Disrupted cellulose aggregation leads to the reduced mechanical performance of wood–adhesive interphase during freeze–thaw cycles

Abstract

The mechanical performance of wooden engineered composites facing the freeze-thaw cycles (FTCs) arises as an attention-worthy issue since the application of timber architectures in cold climates spreads. Here, we reported an investigation to reveal the losses of the mechanical performance of the wood-phenol formaldehyde (PF) adhesive interphase after the FTCs. Results revealed that PF adhesive was barely affected by the FTCs due to the low moisture content and rigid networks, whereas the mechanical properties of the cell wall in wood-PF interphase reduced signi cantly (more than 30%) after 5 FTCs at -40℃. Cracks were observed in the cell wall and compound middle lamella after FTCs. Further investigation into the crystal structure of the cell wall in the wood-PF interphase demonstrated that the FTCs disrupt the aggregations of cellulose macromolecules. The stresses caused by the phase transition of free water and the external hydrogen bonds formed between water and cellulose disrupted hydrogen bond networks in the cell wall. A plausible mechanism for the FTCs reducing the mechanical properties of the wood-PF bonds can be concluded as the cracks and weakened cell walls crippled the structural integrity of the wood-PF interphase, making it a fragile and stress-concentrated site when subjected to load.

Study on the variation characteristics and influencing factors of stem water content of Acer truncatum during the overwintering period

“…Notably, in contrast to the deciduous stage, stem temperature during the dormant stage underwent a substantial decrease, with a uctuation range spanning from − 10 ℃ to 14.4 ℃. Generally, ambient temperature uctuations could induce the phase transition between liquid water and solid ice within the stem tissue, resulting in noticeable alterations in the internal dielectric constant within stem tissue and corresponding variations in stem water content sensor data (Zhao et al, 2021a;Cao et al, 2023). Speci cally, when a decrease in temperature induced the conversion of liquid water into solid ice within the stem tissue, the internal dielectric constant of the stem tissue experienced a signi cant decrease, resulting in a pronounced drop in stem water content sensor data.…”