Understanding and controlling water sensitivity in mycelium composites with beeswax coatings

Mycelium composites (MCs) offer a sustainable alternative to synthetic materials, yet their wider use is limited by high moisture sensitivity and modest mechanical performance. This study investigates surface- and bulk-level water interactions in MCs and the effectiveness of beeswax coatings in addressing moisture sensitivity. Water contact angle (WCA) measurements revealed strong spatial variability. Although initial WCAs were high (>125°), regions with limited mycelial coverage exhibited rapid wetting due to exposure of hydrophilic lignocellulosic functional groups. Topographical analysis revealed that in mycelium-depleted areas with limited mycelial coverage, surface roughness contributes to a metastable wetting state that eventually transitions to full wetting. Dynamic Vapor Sorption (DVS) analysis revealed a Type II isotherm for MCs at high relative humidity, with moisture uptake in the high-RH region likely driven by capillary condensation within the mycelial network. A beeswax coating was applied to partially fill surface pores and defects of MC samples, serving as a moisture barrier. This led to increased surface hydrophobicity (~123° WCA) and reduced bulk moisture uptake by ~68 wt% after 5 hours and 64 wt% after 24 hours of immersion in water. Additionally, the beeswax coating increased the compressive strength of the mycelium by >50% through core confinement and load sharing.