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Ethylene–propylene–diene monomer (EPDM)-based composites including four different types of graphene nanoplatelets (GnPs) were prepared to evaluate the size effects of GnPs in terms of both specific surface area and lateral size on the morphological, mechanical, and viscoelastic properties, swelling ratio, crosslink density, and oxygen permeability. EPDM-based hybrid composites with GnPs and carbon black (CB) fillers were prepared, with the concentrations of 20 and 50 phr of CB and GnPs up to 7 phr. All samples were prepared using the melt mixing method, followed by compression molding. The specific surface area of GnPs is a more important key factor for mechanical and viscoelastic properties than its lateral size. The presence of GnPs leads to a decrease in the swelling ratio and oxygen permeability of the matrix while an increase in the crosslinking density. For a given specific surface area of GnPs (170 m2/g) and the same thickness (5 nm), the optimum lateral size for mechanical properties, swelling ratio, and crosslinking density is about 30 µm. There is a distinct synergic effect on the mentioned properties when hybrid fillers are used. For hybrid composites, the optimum total and each filler concentration are found to be important for achieving the best performance in terms of mechanical properties, swelling ratio, and crosslink density. [ABSTRACT FROM AUTHOR]

High-density polyethylene (HDPE)-based hybrid nanocomposites containing graphene nanoplatelets (GnPs) and multiwall carbon nanotubes (MWCNTs) were fabricated using melt mixing followed by compression molding. The influences of size and weight ratio of both carbon-based nanofillers on the electrical, thermal, and mechanical properties of hybrid nanocomposites were evaluated. This study proves that the size and weight ratio of carbon-based nanofillers play a critical role in determining these properties. The optimum size and weight ratio of GnPs and MWCNTs are determined at the maximum achieved enhancement for each property. The HDPE-based nanocomposites containing GnPs with larger surface area and MWCNTs with higher aspect ratio display the highest electrical conductivity at GnPs/MWCNTs weight ratio of 2/3. The combination of GnPs with larger surface area and MWCNTs with lower aspect ratio provides the maximum Young's modulus enhancement of hybrid nanocomposites at 1/4 weight ratio of GnPs and MWCNTs. The nanocomposite containing GnPs with the largest lateral size and MWCNTs with a higher aspect ratio at a 3/2 weight ratio exhibits the highest thermal conductivity. Also, at around the percolation threshold of GnPs, the incorporation of MWCNTs with larger aspect ratio into the HDPE-based nanocomposites containing GnPs with the largest lateral size shows a distinct synergic effect on the thermal conductivity and Young's modulus, while an additive effect on the electrical conductivity and thermal stability. [ABSTRACT FROM AUTHOR]

In this study, ethylene-propylene-diene monomer (EPDM) composites reinforced with graphene nanoplatelets (GnPs) and carbon black (CB) fillers and their hybrid combinations of various contents were prepared and examined. The size effect (lateral size and specific surface area) of GnPs and filler hybridization effects between GnPs and CB on the electrical and thermal conductivity of the EPDM composites were examined. The lateral size of GnPs is a more decisive factor in the thermal conductivity of composites than their specific specific surface area, and GnPs with a higher lateral size give better thermal conductivity. The addition of GnPs with a high lateral size and low specific specific surface area results in an almost one-fold increase in thermal conductivity. After a certain filler concentration, a synergistic effect of GnPs and CB on the thermal conductivity can be observed. Up to 20 phr GnPs, the specific surface area or lateral size of GnPs has a slight effect on the electrical conductivity of EPDM/GnPs composites. Higher electrical conductivity was achieved when hybrid fillers, 50 phr CB and 7 phr GnPs with higher lateral size were used for composite preparation. The morphology of the composite samples and the dispersion of all used fillers and hybrids were examined using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). [Display omitted] • GnP fillers with the same surface area and thickness but different lateral size have been used in EPDM composites. • The lateral size of GnPs is a more decisive factor in thermal conductivity of composites than their specific surface area. • GnPs with a higher lateral size give better thermal conductivity. • After a certain filler concentration, it can be observed to a synergic effect of GnPs and CB on the thermal conductivity. • The size of GnPs has a slight effect on the electrical conductivity of EPDM/GnPs nanocomposites. [ABSTRACT FROM AUTHOR]

In order to elucidate the mechanism of enhancement of heat transfer in polymer composites, in this work, we investigated two types of polymer-carbon filler composites. This investigation was made using scanning thermal microscopy (SThM) with the Wollaston microprobe operated in active mode as a function of the carbon filler weight fraction within the polymer matrix. Samples consist of high-density polyethylene (HDPE) filled with 50 µm expanded graphite (EG) and polyvinylidene difluoride (PVDF) containing multiwall carbon nanotubes (MWCNTs). For HDPE/EG samples, SThM images allow the detection of zones with a thermal conductance larger than that of the matrix for the highest studied filler concentration. These zones correspond to EG filler agglomerations within the polymer and explain the observed enhancement of the thermal conductivity k of the HDPE/EG composite. For PVDF/MWCNTs samples, it is found that k increases from 0.25 W m−1 K−1 for pristine PVDF to 0.37 W m−1 K−1 for PVDF nanocomposites filled with 8 wt. % MWCNTs. This k variation vs filler concentration is found in good correspondence with that of the β phase relative percentage in the PVDF nanocomposites. This suggests that the observed heat transfer enhancement is rather due to the formation of β phase for PVDF/MWCNTs samples, resulting from the addition of MWCNTs than the addition of MWCNTs itself. Thus, tuning the thermophysical properties of polymer-based nanocomposites can establish new design laws to confer them specific thermal properties. [ABSTRACT FROM AUTHOR]