Effects of internal structure and chemical compositions on the hygroscopic property of bamboo fiber reinforced composites

As a kind of bioresource material, the hygroscopic property of the Bamboo Fiber Reinforced Composite (BFRC) plays the key role in their physical, mechanical and adhesive interface properties which further seriously influence both the indoor and outdoor applications. Herein, the effects of internal structure and chemical compositions on the hygroscopic property of the BFRC was systematically investigated. The results showed that the Equilibrium Moisture Content (EMC) values and sorption rate of the BFRC with the density of 1.02 g/cm³ were much lower than those of the raw bamboo at the same Relative Humidity (RH) level. The decrease in the hygroscopic property for the BFRC was related to the changes in physical structure and chemical properties. Physically, the internal cellular structures with the large diameter and the thinner wall were broken and compressed together to enhance the bulk density and to decrease the porosity. This reduction in the internal voids inhibited the entrance of water molecules and decreased the hygroscopic capacity of the BFRC. Simultaneously, the Phenol Formaldehyde (PF) resin, which was impregnated into ground tissue lumens, intercellular gaps and pits, covered the cell wall surface and protected the raw bamboo substrate from water molecules. Meanwhile, both the thermal treatment and PF resin impregnation changed the chemical compositions, which caused the reduction of the hygroscopic groups in the BFRC contributing to the decrease of the moisture sorption.