Study Of Poplar Powder/PLA Composites And Its Application In 3D Printing

Biodegradable composite is composed of lignocellulosic material and degradable polymers.It not only can efficiently utilize the lignocellulose resources,but also,it can make the material sustainable by substitution of petro-based composites.However,the mechanical properties and brittleness of degradable polymers decreased and increased,respectively,when the lignocellulose was introduced into the matrix.This,somehow,restricted the application of the biodegradable composites.In this study,the methods of cellulose surface modification,polymer grafting and adding of additives were used,respectively,to reinforce and toughen the biodegradable composites.The preparation and scheme of reinforcing and toughening of the composites were systematically analyzed.The method of 3D printing lignocellulose/polylactic acid(PLA)biodegradable composites was proposed,which will provide the theoretical foundation for the application of this biodegradable composite into 3D printing fields.The main contents and results of this study are as follows:(1)The pulping modified poplar powder(BECMP fiber)was used to reinforce PLA.The effect of different concentrations of BECMP fiber on the mechanical,thermal and heological properties of the resulting composites were investigated.Meanwhile,the comparison of the reinforcing effect between unmodified poplar powder and BECMP fiber was analyzed.The distribution of fibers in the PLA matrix and interfacial adhesion between fiber and PLA were observed by scanning electron microscope.Both of the tensile modulus and flexural modulus of the composites increased by adding the poplar powders compared to those of PLA,however,the reinforcing efficacy of BECMP fiber was higher than unmodified poplar powder due to high length-diameter ratio in the BECMP fibers.The complex viscosity,storage modulus and loss modulus of the BECMP fiber/PLA composites were higher than those of unmodified poplar powder/PLA composites,which was resulted from the uneven distribution of BECMP fiber(with high length-diameter ratio)in the composites.(2)Different concentrations of silane coupling agent(KH550)and maleic anhydride(MA)were used to modify the poplar powder,respectively.Subsequently,the composites were fabricated by mixing the modified poplar powder and PLA.The effect of modifier concentration on the properties of composite was studied.Comparison of the reinforcing efficacy and differences of these two modifiers on the properties of the resulting composites were analyzed.The results found that both KH550 and MA can improve the interfacial adhesion between poplar powder and PLA,resulting in enhanced mechanical properties of the composite.The impact strength and enlongation of the composites was improved for KH550 modification from all ranges,but only for MA modification at 5%,decrease was found in the composites at 2-4%MA.The thermal stability of the KH550 modified composites has a slight increase,whereas,the MA modified composites did not show any change.The surface wettability of the MA modified composite was improved because of the increase of the contact angle,however,the wettability of KH550 modified composites was reserved compared to the unmodified composites.(3)The MA grafted PL A(MA-g-PLA)was produced by MA modification initiating by an initiator,and the composite was fabricated by poplar powder and MA-g-PLA.The results showed that MA modification can improve the interfacial adhesion bet-ween poplar powder and PLA,resulting in increase of the mechanical properties of the composites.However,the thermal stability of the composites decreased because of MA modification.When 0.5%MA was added,the impact strength,tensile strength and flexural strength of the composites were 9.36 kJ/m2,44.76 MPa and 76.42 MPa,respectively,with increase of the MA content,the interfacial strength of the composite decreased,resulting in decrease of the mechanical properties of the composites.Therefore,the optimal mechanical properties of the composites were obtained when 0.5%MA was applied.(4)The effect of polyethylene glycol(PEG)and tributyl citrate(TBC)on the mechanical,thermal,and rheological properties of the compsites were investigated.The results demonstrated that the strength and toughness of the composite were improved by adding 5%TBC,and the tensile strength,flexural strength and impact strength of the TBC toughened composites were enhanced by 15%,14%,and 10%,respectively,whereas,the improvement was not found in the PEG toughened composites.Meanwhile,the thermal stability of the TBC toughened composites also enhanced with the increase of the peak degradation temperature by 15° compared to that of PLA.However,the glass transition temperature,melting temperature,and crystallinity of the TBC toughened composites were lower than those of PEG toughened composites,indicating that TBC can improve the processability of the composited during extrusion and compression molding,resulting in improved processing efficiency of materials.The storage modulus,loss modulus and the surface wettability of the TBC toughened composites were improved and reserved,respectively,when 5-10%TBC was added in the matrix.(5)The biodegradable composites were fabricated by combination of 3D printing and modified poplar powder/PLA composites.The optimal properties of the printed composites were obtained when 5%poplar powder was added into the matrix.The effect of printing parameters on the properties of biodegradable composites(with 5%poplar powder)was analyzed,and the results found that the optimal mechanial properties of the biodegradable composites were obtained at the printing temperature of 220 ℃ the printing speed of 20 mm/s and the printing layer thickness of 0.1 mm.Great application potential of this kind of biodegradable composite was found when different functional products such as artware,cellphone case,furnitures,and architecture were printed with the produced biodegradable composites.This will bring a great opportunity for 3D printing biodegradable and environmentally friendly products.