Synergetic effect of O-POSS and T-POSS to enhance ablative resistant of phenolic-based silica fiber composites via strong interphase strength and ceramic formation

As a typical ablative material, silica fiber reinforced phenolic resin composites are widely used in thermal protection system. However, its ablative properties and interfacial strength need to be further improved to meet the growing requirements of aerospace. In this work, reactive octaepoxycyclohexylethyl POSS (O-POSS) and tetrasilanoloctaphenyl POSS (T-POSS) were synthesized to modified high silica fiber cloth (HSC) and phenolic resin (PR) respectively. The flexural strength and interlaminar shear strength of modified HSC reinforced modified PR (PK-HSC/T-PR) composites are 213.1 and 22.4 MPa, 63.6% and 59.5%, higher than those of pristine HSC/PR composites, respectively. Meantime, the obtained PK-HSC/T-PR composites also exhibit lower thermal conductivity (0.2461 W⋅(m K)−1) and ablative rate (liner ablative rate: 0.128 mm/s, decreased by 22.4%). Furthermore, the mechanism of the two POSS synergetic effect for ablative performance enhancement was explored from both the aspects of matrix ceramization and interface structure evolution during ablation process.