Recyclable, Self-Strengthening Starch-Based Epoxy Vitrimer Facilitated by Exchangeable Disulfide Bonds from Garlic

Abstract

Epoxy vitrimers have emerged as a new class of self-healing, recyclable, and reprocessable materials, offering new opportunities to traditional epoxy thermosets by improving life-span and sustainability, while providing additional functionalities. Nevertheless, retaining the original mechanical performances remain difficult for vitrimers after several reprocessing cycles due to progressive changes in the vitrimers network during rearrangements. In this study, we designed a novel and more sustainable bio-based epoxy vitrimer synthesized from epoxidized starch amylopectin together with   diallyl disulfide from garlic and a thiol (pentaerythritol tetrakis(3-mercaptopropionate) (PETMP)). Garlic dilallyl disulfide and PETMP enabled the formation of a recyclable, and reprocesseable, vitrimer network. The epoxy vitrimer displayed unprecedented self-strengthening after 5 recycling cycles (tensile strength increased over 900%) caused by the mechanically-induced homogeneization of the diallyl disulfide/thiol and the starch epoxy phases during the recycling process, thereby increasing the vitrimer cross-linking density during reformation. Reprocessing the vitrimer 5-times increased the mechanical and thermal properties, raising glass transition temperature, Young’s modulus, and tensile strength from 7 °C to  25 °C,  2.98 MPa to 268 MPa, and 1.87 MPa to 18.47 MPa, respectively. Hence, capitalizing on mechanically-induced phase homegeneization during the vitrimer reprocessing, this work introduces a strategy for the design of self-strengthening biobased and recyclable thermosets.

Keywords: Vitrimer, Epoxy resin, Sustainable Materials, Self-strengthening, self-healing, recycling