paper, we compare the morphology of PMMA/HDPE blends prepared by extrusion and compression molding using electron microscopy and EDS elemental analysis. Our principal goal is to determine whether homogeneous fine-scale immiscible polymer composites can be made via preliminary mixing of micrometer-size polymers followed by fast, low shear melt processing. Ultimately, these methods will enable processing of blends that are too fragile to survive the conditions of conventional extrusion.
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EXPERIMENTAL
Materials The polymethylmethacrylate/polyethylene immiscible blend system was selected for this study based on the strong immiscibilit
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