| Shape memory polymers are intelligent materials that can respond regularly to their own shape under external excitation conditions.Combining shape memory polymers with FDM 3D printing technology can meet the demand for complex and personalized design of intelligent structures in the fields of medical,aerospace,soft robotics,etc.Developing shape memory materials suitable for FDM technology has far-reaching significance and broad prospects.Polylactic acid(PLA)is a semi-crystalline polyester polymer composed of soft and hard chain segments,which is widely used in the preparation of FDM printing filaments because of its good printability,biocompatibility and degradability.On the other hand,PLA has limitations in FDM printing due to its disadvantages such as big brittleness,while maleic anhydride grafted styrene-ethylene-butadiene-styrene block copolymer(SEBS-g-MA)is an elastomeric material and conductive carbon black(CB)can effectively improve the electrical behavior of the material.In this thesis,the melt blending and single-screw extrusion process were used to prepare 3D printed PLA-based filaments with good toughness,thermo-responsive and electro-responsive shape memory properties by combining the respective advantages of the three materials,and their properties were characterized and tested.The details of the study are as follows:(1)PLA/SEBS-g-MA thermo-responsive shape memory composites with different components were prepared by melt blending process,which were fabricated into FDM-printable filaments using a single-screw extruder,and the effects of different SEBS-g-MA contents on the composite properties were investigated.The results showed that when the addition of elastomeric SEBS-g-MA reached 30 wt%and above,the microscopic morphology of the composites changed from an island structure to a co-continuous structure,which was conducive to improving the shape recovery rate of the composites.With the increase of SEBS-g-MA content,the tensile strength of the composites gradually decreased,while the toughness gradually increased.Thermodynamic tests revealed that the addition of SEBS-g-MA had a small effect on the thermal stability of the composites,with a minimum initial decomposition temperature of approximately 322°C and a maximum temperature of 70°C to complete the glass transition.As the content of SEBS-g-MA increased,the viscosity and modulus of the composites showed a tendency to increase,and the shape recovery rate gradually increased,while the shape fixation rate slightly decreased.Among them,the shape memory composites with 40 wt%SEBS-g-MA added completed the maximum shape recovery within 15 s,and the shape recovery rate reached 88.1%and the shape fixation rate was 97.8%.(2)Based on the preparation of PLA/SEBS-g-MA thermo-responsive shape mem-ory composites,electro-responsive shape memory FDM filaments were prepared by doping conductive carbon black into the PLA70/MA30 composite with better overall performance,and the effect of carbon black content on the properties of the electro-responsive shape memory composites was investigated.The results showed that the doping of carbon black reduced the tensile strength and elongation at break of the composites,and the mechanical properties of the composites with 5 phr of carbon black were the best among all the composites.In terms of microscopic morphology,the addition of carbon black led to the gradual roughness of the surface of the nozzle-extruded wires,an increase in the interwire gap and a deterioration of the bond.In particular,at a carbon black content of 15 phr,the surface of the extruded wire has a fish scale appearance.The thermodynamic tests showed that the addition of carbon black raised the decomposition temperature and glass transition temperature of the composite compared to PLA70/MA30.The rheological tests demonstrated that the more carbon black is incorporated,the worse the flowability of composites.In terms of electrical conductivity,the volume resistivity of the composites decreased rapidly and then slowly with the increase of carbon black content,and the resistivity reached2.25×10~2Ω·cm when the carbon black content was 15 phr.The results of the electro-responsive shape memory test indicated that only the electro-responsive shape memory composites containing 13 phr and 15 phr carbon black underwent shape recovery under the application of a 60 V DC voltage,with the shape recovery rates of 43.6%and 54.2%,respectively.(3)The effects of FDM printing parameters on the mechanical properties of the prepared electro-responsive shape memory composite specimens were investigated.The results revealed that the best tensile strength was obtained at a nozzle temperature of 205℃,a printing speed of 45 mm/s,a layer thickness of 0.20 mm,and an alignment direction of 60°/150°;the best bending strength was obtained at a nozzle temperature of 205℃,a printing speed of 55 mm/s,a layer thickness of 0.20 mm,and an alignment direction of 0°/90°;The maximum compressive strength of specimens was obtained at a nozzle temperature of 205℃,a printing speed of 35 mm/s,a layer thickness of 0.36mm,and an alignment direction of 0°/90°. |
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