MICROWAVE RADIATION POLYMERIZATION OF EPOXY RESINS

Abstract

Microwave radiation curing of epoxy resins was studied. Gel permeation chromatograph, IR spectroscopy, Proton and Carbon-13 NMR spectroscopy, Differential scanning calorimetry, and Mass spectroscopy were used to measure the epoxy microwave radiation and thermal heating reactions. The epoxy microwave radiation curing reaction degrees were directly affected by microwave radiation power, radiation time, and the sample volume. A higher microwave radiation power, a longer period of radiation time, and a larger volume of the epoxy samples increased the chemical reaction rate as well as the degree of conversion of the epoxide groups. With the help of thin film radiation technique specially designed for the experiment, the thermal effect on post-microwave radiation reaction of epoxy resin was greatly minimized. Isothermal microwave radiation reaction and thermal heating reaction were studied without the effect of exothermal reaction heat of epoxy-amine reaction. The results showed that microwave radiation was different from the heating and it provided extra energy to epoxy resin curing reaction. The chemical reaction rates of microwave radiation were much faster than that of the thermal heating alone at the specified temperature. Different kinds of carbon- 13 NMR spectra of epoxy resins were obtained. The chemical changes of epoxy resin at different reaction stages was followed by a Carbon- 13 NMR method. A method to measure the epoxy resin reaction degree was developed using the proton NMR spectra. The reaction degree of the epoxy resin were measured by several methods: IR method, GPC method, and DSC method etc. A new microwave radiation reaction mechanism has been proposed. Microwave energy was absorbed by molecular dipoles, irrespective of whether they were a segment of a long polymer chain or an inorganic compounds. The energy absorbed by dipoles would be either be accumulated to increase the internal energy state, or be transferred to nearby chemical groups. The chemical reactions took place once alter the internal energy level of the chemical groups were closed to the reaction activation energy. High dipole momentum constants of most of the reactive groups made the microwave radiation reaction rate become faster than that of thermal heating reaction.