Research On The UF Resin Modified By Nano-SiO₂

This paper adopts low F/U molar ratio to prepare modified urea formaldehyde(UF) resin. Because of the limitation of UF resin whose water-resistance is bad and free formaldehyde content is high, the research tries to improve its water endurance bonding strength and reduce its free formaldehyde content by a series of chemical means such as polymerizing for times , adding nano-SiO2. The result shows that the whole performance of modified UF resin is ameliorated. The paper also summarizes the chemical mechanism of UF resin modified by nano-SiO2, which can offer the theoretical direction for production practices.The orthogonal experimental program is mainly used in this paper. According to dissociative formaldehyde release and class 2 water endurance bonding strength index of the plywood which is adhered by UF resin modified by nano-SiO2, the best prepared technics of high performance urea formaldehyde resin is obtained first through observing the influence factors such as F/U molar ratio, dispersing technics, nano-Si02 content and surface processing agents of nano-SiO2. In addition, the results of the orthogonal experiment are tested and consummated by supplementary. Finally, the flame retarding properties of modified UF resin was determined by HC-2 oxygen index equipment and HRR3 Heat Release Rate system and its chemical mechanism is analysed through infrared spectrum and scanning electron microscope(SEM).The results indicate that F/U molar ratio and dispersing technics have remarkable influence on its water endurance bonding strength and free formaldehyde content for the preparation technics of UF resin modified by nano-SiO2,The optimum craft parameters are as follows: F/U molar ratio is 1.15;nano-SiO2 is blended with UF resin by about 15 min high speed mixing(1000 rpm);nano-SiO2 content is 0.5% weight of total UF resin; the surface processing agent of nano-SiO2 is KH550. the hot pressing parameters are as follows: hot pressing temperature 120 C; unit pressure 1.0 Mpa; hot pressing time 0.8 min/mmthickness. The free formaldehyde of modified UF resin prepared with the optimum craft is below 0.2%, the dissociative formaldehyde release of its plywood reaches EI grade, the bonding strength and hot pressing parameters are equal to the ones of urea formaldehyde resin glue that is used extensively at present and it can meet the demands of the existing wood-based plate production technology. It costs 6% more than general UF resin but has good environmental performance , obviously social and zoological benefit. When nano-SiO2 content is 2.0% weight of total UF resin, the modified UF resin has good flame retardant property but it costs 26% more than UF resin.