Synthesis Of Epoxy Resin Model Compounds And Their Decomposition In Near-Critical Water

The disposal of end-of-life epoxies and their composites has posed a serious problem on the environment. Huge economical as well as societal benefits would be obtained if epoxies and their composites wastes were to be decomposed and recovered. Near-critical water possesses an intriguing combination of properties such as low viscosity, high mass transport coefficients, high diffusivity, and solvation power. More importantly, water is safe, non-toxic, readily available, inexpensive, and environmentally benign, and serves as a potential medium for chemical recycling of epoxy wastes.To fully understand decomposition mechanisms of cured epoxy resin in near-critical water, and to provide solid theory foundation for the controllable chemical recycling of epoxy wastes, two epoxy resin model compounds containg ether bond and Bisphenol A structure, ether and tertiary amine bonds, respectively, were prepared, pured, and characterized; and then decomposed in near-critical water under different temperatures at different time. The products were analyzed by gas chromatography-mass spectrometry. The most propable mechanisms at different conditions were proposed according to the decomposed products.The results show that, for epoxy model compound containg ether bond and Bisphenol A structure, water molecules mainly act as nucleophile reactant with the end ether bond at lower temperatures, i.e. 285℃, in near-critical water. When the temperature is increased to 325℃, the water produces higher concentration of H+, and the other ether bond in the middle breaks down more easily under the catalysis of H+. It is also found that the products proceed to be decomposed or oxidized into other small molecules.For the decomposition of epoxy model compound containg ether and tertiary amine bonds in near-critical water, compared to that of the tertiary amine bond, the cleavage of ether bond happens more easily because of more positive charge at the carbon atom at 285℃. At higher temperature, i.e. 325℃, the ether bond energy reduces dramatically after prontonation, and therefore can also be cleaved more readily than the tertiary amine bond. The products give rise to some other compounds, too.