Hydrolytic Degradation of Biorenewable Epoxy Resins

Securing renewable energy sources is pivotal to the future, as our current sources are derived mainly from nonrenewable oil and gas. One alternative is to develop renewable sources like wind, solar, or hydropower. Of importance to our project is wind energy. Current turbine blades are made from epoxy resins derived from bisphenol A (the diglycidyl ether of bisphenol A, DGEBA), an industrial chemical controversial for its health effects and environmental issues. Furthermore, traditional epoxy resins are not biodegradable, and the composites created from epoxy resins reside in landfills after their useful lifetime. Not only are epoxy resins essential as building materials for turbine blades, but they also have a wide range of other applications such as paints, coatings, adhesives, and electronics. It is therefore important to explore other building blocks and curing agents for epoxy resins to replace DGEBA. We have designed epoxy resins that contain triglyceride vegetable oils to replace DGEBA. Vegetable oils are receiving increasing attention in both academic and industrial settings to be used in the synthesis of monomers and polymeric materials, because of their availability and biodegradability. Specifically, we used epoxidized soybean oil (ESO), which was cured with the methylhexahydrophthalic anhydride curing agent. The use of ESO in epoxy resins will potentially result in two beneficial impacts: 1) avoid DGEBA’s harmful side effects and 2) create biodegradable epoxy resins which can be composted after the useful lifetime of the wind turbine blade, because of the presence of ester linkages. We investigated the glass transition temperature of the ESO-based epoxy resins, which is a critical polymer property that governs the temperature range over which the material can be used in applications, and is also predictive of its mechanical properties. We also investigated the accelerated hydrolytic degradation behavior of the ESO-based epoxy resins in base solutions. ESO-based epoxy resins exhibited significantly enhanced rates of hydrolytic degradation in a basic solution, as compared to the conventional DGEBA-based epoxy resins. The challenges tackled in this work could pave the road for deriving epoxy resins from other sustainable materials that have potential for degradability while retaining desirable thermal and mechanical properties.