Abstract The work focuses on the design of sustainable materials that meet key environmental requirements, including the bio-based origin of starting compounds, environmentally friendly preparation methods, as well as easy recyclability and biodegradation at the end of life. To this end, systems based on reagents from renewable sources, such as epoxidized soybean oil acrylate (ESOA) and cystamine (Cys) as a crosslinker, were developed to form covalent adaptable networks (CANs), using a simple reaction carried out under mild conditions, without the need for solvent or catalyst. Two different molar ratios between the acrylate groups of ESOA and the amino groups of Cys were investigated (1: 1, ESOA-Cys₁: 1 and 2: 1, ESOA-Cys₂: 1). The Aza–Michael reaction between the two components was confirmed and monitored during curing at different temperatures by IR spectroscopy, revealing distinct kinetic behaviors for the two formulations, a phenomenon attributed to a change in the reaction mechanism. In both cases, network formation was confirmed by gel fraction (GF%) analysis, which reached 100%, indicating complete cross-linking after 6 h under all temperature conditions tested. DSC measurements of the two formulations were recorded over time, curing the samples at 100 °C, the temperature characterized by the fastest kinetics among those investigated. The glass transition temperature (T g) of the formulations was found to gradually increase over time during curing, with the formulations reaching comparable T g values of -3 °C and − 4 °C for 1: 1 and 2: 1, respectively, which levelled off to the same value of -2 °C after 2 days, thus demonstrating the formation of crosslinks within the systems and confirming the effectiveness of the curing time used for sample preparation. DMTA and rheological measurements of the cured samples revealed the formation of more rigid networks in ESOA-Cys₂: 1, attributed to a higher crosslinking density, while stress-relaxation experiments demonstrated the dynamic nature of the networks in both formulations, although the relaxation behavior depended on the acrylate: amino groups molar ratio, reflecting the crosslinking density. Finally, the developed CANs exhibited excellent recyclability and self-healing properties when heated to 180 °C and were completely degraded by enzymatic hydrolysis.
Giribaldi et al. (Tue,) studied this question.