Modification of radiata pine wood with low molecular weight modifying agents and large molecular weight styrene/acrylic acid copolymer dispersion
Our previous study revealed that treatment with aqueous styrene/acrylic acid copolymer (SA) is a cell-lumen filling process, and the treated wood exhibited negative values for cell wall bulking efficiency (BE) and anti-swelling efficiency (ASE). In this study, three low-molecular-weight agents (LMWAs), 1, 3-dimethylol-4, 5-dihydroxyethyleneurea (DM, 10%), glutaraldehyde (GA, 10%), and n-methylol acrylamide (NMA, 10%), were separately combined with SA (5, 10, 15, or 20%) and used to modify radiata pine wood at the levels of cell walls and cell lumens. The combinative treatments caused positive BE and ASE values, indicating restrained wood deformation, likely due to the diffusion and reaction of LMWAs in the wood cell walls. Infrared spectroscopy and dynamic mechanical analysis showed that LMWAs exhibit little reaction with SA, and the SA copolymer retains thermoplasticity in the wood cell lumen. The combinative treatments resulted in considerable improvement in bending modulus, bending strength, and compression strength of wood of 36, 36, and 124%, respectively, but there was little effect on impact strength. These findings confirm that LMWAs can act as cell wall modifying agents to synergistically improve wood properties, especially the dimensionally stability, when used together with SA.