Aspergillus niger infection weakens the robustness of bamboo-adhesive interphases by damaging the adhesive and detaching the interfacial bonding

Abstract

Engineered bamboo products (EBPs) are promising in timber architecture due to their robustness, environmental sustainability, and light-weightiness advantages. The mechanical stability of EBPs facing mold infection deserves more attention considering limited insights beyond the current investigation into the mold resistance of raw bamboo and simple bamboo crafts. Here, we demonstrated that a 20-day Aspergillus niger (A. niger ) infection significantly weakens the shearing strength of bamboo-phenol formaldehyde (PF) adhesive bonds (>70 %); in one of the cases, the shearing strength of outer-to-inner assembled bamboo-PF bonds reduced from 11.9 MPa (uninfected) to 2.6 MPa after 20-day A. niger infection. Apparent cracks in PF adhesive, along with the noticeable biodegradation and oxidation of the aromatic skeleton, were observed after a 20-day A. niger infection. The detached interfacial bonding and weakened mechanical performance of bamboo cell walls after a 20-day infection were also revealed, provoking the significant strain concentration of bamboo-PF interphase. A plausible mechanism for the A. niger infection weakening the robustness of the bamboo-PF interphase can be concluded as the cracked PF adhesive, detached bamboo-PF interphase, and crippled bamboo cell walls. The three-fold mechanical damage caused by A. niger infection makes bamboo-PF interphase fragile and stress-concentrated when subjected to load.