# Effect of Different Reinforcing Fibers on the Properties of Phenolic Aerogel Composites

## TL;DR

This study examines how different reinforcing fibers affect the thermal and mechanical properties of phenolic aerogel composites for aerospace applications.

## Contribution

The novel contribution is the systematic investigation of quartz, mullite, and carbon fibers in phenolic aerogel composites for thermal insulation and ablation resistance.

## Key findings

- Quartz fiber-reinforced composites show the best thermal insulation with a conductivity of 0.1 W/(m·K).
- Carbon fiber-reinforced composites exhibit superior mechanical strength and ablation resistance.
- Mullite fiber-reinforced composites offer moderate thermal insulation and mechanical properties.

## Abstract

With the rapid development of aerospace technology towards hypersonic vehicles, the synergistic demand for lightweighting and high-efficiency thermal insulation performance of ablation-resistant thermal insulation materials is becoming increasingly urgent. In this study, nanoporous phenolic resin was used as the matrix to prepare quartz fiber-reinforced phenolic aerogel composites (QF/PF), mullite fiber-reinforced phenolic aerogel composites (MF/PF), and carbon fiber-reinforced phenolic aerogel composites (CF/PF), and the influence mechanisms of different reinforcing fibers on the properties of the composites were systematically investigated. QF/PF exhibits optimal thermal insulation performance with a thermal conductivity of 0.1 W/(m·K) at 20–200 °C, followed by MF/PF with a thermal conductivity of 0.11 W/(m·K). Relatively weak thermal insulation performance is demonstrated in CF/PF, whose thermal conductivity reaches 0.14 W/(m·K). However, in terms of mechanical properties, CF/PF is outstanding, with a tensile strength of 54.62 MPa and a bending strength of 29.69 MPa. In addition, the most excellent ablation resistance is displayed in CF/PF, with a linear ablation rate of 0.13 mm/s and a mass ablation rate of 0.0435 g/s, which are significantly lower than QF/PF and MF/PF. This study provides an important basis for the selection of reinforcing fibers in different application scenarios. QF/PF or MF/PF is preferred for high thermal insulation requirements. CF/PF is favored for high load-bearing requirements or extreme ablative environments.