Cellular Structure Optimization in Microwave-Assisted Foaming of Acrylated Epoxidized Soybean Oil

This study demonstrates the effective and rapid foaming of biobased acrylated epoxidized soybean oil (AESO) resins using microwave technology. Utilizing a multimode household microwave oven, AESO could be heated up to 200 °C, enabling the simultaneous decomposition of a chemical blowing agent and cross-linking reaction. Rheometric analysis under nonisothermal conditions revealed that the peroxide-initiated curing of the AESO proceeded rapidly in the 100-120 °C range, with a 6 order of magnitude increase in complex viscosity. Further isothermal rheometric tests at 80 °C successfully demonstrated the ability to precure AESO resin to various degrees of polymerization, both before and beyond its gel point. Foams produced by 2 min of microwave irradiation at 800 W exhibited significantly different morphologies depending on the degree of precuring. The optimal cellular structure was achieved with resin precured just below its gel point, yielding a foam with an apparent density of 0.37 g/cm³, an average cell diameter of 190 μm, and an elastic modulus of 1.84 MPa. These findings highlight the potential of microwave processing for the efficient production of biobased AESO foams with tailored properties.