Risks involved in curing vinylester resins using microwave irradiation

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 s and a power level of 180 W, the shrinkage of 50- and 200-ml composite samples, flyash particulate-reinforced vinylester resin, approached 0%. Despite the success, there are risks in the process of curing the vinylester resins by microwave irradiation. The styrene vapor emitted from the resins is harmful to humans and becomes an inhalation hazard. In addition, the styrene vapor in the cavity of the microwave oven may be heated by the high-voltage transformer around the oven. This may result in flashing. Even if this does not happen, the high concentration of the styrene vapor in the oven cavity may lead to an explosion. Another risk is posed by the hardening agent, methyl ethyl ketone peroxide (MEKP). When interacted with microwaves, with the resulting exothermic reaction, the MEKP could spontaneously ignite. When the usual rate of 1% to 2% of it is used in hardening the resin, however, most of its dangerous properties disappear (John R. Sweet Co. www.johnsweet.com undated). MEKP itself is poisonous and must be handled with care.