# Preparation of Phenolic Aerogel/Quartz Fiber Composites Modified with POSS: Low Density, High Strength and Thermal Insulation

## TL;DR

A new lightweight composite material with high strength and thermal insulation was developed for spacecraft thermal protection using POSS-modified aerogel and quartz fiber.

## Contribution

The novel use of POSS in phenolic aerogel composites via a thiol–ene click reaction improves mechanical and thermal properties for aerospace applications.

## Key findings

- The composite achieved low density (~0.7 g·cm−3) and significant improvements in tensile, flexural, compressive, and interlaminar shear strengths.
- POSS modification reduced thermal conductivity to 0.0619 W/(m·K) and ablation rates through in situ ceramification into SiO2 and SiC phases.
- The material's enhanced oxidation resistance and thermal insulation result from char graphitization and a dense protective barrier.

## Abstract

To meet the requirements of next-generation spacecraft thermal protection systems for lightweight materials with high strength, effective thermal insulation, and superior ablation resistance, a novel POSS-modified phenolic aerogel/quartz fiber composite (POSS-PR/QF) was developed using a thiol–ene click reaction combined with a sol–gel process. Covalent incorporation of polyhedral oligomeric silsesquioxanes (POSS) into the phenolic matrix effectively eliminates nanoparticle aggregation and improves interfacial compatibility. As a result, the modified resin is suitable for resin transfer molding (RTM) processes. The resulting composite exhibited an aerogel-like porous structure with enhanced crosslinking density, thermal stability, and oxidation resistance. At 7.5 wt% POSS loading, the composite achieved low density (~0.7 g·cm−3) and outstanding mechanical properties, with tensile, flexural, compressive, and interlaminar shear strengths increased by 114%, 79%, 29%, and 104%, respectively. Its thermal conductivity (0.0619 W/(m·K)) and ablation rates were also markedly reduced. Mechanistic studies revealed that POSS undergoes in situ ceramification to form SiO2 and SiC phases, which create a dense protective barrier. In addition, this ceramification process promotes char graphitization, thereby enhancing oxidation resistance and thermal insulation. This work provides a promising approach for designing lightweight, high-performance, and multifunctional thermal protection materials for aerospace applications.