| With the progress of science and technology and the increasing demand of social individuation,recently Three-Dimensional(3D)Printing technology has been guadually developed and widely used in the fields of biomedical science,vehicle,construction industry,aerospace and art design.Fused Deposition Modeling(FDM)is one of the trendiest and most commonly used 3D printing technologies,owing to its advantages of simple mechanism,handy manipulation,environmental protection,safety,low cost and so on.However,the commercially available filaments for FDM are mainly thermoplastic plastics such as Polylactic Acid(PLA),Acrylonitrile-Butadiene-Styrene(ABS),etc.,which still lack of high properties and functionalities,hindering the development and application of FDM technology for manufacturing.Since the“Four-Dimensional(4D)Printing technology”concept was proposed,the additive manufacturing of novel materials with high properties and multifunctionalities has become one of the actively researched areas.In this study,Polypropylene(PP)/Nylon 6(PA6)alloy was chosen as a base candidate for FDM;meanwhile,Maleic Anhydride-grafted Poly(Ethylene-Octene)(POE-g-MAH)was used as a modifying agent for the alloy.Then the 3D printing performance,shape memory effect and electrical conductivity of PP/PA6 alloy were systematically investigated,which is of great theoretical and practical significance to develop the diversity of filaments for FDM,to expand the functional application of FDM technology and to promote the development of 4D printing technology.PP and PA6 are not suitable for FDM due to their serious shrinkage and warpage problems.Firstly,PP/POE-g-MAH binary blends were prepared by melt blending in this study,and it was found out that the warpage was effectively improved with the decreasing mass ratio of PP and POE-g-MAH,but other properties were destroyed with too much POE-g-MAH as a result.On the basis of the binary blends,PP/POE-g-MAH/PA6 ternary blends were prepared by introducing PA6,and the relationship between the composition of the ternary blends and the 3D printing performance was studied systematically.The results showed that POE-g-MAH acted as a compatibilizer between non-polar PP and polar PA6.When PA6content was 30wt%,the printing effect became better and the warpage degree of 3D printed products based on the ternary blends decreased gradually with the decreasing mass ratio of PP and POE-g-MAH.Based on the certain mass ratio of 1.5,with the increase in PA6 content,the mechanical properties of printed products were greatly improved,and all of them showed excellent toughness,low warpage and shrinkage,improving surface quality and thermal properties;when PA6 content was up to 30wt%,the comprehensive 3D printing performance of the PP/PA6 alloy was optimal,and it was verified by printing the complex products that this alloy caters to requirements for application.3D printed products are able to change in structure,property,shape or function over time through introducing the fourth dimension of“time”on the basis of 3D printing.Based on the study of the 3D printing performance,the effects of component content and processing parameters on the heat-activated shape memory effect(SME)of PP/PA6 alloy were systematically studied in this study,and the shape memory mechanism of crystalline polymer alloy was preliminarily investigated.The results showed that when the certain mass ratio of PP and POE-g-MAH was 1.5,the shape fixity(R_f)of the printed DMA specimens decreased while the shape recovery(R_r)increased with the increase in PA6 content.When PA6 content was 30wt%,with the increase in the deformation temperature(T_d),R_f increased first and then tended to flatten,while R_r showed the tendency to increase first and then decrease;particularly,the specimen deformed at 175°C had suitable shape memory performance,and R_f and R_r were 90.0%and 89.1%respectively.In this case,PP with lower melting temperature(T_m)acted as a reversible phase for temporary network fixity,while PA6 with higher T_m acted as a fixed phase for permanent network maintenance;moreover,the compatibilizer POE-g-MAH had vital influence on forming physical cross-linked networks between molecular chains of PP and PA6.The infill orientation had a great impact on SME of PP/PA6alloy that 0°/0°orientation aligned with the applid force exbited a lower R_f and a higher R_r,while 90°/90°orientation perpendicular to the applied force showed completely contrary results,and the results of 45°/-45°orientation and 0°/90°orientation were between the orientations mentioned above.However,the infill density had little influence on SME.In addition,it was verified by adjusting component content and process parameters that the printed product with complex shapes fabricated by the infill orientation of 45°/-45°and 100%infill density exhibited a great SME,and it can meet the requirements for functional application.The PP/PA6 alloy and the flake graphite were respectively used as the polymer matrix and filler to prepare electrical conductive composites,then the through-plane electrical conductivity(TPEC)was further investigated in this study.The results showed that with the increase in graphite content,TPEC of PP/PA6 composites increased gradually.The anisotropy flake graphite orientated in the matrix along with the nozzle paths under different printing methods,which also affected the voids distribution of printed specimens based on PP/PA6composites,thus TPEC behaved as“Stand-3D Printing(SP)>Compression molding(CM)>Flat-3D Printing(FP)”with the same graphite content.In addition,the mechanical properties of printed specimens with 40wt%of graphite presented as“0°/0°orientation>45°/-45°orientation>90°/90°orientation”under different printing orientations.With the increasing graphite content,the adhesive strength between layers of printed products increased first and then decreased,but the warpage and shrinkage were not affected;moreover,the thermal properties showed a tendency to decrease first and then increase,and the heat-activated shape memory performance declined. |
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