Research On Toughening Modification Of Polylactic Acid And Their Fused Deposition Modeling

The shortcoming of polylactic acid(PLA)as a molding material for fused deposition modeling(FDM)includes crispness,low melt strength,and slight warpage.In this dissertation,thermoplastic polyurethane(TPU)and methyl methacrylate-silicone-styrene(S-2001)were used to modify PLA.The relationship between structure and performance of the blend system were studied.The influence on the continuity,stability,dimensional stability and molding accuracy of the parts were investigated at the same time.Besides,the influence of forming parameters on the impact properties of modified PLA was investigated.Firstly,PLA/TPU blends with different mass ratios were prepared by melt blending.The dynamic rheological behaviors,mechanical properties,microstructures and thermal performances of the blends were investigated by rotational rheometer,electronic universal testing machine,SEM and differential scanning calorimeter(DSC)respectively.The pellets of blends were drawn into filaments to carry out fused deposition modeling.The results show that the storage modulus and elasticity of blends are enhanced by adding TPU,which is beneficial to the melt-laying.The impact toughness of blends can be increased with the introduction of TPU.In addition,the shrink and warp of models by FDM are inhibited,which is due to the decline of crystalline ability after blending.When the content of TPU is 10 wt%,the melting deposition of the filament is the best.Secondly,PLA/TPU(90/10)blends were synergistic toughened by adding different content of S-2001 particles.The dynamic rheological behaviors,mechanical properties and microstructures of the blends were investigated by rotational rheometer,electronic universal testing machine and SEM respectively.The pellets of blends were drawn into filaments to carry out fused deposition modeling.The results show that the S-2001 particles had a significant effect on the system’s impact strength.When the content of S-2001 reached 6-8 phr,the yield deformation zones of the matrix were connected with each other to form percolation channels,and the system achieved brittle-ductile transformation.The rheological percolation interval of S-2001 particle-filled blend system is 8～10 phr.The storage modulus and complex viscosity of the system in the low frequency region are increased significantly.Han and vGP plots predicted the change of melt properties from liquid to solid.Cole-Cole curve and weighted relaxation spectrum reveal the complete three-dimensional network structure within the system from the relaxation mechanism.In addition,the dimensional stability and molding accuracy of the parts which through fused deposition molding were improved by adding S-2001 particles.Finally,PLA/TPU/S-2001(90/10/8)system was selected to prepare the filaments via melt blending.The influence of fused deposition modeling processing parameters on the impact properties of modified PLA were investigated by orthogonal test,including bed temperature,nozzle temperature,deposition style,layer thickness and printing speed.The results indicate that the impact strength of FDM specimen is greatest with the processing parameters as follows:bed temperature of 90 0C,nozzle temperature of 190℃,deposition style of 45°/45°,layer thickness of 0.4 mm and printing speed of 45 mm/s.Furthermore,the layer thickness and the deposition style have a significant effect on the impact properties of modified PLA FDM specimen.The SEM images show that increasing layer thickness is favour of absorbing energy when the materials were impacted,and there exsits antagonism for the discrepant deposition angle between odd and even number layer.Meanwhile,compared with inj ection molding,the impact strength of FDM specimen is lower,just 71.4%as high as that of injection molding specimen.