Optimization of Acoustic, Thermal, and Flame Retardant Properties in Hybrid Polyurethane Foams Reinforced With Natural Fibers and Metal Hydroxide Nanoparticles Publisher

Summary: Can plant waste improve building insulation? Flax and rice-husk fibers plus mineral nanoparticles improved foam acoustic, thermal and fire performance. #MaterialsScience #Sustainability

Nakhaeipour M ; Forouharmajd F ; Habibi E ; Soltani P ; Tehrani A
Source: Materials and Design Published:2026

Abstract

Modern architectural insulation demands a rigorous balance of acoustic, thermal, fire, and structural performance. This study developed hybrid flexible polyurethane foams utilizing alkali-treated flax/rice husk fibers and co-precipitated Al(OH)3/Mg(OH)2 nanoparticles. Using response surface methodology, the predicted optimal baseline (46.5 mm thickness, 8.7 wt% fiber) targeted a 45 kg/m3 density. The experimentally realized fiber-only foam (47 kg/m3) achieved a sound absorption average (SAA) of 0.764 and thermal conductivity of 0.0315 W/m·K. Integrating 9 wt% endothermic nanoparticles physically densified the matrix to 65 kg/m3. This final hybrid maintained excellent acoustic damping (SAA = 0.767) with an effective thermal conductivity of 0.0360 W/m·K. Furthermore, the combined effect of stiff inorganic fillers and overall densification increased compressive stress (at 50 % strain) from 14.4 kPa (neat PU) to 22.3 kPa. While the natural fibers initially increased matrix hydrophilicity (284.4 %), the nanoparticles partially offset this uptake, reducing it to 259.7 %, which appropriately remains above the 236.8 % neat PU baseline. Finally, the multiphase synergistic shield improved the limiting oxygen index to 24.45 % and secured a UL-94 HB rating, demonstrating a scalable pathway for multi-hazard resistant insulation. © 2026 The Author(s).