Nano SiO2 was filled into gypsum particleboard. Effect of the amount of nano SiO2 particles filled, ultrasonic dissipating duration and treating the nano particles with different coupling agents on the mechanical properties of the board were studied respectively. The results show that nano SiO2 is helpful for the improvement of the properties. Adding 3%(mass fraction) nano SiO2 is the best for the improvement of both modulus of rupture(MOR) and modulus of elasticity(MOE) of the boards formed at 30 ℃ or 40 ℃. For the boards formed at 30 ℃, their MOR and MOE can be improved by 8.77% and 12.24%, and MOR and MOE of the boards formed at 40 ℃ can be improved by 44.44% and 108.38%.3% is also the best addition proportion to improve internal bond(IB) of the boards formed at 30 ℃, while 5% is the best for that of the boards formed at 40 ℃. At room temperature, dissipating nano SiO2 into flake by ultrasonic has better effect on the properties of the final products. Through ultrasonic treating for 1 h and the best treating duration, the MOR and MOE can be increased by 41.99% and 47.80%. In addition, different coupling agents have different effects on the final properties too, and silane coupling agent KH570 is better for the improvement of properties of the boards formed at room temperature.
The microstructures of gypsum board and gypsum particleboard were observed by SEM. The effects of retarder and waterproof agent on the shape and the average dimension of the gypsum crystal were discussed. The mechanism was investigated as well. Four typical instances, i e, the gypsum crystal shape, the gypsum combined with particles on the particles surface, the gypsum combined with particles on the wood cross section and the gypsum combined with particles inside the wood cell cavity were selected and observed. Furthermore, the agglomeration and cementation mechanism between gypsum and particle were studied.
