Rheology of polymers containing carbon black

In order to elucidate the flow behavior of electrophotographic toner systems, shear stress was measured as a function of shear rate in a cone and plate rheometer for polymer melts containing carbon blacks of surface area 24 and 625 m²/g at several concentrations and temperatures. Polymers included high and low molecular weight polystyrene and poly(butyl methacrylate). The addition of carbon black to the polymers caused a large increase in viscosity, especially at low shear rates and shear stresses. As the concentration of carbon black was increased, the viscosity at low shear rates became unbounded below a value of the shear stress designated the yield stress. The absolute magnitude of the yield stress depended primarily on the concentration and surface area of the carbon black and was independent of the polymer and temperature. Apparently, carbon black forms an independent network within the polymer at low shear rates which precludes flow. In some cases, the viscosity of polymers filled with carbon black was lower than that of the pure polymer. This effect was favored for polystyrene compared to poly(butyl methacrylate) and was facilitated by increasing the molecular weight of polystyrene, reducing the surface area and concentration of carbon black, and by increasing the temperature and shear rate.     

Molecular degradation of concentrated polystyrene solutions in a fast transient extensional flow

The extensional degradation of concentrated polymer solutions is studied. Extensional flows are prevalent in the polymer processing industry, but their effect on polymer degradation is often overlooked. Previous research into dilute solution extensional degradation proved that this type of flow is much more effective than shear flow in causing chain scission. This research extends these dilute solution studies into the concentrated regime, where intermolecular entanglements are expected to affect chain scission. A concentrated polystyrene solution is degraded in an opposed pistons device. This device cycles the solution across a sharp contraction, imposing a strong extensional flow. The flow field is modeled to determine the extension rate along the centerline, and the degradation is quantified by measuring the zero shear viscosity and the molecular weight distribution. The results show that degradation is more significant compared to dilute solutions. The zero shear viscosity drops 30% after a single pass across the orifice at high strain rates. As in a dilute solution, the extensional flow leads to preferential cleavage of the high molecular weight chains. All chains longer than a measured critical molecular weight are ruptured. Multiple passes across the orifice increase chain scission, although degradation is the most significant in the first pass through the high strain rate region.     

Rheology of copolymers containing carbon black

The rheological response of random copolymers of styrene and butyl methacrylate containing carbon black simulates the behavior of toner in the electrophotographic process. Both the relative viscosity and the dependence of viscosity on shear rate were increased by raising the temperature and raising the concentration and surface area of carbon black. For high concentrations and surface areas of carbon black and at elevated temperatures, a well-defined yield stress varied from 2.5 × 10² to 1.6 × 10⁴ Pa, depending on the concentration and nature of the carbon black but independent of the type of polymer and temperature, implying the formation of a carbon black network. Plasticization by carbon black was favored at low surface area and concentration of carbon black and at elevated temperatures.     

Hot embossing in microfabrication. Part II: Rheological characterization and process analysis

The dynamic shear viscosity and the transient extensional viscosity of polycarbonate (PC), polymethyl methacrylate (PMMA), and polyvinyl butyral (PVB) were measured at temperatures near and far above their glass transition temperatures. The temperature sensitivity of rheological properties was used to explain the displacement curves during embossing. Numerical simulation of the embossing process was also carried out to compare with the observed polymer flow patterns. It was found that the simulated flow pattern during isothermal embossing agrees fairly well with the experimental observation. The deviation between the simulated and experimental results at the late stage of embossing may be due to air entrapment between the mold feature and the polymer substrate. For non‐isothermal embossing, the observed flow pattern can also be reasonably simulated, i.e. the polymer flows upward along the wall of the heated mold feature, and then compresses downward and squeezes outward. Temperature sensitivity of the dynamic shear viscosity and the transient extensional viscosity is similar for all three polymers. This correlates well with the initial displacement curves in isothermal embossing. Over a longer time, the strain hardening effect of the transient extensional viscosity seems to play a major role in the displacement curves.     

Rheological behavior of brominated isobutylene‐co‐paramethylstyrene: Effect of fillers,oil and blending with EPDM

The melt flow properties of unfilled and filled brominated isobutylene‐co‐paramethylstyrene (BIMS) were measured by means of a capillary viscometer at three different temperatures (90°C, 110°C and 130°C) and four different shear rates (61, 122, 245 and 306 s^?1). The effect of addition of EPDM rubber on melt flow properties of unfilled BIMS was also studied. Evaluation of the processability was done by measuring the extrudate roughness (ER) of the extrudates obtained from the MPT. The viscosity of the systems decreased with the shear rate, indicating their pseudoplastic or shear thinning nature. As expected, the viscosity of BIMS increased with the addition of fillers and decreased with the addition of oil. For the neat systems, viscosity increased with the addition of EPDM, and the blends showed a positive deviation, indicating interdiffusion of the polymer chains across the phase boundaries. The activation energy of the filled systems at constant filler loading increased with increasing filler surface area (N330 > N550 > N774, each at 30 phr loading), and filler loading (50 > 30 > 10 phr, for N330) and decreased with the addition of oil (2.5 > 5.0 > 7.5 phr, for system containing 30 phr of N330). The silica filled system showed a higher activation energy and ER than the carbon black‐filled systems. With addition of N330 and N550 carbon blacks to BIMS, the extrudate roughness (ER) decreased, whereas it increased with the addition of N774 carbon black. With an increase in filler loading, ER initially increased and then decreased as compared to the neat system. For the filled systems, ER initially decreased up to 5 phr of oil, beyond which it increased.     

Mixing of carbon black and polymer: Interaction and reinforcement

Interaction between carbon black and polymer starts during the mixing process; a primary agglomerate is formed, the composition of which is dependent upon the structure. The important carbon black properties are surface area, specific activity, structure (void, volume, anisometry), and porosity of the particles. On heat treatment of black at 3000°C., it loses its sites of high specific activity. Structure and specific activity determine incorporation time and further dispersion. During mixing, bound rubber is formed which is used as a measure of specific surface activity. In the final vulcanizate, the filler–polymer interaction is evident in reduced swelling in solvents (benzene, chloroform, cyclohexane,) etc. Below a certain critical degree of swelling, the percentage swelling is no longer dependent upon the amount of filler in the vulcanizate. Graphitized black vulcanizates exhibit in all solvents the same degree of swelling as the unfilled vulcanizate. This phenomenon is explained by the assumption of mobile adsorption of rubber chains on the carbon black surface. In untreated blacks the mobility on the surface is limited by sites of high energy of adsorption. In graphitized blacks such sites are no longer found, and swelling is unhindered by the presence of black. Reinforcement is explained by the more homegeneous distribution of tension between molecular chains due to slippage on the carbon surface.     

Steady-state behavior of star polymers in dilute flowing solutions via Brownian dynamics

A bead and spring model is considered for the Brownian dynamics simulation of the behavior of regular star polymer chains in a dilute solution under both shear flow and extensional (or elongational) flow. Finite extensibility, excluded volume, and hydrodynamic interaction are taken into account to make the polymer model as realistic as possible. The behavior of star-like chains in flow is similar to that of linear and ring polymers. Thus, dependence of a given property with the arm molecular weight is analogous to that found for linear polymers when using the total molecular weight. In shear flow, the deformation of the chain and the shear rate viscosity dependence (the flow curve), are studied. We find a slope for the shear-thinning region of the flow curve close to −2/3. In elongational flow the coil-stretch transition is characterized by giving the relationship between the critical elongational rate and the arm molecular weight, which turns out to be similar to the power law found in linear chains.     

炭黑填充硫化胶的网络结构同力学性能间相关性——(Ⅰ)炭黑填充硫化胶大形变弹性分子理论

本文提出了炭黑填充硫化胶的网络结构是由交联网,缠结网和炭黑——高分子链网所形成的网络结构模型.基于该微观结构模型和弹性大形变机理用统计力学方法计算了三种网中各链组的末端距机率密度分布函数,三种网的形变自由能和炭黑填充硫化胶的总形变自由能,并根据弹性形变自由能同应力一应变间的关系得到了四种简单形变方式的应力一应变关系式.     

Refinement of the converging flow method of measuring extensional viscosity in polymers

A critical evaluation of assumptions made in the converging flow analysis of Cogswell is made, and a refined analysis is given by relaxing two of these assumptions. This reexamination of the Cogswell method was motivated by some recent encouraging comparative studies by Laun and Schuch of conventional extensional results and converging flow data. Of the two assumptions relaxed in the analysis, the relaxation of the assumption of a constant extensional viscosity above the orifice, into which the converging flow takes place, is shown to be primarily responsible for the substantially improved agreement with conventional extensional viscosity measurements. Because the variation of the extensional viscosity above the orifice is not known, solution of the equations is not given in closed form, and their solution is solved by an iterative procedure. The good agreement of the results of the modified converging flow analysis given here with conventional extensional measurements over a large range of rates demonstrates that converging flow methods can provide an accurate and relatively routine method of measuring extensional viscosity in molten polymers.     

Cationic ring-opening polymerization of 2-substituted-2-oxazolines initiated by carbon black surface

Summary Carbon blacks were found capable of initiating the ringopening polymerization of 2-substituted-2-oxazolines at relativery high temperatures. The activation energy of the polymerization of 2-methyl-2-oxazoline was estimated to be 13.4 kcal/mol. Carbon black lost the initiating activity of the polymerization upon the blocking of carboxyl groups on the surface by the treatment with potassium hydroxide or diazomethane. Therefore, it was concluded that carboxyl groups on carbon black play an important role in the initiation of the polymerization. Furthermore, it was found that during the polymerization, poly(N-acylethyleneimine) was grafted onto carbon black by the termination of growing polymer chain with the surface.     

Scaling of the viscoelasticity of highly filled carbon black polyethylene composites above the melting point

Different types of linear low-density polyethylene and ethylene butylacrylate copolymers were mixed with various types of carbon black in amounts between 25 and 40% by weight. Viscoelastic properties were measured using dynamic mechanical analysis applying a frequency sweep. Typically, the complex modulus approaches asymptotically a constant value at small frequencies, which is referred to as ‘yield modulus’. These results were analysed using a scaling approach according to which the complex modulus and the frequency are normalised by the yield modulus and the quotient of the yield modulus and the polymer viscosity, respectively. Thus a master curve is achieved for nearly all samples independent of the polymer and carbon black type and loading. A similar scaling behaviour has been observed earlier for differently concentrated suspensions of carbon black in Newtonian liquids, but not for filled polymers and different carbon blacks. Thus, contributions from polymer and carbon black to the compounds' viscoelastic properties are discussed.     

Reactions of carbon black. Part I. Nonthixotropic carbon black compositions

The solution polymerization of butyl acrylate in the presence of a furnace black was found to produce a stable dispersion of carbon black which showed Newtonian flow, while the mixture prepared by mixing the same carbon black into a solution of poly(butyl acrylate) homopolymer had a large degree of thixotropy. A marked change in the viscosity of the reaction mixture was also observed at an early stage of polymerization when the initial mixture which was a moist mass with no fluidity, turned to a fluid easily stirred. The change in viscosity and the transition in flow behavior were carefully followed with a rotary cylinder type viscometer. The non-Newtonian initial mixture was found to turn to a Newtonian fluid at low conversion of the monomer. Beside the adsorption of the homopolymer onto the surface of carbon black particles, which would occur also in mechanical mixing, the change in the flow behavior was estimated to be caused by the change in the shape and the size of the dispersed carbon black particles due to the change in the condition of the surface of the particles by which growing polymer radicals, as well as initiator radicals, were captured.     

聚合物熔体延伸粘度的研究方法

聚合物熔体的延伸粘度是影响聚合物熔体流动特性和成型制品性能的重要因素。本文较为系统地介绍了聚合物熔体延伸粘度的理论和实验研究方法,着重介绍了Cogswell、Gibson、Binding和Berstered等人的理论研究工作,为进一步研究熔体的延伸粘度提供思路。     

Viscosity index. II. Correlation with rheological theories of data for blends containing n-octadecyl acrylate

The viscosities obtained for the copolymer blends of the previous paper were correlated with several relations derived to describe more fundamental behavior of polymer–diluent mixtures at both infinite dilution and finite concentrations. Only the most efficient blends showed any appreciable expansion of hydrodynamic volume as temperature increased from 25° to 98.9°C. However, in spite of restricted coil expansion, all of the copolymers were effective viscosity index improvers. The mechanism of viscosity index improvement in multigrade oils was shown to be largely regulated by the translational friction generated by the polymer coils. This greatly increased the apparent negative entropy change of the blends; the enthalpy change characteristic of the base oil was retained. Efficiency resulted from coil contraction at low temperatures, but enthalpy decrease below that of the base oil was small. In contrast, viscosity index improvement using higher molecular weight solvents was accompanied by large enthalpy increases. Thus, undesirably high viscosities resulted at low temperatures. The structure of these blends was uncomplicated by polymer chain entanglements; unit values of the Fox-Flory exponent were obtained for the relation between viscosity and weight-average carbon backbone length. The lack of evidence for coil compression in the thermodynamically miscible blends above a critical reduced concentration was anomalous. Intermingling of side chains and their interaction may have overcome normal excluded volume effects.     

Capillary breakup extensional rheometry of associative and hydrolyzed polyacrylamide polymers for oil recovery applications

High molecular weight polymers used for heavy oil recovery exhibit viscoelasticity that can influence the oil recovery during chemical enhanced oil recovery. Different polymers having similar molecular weight and shear rheology may have different elongation flow behavior depending on their extensional properties. Displacing slugs are more likely to stretch than shear in tortuous porous media. Therefore, it is critical to seek an analytical tool that can characterize extensional parameters to improve polymer selection criteria. This article focuses on the extensional characterization of two polymers (hydrolyzed polyacrylamide and associative polymer) having identical shear behavior using capillary breakup extensional rheometer to explain their different porous media behavior. Maximum extensional viscosity at the critical Deborah number and Deborah number in porous media classified the associative polymer as the one having high elastic‐limit. Extensional characterization results were complemented by significantly higher pressure drop, marginally increased oil recovery of associative polymer in porous media. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46253.     

Preparation and characterization of superhydrophobic conductive fluorinated carbon blacks

Superhydrophobic conductive carbon blacks were prepared by covalent bonding of perfluorocarbon and perfluoropolyether chains on the conductive carbon black surface. Perfluorodiacyl and perfluoropolyether peroxides were used as reagents for the chemical treatment. Their thermal decomposition produced respectively, perfluoroalkyl and perfluoropolyether radicals that directly bonded the polycyclic aromatic structure of carbon black surface. Measurements of contact angles with water on molded pellets made with carbon black powder demonstrated that water droplets were enduringly stable on the treated carbon blacks. Contact angle values were significantly high, exceeding the superhydrophobicity threshold. On the contrary, the droplets were adsorbed in few seconds by the native carbon black. Conductivity measurements showed that the covalent linkage of fluorinated chains weakly modified the electrical properties of the conductive carbon black, even if the surface properties changed so deeply. The relationship between the linkage of fluorinated chains and the variations of physical–chemical properties were studied combining electron spectroscopy, resistivity measurements, X-ray diffraction, scanning electron microscopy, surface area analysis and thermal gravimetric analysis. The superhydrophobic conductive carbon blacks were compared with a superhydrophobic carbon black obtained by direct fluorination of conductive carbon black with elemental fluorine, F₂.     

炭黑在高分子聚合物中的导电性研究

以EVA为高分子聚合物，采用不同级别的导电炭黑，研究了导电炭黑填充高分子聚合物的导电性，讨论了不同级别和不同用量的导电炭黑在聚合物中的分散性，以及对高分子聚合物导电性的影响。实验结果表明，导电炭黑高分子聚合物的导电性主要取决于不同级别的导电炭黑的表面性和结构等特性、炭黑的不同用量以及导电炭黑的聚集体在高分子聚合物的分散程度。     

Step‐strain stress relaxation of carbon black‐loaded natural rubber vulcanizates

Step‐strain stress relaxation experiments were performed on natural rubber vulcanizates of various carbon black (HAF) concentrations by subjecting the samples to a very rapid strain and fixing its length at the deformed state. Time–temperature superposition in the viscoelastic region was evaluated to investigate the effect of temperature on the relaxation times of the rubbery composites. Remarkably, it was observed that, at higher HAF concentrations, increasing the temperature had a lesser effect on decreasing the overall stress values. That was attributed to the lower number of elastomeric chains per unit volume due to the agglomeration of the carbon black particles. The energy barrier resulting from the adsorption of the rubbery chains on the filler particles was insufficient to drastically reduce the diffusion and rearrangement of the polymer chains. The activation energy of the rubber‐like deformation calculated from the time–temperature superposition was shown to be independent of temperature. Interestingly, the viscosity coefficients showed a large increase with a modest addition of the carbon black. This is due to the long‐range nature of the temporary bonds formed between the polymer molecules and the surface‐active carbon black. The stress–strain of the rubbery composites was shown to behave in a Gaussian manner in accordance with the Mooney–Rivlin relationship. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3387–3393, 2004     

Effect of polymer-filler interactions on PTC behaviors of LDPE/EPDM blends filled with carbon blacks

The dependence of electrical resistivities on the temperature of different polymer systems (including rubbers and plastic/rubber blends) loaded with carbon blacks (including oxidized and normal carbon blacks) were studied. We found that polymer-carbon black interactions could greatly influence the electrical resistivity and temperature relations of the polymer composites. The polymer blends filled with oxidized carbon black, or the elastomer which has polar functional groups filled with carbon black, have a very weak negative temperature coefficient (NTC) effect, which is due to the strong polymer-filler interactions. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1885–1890, 1997     

Extensional stresses during polymer flow in ducts

During the flow of high molecular weight, narrow-, and broad-distribution polybutadienes and polyisoprenes rheo-optical measurements were conducted of extensional stresses acting along the flow axis in the preentrance and entrance regions of the duct and of their subsequent relaxation in the duct. The extensional stresses increase in the preentrance region, reach their maximum values at a distance of two or three tenths of the duct width from its edges, and then relax. The position of the maximum extensional stress is independent of polymer characteristics, shear stresses in the duct, and shape of the entrance and dimensions of the rectangular duct. The dependence of the maximum extensional stress on the shear stress of the duct wall can be assumed to be linear for small values. The length of the stress relaxation zone depends on the shear stress at the duct wall and the molecular mass distribution. It is independent of the molecular masses in narrow-distribution polymers. For the polymers investigated, a generalized dependence was obtained for the reduced duct length over which the extensional stresses relax to zero from the reduced deformation rate. This dependence takes into account the characteristic polymer relaxation times and the value of the molecular mass of the chain between the fluctuation entanglement. A considerable decrease in the duct's length-to-width ratio leads to an increase in the maximum values of the extensional stresses. A decreases in the duct entrance angle causes a reduction in the rate of increase of extensional stresses, the maximum values, and the acceleration of the relaxation processes in the duct. A decrease in the ratio of the width of the preentrance region to the duct width leads to a reduction in the maximum in extensional stresses. It is shown that one of the causes for the instability of the polymer flow in the ducts can be the rupture of polymers due to their extension in the preentrance and entrance regions. Calculations were done that describe satisfactorily the relationship between the values of the maximum extensional stresses and the shear rate and stresses on the duct wall.