Thermal and physico-mechanical evaluation of mycelium-based composites for fire retardation

Abstract

The current market of insulation and packaging materials is replete with synthetic foams weighed down by recyclability, manufacturing complexity, toxicity, biodegradability, as well as flammability. These drawbacks could be solved by paying attention to the nature of material inputs and manufacturing process. As such, demand for sustainable products is growing faster than ever before. Biological fungi have lately found application in industry as binder to plant-based residues to grow such materials. This study employed Pleurotus ostreatus as binder to rice husks and sawdust to produce foam materials that could find utilization in insulation, packaging, and construction applications. The Box-Behnken experimental response surface methodology design was used to optimize the effect of substrate type, water content and incubation time on resultant physical, mechanical, thermal, and fire safety properties. The developed mycelium-based bio-composites were lightweight in a range of 0.153 - 0.239 g/cm3. Despite being highly porous and hydrophilic with considerable water absorption in the range 85.46 to 243.45 %, their compressive strength and stiffness peaked at 265 kPa and 0.615 MPa, respectively. Thermal conductivity ranged between 0.069 to 0.080 W/mK whereas residual char measured after thermal degradation ranged between 20 to 38 %. The deduced Limiting Oxygen Index (LOI) from 14 out of 17 tested foams were above 21 %. The LOI results provided proof of the self-extinguishing nature for most of the developed composites. All told, five quadratic and two linear models were generated to elucidate the relationship of responses with interrogated factors. Process optimization of input and output terms yielded the most appropriate conditions for producing the fire-retardant foam composite at (20 w/w substrate type, 60 % water content, and 33.72 days). Despite developed foams being lightweight, good thermal insulators, and possessing self-extinguishing fire properties, more needs to be done to improve their water absorption and mechanical properties.