The Research On Synergist Flame Retardant Of Nano-silica On Wood Plastic Composite Materials

Wood plastic composite（WPC）is a kind of mature material which has been applied in many fields.Wood plastic composite material is a new kind of wood material which was made by mixing polyethylene,polypropylene and polyvinyl chloride rather than ordinary resin adhesive with more than 50% of wood flour,rice husk,straw and other waste plant fiber.After extrusion,molding,injection molding and other plastic processing technology,plates or profiles are manufactured.It can be seen from the definition that the two main components of wood plastic composites are flammable and combustible,so nowadays there are a lot of exploration about the issues of flame retardant has been done.In this study,wood flour（WF）,rice straw powder（SF）and rice hull powder（RHF）were used as plant fiber to react with polypropylene（PP）for wood-plastic composites preparation.Then the combustion performance and mechanical properties were studied after addition of ammonium polyphosphate（APP）.The mechanical test results indicate that the mechanical properties of PP/WF-APP 20 wt% composites were the best.Cone calorimetry（CONE）test results show that only the PP/SF composite flame retardant after the release of total smoke decreased.The results of thermogravimetric analysis（TGA）showed that the residual carbon content of PP/SF-APP 18 wt% composites reached 26.9%.Scanning electron microscopy（SEM）observation shows that the densification of PP/SF-APP 18 wt% composites is the best.X-ray photoelectron spectroscopy（XPS）tests found that the flame retardant difference attributes to the rice straw powder containing silica.PP/SF-APP 18 wt% composites have the best flame retardancy,the oxygen index is 28.1%,UL-94 reaches V-0 level,but the mechanical property is poor.At the same time,the enhancement on flame retardancy of PP/WF-APP 20 wt% composite was studied when adding inorganic nanomaterial.The results showed that among nano-silica,nano-clay,nano-montmorillonite and nano-SiO₂,nano-SiO₂ is the most effective way to improve the flame retardancy of the composites.When the addition amount is 1 wt%,the oxygen index is 28.3%,the increase is 1.4% and the UL-94 reaches the V-0 level.The results of CONE show that the release rate of the composite material decreases with the addition of nano-Si O₂.The TGA results indicate that the residual carbon content of composites increased by 27.9% after the addition of nano-SiO₂.The SEM results show that the density of the carbon layer after the addition of nano-SiO₂ is improved,but the surface of the carbon layer is not smooth.These results suggest that the addition of nano-SiO₂ improves the carbon forming ability of the composites,but there is a problem of the compatibility with the composites is not good and tend to agglomerate.After the nano-SiO₂ was modified by KH-550,the infrared（FIR）test results of KH-550-SiO₂ show that there are new peaks appeared on characteristic peaks of nano-SiO₂,which proves that KH-550 was successfully modified on nano-SiO₂.The transmission electron microscopy（TEM）images show that most of the agglomerated silica particles are dispersed into nanoscale,and the best mass ratio of KH-550 to nano-SiO₂ is 1:19.Three kinds of wood-plastic composites were mixed with KH-550-SiO₂ and APP,the research results indicate that the mechanical properties and flame retardancy of PP/WF composites with 18 wt% APP and 2 wt% KH-550-SiO₂ were the best.Combustion test results show that the oxygen index increased by 2.9%,UL-94 reaches to V-0 level.CONE results showed that the tobacco release rate was the most significant.The TGA results verify that the carbon residue of the composites is increased by 40.5%.The SEM results show that the density of the carbon layer after combustion is improved and the surface of the carbon layer is smooth.Compared with those without KH-550-SiO₂,the tensile strength,flexural strength and impact strength were increased by 9.7%,7.8% and 47.8%,respectively.