The physical, mechanical and fire performance of bamboo scrimber processed with thermal-treated bamboo bundles

Thermal treatment is gaining increasing attention for bamboo modification in practical production due to its advantages of simplicity, effectiveness and environmental friendliness, particularly in the production of bamboo scrimber. The objective of this study is to investigate the effects of two typical thermal modification methods on the physical, mechanical and fire performance of bamboo scrimber, as well as the related physicochemical properties of bamboo bundles for production purpose. The results indicated that the two types of bamboo scrimber processed distinct advantages in terms of physical and mechanical performances. Specifically, the one processed with bamboo bundles treated by superheated steam at a temperature of 200 ℃ (referred to as the "HL group"), exhibited exceptional dimensional stability and fire resistance, while exhibiting slightly lower mechanical properties. Notably, the HL group exhibited a significantly more pronounced hue compared to the LS group, which was treated with saturated vapor at a temperature of 140 ℃. Both demonstrated exceptional water resistance, with the HL group surpassing that of the LS group in either 24-hour room temperature or a combination of boiling-drying cycling treatments. The MORs of the LS group were determined to be 152.3 MPa and 108.5 MPa under dry and wet conditions, respectively, exhibiting significantly higher values than those observed in the HL group. Conversely, the variation of MOEs was found to be opposite. Both MORs and MOEs of the two groups exhibited a significant decrease in wet condition compared to those in dry condition, with reductions linearly correlated to water absorption of the samples. The failure mode of the LS group demonstrated elastoplastic failure characterized by a "Z-shaped", while the HL group exhibited with a relatively flat cross-section. Furthermore, the HL group demonstrated superior fire performance in comparison to the LS group, and as evidenced by a significantly denser char residue surface with fewer and wider cracks than that of the LS group. The variations of chemical components and microstructures in bamboo can be attributed to variances in the extent of degradation of hemicellulose, lignin, and even cellulose during the thermal modification processes. The water resistance, dimensional stability and fire performance of bamboo scrimber can be significantly improved through thermal treatment, while resulting in a decrease in MOR, particularly for the HL group. The HL and LS groups of bamboo scrimber both exhibited excellent performances, making them suitable for application as structural engineering materials. The work we conducted offers experimental and theoretical support for improve the pre-treatment procedures of bamboo in the manufacturing of bamboo scrimber for structural utilizations.