Mechanical and thermoelectric properties of fused deposition modeling (FDM) fabricated ABS and CABS-ZNO composite

Abstract

The mechanical and thermoelectric properties of fused deposition modeling (FDM) fabricated acrylonitrile butadiene styrene (ABS)/ zinc oxide (ZnO) and conductive acrylonitrile butadiene styrene (CABS)/ZnO were studied. The ease of processing, low cost and high flexibility of FDM technique are strong advantages compared to other techniques for thermoelectric polymer composite fabrication. This work focuses the effect of printing spacing (0 mm, 0.25 mm, 0.5 mm), printing pattern (line and rectilinear) and ZnO filler loading on the tensile, dynamic mechanical and thermoelectric properties of CABS/ZnO composites fabricated via FDM technique. A Monte Carlo prediction model was developed to predict the materials’ tensile modulus and conductivity under different printing parameters. The aim was to reduce the experimental period and optimize the parameters for desired properties. The incorporation of precoated fillers in ABS matrix improved the tensile strength and Young’s modulus of the composites by 90 % and 13 % respectively. Density and porosity results proved that the precoating process reduced the voids within the composites. Elongation at break was also improved in FDM fabricated samples with precoated fillers compared with non-precoated fillers. Reduce the printing spacing improved the properties of the composites. Maximum tensile strength of 28.24 MPa was observed for ABS/ZnO sample printed with the combination of line pattern and 0 mm printing spacing. Line pattern which exhibited a more consistent extruder motion allowed for more consistent adhesion between layers, and thus better tensile properties. The reduction of the stiffening effect of fillers at 5 mm printing spacing resulted in lower storage modulus but higher loss modulus and damping factor. Change from 5 mm to 0 mm printing spacing brought 90 % and 13 % improvement on electrical conductivity and Seebeck coefficient for CABS/ZnO composite printed with line pattern. The thermal conductivity improved 6 % with decreasing printing spacing, resulted from better heat transfer when the air gap between filament strands was getting smaller. A relatively small change in thermal conductivity when compared with their electrical conductivity and Seebeck coefficient resulted in high figure of merit (ZT), 5.7 x 10-5. Tensile strength and Young’s modulus of ABS composites increased 22 % and 18 % respectively with 2.8 vol.% filler loading. However, the poor adhesion between carbon black, ABS and ZnO resulted in low tensile strength and modulus of the CABS composites. Increase of storage modulus was associated to the stiffness improvement incorporation with the filler addition. The loss modulus and damping factor were lower for composites with higher filler loading. With the addition of 2.8 vol.% ZnO fillers, the semiconducting behavior of CABS has tremendously improved by 100 % and the ZT value increased to 3.55 x 10-6, which was > 500 times greater than CABS without filler (5.57x10-9). Minor discrepancy (± 10 %) was observed in predicting the thermal conductivity, electrical conductivity and Young’s modulus with different printing spacing and pattern indicated that the prediction models were well fitted to the experimental data. From the results obtained, FDM fabricated CABS/ZnO showed much potential as a promising candidate for thermoelectric application and the developed model was recommended for use in optimizing FDM parameter for desired properties.