Effect of compression ratios on the sorption behaviors of bamboo fiber-based composites

The sorption behaviors of bamboo fiber-based composites (BFC) play a critical role on its applications due to its impact on the dimensional stability and biological durability of the material. The sorption behaviors of Neosinocalamus affinis BFC with compression ratios of 1.50, 1.83 and 2.17 were studied in this project, aiming to optimize the manufacturing process of BFC to reduce the sorption of final products. It was found that the hygroscopicity of BFC samples with all three compression ratios is much lower than that of raw bamboo at all the studied relative humidity (RH) levels. The BFC manufactured with 1.50 compression ratios showed the lowest equilibrium moisture content (EMC). The sorption ability of BFC showed some increase with increasing compression ratio especially when the relative humidity (RH) was above 60%. An evolution in moisture absorption model of BFC was proposed based on the changes in its wettability, pore structures, and chemical compositions. Both introduction of phenolic formaldehyde (PF) resin and material densification reduced the water transfer pathway such as bamboo cell lumens, pits, and gaps, as well as the water absorption space in cell wall. Meanwhile, the BFC with higher compression ratio had increased difficulty to absorb water. The increase in sorption ability of BFC with higher compression ratio at high RH environment is proved to be the consequence of the higher content of its mesopore ratio resulting in increased poly-layer water content. Therefore, the RH of application occasions is critical to determine the optical compression ratio of BFC combining with other performance requirements.