High mechanical strength and low ablation rate of phenolic resin composites incorporated with polyhedral oligomeric silsesquioxane-modified graphene oxide

Hybrid composites of phenolic resin are prepared by incorporating graphene oxide (GO) functionalized with aminophenyl silsesquioxane (NH₂-OPS) for different functionalities. The covalent grafting of NH₂-POSS to GO is favorable for its homogeneous dispersion in the polymer matrix. For this purpose, GO is modified with NH₂-OPS to obtain GO-3NH₂-OPS (GP-3), GO-5NH₂-OPS (GP-5), GO-8NH₂-OPS (GP-8), according to the functionality of NH₂-OPS, respectively. The GP samples are then incorporated into phenolic resin (PR) to obtain PR/GP composites. The successful modification for GO with NH₂-OPS is confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and specific surface and pore size analysis. The thermogravimetric analysis results show that the thermal stabilities of GP-3, GP-5 and GP-8 are significantly increased compared with pure GO. Furthermore, the mechanical and ablative properties of the PR/GP composites are effectively enhanced. In particular, with the addition of 0.5 wt% GP-5, the linear ablation rate of the PR/GP-5 composite is reduced by 55.5% from 0.128 to 0.057 mm/s and the flexural strength is increased by 80.6% from 47.74 to 86.23 MPa, compared with pure PR.