Modification of Poplar Wood Using Polyhexahydrotriazine and Its Effect on Hygroscopicity

Chemical modification is an efficient method for improving the properties of wood. In this study, poplar sapwood was modified via paraformaldehyde, 4,4′-oxydianiline (ODA), and N-methylpyrrolidone solvents through a vacuum-pressure impregnation process. The poplar sapwood underwent a curing process producing the ODA polyhexahydrotriazine polymer, which is a strong thermosetting material. The results showed that the weight percent gain of the modified poplar sapwood was 223.3%. The density of the modified wood specimen increased from 356.8 kg/m3 to 445.0 kg/m3. The water absorption decreased from 159.6% to 0.9% due to the thermosets penetration into the lumen and the cell walls of the wood. Additionally, condensation reactions occurred between the aldehyde groups of the paraformaldehyde and the hydroxyl groups of the poplar wood. The results showed that the modified wood achieved stronger waterproof properties than the unmodified wood.