Studies On PLA/CNCs Composite And Its Application For Fused Deposition Modeling 3D Printing

3D printing has been widely concerned in the field of material processing in recent years due to its capability of fabricating special shape and personalized products without mould.Fused deposition modeling(FDM),which has developed rapidly in recent decades,is one of the rapid prototyping.Poly(lactide acid)(PLA),which is a kind of polymer material with completely biodegradable,good strength and stiffness,has been used in packaging,clothing,decorative materials,biomedical and other fields.Cellulose nanocrystals(CNCs)can be used as an excellent reinforcement filler for PLA because of its good biocompatibility,high elastic modulus,high crystallinity,high Young's modulus,high strength and other great characteristics.However,CNCs prepared by acid hydrolysis has low thermal stability.PLA is very suitable for FDM,but its brittleness,poor heat resistance and other shortcomings limit its application in FDM;hence,PLA modified with CNCs,which used for FDM,has important significance.In this work,we have studied the effects of CNCs and PLA-g-MAH on the mechanical properties,crystalline properties and thermal stability of PLA.The influence of FDM parameters on the mechanical properties of PLA composites was also investigated.The main research contents and results are as follows:CNCs was prepared by sulfuric acid hydrolysis of microcrystalline cellulose(MCC).Compared to the untreated cellulose nanocrystals(uCNCs),the thermal stability of cellulose nanocrystals treated with alkali(aCNCs)and followed blending with PEO(oCNCs),were all improved;alkali treatment could effectively remove sulfonic acid introduced onto the surface of MCC,and followed solution blending with PEO could further enhanced the thermal stability of CNCs by adsorption on the surface of CNCs.Furthermore,uCNCs,aCNCs and oCNCs were respectively blended and extruded with PLA;black impurities,degradation of CNCs,which were observed in PLA/uCNCs did not appear in PLA/aCNCs and PLA/oCNCs.Maleic anhydride grafted onto Poly(lactic acid)(PLA-g-MAH)was successfully prepared by melt extrusion and used to improve the interfacial compatibility between PLA matrix and CNCs.The effect of CNCs and PLA-g-MAH content on the mechanical properties,crystallization properties,thermal stability,rheological properties,Vicat Softening Temperature(VST)and water absorption of composites were studied.Compared with PLA/10% PEO,addition of 5 wt% CNCs could improve the crystallinity of the composites,and shorten the crystallization time of composites;with incorporation of appropriate amount of PLA-g-MAH into the system,the crystallization properties of composites further increased;the thermal stability and VST of composites increased,and the tensile strength and notch impact strength of composites were improved,but the flexural strength of composites did not change.In addition,incorporation of CNCs into PLA/10% PEO could improve processability and saturated water absorption of composites;when PLA-g-MAH was further incorporated into the system,the saturated water absorption of composites increased with increasing content of PLAg-MAH,and the processability of composites showed a trend of first increase and then decrease.Then the influence of CNCs and PLA-g-MAH content on the mechanical properties of composites were studied by fabricating with FDM,including processing parameters and heap patterns.A good surface quality of samples fabricated by FDM could be obtained by using appropriate processing parameters.When the temperature of nozzle,scanning speed,raster angle and orientation were respectively set to 200 °C,35 mm/s,45°/135° and flat,tensile strength and notch impact strength of samples obtained were better;when raster angle was changed and set to 30°/120°,and the other parameters were invariant,the flexural strength of samples obtained were better.In addition,no significant effect of CNCs content on the tensile strength,flexural strength and notch impact strength of samples was observied.When the loading of PLA-g-MAH(PLA basis)was 5 wt% in PLA/CNCs/PLA-g-MAH composites,the tensile strength,flexural strength and notch impact strength of the composites were better.