Flame Retardancy Of Lignin/Wood Flour/HDPE Composites

Wood-plastic composites is a kind of green and environmentally friendly composites,and its application range is more and more wide with it's continuous development.However,it's flame retardant performance is poor,which limits its further development.Lignin is a biomass material derived from the paper industry.It is environmentally friendly,renewable,and has a high carbon content.At present stage,the effective utilization of lignin is extremely low.This thesis takes lignin as a carbon source and applies it to wood powder(WF)/high density polyethylene(HDPE)composites for improving the flame retardance of WF/HDPE composites.The result provided a possibility forthe high value utilization of lignin.The main content of this thesis is divided into four parts.First,we explored the effect of lignin on the flame retardancy of wood flour(WF)/HDPE composites.Second,the flame retardant effect of lignin?ammonium polyphosphate(APP)and FRW(a kind of flame retardant usually used in wood industry,the main components are amidourea phosphate and boric acid)were compared,and the lignin was compounded with APP and FRW to explore its synergistic flame retardant effect.Third,the lignin and APP were used in combination to explore the effect of the total addition of them on the flame retardancy of WF/HDPE composites.Fourth,The composite material with better flame retardant properties was used as the surface layerand WF/HDPE composite material without flame retadant was used as the core layer,and a sandwich constructure was explored to guarantee both flame resistance and mechanical properties.The main results are as follows:(1)Lignin/WF/HDPE composites were prepared by melt blending.Its flame retardant properties,mechanical properties,limit oxygen index were tested.The results show that when the lignin content is ranging from 10%to 20%,the flame retardancy of the composites is improved,the mechanical properties remain good,and the limiting oxygen index reaches 25.3.(2)The total additives were fixed,at a level of 15%.WF/HDPE composites with lignin,FRW,APP as additives were prepared by melt blending and estruding.The flame retardant properties,mechanical properties,residual carbon morphology,and limiting oxygen index of composites were tested.The results show that when the lignin?APP?FRW are used seperately,APP has the best flame retardant effect,and the residual carbon was the most dense,but the total smoke release is large.The mechanical properties of the three composite materials are not significantly different.When lignin is used in combination with APP and FRW,the synergy between APP and lignin is better.The best blending ratio is APP-10%and lignin-5%.The mechanical properties of composites mixed with lignin and APP or FRW are better than those with single of them.(3)Lignin and APP are used as flame retardants,and the ratio of them is 1:1.Lignin/APP/WF/HDPE composites were prepared by melt blending and extruding.Its flame retardancy,mechanical properties,morphology of residual carbon,limit oxygen index and flame retardancy were tested.The results show that with the increase of the total amount of APP and lignin,the flame retardancy of lignin/APP/WF/HDPE composites becomes better,the limiting oxygen index and residual carbon density increase.When the total addition of lignin and APP reaches 30%,the vertical combustion test level of the lignin/APP/WF/HDPE composites reaches V-1 level,and when the addition amount is 50%,the vertical combustion test level reaches V-0 level.However,the increase of the amount of flame retardant reduces mechanical properties of the composite.(4)The lignin/APP/WF/HDPE composites containing lignin and APP was used as surface layer,and WF/HDPE wihtout fire retardant was used as the core layer.The sandwich composites were prepared by hot pressing method.The flame retardancy?limit oxygen index and mechanical properties were tested.The results show that the flame retardant performance of the sandwich composites improves with the increase of the flame retardant added to the surface material and the thickness of the surface material.When the flame retardant content in the surface material is 50%and the thickness is 0.5 mm,the sandwich structure composites reached V-0 level.And the mechanical properties of the sandwich composites are good.This shows that buildinging the sandwich structure is a feasible method to balence the mechanical and flame retardant properties of WF/HDPE composites.