Addition Of Carbon Black Research Articles

Study of Polymer-Coating on Various Types of Carbon Supports to Enhance Platinum Utilization Efficiency in Polymer Electrolyte Membrane Fuel Cell Electrocatalysts

Polymer electrolyte membrane fuel cells (PEMFCs) have been receiving ample attention as an efficient and clean power source for stationary and automotive applications.1 One of the challenges for commercialization of PEMFCs is to minimize the amount of Platinum (Pt) to lower the cost of PEMFC. Pt is the most stable and active catalyst for oxygen reduction reaction (ORR).2 Incorporation of non-precious metals and decreasing the catalyst particle size are common methods to reduce the amount of Pt used in PEMFC. However, these methods involve dissolution of non-precious metals in acidic condition3 and agglomeration of small sized Pt4, resulting in decreased Pt utilization. Therefore, improvement of Pt utilization efficiency is required. Optimizing catalyst structure by increasing number of reaction sites is a promising strategy to improve the Pt utilization efficiency. One approach is increasing mass diffusion (oxygen, proton) by selecting a non-porous carbon support like acetylene black (AB).5 However, Pt durability and utilization are limited due to lack of anchoring sites for Pt particles in AB.6 Another approach is optimizing ionomer/carbon ratio. However, recent high-resolution transmission electron microscopy studies suggest that the ionomer coverage in the electrode may be rather inhomogeneous.7 In this study, we demonstrate a novel approach to improve Pt utilization efficiency in PEMFC by preventing deposition of Pt particles into interior pores of carbon support and simultaneously providing homogeneous ionomer; Nafion coverage. This approach involves polymer coating onto carbon blacks (CBs). Polybenzimidazole (PBI) is used as the surface coating material of CB where PBI interacts with CB via π-π and acid-base interactions. It is reported that PBI coating works as the micropore capping agent of CB.8 Therefore, PBI coating can reduce number of Pt particles deposited into geometrically restricted areas of CB. Moreover, PBI coating may trigger a homogeneous Nafion coverage due to the acid-base interaction between Nafion and PBI concurrently. Three morphologically different CBs; Vulcan, Ketjen black (KB) and AB were used to investigate the Pt utilization efficiency in polymer coated CBs. The PBI coating onto CB was easily done by addition of CB into PBI dissolved N,N-dimethylacetamide and 1 hr sonication to the mixture to prepare Vulcan/PBI, KB/PBI and AB/PBI. Then Pt nano-particles were deposited via polyol reduction to prepare Vulcan/PBI/Pt, KB/PBI/Pt and AB/PBI/Pt and compared with their non-coated Vulcan/Pt, KB/Pt and AB/Pt. AB/PBI/Pt shows homogeneous Pt dispersion over AB/Pt due to the presence of binding sites through coordination of Pt with imidazole groups in PBI as an additional advantage. The micropore density of CBs is increasing in the order of AB < Vulcan < KB. Power density of CB/Pts was decreased in the following order; AB/Pt < Vulcan/Pt < KB/Pt, consistent with the order of increasing micropore density. The lower performance of KB/Pt is due to the decreased number of accessible Pts for the electrochemical reaction especially for ORR5. Interestingly, power densities of CB/PBI/Pts were higher than that of respective CB/Pts. The higher power density of CB/PBI/Pt can be attributed to the reduced inaccessible amount of Pt deposited into the micropores of CB and the reduced protonic resistance in the catalyst layer due to the homogeneous Nafion layer.9 Furthermore, power densities of CB/PBI/Pts were increasing in the order of KB/PBI/Pt < Vulcan/PBI/Pt < AB/PBI/Pt. The highest performance of AB/PBI/Pt is believed to be due to lower mass transfer limitation in the catalyst layer which is caused by the lower pore density of AB/PBI along with the uniform Nafion coverage. References Kibsgaard, J.; Gorlin, Y.; Chen, Z.; Jaramillo, T. F., J. Am. Chem. Soc. 2012, 134, 7758.Nørskov, J. K.; Rossmeisl, J.; Logadottir, A.; Lindqvist, L.; Kitchin, J. R.; Bligaard, T.; Jónsson, H., J. Phys. Chem. B 2004, 108, 17886.Colón-Mercado, H. R.; Kim, H.; Popov, B. N., Electrochem. Commun. 2004, 6, 795.Tang, L.; Han, B.; Persson, K.; Friesen, C.; He, T.; Sieradzki, K.; Ceder, G., J. Am. Chem. Soc. 2010, 132, 596.Park, Y.-C.; Tokiwa, H.; Kakinuma, K.; Watanabe, M.; Uchida, M., J. Power Sources 2016, 315, 179.Badam, R.; Vedarajan, R.; Matsumi, N., Chem. Commun. 2015, 51, 9841.Lopez-Haro, M.; Guétaz, L.; Printemps, T.; Morin, A.; Escribano, S.; Jouneau, P. H.; Bayle-Guillemaud, P.; Chandezon, F.; Gebel, G., Nat. Commun. 2014, 5, 5229.Fujigaya, T.; Hirata, S.; Berber, M. R.; Nakashima, N., ACS Appl. Mater. Interfaces 2016, 8, 14494.Jayawickrama, S. M; Han, Z. et al., in review.

Processing of solid state sintered α-SiC ceramics with carbon-black addition

The efficient removal of surface silica layer from SiC particles by the addition of carbon is required for solid state sintering (SSS) of SiC ceramics. While wax-based organics are generally utilized as carbon source in many commercial SSS-SiC ceramics, carbon black powders with high specific surface area (SSA) are potential alternatives as carbon source, which can be dispersed in ceramic slurries directly without needing any additional pyrolysis reactions. In this study, carbon black powders were utilized as carbon source for sintering of SiC. The effect of particle size of carbon black powders on densification and microstructural development during pressureless and spark plasma sintering (SPS) were investigated. It was observed that while the density of the SiC samples increased with increasing SSA of carbon black powders, complete densification was not achieved for all samples in case of pressureless sintering due to the flaws originated by carbon black segregation on granule surfaces. SPS was found an effective sintering method for the elimination of such flaws and SiC ceramics were sintered to 100% of theoretical density independent from the particle size of the carbon black powders in this sintering technique.

Creep Resistance of Polyethylene-based Nanocomposites

The purpose of this work is to investigate the effects of carbon black (CB), carbon nanotubes (CNTs) and nanoclay sheets addition on the creep behavior of polyethylene-based nanocomposites synthesized with an in-house processing method. A blend of 75 wt.% UHMWPE and 25 wt.% HDPE, abbreviated to U75H25, was used as the hybrid PE matrix to accommodate the nanofillers. A 0.5 wt.% of CB, CNTs or nanosheets clay was embedded separately into the blend matrix in order to improve the creep resistance. The scanning electron microscope (SEM) and transmission electron microscope showed that the nanofillers were homogeneously dispersed in the U75H25. The addition of just 0.5 wt.% nanoclay resulted in a significant increase in the creep resistance of the polyethylene blend. Conversely, the addition of CB or CNTs caused a reduction in the creep resistance. The embedding of CNTs into the matrix resulted in creep behavior almost close to the creep behavior of pure UHMWPE. The Burger’s model was employed to understand the effect of the nanoparticle addition on the creep mechanism.

Study of hydration and hardening processes of self-sensing cement-based materials with carbon black content

In this paper was assessed the influence of carbon black (CB) powder on the hydration and hardening processes of Portland cement (PC)-based materials; this type of materials is designed to be used as cement-based sensors in structural or pavement health monitoring. The rate of PC hydration and hardening processes is influenced by the amount of CB addition, with direct consequences on some properties of these materials, i.e., water for normal consistency and setting time. These results coupled with those obtained by thermal and X-ray diffraction analyses suggest a delaying effect of PC hydration and hardening processes in the presence of carbon black powder, most likely as a result of CB nanoparticles high adsorbent surface. Compressive strength values of PC mortars with CB content up to 1 mass%, assessed after 28 days of hardening, are comparable with those of PC mortars; thus, these materials can be successfully used in construction.

Tuning the properties of functional adhesives with hybrid nanofillers for structural health monitoring

ABSTRACT Monitoring the damage of adhesive joining could avoid potential accidents in multimaterial lightweight vehicles. Different from the additional sensors, a kind of functional adhesives with hybrid fillers of carbon nanotubes (CNTs) and carbon black (CB) was developed, and verified by in-situ sensing of adhesion damage in single-lap shear joints (SLAJ) of composite-to-metal. The influences of the total weight percent of fillers and relative ratio of CNT-to-CB on the mechanical, piezoresistive and the microwave absorption performance of SLAJ were investigated experimentally. The addition of both CNTs and CB increases the cohesive shear strength but decreases the failure strain at the same time. For the formula of total 2wt.% fillers and CNT:CB = 1:3, the shear strength of SLAJ is nearly 37.50% higher than that of pure adhesives. Both CNT and CB lead to the reduction of electrical resistivity. When approaching the failure strain, the electric resistances for all CNT-to-CB ratios increase sharply. For this formula, the relative electric resistance ratio is 29% at strain 0.038, close to the failure strain. The adhesives with this formula also show a better microwave absorption. This research shows a potential application of adhesives with hybrid nanoparticles in lightweight and low-cost structural health monitoring.

Metakaolin/carbon black geopolymer with enhanced electrical properties

Alkali-activated binders represent a promising material for composites with self-sensing properties both for their lower environmental impact and ability to transfer the electric charge through ionic mobility. Metakaolin geopolymers with carbon black conductive admixture up to 4% were produced to test their electrical properties, mechanical properties and microstructure. Electrical capacitance, resistance and relative permittivity were determined via impedance spectroscopy analysis. Notable enhancement of all mentioned electrical parameters was registered from 2% carbon black content, especially at lower frequency range. Another carbon black addition was rather unreasonable due to only slight improvement in electrical properties but significant drop of compressive strength and unfavourable changes in pore volume and binder microstructure determined by mercury intrusion porosimetry and electron microscope.

Properties of carbon black-PEDOT composite prepared via in-situ chemical oxidative polymerization

AbstractA new conductive composite composed of nanoscale carbon black (CB) and poly(3,4-ethylenedioxythiophene) (PEDOT) was prepared by a simple in-situ polymerization. The morphology of the composite was characterized by scanning electron microscopy and transmission electron microscopy. The structure and thermal stability were examined by Fourier transform infrared spectroscopy and thermal gravimetric analysis, respectively. The results indicated that the addition of CB improved the agglomerated state of PEDOT. On the one hand, CB effectively hindered the agglomeration of PEDOT during the polymerization. Thus, the obtained CB-PEDOT composite dispersed well in solution, which can facilitate the reprocessing of CB-PEDOT. On the other hand, CB covered most of the surface of PEDOT, which enhanced the electrical conductivity of CB-PEDOT. Furthermore, the interfacial interaction between CB and PEDOT improved the thermal stability of CB-PEDOT. The findings of this research suggest that CB can replace polyelectrolyte poly(styrenesulfonic acid) (PSS) to achieve reprocessable materials for certain applications.

PEGylated carbon black as lubricant nanoadditive with enhanced dispersion stability and tribological performance

Abstract Poly(ethylene glycol) (PEG) chains were covalently grafted onto carbon black (CB) using a PEG-terminated trimethoxysilane, yielding PEGylated CB additives (CB-SiPEG) with different SiPEG contents. Unlike pristine CB, CB-SiPEG was readily dispersed in PEG200 base oil, with CB-SiPEG hydrodynamic particle sizes being considerably smaller than those of pristine CB. At optimal SiPEG content, friction coefficient and specific wear rate in ball-on-disk tribometer tests were reduced by 35% and 67% respectively, with 1% wt. CB-SiPEG compared to PEG200 alone. In contrast, pristine CB, alone or with unbound SiPEG, did not show friction-reducing or antiwear capacity. Disk analysis supports CB-SiPEG surface deposition forming a protective tribofilm. Hydrodynamic particle size and lubricating performance of CB-SiPEG/PEG200 blends were preserved after 6 months, indicating high dispersion stability.

Electro-Responsive Green Gels for Lower Environmental Impact Shale Gas Extraction

In this work, carbon black (CB) is added in small amounts (3–10% w/w) to green aqueous dispersions based on sodium oleate, guar gum, sodium hyaluronate, or hydroxypropyl cellulose gels to enhance their stability against mechanical and thermal stresses and to provide electric responsiveness to an external voltage. Rheology, optical microscopy, small angle X-ray scattering, and conductivity measurements are performed to compare the properties of CB-enriched formulations to those of pristine dispersions. Our results demonstrate that even small amounts of CB are able to confer interesting physicochemical properties to these formulations: a remarkable increase in the viscosity of at least 1 order of magnitude is observed for all systems even at high temperature (up to 60 °C) upon CB addition, indicating that carbonaceous particles play a structuring role for the polymeric network. Furthermore, the application of an external voltage of 30 V for 60 min to CB-containing formulations imparts a significant electric responsiveness to the systems, allowing the modification of their rheological behavior. The CB-loaded formulations can be recycled at least three times. All these results suggest that CB can be effectively used as an alternative green additive to enhance the mechanical and thermal stabilities of the formulations and that its addition can be a feasible way to easily tune the properties of viscoelastic materials, thereby avoiding the use of toxic or potentially dangerous chemicals. The possibility of achieving remote control of mechanical and thermal properties of viscoelastic formulations significantly expands the horizon of their potential applications, for example, in the field of shale gas extraction.

Soild-phase synthesis of MgAl2O4 powder in reducing atmosphere: effects of alumina sources and addition of carbon black

Magnesium aluminate spinel powder was prepared by one-step carbon-bed sintering at 1400 °C for 4 h with light magnesium oxide as magnesia source, alumina/boehmite/alumina-sol as alumina source, respectively. The phase composition of synthesized powders was characterized by X_ray diffraction, and the microstructure was depicted by field-emission scanning electron microscopy. The effects of alumina type and carbon black (CB) on the phase composition and morphology of synthesized powders were studied. The results show that the type of alumina source has remarkable influence on the morphology of spinel powder. The average particle sizes of the product with both alumina and boehmite as alumina source are about 1.5 μm. However, the shape of the former is cobblestone while that of the latter is regular rhombic plate. Additionally, the morphology of boehmite was preserved in its corresponding product, implying that the spinel grows by template mechanism. The average particle sizes of the product with alumina-sol as alumina source were about 0.6–2.1 μm, and it possesses a regular octahedral structure. CB can be distributed more uniformly in the powder when polyvinylpyrrolidone (PVP) solution was used as a dispersant. The uniformly dispersed CB could significantly decrease the grain size of the product when alumina-sol was used as alumina source, but it had little effect on the particle size of products with alumina or boehmite as alumina source.

Enhancing the Performance of Motive Power Lead-Acid Batteries by High Surface Area Carbon Black Additives

The effects of carbon black specific surface area and morphology were investigated by characterizing four different carbon black additives and then evaluating the effect of adding them to the negative electrode of valve-regulated lead–acid batteries for electric bikes. Low-temperature performance, larger current discharge performance, charge acceptance, cycle life and water loss of the batteries with carbon black were studied. The results show that the addition of high-performance carbon black to the negative plate of lead–acid batteries has an important effect on the cycle performance at 100% depth-of-discharge conditions and the cycle life is 86.9% longer than that of the control batteries. The excellent performance of the batteries can be attributed to the high surface area carbon black effectively inhibiting the sulfation of the negative plate surface and improving the charge acceptance of the batteries.

Co-CoO-Co3O4/N-doped carbon derived from metal-organic framework: The addition of carbon black for boosting oxygen electrocatalysis and Zn-Air battery

Electrocatalysts with high activity toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential and desired for metal-air batteries, fuel cells, water-splitting and CO2 reduction. Here, a series of Co-CoxO/N-doped Carbon (NC) is developed as bifunctional electrocatalysts via the pyrolysis of a simple physical mixture of cobalt-based metal-organic framework (MOF) and carbon black (CB). The obtained electrocatalysts exhibit considerably enhanced bifunctional activity as compared to the pure MOF derived counterpart. The essential roles of added CB in boosting the bifunctional activity are investigated. With the addition of CB, the surface concentrations of active pyridinic-N and graphitic-N for ORR and the surface CoIII/CoII ratios for OER are increased. Furthermore, the charge transfer efficiency and the electrochemically active surface areas (ECSAs) are also enhanced for the resulting electrocatalyst. The optimized Co-CoO-Co3O4/NC exhibits excellent bifunctional activity and durability, surpassing the commercial 20 wt% Pt/C (for ORR) and IrO2 (for OER). When applied in an air electrode, the corresponding Zn-air battery with Co-CoO-Co3O4/NC presents the better performance than that with 20 wt% Pt/C.

Improvement of the piezoelectricity of PVDF-TrFE by carbon black

In order to prepare PVDF-TrFE films with high piezoelectric performance, carbon black (CB), in the range of 0.0 wt% to 0.8 wt%, was added into PVDF-TrFE/DMF solutions. To investigate the effects of CB on the power generation capability, various fabricated films were attached on a vibrating plate, and then the output voltages and harvested power density were measured. The composite film was optimized with a calibrated open circuit voltage of 10.09 V when the CB content was at 0.8 wt%, which was about 79% higher than that of the pure PVDF-TrFE films (5.63 V). Meanwhile, the energy harvesting capability was enhanced by 164%. Fourier transform infrared spectroscopy and other characterization techniques show that the addition of CB resulted in the easier formation of β-phase (piezoelectric) rather than α-phase (non-piezoelectric) due to the nucleate role of CB during the preparation process of the composite films.

Carbon black-modified SnO nanocomposites with improved photocatalytic activity

SnO/CB composite photocatalysts with different carbon black (CB) contents were prepared by ultrasonic reaction method. CB addition significantly affected the morphology and photocatalytic activity of the composites. CB addition may enhance the formation of agglomerates with different sizes and morphologies. SnO and CB composites with high absorption in the visible light zones were obtained. All SnO/CB composites exhibited markedly higher photocatalytic activity than the SnO sample. The SnO/13%CB composites exhibited the highest photocatalytic properties, degrading 97.5% of MO for 45 min.

Optimization of Thermal Stability of High-Density Polyethylene Composite Using Antioxidant, Carbon Black and Nanoclay Addition by a Central Composite Design Method: X-ray Diffraction and Rheological Characterization

The thermal stability of high-density polyethylene, as characterized by an Oxidation Induction Time (OIT) test in the presence of the three additives, antioxidant, carbon black and nanoclay, was investigated. The twenty experiments used were designed by using the Central Composite Design (CCD) method, and the effects of the main parameters and their interactions were analyzed. The results of Analysis of Variance (ANOVA) showed that the antioxidant, nanoclay and carbon black contents, the antioxidant-nanoclay interaction and the antioxidant-carbon black interaction, had significant effects on the thermal stability. By optimization of the percent compositions used, the best composition was obtained, 0.26%, 2.21% and 4.69% for antioxidant, carbon black and nanoclay, respectively, to achieve thermal stability equal to the targeted value of 60 minutes. X-ray diffraction confirmed a weak polymer-nanocaly interaction in the optimal sample structure. The rheology frequency sweep test showed an increase in the elastic and viscous modulus in the optimal sample relative to the control samples. The Melt Flow Index (MFI) test for an optimum sample showed a pseudo-plastic structure with the lowest melt flow index of 0.2614 g/10 min, which was consistent with the results of the complex viscosity, with the optimal sample having the highest value (128500 Pa.s). The density test indicated the most crystalline structure for the optimized sample, with the highest value (0.976 g/cm3) compared to the control samples (0.962 and 0.957 g/cm3 for the polyethylene/nanoclay and the polyethylene/carbon black sample, respectively).

Polyamide 6 composite fibers with incorporated mixtures of melamine cyanurate, carbon nanotubes, and carbon black

AbstractPolyamide 6 (PA6) composite filament yarns were produced by the simultaneous incorporation of melamine cyanurate (MeCy) with multiwalled carbon nanotubes (CNTs) and carbon black (CB) into a composite matrix in a melt‐spinning process. The results show that the simultaneous incorporation of MeCy with CNTs or CB additives provided filaments with a uniform black color. Tensile analysis confirmed that a reinforcing effect was achieved when CB was used, whereas the CNTs induced a reducing effect on the filament tenacity. With regard to the burning behavior, the flame‐retardant action of MeCy was preserved in the presence of CB but was significantly hindered when used in combination with CNTs. These results indicate that the mixture of MeCy and CB was much more compatible for the production of reinforced PA6 composite filaments with increased thermal stability and improved flame retardancy over those of the MeCy and CNTs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47007.

Effect of carbon black addition on thermal stability and capacitive performances of supercapacitors

In this study, we propose a simple way to improve thermal stability of solid-state supercapacitors (SCs) by adding carbon black (CB) into reduced graphene oxide (rGO) electrodes. The CB used as a heat-resistant additive contributes to stable operation of the rGO-CB SC even after 1000 charge/discharge cycles at 90 °C. In the case of the rGO SC without CB, it fails after the 166th cycles at 90 °C. Compared with the rGO SC, the rGO-CB SC exhibits the decrease in internal resistance from 42 to 18 Ω and the increase in specific capacitance from 115 to 160 F/g. Moreover, the rGO-CB SC shows a smaller variation in specific capacitance (12%) than that of rGO SC (30%) as the temperature increases from 30 to 90 °C. The observation reveals that the addition of CB being a heat-resistant additive helps improve performance of thermal stable SCs.

Carbon black filled shell of high density wood-polyethylene composites to balance the antistatic properties and mechanical properties

Carbon black (CB) was used to fill the shell of wood high-density polyethylene (HDPE) composite to improve its antistatic properties and simultaneously maintain its mechanical properties. The conductivity analysis revealed that the percolation threshold of the CB in coextruded WPC was between 15% and 20%, and the surface resistivity of the sample containing 20% CB (CW-20) achieved the floor antistatic requirements of an electronic information system room and its support area according to GB/T 50174 (2017). The addition of CB into the shell of the coextruded WPC inhibited its crystallization. The mechanical properties of coextruded WPC were increased when the CB content was increased. The flexural strength, flexural modulus, and impact strength of the CW-20 sample were increased by 21.6%, 10.8%, and 26.1%, respectively. In addition, the dosage of CB in regular WPCs was 6.71 times as much as that of coextruded WPCs, which achieved similar antistatic and mechanical properties of the two structural WPCs. These results demonstrated that the low CB filled shell of HDPE composite exhibited a large reduction in its surface resistivity and a significant enhancement in its mechanical properties, which expands the application of coextruded WPCs in flammable and explosive uses while also improving the antistatic and mechanical properties.

MICRO CARBON ADDITIVE FOR PERFORMANCE IMPROVEMENT OF THE LEAD−ACID BATTERY

The features and changes in the microstructure of the negative electrode material of a lead−acid battery appearing after adding of carbon black and hybrid carbon were investigated. As shown by X−ray phase analysis and scanning electron microscopy, carbon black and hybrid carbon additives influence the electrode material structure causing changes in soaking and formation processes. In accordance with the structural research, hybrid carbon increases the dispersity of the negative active material and impedes sulfate ions diffusion into its internal layers. Electrical tests of lead−acid batteries including high rate partial state of charge cycling were conducted and the roles of each kinds of carbon additives were estimated. It was shown that the addition of hybrid carbon increases the cycle life of the batteries at high rate partial state of charge operation, improving charge acceptance approximately by 9 % and deep discharge stability. Capacity loss after deep discharge is less than 4.4 % if hybrid carbon is used as an additive and 7.2 % in case of carbon black.

Structure-property-processing investigation of electrically conductive polypropylene nanocomposites

Abstract This paper investigates the structure-property-processing correlations of electrically conductive polypropylene (PP) nanocomposites. The process parameters and fabrication techniques of PP-based composite materials were studied. Various structures of carbon allotrope-based materials, including synthetic graphite (SG), exfoliated graphene nanoplatelets (xGnP), multi-walled carbon nanotubes (MWCNTs) and carbon black (CB), were used to fabricate the PP-based nanocomposites. The nanocomposites were prepared by either direct melt mixing using an internal mixer or by ball milling of components before the melt mixing process. The electrical and flexural properties were measured. In order to understand the conductivity behavior, both in-plane and through-plane electrical conductivities were measured. The results showed that the incorporation of the xGnP into PP/60 wt.% SG composites resulted in a slight increase of the in-plane conductivities and had a minimal effect on the through-plane conductivities. The addition of MWCNTs and CB to the PP/SG/xGnP composites had a significant effect on the electrical properties and was more pronounced in the case of MWCNTs. The flexural properties of all samples were much lower than those of pure PP. The interface between the filler and the PP matrix and the morphology of the composite materials were observed from the fracture surfaces of the composites using scanning electron microscopy (SEM). In addition, SEM was employed to observe adhesion, microstructural homogeneity, orientation of the xGnP platelets and agglomeration in the composites.