Effects of different pretreatment methods on the dimensional stability of steamed bamboo units

To optimize steam pretreatment conditions and solve the problem of bamboo deformation more effectively under standard atmospheric pressure, the dimensional stability of bamboo units was used as the main evaluation index to compare acid, alkali, and ultrasound combined steam heat pretreatments in this paper. An optimized process of zinc chloride pretreatment, 40% initial moisture content, and 140 degrees C (0.1013 MPa) by orthogonal experimental analysis was proposed. Under the optimized condition, the moisture excluding efficiency (MEE) of treated bamboo could reach 31.14% and the anti-swelling efficiency (ASE) could reach more than 37.10%. Moreover, the samples were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and colorimeter. The results showed that the relative crystallinity of bamboo increased by 1.82%, the hydroxyl percentage (HP) decreased by 1.99%, and the total color change ( increment E*(ab)) increased by 21.19 - 25.09. The treated surface became rougher, and cracks appeared in some weaker areas, accelerating starch loss and removing granular attachments around the pits. This work provides an effective pretreatment for improving the dimensional stability of steamed bamboo units.