Industrial Production Technology And Flame Retardant Properties Of Ultra Low Density Flame Retardant Fiberboard

Development and application of environmentally-friendly ultra-low density wood-based panels is an important measure to meet the new market demands.The application of ultra-low density flame-retardant fiberboards is an effective strategy to replace some higher-density wood-based panels as non-structural furniture and decorative panels.It will significantly reduces wood consumption,alleviates the contradiction between China's timber supply and demand,and helps China's economic and social sustainable development.However,ultra-low density fiberboards have low mechanical strength,potential formaldehyde release and flammability due to their low density,which hinders their development in the wood-based panel industry and their use in decorative and other fields.Therefore,lightweight,high-strength,environmentally-friendly,flame-retardant ultra-low density fiberboard products have become one of the key development directions of the wood-based panel industry.In this study,eucalyptus fibers combining environmentally-friendly melamine-urea-formaldehyde resin?MUF?adhesive?E1 grade?,isocyanate?PMDI?and soybean gluten adhesive were used to prepare ultra-low density flame-retardant fiberboards basing on the technologies in continuous production line of the fiberboard.According to the optimization of the ultra-low density fiberboard manufacturing process and flame retardant performance,the process factors such as glue spread,hot pressing temperature,hot pressing time and flame retardant addition in the preparation were optimized through physical,mechanical and fire-retardant properties.The flame-retardant mechanism,the effect of density on the flame-retardant properties of the products,and the market economy effects of the products were analyzed.The main conclusions are as follows:?1?Optimization of production process of ultra-low density fiberboard.The optimal production process of MUF ultra-low density fiberboard was fiberboard billet moisture content of 17%,hot pressing time of 390 s,hot pressing temperature of 190?,hot pressing pressure of5.5 MPa,press closing time of 40 s,and glue spread of 13.1%.While optimal production process of hot pressing temperature of 190?,hot pressing time of 390 s,and glue spread of4.0%for PMDI ultra-low density fiberboard.The performance of the prepared panels met the requirement of standard LY/T 1718-2017.Furthermore,moisture content of billet was an important factor affecting the performance of MUF ultra-low density fiberboard.As the moisture content increased from 11%to 21%,the static bending strength and elastic modulus of the fiberboard showed a decreasing trend,and the internal bonding strength showed a tendency to increase first and then decrease.This moisture-induced trend was not suitable for the the water absorption thickness expansion ratio and the formaldehyde emission.?2?Optimization of fire retardant.P-N-B compound flame retardant,P-N flame retardant and Boron flame retardant had excellent thermal stability at temperatures below 200?.The oxygen index of ultra-low density fiberboard increased from 25.5%to 32.5%?33.5%with flame-retardant treatment.The heat release rate and total heat release significantly reduced,indicating excellent fire-retardant performance.Compared with the blank sample,the mechanical properties of the ultra-low density flame-retardant fiberboard reduced.The fire boron flame retardant showed the greatest damage to the physical and mechanical properties of the fiberboard among the three fire retardants,and the internal bond strength and static bending strength of the corresponding flame-retardant board were failure to meet the requirements of the standard LY/T 1718-2017.The internal bond strength,static bending strength and 24h water absorption thickness expansion?24h TS?of the flame retardant A and the flame retardant B met the standard requirements.Considering the cost of the flame retardant and the physical,mechanical and flame-retardant properties of the treated fiberboard,fire retardant A was the optimized group for the three kinds of flame retardant.?3?Optimization of production process of ultra-low density flame-retardant fiberboard.The effects of MUF,PMDI and soybean meal adhesive on the performance of ultra-low density flame-retardant fiberboard was consistent.As the amount of glue spread increased,the performance of boards except oxygen index showed improvement.The preferred glue spread parameters were 13.5%,4.0%and 3.5%,respectively.With the increase of hot pressing temperature and hot pressing time,the internal bond strength,static bending strength and elastic modulus of MUF and PMDI ultra-low density flame-retardant fiberboards showed an upward trend,while the 24h water absorption thickness expansion rate decreased slightly.The preferred process parameters were hot pressing temperature of 190?and hot pressing time of20 s/mm.With the increase of the addition amount of flame retardant,the strength of fiberboards showed a downward trend,while the 24h TS showed an increase trend.The preferred process parameters of the addition amount of flame retardant were?6%,?6%and?7%,respectively.As the addition amount of flame retardant increased from 2%to 8%,the formaldehyde emission of ultra-low-density flame-etardant fiberboard bonded with PMDI/soybean gluten adhesives gradually decreased compared with the control.The oxygen index gradually increased 8.3%?30.8%,and the heat release rate,total heat release and CO₂yield showed a trend of gradual decrease.The total smoke yield showed a trend of decreasing first,then increasing and then stabilizing.?4?Fire-retardant properties and market economy effects of ultra-low density flame-retardant fiberboard.According to results of the thermogravimetric analyzer and cone calorimeter,and the results of flame retardant performance,the flame-retardant effect of A#fire retardant could be ascribed the formation of more wood charcoal under catalytic effect and the release of ammonia gas,water vapor and other dilution gases.As the density of flame-retardant fiberboard increased from 430 kg/m³to 590 kg/m³,its oxygen index increased from 30.5%to 34.3%.The heat release rate and total heat release showed a decrease in the pre-combustion period and remained stable in the later stage of combustion.The total smoke yield and CO₂yield increased gradually,and the CO yield showed a tendency to stabilize after decreasing.When the density was greater than 520 kg/m³,the internal bond strength,static bending strength and 24h TS of the sample met the requirements of the standard LY/T1718-2017.