Healable thermoset polyurethanes with high biomass content driven by dynamic phenol–carbamate bonds

Bio-based healable polymer networks have attracted considerable attention because of their carbon neutrality and healability, which lead to long service life. In this study, pyrogallol (PGL), poly(trimethylene glycol) (PO3G), and 1,5-pentamethylene diisocyanate (PDI) produced phenolic polyurethane networks (PUN-PG/PO) with a high biomass content (89–94 wt.%). Most of the PUN-PG/POs displayed two tan δ peaks corresponding to the glass transition of PGL- and PO3G-based segments in the dynamic mechanical analysis. No phase separation with diameters higher than submicron size was observed in the FE-SEM images of the fractured surfaces of PUN-PG/POs. The 5% weight loss temperature for the PUN-PG/POs decreased and the tensile strength and modulus increased as the ratio of PGL to PO3G increased. The decomposition test of the cured product of PGL and PDI in excess 1-hexanol revealed that the dissociation of phenol–carbamate bonds started at approximately 100 °C. All of the PUN-PG/POs were healable by hot-pressing at 100 °C for 2 h under 1 MPa at least three times. The healing efficiency in terms of tensile strength increased with a decreasing ratio of PGL to PO3G, and the maximal healing efficiency was 85%.