Significant improvement of thermal oxidative mechanical properties in phthalonitrile GFRP composites by introducing microsilica as complementary reinforcement

High performance composites are not only pursued with the high modulus, high strength and high service temperature, but also most of their mechanical performances should be maintained after the high-temperature thermal aging. To improve thermal oxidative mechanical properties of phthalonitrile (PPN) composites, microsilica (MS) as complementary reinforcement was introduced into PPN to form particle-filled GFRP (MS/PPN/GF) composite. DSC and DRA studies showed that the introduction of MS could lower the curing temperature and increase melt complex viscosity of MS/PPN prepolymers. Thermal oxidative stabilities of the MS/PPN composites with 16 wt% MS content were improved by 25.4 °C in T5%, 41.3 °C in T10% and 14.7% in char residue at 800 °C compared those of PPN matrix, respectively. Mechanical performances of MS/PPN/GF composites were significantly improved with the increasing MS content. More importantly, most of their mechanical performances could be maintained after being aged at 400 °C for various durations. After 400 °C/12 h thermal aging, all MS/PPN/GF composites showed a retention ratio of flexural modulus and strength higher than 90% and 70%, respectively. These improvements can be mainly attributed the complementary reinforcement of MS and better thermo-oxidative stabilities of the MS/PPN composites. Fracture surface images of MS/PPN/GF-8 composite reveal an obvious interfacial structure transformation as the thermal oxidative process goes. This study demonstrate that the introduction of particles like MS into polymer-based GFRP composite as complementary reinforcement can be an easy and effective way to improve the thermal oxidative mechanical properties.