Naturally Occurring Acids as Cross-Linkers To Yield VOC-Free, High-Performance, Fully Bio-Based, Degradable Thermosets

Abstract

Naturally occurring carboxylic acids when used as cross-linkers with a highly functional bio-based epoxy resin result in thermosets having excellent physical and mechanical properties which are also degradable. Thermosets have many important applications (coatings, composites, adhesives, etc.), but they are typically made of nondegradable, nonrenewable materials. In this paper, di- and multifunctional carboxylic acids found in fruit juices as well as other naturally available dicarboxylic acids were used to cross-link epoxidized sucrose soyate (ESS) without the use of extra catalyst or toxic compounds except for water. For the sake of understanding the mechanism of the water-assisted curing reaction between ESS and the acids, the reactivity of the natural acids toward ESS and the curing process were investigated. Water enabled the natural acids with high water solubility and acidity to be dispersed well in ESS and led to rapid cross-linking with ESS. The thermosets possessed excellent thermal and mechanical properties and displayed great potential to be utilized in fully green coatings. The thermosets could be degraded and completely dissolved in NaOH aqueous solutions very rapidly—as fast as 13 min—and they could also be thermally degraded.