Multifunctional mycelial fragments: Enhancing mechanical strength, water vapor transmission, flame retardancy, and antibacterial properties of waterborne polyurethane coatings

This study investigates the functionalization of mycelium fragments (MFs) through NaOH hydrolysis into hydrolyzed mycelium fragments (HMFs) for use as effective reinforcements in waterborne polyurethane (WPU) composites. MFs and HMFs were incorporated into a WPU matrix, synthesized via a two-step prepolymer method using isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI), at weight ratios from 0.1 % to 1.1 % during in-situ emulsification. Physicochemical analyses confirmed that NaOH treatment effectively modified MFs. This modification resulted in reduced particle size, increased surface roughness, and selective removal of proteins and soluble polysaccharides. Notably, a significant increase in surface amino groups occurred due to chitin deacetylation. Consequently, composite films incorporating HMFs exhibited markedly superior performance. Specifically, HMFs significantly improved tensile strength (reaching maximum 0.3 wt% HMFs), breaking elongation (peaking at 0.5 wt% HMFs), wear resistance, antibacterial efficacy against S. aureus , E. coli , and C. albicans , and flame retardancy. These property enhancements, including superior moisture management (water vapor transmission and absorption), were primarily attributed to the improved interfacial adhesion and compatibility between the functionalized HMFs and the WPU matrix, facilitated by stronger hydrogen bonding. This work demonstrates alkaline hydrolysis as an effective strategy to develop high-performance, multifunctional mycelium-based bio-fillers for WPU composites.