Valorisation of Chitosan Natural Building Block as a Primary Strategy for the Development of Sustainable Fully Bio-Based Epoxy Resins

The non-toxic and biodegradable nature of chitosan makes it a valuable resource offering promising opportunities in the development of bio-based materials with enhanced mechanical and thermal properties. In this work, the combination of epoxidized linseed oil, oxalic or citric acids, and chitosan (CHI) as a curing accelerator presents an attractive strategy to create bio-based and sustainable thermosetting materials. This article aims to provide a comprehensive exploration of the systems reactivities, characteristics, and performance evaluation of the designed bio-thermosets. Both the nature of the two carboxylic acids and the presence of chitosan are shown to have a big impact on the thermomechanical properties of the developed networks. While oxalic acid favours the formation of elastic networks, with low T-g values (increasing with CHI content between 0.7 and 8.5 degrees C) and relatively low Young's modulus (similar to 2.5 MPa), citric acid promotes the formation of very dense networks with lower mass of the segments between the crosslinks, having 20 times higher T-g values (from 36 to 45 degrees C) and similar to 161 times higher Young's modulus (from 94 MPa up to 404 MPa in these systems). The CHI has a strong impact on the curing reaction and on the overall properties, by increasing the materials' performance.