Fabrication of a new bamboo composite with large-size high-quality flattened surface

Bamboo is a highly lignified grass with a thin wall and hollow interior. Recombination technology is commonly used to realize its scaling utilization. In this study, a high-quality flattened bamboo recombination panel (BRP) was fabricated based on the full utilization of bamboo. The BRP was designed with sandwich structure and a core layer composed of a mixture of bamboo skin strips and bamboo pith particles upon hot pressing, resembling a reinforced bar-concrete structure. The surface layer was made from densified bamboo slices through thermal-flattening (TF) to achieve stress relief and realize deformation resistant, surface modified resulted in decreased hydrophilicity. The performance of the flattened bamboo slices and BRP was analyzed, the results showed that the TF treatment was successfully modified the bamboo mid-slices, which were compressed and densified during the process. The TF treatment realized stress relief and increased surface hardness and hydrophobicity, because of a reduction in the number of free hydroxyl groups in hemicellulose. The vascular bundles and parenchyma cells of the bamboo mid-slices underwent different extents of contraction. Further, the initial moisture content was negatively correlated with the compression rate. Dynamic mechanical analysis results showed that through the TF treatment conducted at an initial moisture content (MC) of 30%, temperature of 160 ℃ and time of 4 min (30%−160 ℃−4 min) the storage elastic modulus of bamboo mid-slices increased from 5133 to 8867 MPa. The average internal bond strength, surface bond strength, and thickness swelling of the BRP bonded by phenol formaldehyde (PF) and urea-formaldehyde (UF) resins were 0.71, 0.6 MPa; 0.89, 0.82 MPa; and 9.1%, 14.7%, respectively, which meet national standards. The BRP had a high-quality flattening effect, and the flattened width could reach 2–5 times the circumference of the bamboo culm, and the performance matched that of oriented strand boards, confirming to be an upgraded product of bamboo-flattening boards and bamboo- oriented strand boards.