Application effect of mineral fibers on hydration and properties of gypsum-bonded fiberboard manufactured from kenaf and bagasse fibers

Background and aims: with respect to the special advantages of lignocellulosic materials, substitution of mineral reinforcement agents (fiber glass, asbestos and etc.) by organic-based fibers such as sisal, cellulosic fibers can be performed. However, using these natural fibers have some defects which could decrease curing and hardening speed of gypsum due to dissolution water-soluble extractives of fiber, while wood materials shortage in country, cheapness and abundance of lignocellulosic resources during the seasons of the year are some reasons of using agricultural waste. Hence, in this research the possibility of gypsum-bonded fiberboard production from bagasse, kenaf and synthetic fiber (fiber glass) was investigated.
Materials and methods: any of bagasse fiber and kenaf fiber at three levels of 0, 7.5 and 15% (based on the dry weight of panels) and fiber glass at three levels of 0, 3 and 6% as effective variables on the physical and mechanical properties of gypsum-bonded fiberboard manufactured with gypsum to inorganic or organic fibers ratio of 1:2.75 and nominal density of 1.10g/cm3 were evaluated. Production methods of panels was semi-dry process. At first, water containing citric acid (99.50% water+0.5% acid) was sprayed on the dry fibers. After agitating fibers in the laboratory blender for 5min, gypsum was added to fibers and mixed together in blender with high circuit speed again. Then, admixture poured into the wood mould with dimension of 30×30 cm and pressed under cold press with pressure of 3MPa for 48 hours. After discharging, panels were treated at the fresh air condition for 5 days in order to climatization. Then, panels set in oven dryer with temperature of 50°C for 5 hours in order to complete hardening and reach to maximum strength. Drying the panels continued to 5-7% humidity. After ending manufacture process, physical and mechanical properties of panels tested and results was analyzed by response surface methodology based on second order polynomial regression model.
Finding: results showed that there is a good conformity between predicted and estimated values, so with increasing bagasse and kenaf fibers MOR and IB increased.
Results: results of determination of hydration temperature and time of gypsum paste test showed that with increasing extractives of lignocellulosic materials temperature and hardening time of complex decreased and increased, respectively.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .