Study On Modified Continuous Aramid Fiber Reinforced Wood Flour/High Density Polyethylene Composites

As a new environmental protection material,wood-plastic composite(WPC)has been widely applied in building,interior decoration,automobile and other fields.However,the applications of WPC in engineering structural materials are still restrict because of the low strength,poor toughness and easy creep.Therefore,the development of high-performance of WPC to expanding application fields is increasing significantly.In this paper,continuous aramid fiber(CAF)reinforced wood flour/high density polyethylene(CAF-WF/HDPE)composites were prepared by co-extrusion method.The effects of virgin and treated CAF on the mechanical properties,creep behavior and dimensional stability of the resulting CAF-WF/HDPE composites were investigated.(1)The continuous aramid fiber(CAF)reinforced WF/HDPE composites were prepared by co-extrusion method,and the effect of adding CAF on the properties of the resulting CAF-WF/HDPE composites was investigated.The results showed that the tensile,bending,and impact strength of the ternary(CAF/WF/HDPE)composites were increased by increasing the CAF content.When three aramid fiber bundles were added,tensile strength,bending strength and impact strength were increase by 162.20%,62.38%,and 188.78%,respectively.When CAF was added,the creep deformation rate of the resulting composite slows down,and the creep and residual deformation were also reduced.However,both the water absorption and thickness expansion ratio of the resulting composite material were increased by increasing the content of CAF.(2)In order to improving the interface compatibility between CAF and HDPE/WF composites,the CAF was treated by NaOH,H3PO4 and KH550,respectively.XPS analysis showed that the O/C and C-N/C-O ratio of CAF surface were increased,but the relative atomic percentages of C and the C=O ratio were decreased after NaOH and H3PO4 modification.This result indicated that the carboxyl group and amino group were coated on the fiber surface.When the CAF surface was treated with KH550,the peaks of Si-N and Si-O were observed;in addition,relative atomic percentages of Si was decreased,and the ratio of O/N and N/C were increased.This results confirmed that KH550 was successfully coated on the surface of the fiber.After modification of CAF with those three agents,all the modified CAF surface were rougher than that of virgin CAF.The rough surface may improve the interfacial interaction with HDPE/WF composites due to lager surface area.Moreover,the CAF surface treatments didn't affect the crystal type of CAF but the tensile strength was decreased,and H3PO4-treated CAF showed the lowest tensile strength.(3)Compared with the virgin CAF-WF/HDPE composites,treatments of CAF with NaOH,H3PO4,and KH550,showed significantly improved in mechanical properties of resulting composites,especially for the KH550-treated CAF-WF/HDPE composites.The tensile,impact,and interfacial shear strength of the KH550-treated CAF-WF/HDPE composites was increased by 9.8%,12.7%,and 25.35%respectively.After modification of CAF,the creep deformation of resulting composites was significantly reduced.For KH550-treated CAF-WF/HDPE composites,when the bending force was applied,the creep deformation at 30? was decreased by 8.0%but the change at 60? was not obvious;however,when the torsional force was applied,the creep deformation at 30 and 60? was decreased by 10.5%and 20.0%,respectively.After modifications of CAF with both NaOH and H3P04,the water absorption and thickness expansion ratio of the resulting composites were reduced;whereas,the water absorption rate and thickness expansion ratio of the KH550-treated composites increased slightly.After all samples were soaked in boiling water for 2 hours,the composites with modified CAF exhibited less reduction in tensile strength.(4)Aiming at promoting the grafting efficiency of KH550,the dopamine was used to anlysis the synergic influence between KH550 and dopamine.XPS analysis showed that the peak of C-O was observed,and the O/C ratio was increased but relative percentages of-C=O was decreased after treatments with dopamine.This result indicated that dopamine was coated on the fiber surface.Compared with KH550 modification,the relative percentages of Si,Si-O,and the O/C,N/C ratios were further increasedafter the modification of CAF with both dopamine and KH550.These result indicated that more KH550 was grafted on the fiber surface.After the modification of CAF with dopamine-KH550,protrusions was observed on the surface of the fiber,indicating that a rough surface was formed.The modification didn't affect the crystal type of CAF,and there was also no changes in tensile strength compared with virgin CAF.(5)Compared with virgin CAF,the tensile,impact,and interfacial shear strength of the dopamine-KH550 treated CAF-WF/HDPE composite was increased by 16.3%,18.0%,and 35.2%.In addition,the creep deformation under bending forceat 30,60? were decreased by 20.0%and 13.0%,respectively:the creep deformation under torsional force at 30 and 60?decreased by 18.4%and 25.0%.The thickness expansion ratio decreased but the water absorption rate was no change.The composites reinforced with dopamine/KH550-treated CAF exhibited less reduction in tensile strength after soaking in boiling water for 2 hours.