The water uptake, thermal and mechanical properties, and aging resistance to thermo‐oxidation of phenylboronic acid‐modified benzoxazine‐glass fiber composites

Polybenzoxazines, also known as Benzoxazine (Bz) is one kind of high‐performance thermoset polymers. It manifests several advantages when used for thermal protection applications, such as thermal and dimensional stabilities, low rate of moisture absorption and near zero volatility in curing process. However, benzoxazine shows its drawbacks in terms of curing temperature, char yield at elevated temperature, and resin toughness. Thus, modification of Bz matrix would be essential in order to improve these unfavorable properties. In this study, a facile synthesis of phenylboronic acid‐modified (PBA) benzoxazine (PBz) and glass fibers (GF) composites with varied PBA ratios were prepared. Briefly, GF fabrics were impregnated with each of Bz or PBz/acetone solution and baked to form B‐staged prepregs. Then, the prepregs were stacked, molded and cured in a hot‐pressing machine to form composites. The present study shows the 10 wt% PBA modified‐Bz/GF composite is the optimal formulation as it exhibits minimal water uptake, enhanced char yield, decent thermomechanical stability in terms of glass transition temperature, exceptional interlaminar shear strength (ILSS) and highest flexural strength. Moreover, the PBz 10/GF composite subject to thermo‐oxidative aging still maintains good levels of shear and flexural properties for potential service as thermal protection layer. The PBz composite manufacturing process and its enhanced properties are displayed.