Preparation And Properties Of Wood Flour/Polylactic Acid Composites For 3D Printing

In recent years,3D printing technology and 3D printing materials have attractedextensive attention.Among them,FDM type 3D printing technology has stronger vitality because of the advantages of 3D printers and 3D printing consumables,such as simple operation,low price,easy manufacture and production,large print size range and so on.Degradable polylactic acid（PLA）,a material which is suitable for FDM type 3D printing,is the most valued.However,PLA has poor toughness,easy fracture,low melting point and poor thermal stability,which greatly limits its application as a 3D printing material.Therefore,it is common to add reinforcing materials to improve the mechanical properties and thermal stability of PLA which based 3D printing materials.Because natural plant fiber has the advantages of low density,good mechanical properties,low price,environmental protection and so on,it is very important to prepare biomass-based 3D printing materials by combining it with PLA.（1）In order to improve the interfacial property between pine wood flour or cypress wood flour（PWF/CWF）and matrix material,the surface of PWF/CWF was modified by alkali and coupling agent（KH590）.IR and TG test shows that alkali treated wood powder can effectively remove pectin,hemicellulose and lignin in the fiber.PWF/CWF which modified by alkali treatment and KH590 have better thermal stability.The SEM results showed that the interface compatibility between PWF /CWF and PLA was improved by chemical modification of wood powder.PWF/ CWF were well wrapped in PLA,and there were no obvious holes caused by fiber being pulled out,and the distribution was more uniform in PLA.（2）Chemical modified PWF/CWF reinforced PLA composites were prepared by twin-screw melt extrusion blending and injection molding.The tensile strength,the bending strength and the notched impact strength of the composites increased first and thenIV decreased with the increase of the content of chemically modified materia The printed wirewhich made of PWF/CWF.PWF/ PLA and CWF/PLA composite are test on FDM type 3D test.The Mechanical strength can reach more than 90% of the injection molding strength,thereby completely meeting the requirement of 3D printing.PWF/PLA wood-plastic composites wire rod has good 3D printing performance,strong adhesion,no warping,continuous layer,no plug,smooth printing process,and the process of printing filled with costustoot.The bending strength and tensile strength of CWF/PLA composites are not as high as those of PWF/PLA composites,but the impact strength of CWF/PLA composites is about three times as high as that of PWF/PLA composites.Considering the comprehensive application of 3D printing,PWF was finally selected as wood powder for 3D printing.（3）The mechanical properties of WPC can be greatly improved by adding nano-SiO₂ into modified PWF/PLA composites,and the thermal stability of WPC is also improved.With the increase of nano-SiO₂ content,the mechanical properties of WPC are gradually enhanced.However,because that texture of the nano-SiO₂ is fluffy and considering of the convenience of proces,we chosen the content of the nano-silica is 5wt% because of the small improvement of the performance after 5wt%.Under these conditions,the water absorption of WPC increased with the increase of wood flour content,and the mechanical strength of WPC increased first and then decreased with the increase of wood flour content,and reached the best when the wood flour content was 15wt%.（4）The mechanical strength of the composite can be improved by adding nano-TiO₂ into modified PWF/PLA.The antibacterial performance of the composite is endowed by adding nano-TiO₂.When the content of nano-Tio2 is 5wt%,the antibacterial rate of the composite to Escherichia coli reaches 86.23%.The mechanical properties of the composites increased firstly and then decreased with the increase of nano-TiO₂ content.the best mechanical properties were obtained when the content of nano-TiO₂ was 2wt%.（5）The mechanical strength and the fire resistance of the composites were improved by adding montmorillonite into modified PWF/PLA.The fire resistance of the composites increased with the increase of montmorillonite content.the oxygen index of the composites was 33.5 when the content of montmorillonite was 10%.The mechanical properties of the composites increased firstly and then decreased with the increase of montmorillonitecontent.The best mechanical properties were obtained when the content of montmorillonite was 6wt%.（6）The WPC prepared by adding nano-SiO₂,nano-TiO₂ and montmorillonite into modified PWF/PLA can be applied to 3D printing technology,and have good 3D printing performance.