Processing of Polymers and Polymer Composites in a Microwave Applicator
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Processing of Polymers and Polymer Composites In a Microwave Applicator Martin C. Hawley and Jianghua Wei Department of Chemical Engineering, MI 48824
Michigan State University, E. Lansing,
ABSTRACT Polymers and polymer composites have been processed In a cylindrical resonant microwave applicator at a frequency of 2.45GHz. Stoichlometric mixtures of two epoxy/amine systems, DGEBA (Diglycidyl Ether of Bisphenol A)/DDS (4,4'-Diaminodiphenyl Sulfone) and DGEBA/mPDA(m-Phenylene Diamine), were microwave and thermally cured Isothermally using a thin film technique. FTIR was used to determine the extent of cure. Increased reaction rates were observed In microwave cure when compared to those of thermal cure. The rate Increase due to microwave effects was much greater for the DGEBA/DDS system than for DGEBA/mPDA. Also, crossply and unidirectional 24-ply and 72-ply graphite/epoxy laminates(AS4/3501-6 prepreg, Hercules Corp.). were processed using microwave radiation. The flexural properties of the microwave processed composites were strongly dependent on the resonant heating mode. Comparable flexural properties were obtained for the unpressurized microwave processed composites and the pressurized autoclave processed composites. Proper controlled-hybrid modes are required to process composites of high mechanical properties. The procedures for obtaining these controlled-hybrid modes are described. Introduction The control of heating rate and temperature Is essential In the processing of polymers and polymer composites in order to obtain high quality products. Microwave heating offers several advantages when compared These advantages Include; high to conventional thermal heating (1,21. efficiency of energy conversion, rapid heating rate, high heating selectivity, relatively uniform heating through the cross-section, and good process controllability. Because of these advantages, microwave heating can be used in many applications, such as food processing 131, chemical The control of heating rate during processing, and medical therapy [4]. microwave processing of thermosetting polymers and polymer composites can be used to eliminate the temperature excursion during the process. Several types of microwave applicators have been used to Investigate the processing of polymers and polymer composites at a frequency of 2.45 GHz. These include; commercial multimode microwave ovens[9,121, waveguides[8,121, and single mode resonant cavities (1.5,6,7,10,13,14,15). Generally speaking, all of these applicators can be used to process polymers and non-conducting fiber reinforced polymer composites. Only the tunable resonant cavity, however, has been used successfully to process crosspiy and The Inability to process thick-section graphite fiber/epoxy composites[lJ. crossply and thick-section graphite fiber/epoxy composites In waveguides was attributed to a strong skin depth effect [8,91. Graphite fiber/epoxy composites processed In a commercial microwave oven resulted In fixed field strength distributions, and the input power could not be trans
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