Structure Of Carbon Black Aggregates Research Articles

THIXOTROPIC FLOCCULATION EFFECTS IN CARBON BLACK–REINFORCED RUBBER: KINETICS AND THERMAL ACTIVATION

ABSTRACT A new rheological methodology is used to quantify the kinetics and thermal activation of thixotropic recovery (flocculation) of uncrosslinked carbon black–reinforced emulsion SBR following high shears and over a range of annealing temperatures. A wide range of carbon black types are examined to determine the influence of aggregate morphology and surface area on compound flocculation. Several kinetic parameters are correlated with the carbon black aggregate structure and surface area, the results of which imply a transition in mechanisms controlling modulus recovery between shorter and longer recovery time scales. Thermal activation of flocculation is found to scale to the surface area and to the mean aggregate diameter of the carbon blacks following power law relationships. The thermal activation data for a subset of compounds with different carbon blacks prepared at different loadings collapses onto a single master line by rescaling the data to a parameter that is proportional to the theoretical interparticle force calculated for the idealized situation of two spherical particles in proximity. Three different van der Waals force models are evaluated, and in each case, an effective superposition of the thermal activation data is achieved. This indicates that the attractive force between aggregates plays a key role in the flocculation of carbon black in rubber, and this force can be traced back to the aggregate and primary particle sizes, interaggregate distances, and effective volume fractions. The activation energy for the viscosity of the unfilled, uncrosslinked SBR is similar to analogous values calculated for the thermal activation of flocculation. This coupling of energetics may be the result of creep/flow of rubber out of gaps between aggregates resulting from interaggregate attractive forces and any potential diffusive motion of the aggregates. Bound rubber data appear to contain information relating to aggregate packing, which could be exploited in future work to further explore the mechanism of flocculation.

Effect of Carbon Black Aggregate Structure on Transport Phenomena of PEFC

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Modeling Carbon Black Aggregate Structure and Ionomer Coat for Optimum Design of PEFC Catalyst Layer

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Verification of Selective Adsorption of Polymer on Filler Surface in a Binary Immiscible Polymer Solution Blend Based on Nanoconfinement: Changing the Aggregate Structure and the Surface Character of Carbon Black

The limiting cause of nanoconfinement of rubber molecules for their selective adsorption onto filler surface has been examined by changing: (1) the void size of carbon black aggregates, (2) the atomic scale roughness and chemical character of carbon black surface, and (3) the kind of filler from carbon black to silica. Nanoconfinement of rubber molecules into carbon black aggregate structure occurs at the concave (∼5 nm) formed in between carbon black primary particles. Nanoconfinement is the primary mechanism, whereas chemical interaction between filler and the polymer plays a minor role in the selective adsorption. The new adsorption concept is also examined with silica nanoparticles.

PP/ABS blends with carbon black: Morphology and electrical properties

AbstractPhase morphology of melt‐mixed polypropylene (PP)/acrylonitrile‐butadiene‐styrene (ABS) blends was found to be blend ratio dependent, viz., matrix‐particle dispersed type of morphology which was observed up to 30 wt % of ABS level beyond which the morphology showed co‐continuous type. The domain size of 80/20 PP/ABS blends was found to decrease significantly at 10 wt % carbon black (CB) level, and in case of 70/30 blends morphology was transformed into co‐continuous type in the presence of CB, which was retained up to 60 wt % ABS. The finer morphological features were associated with the compatibilizing action of CB particles. Continuous network was achieved through aggregated CB particles predominantly in the PP phase wherein one could find CB‐rich PP phase and CB‐less PP phase. Solution experiments further supported the existence of CB particles preferentially in the PP phase. AC electrical conductivity measurements indicated a 3D network‐like structure of CB aggregates in the co‐continuous compositions which showed enhanced electrical conductivity as compared to the matrix‐dispersed type of morphology in 80/20 PP/ABS blends which exhibited insulating behavior. On increasing ABS content in the blends the electrical conductivity decreased progressively due to a difficulty in retaining 3D continuous network of CB aggregates especially at 40/60 composition. Increased processing temperature led to a higher electrical conductivity in the respective blends. Dielectric measurements revealed the existence of metallic type of conduction in the co‐continuous compositions. However, 80/20 blends showed low ε′ value. Overall, structure property relationship studies were conducted in PP/ABS blends with CB. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

A New Concept for Nanoparticle Distribution in SBR/NBR Blend Solution and Films via Molecular Confinement

A novel mechanism of carbon black network formation in a binary immiscible rubber blend has been proposed in this paper. The network formation implies that the specific rubber molecules are selectively confined into the void of carbon black aggregate structure during their solution mixing. The selective adsorption and the feature of the conductive network formation have much potential concerning both fundamental understanding and industrial application to improve conductive polymer composites.

Anisometry Measurements in Carbon Black Aggregate Populations

Abstract Transmission electron microscopy with automated image analysis (TEM/AIA) was used to characterize the three-dimensional morphology and anisometry of carbon black aggregates. Individual carbon black aggregates were imaged at multiple goniometer angles, and their three-dimensional aggregate structure was modeled, yielding greatly enhanced morphological information. Aggregate size distributional properties were determined at multiple goniometer orientations for N300 and N600 series grades of varying aggregate structure levels. Aggregate projections were found to exhibit statistical decreases of 10 to 25% in area and perimeter with rotation. Decreases in other morphological parameters, including non-dimensional shape parameters, were also observed. In general, higher structure grades (aggregates) were found to display larger relative changes in morphological parameters with rotation than lower structure grades. Ramifications for conventional TEM/AIA and void-volume/polymer occlusion capacity measurements are addressed. Further analysis includes an assessment of aggregate anisometry on the TEM sample grid and new insights into the three dimensional nature of carbon black aggregate structure.

3-D morphological characterization of carbon black aggregates using atomic force microscopy

We use atomic force microscopy (AFM) to characterize the structure of carbon black aggregates. From the images we determine the lateral sizes and the height of the aggregates and from this data we calculate the flatness index. The flatness indices reveal that aggregates generally exhibit anisotropy, in the form of a reduction of aggregate breadth, or flatness, in one direction. The flat sides tend to align preferentially along the plane of the substrate. The flatness index depends on the grade and is related to the turbulence of the flow of gases inside the reactor. The data on the flatness index are compared with similar data obtained from transmission electron microscopy (TEM) and compressed CDBP analysis.

A Simple Methodology for the Modeling of Carbon Black Aggregate Structure

Abstract A procedure for modeling some morphological characteristics of carbon black aggregates is presented. The method uses a standard reaction limited aggregation algorithm to predict the location of the centers of primary particles within an aggregate. The shape of the aggregate is determined by drawing simple linear links between extreme points of primary particles centered on these loci. Analysis of the particle distribution function computed from the simulated structure leads to definitions of the interior and periphery of the aggregate structure. Direct comparisons between simulated aggregates and two commercial carbon blacks are presented to illustrate the usefulness of the approach. The perimeter fractal dimension of simulated aggregates can be made to match the perimeter fractal dimension of the commercial carbon black aggregates through proper choice of the sticking probability in the simulation algorithm. With this proper choice of sticking probability, the relative amounts of voids in the periphery and interior of the simulated aggregate correspond to relative amounts of filled and unfilled voids in actual aggregates that have been soaked for extended periods of time with processing fluids.

Influence of Aggregate Structure and Matrix Infiltration on the Dispersion Behavior of Carbon Black Agglomerates

Abstract The dispersion of carbon black agglomerates in poly(dimethyl siloxane) (PDMS) has been studied experimentally. Both the structure of carbon black aggregates comprising the agglomerate and the presence of the matrix within the agglomerate were found to affect the mode of dispersion, critical stress conditions, and the kinetics of the dispersion process. Agglomerates of high structure carbon black are generally more difficult to disperse than agglomerates of low structure carbon black at the same agglomerate density. Depending on the degree of saturation of the agglomerate by PDMS, the dispersion process may be either enhanced or retarded compared to the dry state.

3D Morphological Characterization of Carbon-Black Aggregates Using Transmission Electron Microscopy

Abstract A three-dimensional modeling technique is used to characterize the structure of carbon-black aggregates. The relative positions of individual particles in aggregates are determined using transmission electron microscopy (TEM). Data are acquired from two-dimensional projections taken with the aggregates at two different orientations with respect to the electron beam. Computerized aggregate models are generated using data from TEM projections in our reconstruction algorithm. Inspection of these models shows that their projections very closely replicate the TEM micrographs. Quantitative analysis of the aggregate models reveals that aggregates generally exhibit anisotropy, in the form of a reduction of aggregate breadth, or “flatness,” in one direction. The flat sides tend to align preferentially, along the plane of the TEM sample grid. The dimensions for each aggregate with respect to its best-fitting plane of flatness are determined, and are related through a “flatness index.”

Melt viscosity and electrical conductivity of carbon black‐PVC composite

AbstractThe effect of the structure of carbon black aggregates on the melt behavior and electrical conductivity of carbon black‐vinylchloride‐vinylacetate copolymer systems was analyzed. As the amorphous carbon aggregates are roll‐milled, they become cylindrical, then, as the milling time is prolonged, spherical. During milling, polymer adsorption and dispersivity increases in the same manner, causing the viscosity of the composite to decrease. It was established that during a certain milling time, conductivity rises to a peak, after which it falls. We attribute this phenomenon to there being an optimum aspect ratio and degree of dispersion of the cylindrical carbon aggregates. A model explaining the relationship between milling time and change in conductivity is proposed. When oxidized carbon black was dispersed into the copolymer, it was found that it disperses better than unoxidized carbon black, although the conductivity of the resulting composite is lower.