Fiber Bundling in SiO ₂ Particle‐Modified Glass Fiber Felt Composites Enables Synergistic Enhancement of Short‐Beam Shear Strength and Thermal Insulation

ABSTRACT This study tackles challenges in improving both thermal insulation and short‐beam shear strength (SBSS) of glass fiber felt composites (GFFCs). It proposes modifying glass fiber felts with silica (SiO 2 ) particles using a waterborne epoxy sizing agent. SiO 2 particles (0, 5, and 9 wt%) were loaded onto fibers using ultrasonic‐assisted dispersion. Sandwich composites were then made by the vacuum‐assisted resin transfer molding (VARI) process. Results indicate SiO 2 modification changes the interface structure. Dense fiber bundles formed in the 9 wt% samples. XPS‐confirmed increased polar groups. The C‐O/C‐C ratio rose from 0.32 to 0.54. This structure increased SBSS by 28.8%, from 4.62 to 5.95 MPa. The failure mode also changed from fiber pull‐out to combined resin/fiber fracture. Thermal conductivity decreased significantly in the thickness direction by 24.3%, from 0.1938 W/(m·K) to 0.1467 W/(m·K). However, the decrease was only slight in the in‐plane direction. This physical strategy achieves mechanical reinforcement and heat flow control through fiber bundling. It offers a new approach for low‐cost, large‐scale production of high‐performance thermal insulation structural materials.