Development of a Variable Frequency Microwave Processing System for Post-Curing of Thermoset Polymer Matrix Composite...

The proposed project is to develop a microwave processing system for variable frequency processing of thermosetting polymer matrix composites (PMCs). Combining an existing production technology with an innovative application of DoD Traveling Wave Tube (TWT) technology will enable an increase in the production rate of thermoset PMC products -- significantly reducing the cost of finished parts. PMCs are a leading component in the expanding field of advanced materials; however, applications are often limited by the processing speed -- particularly in the post-curing steps. The use of the proposed variable frequency technology for the post-curring of isocyanate/epoxy mixtures will lead to faster curing than in possible using conventional heating methods and more uniform curing than is possible using other microwave heating methods. The technical approach of the Phase I effort will be to use an existing prototype variable frequency microwave furnance available at MLI, which is capable of providing up to 200 Watts of CW microwave power over the 2.4 to 7.5 GHz frequency range. Near-production-scale plates of the thermoset PMC material (20 cm by 20 cm by 2.5 mm thick) will be provided by EniChem America, Inc., which will support MLI in this effort. Characterization and optimization of the variable frequency microwave heating properties of the material will proceed along two primary lines of inquiry: (1) the effect of material thickness on processing speed and uniformity and (2) the effect of frequency range of processing uniformity. The final technical objective of the Phase I effort will be to demonstrate uniform heating of the near-production-scale thermoset PMC plates. Anticipated Benefits: Potential applications for the variable frequency microwave furnace technology include polymer and epoxy curing, ceramic sintering, microwave-assisted CVD and CVI, and the processing of a wide range of advanced materials. Potential applications for thermoset PMCs include structural reaction injection molding, electrical insulation, rigid foams, and any polymer process which requires fast polymerization.