A tough, strong, and fast-curing phenolic resin enabled by dopamine-grafted chitosan and polyethyleneimine-functionalized graphene.

Phenolic resins are widely used for outdoor and structural wood-based panels; however, they are challenged by high curing temperatures, low curing rates, and high brittleness. Inspired by lobster epidermis hardening, a tough, strong, and fast-curing phenolic resin (named DCS/PG/PF) was proposed herein. In this approach, dopamine-grafted chitosan (DCS) and polyethyleneimine-functionalized graphene (PEI@G) were incorporated into neat phenol formaldehyde (PF) resin. The gel time and maximum curing temperature of DCS/PG/PF resin were considerably reduced from 445 s and 147.8 °C for the neat PF resin to 317 s and 127.8 °C, respectively. This was attributed to the oxidative crosslinking of catechol moieties in DCS and amino groups in PEI@G within the naturally alkaline environment of phenolic resins in addition to the high reactivity between catechol moieties and PF chains as well as between amino and PF chains. The prepared resin demonstrated a dry bonding strength of 2.56 MPa, wet bonding strength of 1.81 MPa, and debonding work of 0.714 J, exhibiting a considerable increase of 16.9 %, 52.1 %, and 95.1 %, respectively, compared with those of the PF resin. These improvements were attributed to the dense organic-inorganic hybrid crosslinking network formed in the DCS/PG/PF. Furthermore, the DCS/PG/PF resin exhibited enhanced thermal stability.