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In this work, nanocomposites of poly(lactic) acid incorporating two kinds of highly thermal conductive graphene nanoplatelets differing in size and purity were fabricated by melt extrusion. Nanocomposites of 1.5÷9 wt% filler contents were characterized using thermal constant analysis, X-ray diffraction and infrared spectroscopy to clarify their functionality, related to composition and morphology. The thermal conductivity increases linearly with increasing the filler concentration, but it is essentially determined by the size and purity of fillers and thermal interfacial resistance.

In this study, rheology, structure, and mechanical properties are investigated in point of their enhancement by incorporation of graphene nanoplates (GNP) and multiwall carbon nanotubes (MWCNTs) in poly (lactic acid) matrix. PLA-based nanocomposites with 6% total amount of GNP and MWCNT in different combination, produced by melt extrusion method, are investigated. Incorporating of GNP to PLA at the binary nanocomposites and GNP and MWCNT (i.e. increasing of GNP concentration and an analogous decrease of MWCNT concentration) to PLA at the ternary nanocomposites leads to reduction of the linear viscoelastic range and critical strain. For pure molten polymer, a terminal-like behavior has been observed in low frequencies and the slope n is proportional to 2 (G0 ∼ ω n). From the results, we can observe that as the GNP concentration increases, n decreases gradually. All samples are characteristic as a “gel” type structure, which is usually associated with reaching the percolation threshold. We demonstrated that XRD can be used as a quick and unambiguous method to determine the homogeneity of the nanocomposites in terms of carbon filler dispersion in a polymer matrix. GNP and MWCNT addition improved the impact strength of PLA composites, which confirm the successful reinforced effect on polymer matrix of both fillers.

The surface properties of nanofillers and surface/interfacial interactions between fillers and matrix play crucial roles in the control of the properties of composites, especially considering hybrid materials used in biomedical, electronic and energy applications. In the present work, we investigate the surface properties of mono-filler and bi-filler composites of poly (lactic acid) (PLA) with graphene nanoplatelets (GNP) and multi-walled carbon nanotubes (MWCNTs) prepared by melt extrusion method. Zeta potential, contact angle (surface energy), Raman spectroscopy, and atomic force microscopy were used to evaluate the interaction between PLA matrix, GNP and MWCNTs particles, and also to characterize filler-polymer composite properties at the surfaces of the film. The effect of filler loading in the GNP/PLA and GNP/MWCNT/PLA composite films surface properties was investigated using surface Zeta potential by streaming and Contact angle measurements. The results suggest that the surface characteristics of the composite film may be synergistically tuned by incorporation of GNPs and MWCNTs with controlling the filler contents and filler combinations.

In this study, the structure, electrical and thermal properties of ten polymer compositions based on polylactic acid (PLA), low-cost industrial graphene nanoplates (GNP) and multi-walled carbon nanotubes (MWCNT) in mono-filler PLA/MWCNT and PLA/GNP systems with 0–6 wt.% filler content were investigated. Filler dispersion was further improved by combining these two carbon nanofillers with different geometric shapes and aspect ratios in hybrid bi-filler nanocomposites. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy exhibited uniform dispersion of nanoparticles in a polymer matrix. The obtained results have shown that for the mono-filler systems with MWCNT or GNP, the electrical conductivity increased with decades. Moreover, a small synergistic effect was observed in the GNP/MWCNT/PLA bi-filler hybrid composites when combining GNP and CNT at a ratio of 3% GNP/3% CNT and 1.5% GNP:4.5% CNT, showing higher electrical conductivity with respect to the systems incorporating individual CNTs and GNPs at the same overall filler concentration. This improvement was attributed to the interaction between CNTs and GNPs limiting GNP aggregation and bridging adjacent graphene platelets thus, forming a more efficient network. Thermal conductivity increases with higher filler content; this effect was more pronounced for the mono-filler composites based on PLA and GNP due to the ability of graphene to better transfer the heat. Morphological analysis carried out by electron microscopy (SEM, TEM) and Raman indicated that the nanocomposites present smaller and more homogeneous filler aggregates. The well-dispersed nanofillers also lead to a microstructure which is able to better enhance the electron and heat transfer and maximize the electrical and thermal properties. The obtained composites are suitable for the production of a multifunctional filament with improved electrical and thermal properties for different fused deposition modelling (FDM) 3D printing applications and also present a low production cost, which could potentially increase the competitiveness of this promising market niche.

This paper aims to address current limitations of 3D printed conductive materials through the development of a novel formulation of a thermoplastic composite. In particular, a conductive filament suitable for three-dimensional printing is obtained on the basis of Polylactic acid (PLA) filled with two types of highly conductive nano-carbon materials, i.e. multi-walled carbon nanotubes (MWCNTs), graphene nanoplates (GNPs) and a combination of both fillers (MWCNT/GNP). A systematic rheological and electrical characterization of the resulting nanocomposites is presented. Viscoelastic properties and rheological percolation threshold are determined for the binary and ternary composites and related to the size of nanoparticles. Comparable values for the percolation threshold are found by means of rheological and electrical studies. Low electrical percolation thresholds and high values of the electrical conductivity of the order of S/m are achieved for the investigated formulations. At the highest filler loading (i.e. 12 wt%) the electrical conductivity reaches the value of 4.54 S/m, 6.27 S/m and 0.95 S/m for the composites based on MWCNTs, GNPs and multiphase system, respectively. These results, together with the good stability shown by the nano-reinforced PLA in the frequency range [100 Hz-1MHz] make these composites promising candidates for 3D printed conductive devices for electromagnetic (EM) applications.

Graphene/polymer nanocomposites are the latest trends in materials science in the recent years, but the technology of their preparation plays a crucial role in obtaining reliable materials with repeatable and enhanced properties. Up to now, there are many unresolved problems in controlling the dispersion of the graphene filler and the corresponding influence on the properties of the final nanocomposite materials. In the present study, we apply rheological methods for controlling the quality of the graphene dispersion. We prepare and characterize epoxy/graphene nanodispersions with graphene contents varying from 0.05 to 1 wt% and explore the effect of different mixing regimes on the dynamic moduli and viscosity, thus assessing the degree of the dispersion. The rheological percolation threshold and relaxation time spectra are determined, in order to evaluate the internal structure of the nanodispersions. The relaxation spectrum is highly efficient to probe the effects of interfaces and interconnections on the relaxation dynamics of molecules in nanodispersions. Rheological results combined with transmission electron microscopy (TEM) observations confirm that the low frequency dynamic viscosity and moduli strongly increase, with increasing the degree of dispersion due to the exfoliation of graphene sheets. The rheological percolation threshold was found at very low concentration depending from the processing conditions. The weight of the relaxation spectra is strongly shifted to higher values, compared to the neat epoxy resin and this effect is much stronger around and above the rheological percolation threshold. ©2017Applied Rheology.