Molecular dynamics simulation of the impact of the surface topology of carbon black on the mechanical properties of elastomer nanocomposites

Carbon black has always played a pivotal role in reinforcing elastomers because it remarkably improves the mechanical properties. The reinforcing effect of carbon black is influenced by its grades, which mainly depend on the difference in the structure of the carbon black particles. Despite many traditional experiments on the performance of carbon black composites, there has been less emphasis on reinforcement mechanisms due to the challenges associated with unraveling the intermolecular interactions. In this paper, a coarse grained molecular dynamics simulation was employed to examine the relationship between the morphology of the carbon black particles and the mechanical properties of the elastomer nanocomposites. Specifically, three different morphological carbon black nanoparticle models, including the smooth particle model, rough particle model, and the rough ellipsoid model, were constructed first. We then focused on investigating the changes of the mechanical properties by systematically varying the filling fraction of the carbon black particles, and the strength of the interfacial interaction between the filler and the rubber. The results indicated that the surface roughness and the filler's shape had a significant impact on the mechanical properties of the filled rubber models. The mechanical enhancement effect of the rough ellipsoidal carbon black is around 50-400% higher than that of the smooth carbon black, and the stronger the interfacial interactions, the more pronounced the enhancement. In addition, the rough ellipsoid filled system has low hysteresis, low permanent deformation, and high fatigue resistance. In general, this work explores the strengthening mechanism of carbon black on the elastomer at the molecular level and generates new insight into the design and fabrication of novel reinforcing fillers.

Effect of Melt-Compounding Protocol on Self-Aggregation and Percolation in a Ternary Composite

A ternary composite of poly(lactic acid) (PLA), poly(caprolactone) (PCL), and carbon black (CB) shows the PCL-induced CB self-aggregation and percolation formation when the amount of the PCL phase as the secondary phase is as small as the amount of CB. Furthermore, when the drop size of the PCL phase becomes smaller, the ternary composite forms a percolation of high order structure, resulting in a remarkable enhancement of the electrical conductivity (~4 × 10^-2 S/m with 4 wt.% CB). To further control the percolation structure, the composite fabrication is controlled by splitting a typical single-step mixing process into two steps, focusing on the dispersion of the secondary PCL phase and the CB particles separately. Under the single-step mixing protocol, the ternary composite shows a structure with greater CB aggregation in the form of a high aspect ratio and large aggregates (aggregate perimeter~aggregate size 0.7). Meanwhile, the two-step mixing process causes the CB aggregates to expand and create a higher structure (aggregate perimeter~aggregate size 0.8). The reduced size of the secondary phase under a mixing condition with high shear force prior to the addition of CB provides a larger interfacial area for CB to diffuse into the PCL phase during the subsequent mixing step, resulting in a further expansion of CB aggregation throughout the composite. The particle percolation of such a high order structure is attributed to high storage modulus (G'), high Young's modulus, high dielectric loss (ε″), and negative-positive switching of dielectric constant at high frequency (of 103 Hz) of composite.

Application Properties Analysis as a Dielectric Capacitor of End-Of-Life Tire-Reinforced HDPE

The purpose of the present research is to obtain waste of polymeric composite as an insulator capacitive application. Rubber materials, once they end their useful life, may be difficult to reuse or recycle. At present, research only uses one tire recycling method, which involves grinding and separating steel and fibers from vulcanized rubber, and then using the rubber particles for industrial capacitors. The methodology for this research is to compare the permittivity (ε′ and ε″) between high-density polyethylene (HDPE) and the polymer matrix compound, consisting of an HDPE polymeric matrix blended with end-of-life tire particles (ground tire rubber (GTR)), to analyze the feasibility of using such tires as electrically insulating materials (dielectrics). The incorporation of carbon black in the GTR compounds modifies conductivity; GTRs carry a significant amount of carbon black, and therefore some electrical properties may change significantly compared to highly insulating polymer substrates. The performed experimental study is based on a dynamic electric analysis (DEA) test developed in the frequency range of 10⁻² Hz to 3 MHz and at different temperatures (from 35 to 70 °C) of different samples type: HDPE neat and HDPE compounds with 10%, 20% and 40% of GTR loads. A sample’s electrical behavior is checked for its dependence on frequency and temperature, focused on the permittivity property; this is a key property for capacitive insulators and is key for examining the possible applications in this field, for HDPE + GTR blends. Results for the permittivity behavior and the loss factor show different electrical behavior. For a neat HDPE sample, no dependence with frequency nor temperature is shown. However, with the addition of 10%, 20%, and 40% amount of GTR the HDPE compounds show different behaviors: for low frequencies, interfacial polarization relaxation is seen, due to the Maxwell–Wagner–Sillars (MWS) effect, performed in heterogeneous materials. In order to analyze thermal and morphological properties the differential scanning calorimetry (DSC) test and scanning electron microscopy (SEM) have been used. Results obtained show that adding waste tire particles in an HDPE matrix allows HDPE + 40% GTR blends to act as a dielectric in capacitors, increasing the capacitor dielectric efficiency in the low frequencies due to the MWS effect, which increases the dielectric constant.

Effects of SEBS-g-MA on Rheology, Morphology and Mechanical Properties of PET/HDPE Blends

The effects of additive styrene/ethylene-butylene/styrene copolymer grafted with maleic anhydride (SEBS-g-MA) were investigated on the rheology, morphology and mechanical properties of a polyethylene terephthalate (PET)/high density polyethylene (HDPE) blend. The ratio of the two components was changed in small increments to track phase inversion. The rheology measurements show that SEBS-g-MA acts differently on HDPE and PET, as different morphologies are formed due to viscosity ratio change. With the help of electron microscopy various phases after extrusion and after injection molding were revealed and identified. Because of the high viscosity of HDPE the co-continuous morphology was immediately formed when PET reached 30 vol%. The range of the co-continuous structure of the blend was wider when SEBS-g-MA was added, and the elongation at break also improved as additive content increased, without a significant strength decrease. The divergence of the mechanical properties from the theoretical value, i.e. the value determined by the mixing rule, can be explained by the changing phase structure.

Carbon Black Filled Polyester as Electrically Conductive Master Batch for Fibers

Carbon black (CB) was added into a matrix of poly(ethylene terephthalate) (PET) by melt processing to prepare electrically conductive master batch (ECMB) for fiber applications. The amount of CB required to achieve a desired electrical property often results in poor mechanical properties of the final fibers. To solve this problem, a type of ECMB with a lower percolation threshold was designed by incorporating titanate coupling agent treated CB and using a matrix blend (adding polyethylene (PE) into PET). The effects of titanate coupling agent treatment and the matrix blend on the percolation threshold of ECMB are discussed and the effect of lower percolation threshold on the mechanical properties of final melt-spun fibers was investigated. The results indicated that titanate coupling agent treatment and a matrix blend are able to reduce the percolation threshold and thereby minimize problems with the mechanical properties of the final fibers, yet maintain the desirable electrical property.

Análise termodinâmica do comportamento mecânico na região elástica de blendas de poli (tereftalato de etileno) reciclado e poliolefinas recicladas

Este trabalho descreve o estudo de blendas de poli(tereftalato de etileno) reciclado e poliolefinas recicladas, com e sem adição de polipropileno funcionalizado com anidrido maleico e poli(etileno-co-octeno-1) utilizando ensaios mecânicos e microscopia eletrônica de varredura. Foi aplicado um formalismo termodinâmico com base na função trabalho de Helmholtz para o comportamento mecânico na região elástica, correlacionando-se com o armazenamento de energia elástica para os materiais estudados. Também foi analisada a dissipação de energia relativa ao fenômeno elasto-plástico na região de baixas deformações. Para as blendas estudadas, observou-se que o armazenamento de energia e o efeito do compatibilizante são muito mais acentuados na região rica em poliolefinas, corroborando com as imagens da morfologia observadas via microscopia eletrônica. A análise termodinâmica apresentada mostrou-se uma ferramenta útil e confiável e de baixo custo, para avaliar o efeito de compatibilização de sistemas poliméricos imiscíveis. No presente trabalho, particularmente para a avaliação do comportamento mecânico de misturas de materiais "commodities" reciclados.

Polysulfone hollow fiber gas separation membranes filled with submicron particles

Three different fillers, carbon black (CB), vapor grown carbon fibers (VGCF), and TiO(2), were incorporated into polysulfone spinning solutions with the intention of producing highly selective membranes with enhanced mechanical strength. The effect of filler presence on gas permeation characteristics, mechanical strength (bursting pressure), and morphology was investigated and compared to unfilled membranes. As well as studying filler types, the influence of CB filler concentration on membrane performance was also examined. For all filler types (at a concentration of 5%w/w), the pressure-normalized flux of O(2), N(2), and CH(4) was greater in the composite than in the unfilled membranes. The CO(2) pressure-normalized flux was only greater in the TiO(2) composite membranes. For CB and VGCF, the CO(2) pressure-normalized flux was reduced compared with unfilled membranes. Three CB concentrations were investigated (2, 5, and 10%w/w). For O(2), N(2), and CH(4), pressure-normalized flux peaked at 5%w/w CB. CO(2) exhibited the opposite trend, showing a minimum pressure-normalized flux at 5%w/w. Considering O(2)/N(2) and CO(2)/CH(4) gas pairs and the various filled membrane categories, only the O(2)/N(2) selectivity of the 2%w/w CB filled membranes was higher than that of the unfilled fibers-all other selectivities were lower. In terms of CB concentration, selectivity was a minimum at the intermediate concentration of 5%w/w. All the filled membrane types exhibited greater mechanical strength (bursting pressure) than unfilled fibers apart from the 5%w/w VGCF composites. The 2%w/w CB composites were the strongest. Electron microscopy showed no visible differences in general morphology between the various filled and unfilled membranes.