Enhancing interfacial bonding in basalt fiber/phthalonitrile (<scp>BF</scp>/<scp>PN</scp>) composite through in‐situ iron phthalocyanine growth on <scp>BF</scp> surface using liquid bio‐based <scp>PN</scp>

Abstract The application of basalt fiber‐reinforced polymer composite (BFRP) is largely restricted by the poor interfacial interaction between BF and matrix due to the intrinsic incompatibility. Herein, the current study reported the enhancement of interfacial bonding in BF/phthalonitrile (PN) composite through in‐situ growth of iron phthalocyanine on BF surface using a liquid bio‐based PN monomer (BCPN). BCPN was first synthesized, characterized, and used to initiate the complexation reaction from iron in BF and CN groups in BCPN, resulting in the increased roughness of BF surface. Consequently, the flexural strength, flexural toughness, tensile strength, tensile toughness, and interlaminar shear strength (ILSS) of BCPN‐treated BF/benzoxazine–functional phthalonitrile (BZPN) composites were improved in comparison with those of BF/BZPN composite, with an increment of 36.6%, 72.6%, 36.2%, 96.9%, and 64.9%, respectively. Meanwhile, these BFRPs show high mechanical retention rates after thermal exposure of 300°C/1 h. Due to the compatibility/co‐curing between iron phthalocyanine on BF surface and BZPN resin, physical entanglement and chemical anchoring obviously improved the interfacial bonding of BF and BZPN, thereby leading to a higher stress transfer efficiency. This work will enrich the interface construction methods of BFRPs and also provide references for the practical applications of high‐performance BF/PN composites. Highlights In‐situ reaction of Fe in BF and CN in PN induced iron phthalocyanine onto BF. Flexural strength, tensile strength, and ILSS of BF/PN composite were improved by 36.6%, 36.2%, and 64.9%, respectively. Interfacial bonding was enhanced via well compatibility/co‐curing reactions of BF and PN.