The Preparation And Properties Of Foamed Wood Flour/Polypropylene Composite

Wood plastic composite(WPC)has been developed rapidly in recent years because of its environment-friendly characteristic and both advantages of wood and polymer.However,the drawbacks of high density and low impact strength restrict the further development of WPC.In this paper,the foamed wood flour/polypropylene composite was prepared by hot pressing method using modified azodicarbonamide(AC)as foaming agent.The effects of foaming agent,coupling agent,wood flour,different types of PP and PP/LDPE blends on the cell morphology,density,mechanical and rheological properties of foamed WPC were investigated.The balance torque value and the zero shear viscosity of foamed WPC melts were decreased when the AC content not more than 1.5phr.This is because the appropriate gas content generated from AC can be better dissolved and diffused into the melted matrix.Especially,when the content of AC is 1.0 phr,the foamed WPC had the highest specific strength and impact strength.The increase of the melts viscosity was improved with the increasing of wood flour content,which inhibits the cell growth resulting in the smaller and fine cell size.The flexural strength increase depending on the wood flour increase when the content is not more than 30 phr.Beyond 30 phrmthe wood flour was not easy to distribute,resulting in stress concentration,so the flexural strength will be decreased,and the impact strength is always reduced with the increase of wood content.However,the flexural strength is improved with the increasing of wood flour content in the presence of maleic anhydride grafted polypropylene(MAPP).The addition of MAPP improves the interfacial adhesion between wood flour and PP matrix,so the movement of PP macromolecular chain is restricted leading to the increase of melts viscosity.It is benefit to obtain the foamed WPC with the fine cell structure.As coupling agent bonding effect and small size effect of the cell structure,the bending strength and impact strength of foamed WPC were increased with the addition of MAPP.However,excess MAPP mainly served as small molecular plasticizer in the system,which could reduce the foamed WPC melts viscosity,resulting in the distortion of cell morphology and the decrease of the mechanical properties of the WPC.The density is various when the foamed WPC was prepared with different types of PP matrix.The high-melt-strength polypropylene with a certain branched structure had good foaming properties.Adding LDPE into the formulation improved the foaming performance of PP,obtained good structure of cell and improved the impact strength of foaming WPC,however,the flexural strength of foamed WPC was decreased significantly.