Mechanical properties, thermal stability, and mechanism of main‐chain polybenzoxazine composites fabricated based on multi‐scale effects and surface functionalization of graphene oxide nanosheets

Abstract

Polybenzoxazine (PBZ) has been recognized as a potential substitute for traditional phenolic resin. However, poor flexibility and low heat resistance limited obviously the application of PBZ. Herein, graphene oxide (GO) nanosheet and its amino‐rich derivatives (fGO‐g‐SiO2) with multi‐scale surfaces were designed, synthesized and incorporated into main‐chain PBZ through in‐situ polymerization to fabricate PBZ composites. The morphology, mechanical properties, and thermal stability of the composites were systematically investigated using x‐ray diffraction (XRD), contact angle tests, field emission scanning electron microscopy (FESEM), tensile and impact tests, and thermogravimetric analysis (TGA). FTIR and XRD analyses confirmed the multi‐scale surfaces of GO derivatives and ordered structures, respectively. The size of the in‐situ grown SiO2 and the thickness of GO coated on PBZ were estimated as 6.5 and 19.07 nm, respectively. The contact angle test revealed that fGO‐g‐SiO2 and BZ had the closest solid surface energy of 32.002 and 43.519 mN/m, respectively, among the components of the composites. The impact and tensile evaluation revealed the highest impact, tensile strength and Young's modulus of 16.75 kJ/m2, 107.24 MPa and 3.17 GPa, respectively for 1.2% fGO‐g‐SiO2/PBZ composite. The modified Halpin‐Tsai equation was also utilized to develop a predictive function for the tensile strength. FESEM of fGO‐g‐SiO2/PBZ composites indicated that the multi‐scale effect and amination effectively improved the restriction of GO derivatives on crack propagation in PBZ composites and played a more significant role in crack deflection and bridging. In addition, the highest thermal decomposition activation energy of 166.94 kJ/mol was achieved for 1.2% fGO‐g‐SiO2/PBZ composite.Highlights Graphene oxide (GO) nanosheets were incorporated into main‐chain polybenzoxazine (PBZ) to improve its mechanical properties and heat resistance. GO with multi‐scale structure and amino‐rich interface were designed, synthesized to improve the interface interactions with PBZ matrix. The GO with multi‐scale structure and amino‐rich interface showed excellent similarity in the term of solid surface energy with benzoxazine oligomers. The morphology, mechanical and thermal stability of resulting PBZ composites was systematically investigated by using experimental and mathematical model to elucidate the relationships between the structure and properties. The composites exhibited excellent mechanical and thermal properties, and it is expected to be used as advanced engineering material in demanding environments.