Flexible Biobased Thermosets from Epoxidized Plant Oils: A Study of Aliphatic Cross-Linking Agents

This study investigates the preparation of flexible biobased thermosets by cross-linking epoxidized linseed oil (ELO) with three different hardeners: hexamethylene diamine (HMDA), bis(hexamethylene)triamine (BHMT), and sebacic acid. In a comparative analysis of amine and carboxylic acid cross-linkers, the mechanical, thermal, and chemical properties of the resulting thermosets were evaluated using Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and tensile testing. FT-IR spectroscopy revealed the formation of an amide network in samples cured by using amine hardeners. HMDA and BHMT provided superior mechanical properties, with tensile strengths of 3.7 MPa and 2.3 MPa, respectively, compared to 2.0 MPa for sebacic acid. Glass transition temperatures were also higher for HMDA (16.0 °C) and BHMT (12.4 °C) compared with sebacic acid (-1.4 °C). Moreover, TGA showed that samples cured using sebacic acid reached the point of fastest mass loss at lower temperatures (385 °C) than thermosets cured using amine hardeners (450-470 °C), indicating their improved thermal stability. However, HMDA samples exhibited a significant mass loss of up to 40% due to evaporation during curing. This study shows the potential of amine cross-linkers for enhancing performance and underscores the need for further research into optimizing curing conditions and cross-linking chemistry.