Properties Of Poly(Lactic Acid)/Nutshells Composites And Fused Deposition Modeling Research

Polylactic acid(PLA)synthesized from biologic materials(e.g.,corn and potato)with consuming very low energy,which can greatly decrease the dependence on petrol resources.PLA can degrade completely into water and carbon dioxide without producing any pollution.PLA was able to be implanted into a living body due to its excellent biocompatibility.However,PLA is brittle and relatively hydrophobic,and degrades in very low speed.Nutshells powder(walnut shell powder,WSP,almond shell powder,ASP and macadamia shell powder,MSP)are natural solid and waste materials,which possess many merits,such as,lighter weight,low price and non-toxic.However,nutshells are hydrophilic materials,leading to be poorly compatible with PLA.It is necessary to modify nutshells for compositing with PLA.Fused deposition modeling(FDM)technology is currently one of the most popular Additive Manufacture(AM)techniques,due to its low cost and easy operation.FDM can free fabricate complex-shaped parts.However,FDM of polymer/natural-fibers composites was rarely reported in literature.Therefore,the development and popularization of FDM were limited.The main goals of this study were: modifying nutshells to improve the compatibility between PLA and nutshells;investigating properties of PLA/nutshells composites;exploring the microstructure,mechanical properties and toughing mechanism.The main study and results were shown below.Effect of various treated methods(alkali,silane,alkali/silane,microwave,water bath and alcohol)on microstructure,crystallization index and thermal stability of WSP,ASP and MSP was investigated.Results showed: there was some relationship between thermal stability and constitutes of nutshells,the former was enhanced with the increasing of cellulose of nutshells;all treatments eliminated aggregation and roughed the surface of nutshell powder.Alkali treatment removed hemicellulose of nutshell.Silane reacted and physically tangled with nutshells.The thermal stability and reactivity of WSP was enhanced,by all treatments for WSP,by microwave,water bath and alcohol for ASP and MSP.The crystallization index,melt flow index(MFI)and thermal property of nutshell/PLA was investigated.When the silane concentration was 4 wt.% for PLA/ASP and PLA/MSP,or was 6 wt.% for PLA/WSP,the dependence between PLA and nutshell was the strongest.MFI increased with the increasing of testing temperature,loading and mesh size of nutshells.MFI reached to the highest values at 10 wt.% for three nutshells/PLA composites.The relationship among shear rate,shear stress and shear viscosity showed that PLA/ASP and PLA/MSP was pseudoplastic fluid,and PLA/WSP was expandable fluid.In order to predict MFI at another temperature,the standard reference temperature T_s in Shenoy model was amended to T_s=T_g.With the amended T_s,the computed value was identical with experimental value.Comapred with that of PLA,PA5S4?PWS-4Si?PWS-6Si and PWS-8Si possessed higher melting point,PA5S4 and PA5S6 had higher glass transition point.The thermal stability of PLA was enhanced by inputting either ASP-6Si or 3 wt.% ASP.The crystal degree of treated PLA/ASP and treated PLA/WSP was much higher than that of PLA(1.8%),with values between 2.21-4.45% and 3.02-3.5%,respectively.The non-isothermal crystallization kinetics showed that PLA/ASP composite crystallized firstly as one-dimensional acicular crystal in the former half,following by two-dimensional sheets or three-dimensional spherocrystal in the later half.The mechanical properties,microstructure,water uptake and crystallization index of FDM nutshell/PLA composites were studied.The tensile strength of PA3 was higher 1.8 MPa than that of PLA.Alkali treatment improved the tensile properties of composites.PLA/ASP-Na had the highest growth of 9.2% in tensile strength.PLA/WSP-Na had the highest growth of 42.7% in tensile elongation.Silane treatment improved the tensile and compressive properties of composites: which of PLA/ASP increased by 28.3% and 13.9%,and which of PLA/WSP increased by 8.5% and 23.3%.When the content of treated ASP was10 wt.%,the tensile strength of PA10S4 was higher 3.62 MPa than that of PLA.The toughing mechanism included cold drawing,pulling-out toughing and crack deflection.PLA possessed the lowest water uptake by 0.63%.The water uptake was increased to 4-10% and 2-5% by inputting untreated and treated nutshells,respectively.Therefore,nutshells can accelerate the degradation of PLA and enhance its cell infinity.Two math models of water uptake were built,and were testified identical with experimental value.The FDM samples of nutshell/PLA composites possessed higher crystal degree than its powders without changing the chemical structure of composites.Porous PLA/nutshells scaffolds with interconnected pores were manufactured with FDM.The porosity and pore size can be adjusted by the FDM processing parameters,extrusion ratio and fill ratio.PLA/WSP scaffold was made with medical materials,PLA and WSP.The possibility of PLA/WSP scaffold using as potential bone implant material was explored to widen the material choice for bone implant.The PLA/WSP scaffold can satisfy the requirements of human cancellous bones for porous size and elasticity modulus,and can expand the material choice of human non-load bearing bone.All scaffolds lowered weight of PLA,reduced cost of PLA by 10-15% and achieved the comprehensive utilization of solid waste material.