Objective Conventional phenol-formaldehyde (PF) resins suffer from poor impact toughness and a limited ability of strengthening and toughening simultaneously. Inspired by the adhesive proteins of mussels, we introduced hyperbranched polyamide-modified graphene nanoplatelets (HGNP) as a toughening unit and constructed an organic-inorganic hybrid network within the PF matrix. The goal was to clarify the mechanism of HGNP on the bonding performance and toughness of the resin.
Method Hyperbranched polyamide was covalently grafted onto graphene nanoplatelets (GNP) to obtain HGNP. Then, the resulting HGNP was then dispersed in neat phenol-formaldehyde resin to produce the modified adhesive. Gel time, bond strength, debonding work, and fracture surface morphology were used to quantify the effects of HGNP loading on resin performance and to elucidate the underlying toughening and strengthening mechanisms.
Result The HGNP-modified phenolic resin exhibited a marked increase in bond-line toughness. With only 0.15% HGNP, the fracture work of the modified adhesive was 1.72 times of neat PF and 2.06 times of GNP-filled PF, while boil-proof shear strength rose from 1.15 MPa to 1.65 MPa. This gain stems from the hyperbranched coating that disperses the platelets uniformly and builds multiple interfacial links, enabling efficient energy transfer/dissipation and micro-crack arrest, thereby delivering simultaneous strengthening and toughening.
Conclusion This work overcomes the long-standing trade-off between strength and toughness in PF resins, offering a simple, efficient and readily scalable route to high-performance adhesives for plywood and particle-board production. The hyperbranched topology can be further tailored and the strategy extends to other brittle thermosets.
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