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In recent years, conductive polymer nanocomposites have gained significant attention due to their promising thermoresistive and Joule heating properties across a range of versatile applications, such as heating elements, smart materials, and thermistors. This paper presents an investigation of semi-crystalline polyvinylidene fluoride (PVDF) nanocomposites with 6 wt.% carbon-based nanofillers, namely graphene nanoplatelets (GNPs), multi-walled carbon nanotubes (MWCNTs), and a combination of GNPs and MWCNTs (hybrid). The influence of the mono- and hybrid fillers on the crystalline structure was analyzed by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). It was found that the nanocomposites had increased amorphous fraction compared to the neat PVDF. Furthermore, nanocomposites enhanced the β phase of the PVDF by up to 12% mainly due to the presence of MWCNTs. The resistive properties of the nanocompositions were weakly affected by the temperature in the analyzed temperature range of 25–100 °C; nevertheless, the hybrid filler composites were proven to be more sensitive than the monofiller ones. The Joule heating effect was observed when 8 and 10 V were applied, and the compositions reached a self-regulating effect at around 100–150 s. In general, the inclusion in PVDF of nanofillers such as GNPs and MWCNTs, and especially their hybrid combinations, may be successfully used for tuning the self-regulated Joule heating properties of the nanocomposites. [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA) containing 12 wt% of nanofillers, such as multi‐walled carbon nanotubes (MWCNTs), graphene nanoplates (GNPs), is considered to obtain a non‐conventional filament suitable for additive manufacturing (AM) process with enhanced thermal and electrical properties. In details, three‐dimensional (3D) printed specimens obtained by means of fused deposition modeling (FDM) are experimentally characterized in terms of thermal conductivity and relative permittivity. The results are interpreted on the basis of the different features of the fillers and their interaction with the PLA, as evidenced by a morphological analysis. It is found better thermal transport by using two‐dimensional (2D) shape nanoparticles (GNPs) with an improvement of about 260% respect to the unfilled polymer most likely due to its favorable arrangement and the lower thermal boundary resistance between the two phases, matrix, and fillers. Differently, mono‐dimensional filler like MWCNTs is to be preferred in order to obtain higher value for the relative permittivity, due to the enhancement of the interfacial polarization and the presence of functionalized groups. It is found a value of 5.35 × 103 much greater than that of 3.7 measured for pure PLA. Given the good combined thermal and dielectric properties, such materials are promising candidates for packaging applications with electromagnetic (EM) shielding capability. [ABSTRACT FROM AUTHOR]

Polymer composites filled with high thermal and electrical conductivity nanofillers show enhanced thermo‐electric properties which encourage their use in heat transfer applications. In the present study, nanocomposites based on polylactic acid (PLA) containing up to 9 wt% of multi‐walled carbon nanotubes (trade name: N7000) and graphene nanoplates (trade name: TNIGNP) are produced via melt compounding and then morphologically, electrically, and thermally investigated. The results are correlated to the different characteristic of the fillers and their interaction with the PLA. At the highest investigated filler concentration, an electrical conductivity of about 2 S m–1 and a thermal conductivity of 0.725 W m–1 K–1 are measured respectively for nanocomposites based on N7000 and TNIGNP, which are decisively higher than the values measured for unfilled PLA (5.9 ×∙10–2 S m–1 and 0.205 W m–1 K–1). Moreover, multiphysics simulations are performed on the best performing nanocomposites for evaluating their thermo‐electric properties when an electrical heating or a direct heat flux are applied. [ABSTRACT FROM AUTHOR]

Resistivity and low‐frequency (10 Hz–20 kHz) noise characteristics of composite materials with multi‐walled carbon nanotubes (MWCNTs) of different surface treatment, that is, MWCNTs covered with bisphenol‐A based liquid epoxy resin (epoxy‐grafted) and polyethylene polyamine (amino‐grafted), have been carried out over the temperature range from 73 to 380 K. The resistivity of the investigated materials decreases with temperature increase up to 250 K; at higher temperatures polymer matrix expansion leads to the resistivity increase and above 340 K the conductivity in the matrix becomes significant. Low‐frequency noise spectra of the investigated materials are 1/fα‐type and noise spectral density is proportional to the squared voltage. The observed fluctuations in the investigated materials are resistance fluctuations. The conduction in the investigated composites is caused by tunneling inside and between MWCNTs controlled by charge carrier capture and release processes in localized states. MWCNT's surface treatment by polyethylene polyamine leads to the larger density of surface states what causes lower resistivity and more intensive low‐frequency fluctuations. POLYM. COMPOS., 39:E1224–E1230, 2018. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Poly(lactic) acid (PLA) film with 2 wt% mixed carbon nanofillers of graphene nanoplates (GNPs) and multiwall carbon nanotubes (MWCNTs) in a weight ratio of 1:1 with impurities of fullerene and carbon black (CB) was produced by layer-to-layer deposition and hot pressing. The release of carbon nanoparticles from the film was studied at varying time–temperature conditions and simulants. Migrants in simulant solvents were examined with laser diffraction analysis and transmission electron microscopy (TEM). Film integrity and the presence of migrants on the film surfaces were visualised by scanning electron microscopy (SEM). The partial dissolution of PLA polymer in the solvents was confirmed by swelling tests and differential scanning calorimetry (DSC). Nanoparticle migrants were not detected in the simulants (at the LOD 0.020 μm of the laser diffraction analysis) after migration testing at 40°C for 10 days. However, high-temperature migration testing at 90°C for 4 h provoked a release of GNPs from the film into ethanol, acetic acid and oil-based food simulants. Short carbon nanotubes were observed rarely to release in the most aggressive acetic acid solvent. Obviously, the enhanced molecular mobility at temperatures above the glass transition and partial dissolution of PLA polymer by the food simulant facilitate the diffusion processes. Moreover, shape, size and concentration of nanoparticles play a significant role. Flexible naked GNPs (lateral size 100–1000 nm) easily migrate when the polymer molecules exhibit enhanced mobility, while fibrous MWCNTs (> 1 μm length) formed entangled networks on the film surfaces as the PLA polymer is partly dissolved, preventing their release into food simulants. The impurities of fullerenes and CB (5–30 nm) were of minor concentration in the polymer, therefore their migration is low or undetectable. The total amount of released migrants is below overall migration limits. [ABSTRACT FROM PUBLISHER]

Polymer composites containing nanofillers are among the most promising research fields for advanced materials. Carbon nanotubes (CNTs) are considered an ideal inclusion for polymer nanocomposites due to superior electrical, thermal, and mechanical properties which can be explained with the unique atomic structure of the nanotubes. Multi-walled carbon nanotubes (MWCNTs) are used as extremely strong nano-reinforcements for composites to produce a new generation of fiber-reinforced plastics with better application properties. In this experimental study, PP/MWCNT polymer nanocomposites with nanofiller concentrations in the range of 0.05–1 wt% MWCNT and the maleic anhydride amount from 0 to 7.5 wt% were investigated. An experimental study is conducted to examine the influence of MWCNT and compatibilizer contents on the thermal, mechanical, and viscoelastic properties of polypropylene (PP)/MWCNT nanocomposites. Extruded samples are characterized by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and microindentation tests. Standard Berkovich indentation test determined by residual surface impression method based on load–displacement curves was used. DSC results show an increase in the crystallization temperature of maleinated PP with the increase of MWCNT contents proving the nucleation effect of CNTs. DMTA results prove the good modification properties of maleic anhydride in MWCNT/PP nanocomposites at 0.05 wt% nanotubes concentration. Elastic moduli, obtained from both DMTA and microindentation, are compared to investigate the difference between surface and bulk mechanical properties of nanocomposites with increasing nanotubes concentration. Measured values of elastic moduli are within comparable ranges, but the absolute values are different. [ABSTRACT FROM AUTHOR]

Polymer composites containing nanocarbon fillers are under intensive investigation worldwide due to their remarkable electromagnetic properties distinguished not only by components as such, but the distribution and interaction of the fillers inside the polymer matrix. The theory herein reveals that a particular effect connected with the homogeneity of a composite manifests itself in the terahertz range. Transmission time-domain terahertz spectroscopy was applied to the investigation of nanocomposites obtained by co-extrusion of PLA polymer with additions of graphene nanoplatelets and multi-walled carbon nanotubes. The THz peak of permittivity's imaginary part predicted by the applied model was experimentally shown for GNP-containing composites both below and above the percolation threshold. The physical nature of the peak was explained by the impact on filler particles excluded from the percolation network due to the peculiarities of filler distribution. Terahertz spectroscopy as a versatile instrument of filler distribution diagnostics is discussed. [ABSTRACT FROM AUTHOR]

The aging, annealing, and reprocessing of the biodegradable poly (lactic) acid (PLA) based composite films incorporating graphene and carbon nanotubes were investigated in this work. Various monofiller and bifiller nanocomposite films with 6 wt.% filler content were produced by a solution-phase technique followed by extrusion. The freshly produced films were compared with the aged films after 18 months of shelf life in a room environment. The effects of aging, annealing, and melt reprocessing on the crystalline structure, the thermal stability, the hardness, and Young's modulus were analyzed by differential scanning calorimetry (DSC), TGA, and nanoindentation methods. The fresh and the aged samples were found to have semi-crystalline materials with 3%–7% crystallinity, while the crystallinity was significantly enhanced to 34%–38% by annealing at 80 °C and subsequent slow cooling. A good dispersion was observed in the bifiller films with filler ratios of 4.5:1.5 and 1.5:4.5 [graphene nanoplatelets (GNP) to carbon nanotubes (CNT)], which affected the crystallization processes. The reprocessing at 200 °C followed by fast cooling resulted in amorphous films, which significantly reduced the hardness and Young's modulus. The nanoindentation properties were dependent on the dispersion of nanofillers at the surfaces. The efficiency of annealing and reprocessing for the recovery and the reuse of aged nanocomposite films is discussed herein. The paper underlines that properties of the nanocomposites under investigation were influenced not only by the composition, the chemical nature of the added filler, and the processing condition, but also by the aging processes, which in turn depended on the type of nanopartcles added to PLA and the compositions. The paper provides valuable information for selection of material and processing conditions. [ABSTRACT FROM AUTHOR]

Abstract 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. [ABSTRACT FROM AUTHOR]