[Abstract]: Preliminary studies have been carried out to cure vinylester particle reinforced resins in microwaves to reduce shrinkage of the composites. The results were encouraging. With an exposure time of 35 to 40 seconds and a power level of 180 W, the shrinkage of 50 ml and 200 ml composite samples, flyash particulate reinforced vinylester resin, approached zero percent. Despite the success, there are risks in the process of curing the vinylester resins by microwave irradiation. The styrene vapour emitted from the resins is harmful to human beings and becomes an inhalation hazard. In addition, the styrene vapour in the cavity of the microwave oven may be ignited arcing within the oven. Alternatively, arcing from the high voltage (HV) transformer behind the oven cavity may ignite vapour leaking from the cavity. Even if this does not happen, the concentration of the styrene vapour in the oven cavity is high may lead to explosions. Another risk is posed by the hardening agent, methyl ethyl ketone peroxide (MEKP), which undergoes an exothermic reaction when irradiated with microwaves and could spontaneously ignite. However, if the usual rate of 1-2% of it is used in hardening the resin, most of its dangerous properties will disappear (Sweet, undated). MEKP is itself poisonous and has to be handled with care.
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