Hydrogenolytic degradation of thermosets

Abstract

The feedstock recycling of thermosets using the transfer hydrogenolysis with partially hydrogenated aromatics such as tetraline (1,2,3,4-tetrahydronaphthaline) and 9,10-dihydroanthracene was studied. It was possible to cleave an epoxy resin crosslinked with phthalic anhydride with a yield of more than 99 wt.% soluble products at a temperature of 340°C in 2 h. A reaction mechanism was proposed. First the thermally most labile bonds in the resin suffer homolysis, then the radicals formed that way are saturated by abstraction of hydrogen from the hydrogen donor. The most important reaction products like phenol, p-isopropylphenol and phthalic anydride were quantitatively analyzed by gas chromatography. This method also worked with a technical epoxy resin sheet reinforced with glass fiber mats and covered with copper foil. Grinding of the resin was not necessary and it was possible to reeover the glass fiber mats and copper foils with very little pollution. Carbon fibers could also be recovered undamaged from a reinforced epoxy resin. The hydrogenolysis was successfully applied to liquefy other thermosets such as phenolic resins, melamine resins and crosslinked unsaturated polyesters. lt could be shown that the degradation of crosslinked polymers can be carried out at lower temperatures with a mixture of a hydrogen donor and an amine, such as tetraline and ethanolamine.