Date of Award

1-2005

Document Type

Thesis

Degree Name

Master of Science in Material Science Engineering (MSMatSE)

Department

Materials Science

First Advisor

D r. Adel Hammami

Second Advisor

Dr. Moussa Hussein

Third Advisor

Mohammed Mohsin

Abstract

Microwave curing of polymer matrix composites has proven to be an attractive substitute for conventional thermal curing. Industrial applications are currently developed including telecommunications, aerospace, food industry, enhancement concrete setting, composites manufacturing, and many others. Many universities and research centers around the globe are endeavoring to make use of this technology to the most. Common research objectives include homogeneity of the cure, the acceleration of cure kinetics, cure reaction mechanism, and enhancement of mechanical properties. In order to efficiently utilize this form of energy, precise control over power, temperature, and time were applied to achieve set goals: reduce cure time and thermal overshoots, assure complete cure, and maximize mechanical properties. This work discusses an optimization scenario to achieve these set goals by combining data from calorimetric analysis, insitu temperature and power monitoring, and energy conservation studies. An experimental setup is assembled consisting of laboratory equipped multi mode microwave applicator and programmable feedback controllers. For thermal curing, a typical electric furnace is used with three thermocouples measuring the cavity, mold, and sample temperatures. Test samples consisted of both neat blend of DGEBA resin together with samples of glass fiber reinforced epoxy. Prior to testing, the microwave cavity has been calibrated to approximate heat losses in the system and thus determine the expected data accuracy. Curing experiments for a specific temperature-time profile show that microwave applicator not only follows the set temperature but also eliminates thermal lag and temperature overshoot. While holdback technique could not deliver the required cure cycle, PID control strategy succeeded in homogenously curing successful epoxy and epoxy/fiberglass samples. Kinetic knowledge is enriched using DSC to determine expected curing times at different curing temperatures. Based on these data, a selected isothermal temperature of 100°C was used with variable dwell times between 13-30 minutes for microwave curing. Mechanical testing data shows that microwave cured samples have relatively exceeded the conventionally cured ones in both flexural strength and modulus. The DSC recommended time of cure 13 minutes, at 100 °C, is a good approximate which suggests similar curing mechanism of cure kinetics in both thermal and microwave· methods. High ramp rate, 200 °C/min could also be achieved without material degradation or temperature overshoot by carefully controlling power during the ramp stage. Effect of gelation time and vacuum degassing, being a major time saving area, were also tested. The gelation time has particularly enhanced the flexural modulus of the epoxy samples. In short, the use of efficient process controller resulted in superior mechanical properties at practically optimum time durations.

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