| Wood plastic composite(WPC)is a kind of green and environmental protection composite material,but its poor flame retardant performance limits its further development.The flame retardant property can be improved by introdcing flame retardant into the WPC,the mechanical properties of the composite will decreased.Therefore,the sandwich structure is adopted in this paper to combine the surface layer of flame retardant material with the core layer WPC,which can improve the flame retardant property of wood plastic while maintaining its mechanical properties.This is of great significance to promote the wide application of WPC.Firstly,the ratio of surface flame retardant material was studied.Secondly,the flame retardant and mechanical properties of sandwich composites were studied by combining three kinds of surface flame retardant materials with core wood plastic by hot pressing respectively.Finally,a new rollpressing technology was developed to prepare sandwich composite materials to improve the performance and efficiency.The main research contents and results are as follows:(1)Research on flame retardancy of stone plastic compositesThe lignin and polyphosphate were mixed at 1:1,and the stone plastic composites with flame retardant were prepared by hot pressing.The flame retardant properties,limiting oxygen index and mechanical properties of the composites were tested.The results showed that when the total content of flame retardant is 40%,the flame retardant performance reaches the best,the smoke emission is less,and the limit oxygen index is 30.3.However,the mechanical properties of stone plastic with flame retardant decreased significantly with the increase of flame retardant content.(2)Study on flame retardancy and mechanical properties of sandwich structure compositesLignin and ammonium polyphosphate used as flame retardants,stone plastic with flame retardant(Flame retardants make up 40% of the surface),wood plastic with flame retardant(Flame retardants make up 50% of the surface)and pure flame retardant plastic(Flame retardants make up 60% of the surface)composites as the surface layer,combined with the core layer of WPC by hot pressing method to prepare sandwich structure composite materials respectively.The flame retardancy,limit oxygen index,mechanical properties,dynamic mechanical properties and creep of sandwich structure composites were analyzed.The results show that compared with the other two materials,stone plastic with flame retardant has the best flame retardancy,and can inhibit the generation of smoke,the limit oxygen index is higher than 29,and the sandwich structure can meet the requirements of mechanical properties.When the thickness of the surface stone plastic with flame retardant is 1.5mm,the energy storage modulus and loss modulus of the composites can be significantly improved,and the creep resistance is better.(3)Study on the preparation technology and flame retardancy of rolling pressed veneer compositesA rolling veneer technology was designed to heat the flame retardant surface sheet and the substrate to melt one side of the flame retardant sheet.At the same time,the back of the sheet is rolled to combine it with wood plastic.The surface bonding,internal bonding strength,water absorption thickness expansion rate and impregnation and stripping ability of the sandwich structural materials were tested and analyzed,and the flame retardant effect of 1.5mm thick stone plastic with flame retardant surface layer on wood plastic core layer of different thickness was discussed.The results show that the composites prepared by rolling veneer technology meet the industry requirements of wood-plastic flooring.The flame retardant stone plastic with a thickness of 1.5mm can play a flame retardant role on the core layer of 4-9mm,and the flame retardant effect of the first 200 s is basically same.Compared with the hot pressing method,the rolling veneer technology improves the mechanical properties,saves energy,and the preparation period is greatly shortened. |
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