Bio-spiroacetal polyurethane covalent adaptive network with close-loop recycling, self-healing and reprocessability

Conventional polyurethanes from non-renewable resources have been widely used for their excellent mechanical properties and thermal stability, which are difficult to be reprocessed and recycled due to the permanent crosslinked networks. In this study, dynamic acetal bonds were synthesized using bio-based vanillin and then embedded in polymer with castor oil to construct bio-based recyclable polyurethane. The ratio of castor oil to bio-spiroacetal diols was varied to control the thermodynamics and mechanical performance of bio-based polyurethanes. Experimental results of dynamic mechanical analysis, differential scanning calorimetry, tensile test and stress relaxation test suggested that a decrease in the content of acetal diols as a hard segment, led to a decrease in the glass transition temperature and tensile strength. Additionally, the activation energy initially increased and then decreased. The reversibility of the acetal structure endowed green polyurethane materials with the ability of reprocessing, self-repairing and closed-loop recycling.