Fully recyclable and high performance phenolic resin based on dynamic urethane bonds and its application in self-repairable composites

A fully recyclable phenolic resin (TDNR) with dynamic cross-linked network was facilely prepared without any catalyst using commercial novolac and toluene diisocyanate by forming hindered urethane bonds. TDNRs not only preserved the intrinsic mechanical strength of classic phenolic resin, but also displayed efficient stress relaxation behaviour. The bulk TDNR exhibited a glass transition temperature up to 200 °C and tensile strength up to 55 MPa. Both the chemical and mechanical features of TDNR were effectively preserved after five recycle circulations. The recyclable TDNR can serve as a universal resin matrix either for molding compounds which are easily repairable or for fiber-reinforced composites with good processibility. The exchangeable network of TDNR ensures good processibility for long fiber prepregs, which are suitable for hand molding and reshape of composites. By utilizing a “simple” chemistry mechanism, the close-loop recycle of phenolic resin with high working temperature and good mechanical properties are successfully achieved.