Fire Retardant Properties And Mechanism Of Ultra-low Density Wood Fiber-based Material

The ultra-low density wood-based foaming material （ULDM）, prepared by liquidfoaming process, density in0.03-0.09g·cm^-3, can be used in packaging and thermalinsulation applications to replace the expanded polystyrene sheet （EPS）. However,because of the ultra low density, the ULDM’s fire performance still faces severechallenges just as the EPS.In this study, one kind of four components composite inorganic fire retardant,including boron, nitrogen-phosphorus, silicon and halogen, is used to prepare flameretardant ULDM. By limiting oxygen index method and nitrogen atmospherecalcination method at room temperature to optimize the inorganic compositeflame-retardant component ratio, the best fire retardants formula has been determined.By means of thermal analysis, cone calorimeter, X-ray diffraction and infraredspectrum instrument analysis, the ULDM has been researched systematically on itsunique pyrolysis and combustion characteristics, heat release and exhaust smoketoxicity in the combustion process, the fire retardant mechanism and fire retardantcomponents synergism.Research shows that the pyrolysis and combustion of ULDM has thedeflagration phenomenon different from other wood materials. The deflagrationcaused high heat release instantly and more harm in fire. Because cellulose crystallineregion instantly collapse at400℃thermal decomposition temperature leads to thedeflagration phenomenon, So the key is to enhance the thermal stability of cellulosecrystalline region. Research proved that silicone flame retardant component formedorganosilicon compounds and reinforced carbon layer by Si-C and Si-O-C, whichassisted acid catalyzed dehydration charring to improve the thermal stability ofcellulose crystalline region effectively. The flame combustion time was less than30s,smoldering state could maintain in high temperature and smoke suppression wasexcellent when the ULDM had been dealed with inorganic composite flame retardant.The best formula of inorganic composite flame-retardant agent was that boronagent dosage was35%, nitrogen-phosphorus agent dosage was27%, silicon agent dosage was15%and the halogen agent dosage was28%. Using this formula, theoxygen index of the materials prepared for43, burning charcoal residue rate is61.3%.Boron, nitrogen-phosphorus and silicon component have condensed phase flameretardant effect, especially, boron component can form glassy isolation layer at lowtemperature rapidly, so it played a key role in the smoke suppression and reduceexhaust toxicity. Halogen and nitrogen-phosphorus have gas phase flame retardancy,and halogen can reduce the unit heat release effectively by blocking free radicalreaction, act an important role to reduce the surface pyrolysis temperature. Boron,nitrogen-phosphorus and halogen component can produce acid catalyzeddehydration charring effect, silicon can increase carbon layer density and enhancethermal stability of fiber. Therefore, components of the flame retardant play asynergistic effect reached ULDM to non-inflammable B1standard （GB8624-2006）.