Hard and Flexible, Degradable Thermosets from Renewable Bioresources with the Assistance of Water and Ethanol

Abstract

A carboxylic acid functional trimer made from the reaction of isosorbide with maleic anhydride was used to cross-link epoxidized sucrose soyate (ESS), resulting in bio-based, degradable thermosets having a good combination of hardness and flexibility. This work addresses some critical needs for thermosets such as improving the sustainability of raw materials, enabling recycling, and achieving both good material hardness and flexibility/ductility simultaneously. In this paper, a dicarboxylic acid, MI, was synthesized from isosorbide and maleic anhydride and characterized in detail by FTIR and 1 H NMR. It was utilized to cross-link ESS without using extra catalyst or toxic compounds except for ethanol and water. For comparison, a dicarboxylic acid from 1,3-propanediol and maleic anhydride (MP) was also synthesized and used to cross-link ESS. Because of the carbon–carbon double bond in conjugation with the carboxylic acid group, both MI and MP showed high reactivity toward ESS and could cross-link ESS with the assistance of water and ethanol. The MI cross-linked thermosets exhibited superior thermal and mechanical properties and excellent coating performance including a high level of flexibility (reverse impact >168 in.-lb and elongation at break from mandrel bend >28%), adhesion (5B), and solvent resistance as well as high hardness (König pendulum hardness 189 s). The thermosets could be degraded and completely dissolved in NaOH aqueous solution at 50 °C—as fast as 10 min—but they are stable in an HCl aqueous solution at 50 °C. The thermosets could also be thermally degraded.