Study On The Synergistic Flame Retardant Performance Of The Poplar Fiber/Polypropylene Composite

Both ammonium polyphosphate(APP)and zinc borate(BZ)are commonly used flame retardants for wood-plastic composites(WPC).APP alone has been applied to WPC in flame retardant research,but there is a problem that the amount of addition is large and the amount of smoke of the composite material is large when burned;while the flame retardant efficiency of BZ is not high when used alone.This paper studies the synergistic flame retardant effect of APP and BZ compound paired poplar fiber/polypropylene composite;and on this basis,studies the effect of nano-SiO₂ and compound phosphorus boron flame retardant in WPC Synergistic flame retardant effect.In addition,due to the poor interface compatibility between flame retardants and composite materials,the mechanical properties of WPC will decrease,so APP and nano-SiO₂ are surface modified,and APP,BZ and nano-SiO₂ are ternary composites.The flame retardant mechanism of the flame retardant is discussed in depth,and the main research contents and results are as follows:(1)Flame retardant WPC was prepared with APP and BZ compound and other components,and the samples were subjected to horizontal-vertical combustion test,limiting oxygen index test(LOI),thermogravimetric analysis(TG),cone calorimetry test(CONE)and testing and analysis of mechanical properties.The test results show that when APP:BZ is 4:1 and the total added amount is 25 wt%,the various properties of WPC are the best;the CONE test shows that the synergistic flame retardant performance at this time is better than the flame retardant performance of a single flame retardant;TG results show that the thermal stability of WPC is greatly improved,and the amount of carbon residue increased by 266%,reaching 23.95%;the morphology of CONE carbon residue and the scanning electron microscope(SEM)characterization results show that the composite material is formed more densely after combustion The carbon layer;horizontal-vertical combustion and limiting oxygen index tests show that the material can meet the flame retardant requirements.(2)The effect of adding nano-SiO₂ to enhance the flame retardancy and mechanical properties of APP/BZ modified WPC was studied.The research results show that the optimal addition amount of nano-SiO₂ is 4 wt%;at this time,the maximum oxygen index of APP/BZ/nano-SiO₂ WPC is up to 25.65%,and the vertical combustion grade is V-0;the CONE test shows that nano-SiO₂ can Effectively reduce the total heat release and smoke release of WPC,and reduce the total burning time;TG test shows that nano-SiO₂ can increase the carbon residue rate of WPC to 32.32%and reduce the maximum thermal weight loss rate;SEM results show,Nano-SiO₂ can make the carbon layer of the composite material more compact after burning,indicating that nano-SiO₂ effectively improves the charcoal formation performance of WPC combustion;the mechanical performance test shows that the addition of nano-SiO₂ can slightly increase the tensile strength of WPC.(3)Use KH-550 to modify the surface of APP and nano-SiO₂.The Fourier Infrared Spectroscopy(FTIR)test showed that KH-550 successfully grafted modified APP and nano-SiO₂.Combine modified APP(k-APP),modified nano-SiO₂(k-nano-SiO₂)and BZ to prepare flame-retardant WPC,study the changes of its mechanical properties and water absorption properties,and further discuss the ternary compound The flame retardant mechanism of flame retardants on composite materials.Mechanical strength analysis shows that KH-550 surface modification treatment can improve the interface compatibility between APP and nano-SiO₂ and the matrix material.The prepared k-APP/BZ/k-nano-SiO₂ compound synergistically modifies the stretching of WPC Compared with APP/BZ/nano-SiO₂WPC,the strength and impact strength are increased by 5.40%and 45.91%respectively,and the water absorption and weight gain rate is significantly reduced,which is lower than the blank group WPC without flame retardant;scan the composite material impact strength test section Electron microscopy analysis shows that the voids at the section are obviously reduced and there is no obvious gap;the principle of the gas phase flame retardant effect of the compound flame retardant is:the decomposition of APP can release NH₃,and the BZ can release water to dilute the oxygen concentration and carbon around the substrate Combustible components such as hydrogen compounds and carbonyl compounds can absorb part of the heat when water evaporates;Raman spectroscopy tests further illustrate the mechanism of nano-SiO₂'s solid-phase flame-retardant effect—improving the graphitization degree of carbon residue after the composite material is burned,Thereby improving its thermal insulation performance.