Effects of Filament Extrusion, 3D Printing and Hot-Pressing on Electrical and Tensile Properties of Poly(Lactic) Acid Composites Filled with Carbon Nanotubes and Graphene

Abstract

In this study, the effects of three processing stages: filament extrusion, 3D printing (FDM), and hot-pressing are investigated on electrical conductivity and tensile mechanical properties of poly(lactic) acid (PLA) composites filled with 6 wt.% of multiwall carbon nanotubes(MWCNTs), graphene nanoplatelets (GNPs), and combined fillers. The filaments show several decades’ higher electrical conductivity and 50–150% higher values of tensile characteristics, compared to the 3D printed and the hot-pressed samples due to the preferential orientation of nanoparticles during filament extrusion. Similar tensile properties and slightly higher electrical conductivity are found for the hot-pressed compared to the 3D printed samples, due to the reduction of interparticle distances, and consequently, the reduced tunneling resistances in the percolated network by hot pressing. Three structural types are observed in nanocomposite filaments depending on the distribution and interactions of fillers, such as segregated network, homogeneous network, and aggregated structure. The type of structural organization of MWCNTs, GNPs, and combined fillers in the matrix polymer is found determinant for the electrical and tensile properties. The crystallinity of the 3D printed samples is higher compared to the filament and hot-pressed samples, but this structural feature has a slight effect on the electrical and tensile properties. The results help in understanding the influence of processing on the properties of the final products based on PLA composites.

Characterization of Electrical Heating Performance of CFDM 3D-Printed Graphene/Polylactic Acid (PLA) Horseshoe Pattern with Different 3D Printing Directions

“…As mentioned previously, carbon nanomaterials have different electrical properties depending on their orientation [11]. In addition, the 3D printing directions and raster angles of the samples are determined by the direction in which the nozzle moves in the 3D printing process [5,[13][14][15]20]. In this study, the electrical surface resistivities of the PLA-HP samples made with different 3D printing directions were all indicated to be higher than 10 13 Ω/sq, which is confirmed by the insulating properties of PLA.…”

Essential Nanostructure Parameters to Govern Reinforcement and Functionality of Poly(lactic) Acid Nanocomposites with Graphene and Carbon Nanotubes for 3D Printing Application

“…In contrast, in the second line of Figure 5 , the 6 wt.% MWCNT-a nanocomposite shows a segregated network structure of interconnected carbon nanotubes or their small agglomerates, which form continuous pathways in the polymer matrix [ 7 , 22 ]. The segregated network structure is composed of regions rich and poor in nanofillers.…”

“…Meanwhile, the aggregated structure of GNP-a and GNP-b nanocomposites leads to almost unchanged Young’s modulus by increasing the filler content, however the ultimate strength and elongation are significantly compromised if the aspect ratio of GNPs is lower than 500. Obviously, the homogeneous network structure with high filler density, followed by the segregated network structure are preferable for MWCNT nanocomposites, for obtaining tensile properties enhancement, as they carry high levels of transferring stress across filler-polymer interfaces [ 22 , 23 , 24 ], in contrast to the aggregated structure of GNP nanocomposites.…”

“…It may also be assumed that the high degree of dispersion of the MWCNT-b, followed by MWCNT-a filler, determined as well by rheology, allow to express the unique mechanical strength of the individual carbon nanotubes and to transfer load to the polymer [ 22 , 24 ]. However, at high filler contents, e.g., 9 and 12 wt.%, the homogeneity of MWCNT dispersion could deteriorate, and this could destroy the homogeneity of the network structure, resulting in a decrease of tensile strength and elongation.…”

“…The printability window of the nanocomposite filament was identified to be similar to that of the neat PLA for the percolated nanocomposites, while at filler contents highly above the percolation threshold, the printability window is shifted towards higher printing rates. A comparison was made between the extruded filament, the 3D printed samples, and the hot pressed one [ 22 ] with respect to their electrical conductivity and tensile properties. It was found that the filament demonstrates 2–3 decades higher electrical conductivity and 50–150% higher tensile mechanical characteristics, compared to that of 3D printed and hot-pressed samples, due obviously to some preferential orientation of anisotropic carbon nanoparticles during the filament extrusion, which favor the percolation network.…”