Study On The Retarding Mechanism And Interface Bonding Strength Of Gypsum Particle Board

The retarding mechanism of different retarders was explored by analysing the concentration of Ca2+ in the hydrating system, the morphology of gypsum crystals and effect of pH value on the retarding efficiency of citric acid with some morden instruments, such as Fire Atomic Absorption Spectrophotometer (FAAS), Scanning Electron Microscope (SEM) and so on. And Effect of different materials on the physical and mechanical properties of gypsum particleboard was also studied.The retarding efficiency of inorganic retarder is very different from that of organic retarder. As an organic retarder, citric acid has no effect on the initial supersaturation of the hydrating system, but holds back the combination of Ca2+, SO42-and water by chelated reaction with Ca2+ in the liquid. Meanwhile, the calcium citrate covers the surface of the nuclear of dihydrate gypsum crystal. So the form and growth of dehydrate gypsum crystal was delayed. In contrast, anhydrous sodium carbonate (a kind of inorganic retarder) delays the hydrating process by the adhering of calcium carbonate to the gypsum crystal. Its lacking of chelated reaction leads to quite poor retarding efficiency compared with citric acid. Test results showed that pH had remarkable effect on the properties of gypsum particleboard, and the integrated properties were better when the pH is 4-5. That's because weak acidic condition is good for gypsum curing. When the pH gets higher, the alkalinity becomes stronger. The stronger the alkalinity is, the better the retarding efficiency of citric acid is, and the worse the properties are.Organosilicon waterproof agent or nano-material at an appropriate concentration can improve the physical and mechanical properties of gypsum particleboard. Organosilicon waterproof agent can improve the bonding between the gypsum and wood particle by promoting the reaction of hydrating, and changing the morphology of gypsum crystal. However, the higher the organosilicon waterproof agent content, the greater is the alkalinity. High alkalinity reduces the bonding strength of gypsum. So the concentration can not be too high, 3%-5% is appropriate. There are many factors that can affect the properties of gypsum particleboard when the wood particle was treated with nano-material. While the effect of the sort and content of nano-material is the most important.