Abstract:

Objective: Rubber wood was modified by silica sol combined with glyoxal-urea(GU) resin, and by silica sol combined with glyoxal-melamine-urea(GMU) resin. The effects of type and solution concentration of modifiers on the physico-mechanical and thermal properties of rubber wood were studied. Method: GU resin and GMU resin were prepared by adopting glyoxal, melamine and urea as the modified monomer. By controlling the mass ratio of GU/GMU resin to silica sol, a homogeneous, stable, and water-soluble solution was prepared. Furthermore, weight percent gain, dimensional stability and mechanical properties of modified rubber wood with the mixture of GU/GMU resin and silica sol were determined, and the performances of the thermal stability, chemical structure, and microcosmic structure were also investigated by thermogravimetry(TG), Fourier transform infrared spectroscopy(FTIR), and field emission scanning electron microscopy-energy dispersive X-ray spectroscopy(FESEM-EDS). Furthermore, those properties of silica sol modified rubber were compared. Result: 1) With the increase of solution concentration of modifier, the weight percent gain and dimensional stability of modified wood with the mixture increased. The weight percent gain and dimensional stability of S-GMU modified wood were superior than those of S-GU modified wood with the same fraction of solution for modified wood. The highest values of weight percent gain and anti-swelling efficiency were 28.32% and 42.02% under S-20%GMU modified wood, which raised 16.98% and 14.40% than those of modified rubber with S-20%GU modified wood, respectively. 2) With the increase of weight percent gain, the bending strength of modified wood with the mixture increased. The bending strength of S-20%GMU modified wood was 114.96 MPa, which raised 11.97% than that of modified rubber with S-20%GU modified wood, and no obvious difference in elasticity modulus was observed between unmodified wood and modified wood. 3) S-GMU mixture played a role in stabilizing wood residues, and the thermal stability of S-GMU modified wood was enhanced. The wood residues rates of S-20%GMU modified wood, were 5.25, 1.20 and 1.12 times that of unmodified wood, silica sol modified wood and S-20%GU modified wood, respectively. 4) The absorption peak of Si-O-Si and C-O-C could be seen near to 470 cm^-1 and 1 110 cm^-1, respectively, which proved that the silica sol and GMU resin had entered into S-GMU modified wood. Simultaneously, the absorption peak intensities near to 1 656 cm^-1 and 1 510 cm^-1 were weakened, which indicated that the lignin and carbohydrates of modified wood were degraded to a certain extent. While S-20%GMU modified wood had the lowest degree of degradation. 5) The solution for modified wood was entered into and deposited in the cell lumen and cell wall. There were more Si elements in S-20%GMU modified wood. The Si elements and mixture were evenly distributed of S-20%GMU modified wood, and the modification effect was better. The content of N elements in S-20%GMU modified wood increased, indicating that GMU resin entered the wood. Conclusion: The weight percent gain, dimensional stability and mechanical properties of modified wood with the silica sol combined with GU/GMU resin were superior than those of silica sol modified wood. The properties of S-GMU modified wood were superior than those of S-GU modified wood with the same fraction of solution for modified wood. The silica sol and S-GMU resin were entered into and deposited in the cell lumen and cell wall of S-GMU modified wood. The S-GMU mixture played a role in stabilizing wood residues, and the thermal stability of modified wood was enhanced. Therefore, this study produced evidences of improvement in physico-mechanical and thermal properties of rubber wood treated with S-GMU.

Key words: rubber wood, modification, silica sol, glyoxal-urea resin, glyoxal-melamine-urea resin