Strengthening And Toughening Of Eucalyptus Wood Flour / Polypropylene / High Molecular Weight Polyethylene Composites Prepared Under Elongation Flow

The poor impact resistance of wood-plastic composites(WPCs)limits its application in the high toughness and high strength application environment.Traditional chemical modification to reinforce and toughen WPCs are complicated and toxic reagents are used.Blending rubber or other elastomers will reduce the rigidity of wood-plastic composites.In this paper,high molecular weight polyethylene(HMWPE)with high toughness as toughening agent,an eccentric rotor extruder(ERE)based on elongation flow was used to process eucalyptus wood flour/polypropylene(PP)/HMWPE wood-plastic composites,enhancing and toughening WPCs in same time.The influence of the addition of HMWPE and elongation flow on the structure and properties of WPCs was investigated,and the mechanism of toughening and strengthening was analyzed.The research result of this paper has important research significance and application value for the plastic blending technology based on elongation flow and the high-value application of WPCs.Firstly,PP/HMWPE polymer blends was processed by two kinds of processing methods,the ERE and torque rheometer processing.The effects of elongation flow processing and shear flow processing on the microstructure and macroscopic properties of PP/HMWPE blends with different contents were compared by characterization tests such as two-dimensional wide angle X-ray diffraction(2D-WAXD),Raman spectroscopy,differential scanning calorimetry(DSC),dynamic thermomechanical analysis(DMA),scanning electron microscopy,heat deflection temperature(HDT),dynamic rheological properties and mechanical properties test.It is proved that,compared with torque rheometer processing,the extruding process of ERE dominated by elongation flow can promote the orientation of the polymer molecular chain,improve the orientation degree,and thus improve the crystallinity of the polymer.Meanwhile,the elongation flow also promotes the mutual diffusion of PP and HMWPE molecular chains and improves the interface bonding of PP/HMWPE,which is beneficial to improve the strength and toughness of PP/HMWPE blend.When the mass ratio of HMWPE/PP is 1/4,the tensile strength,elongation at break,flexural strength,flexural modulus and notched impact strength of PP/HMWPE are 27.9 MPa,472.8%,40.1 MPa,1364 MPa and 48.6 k J/m~2respectively.Compared to PP,the tensile strength,flexural strength and flexural modulus of PP/HMWPE did not decrease obviously,while the notched impact strength increased by100.8%,showing good comprehensive mechanical properties.Therefore,the mass ratio of PP/HMWPE is used as the mass ratio of WPCs matrix.Based on eucalyptus wood flour/PP/HMWPE wood-plastic composites,the effects of ERE processing on the structure and properties of WPCs were studied.The results showed that the mechanical properties of eucalyptus flour/PP/HMWPE composites produced by torque rheometer processing were greatly reduced.WPCs processed by ERE have better mechanical properties.The tensile strength,flexural strength,flexural modulus,notched impact strength and un-notched impact strength are:28.7 MPa,55.2 MPa,2508 MPa,8.2 k J/m~2 and 48.6 k J/m~2,with 19.6%,21.6%,23.5%,57.7%and 50.4%improvement compared to eucalyptus wood flour/PP processed by torque rheometer,respectively.This is due to the effect of the decreased liquidity of the system after adding the wood flour,the role of elongation flow is further strengthened at same speed,improved orientation and crystallinity,increased interfacial adhesion between wood flour and polymer matrix.Due to the orientation crystal structure and high crystallinity of the plastic matrix,the improved interface bonding strength between the wood flour and the plastic matrix,the rigidity of the wood plastic composite increased.The interface between PP/HMWPE and the interface between wood flour/plastic matrix is improved to enhance the transmission of stress in the material,which is conducive to the toughening effect of HMWPE.HMWPE and PP deformed plastic under impact load,and the impact resistance of the material is improved.In summary,WPCs prepared by adding an appropriate amount of HMWPE and using ERE processing has excellent strength,impact resistance and heat resistance,and the preparation method is simple,with a broad prospect of industrial application.