Enhanced thermal insulation,flame retardancy and mechanical properties of rigid polyurethane foam modified with coconut fiber and bio-based mycelium powder

Abstract

This study presents the design and comprehensive characterization of sustainable rigid polyurethane foam (RPUF) composites reinforced with coconut fiber and mycelium powder to improve their structural, mechanical, thermal, and flame-retardant performance. The incorporation of these bio-based reinforcements aims to enhance the sustainability and multifunctional efficiency of conventional RPUFs through environmentally benign, renewable, and resource-efficient modification strategies. Comprehensive analyses, including particle size distribution, ATR–FTIR spectroscopy, and SEM imaging were performed to evaluate the effects of filler concentration on microstructure, interfacial chemistry, and thermomechanical response. The incorporation of bio-fillers refined the foam morphology, yielding smaller, more uniform, and closed-cell structures at moderate loadings (≤3 wt.%), which enhanced compressive strength and mechanical integrity through improved interfacial adhesion and hydrogen bonding between filler hydroxyl and matrix carbonyl groups. Thermal conductivity measurements revealed that optimized formulations achieved values as low as 23.39 mW/m·K, attributed to reduced cell size, higher closed-cell content, and the intrinsic thermal barrier function of the lignocellulosic-chitinous hybrid structure.The limiting oxygen index (LOI) systematically increased from 18.75% for neat RPUF to 21.75% for the highest filler-loaded composite, accompanied by shorter burning times and reduced burning speeds, confirming significantly improved flame retardancy. Post-combustion surface analysis demonstrated a clear transition from severe cracking and melting in pristine RPUF to the formation of a dense, cohesive char layer in filler-modified systems, evidencing enhanced heat resistance and self-extinguishing behavior. Consequently, the synergistic interplay between coconut fiber and mycelium powder improved interfacial cohesion, stress transfer, and thermal stability, resulting in multifunctional RPUF composites with superior mechanical, thermal, and fire-resistant properties. This work provides a sustainable route toward high-performance, bio-derived polyurethane foams for energy-efficient, fire-safe applications in construction, packaging, and thermal management systems.