Dynamic mechanical behavior of polymers containing carbon black

The dynamic mechanical behavior of carbon black filled polymers of styrene and butyl methacrylate was examined at low strain amplitude and frequency in order to minimize destruction of the composite structure and elucidate the basis of yield and plasticization observed in steady shear. For specific filled systems, both G′ and G″ became independent of frequency and temperature at low frequencies, consistent with a yield phenomenon and the formation of a carbon black network. On the other hand, although the high molecular weight polystyrene showed plasticization effects at higher shear rates in steady shear rheology, such, plasticization effects were never observed in dynamic mechanical analysts. Yield behavior was observed most readily for the low molecular weight polystyrene. Limiting moduli for filled polystyrenes were independent of temperature, whereas, for polybutyl methacrylate, were sensitive to temperature. It is suggested that an independent network of carbon black is strongest in the low molecular weight polystyrene and weakest in poly (butyl methacrylate).     

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.     

Viscosity of copolymers containing carbon black

The flow behavior of random copolymers of styrene and butyl methacrylate containing specific carbon blacks varying in surface area were studied at various temperatures and shear rates. Master curves of reduced viscosity as a function of shear rate were prepared for the pure copolymers at 150°C. The superposition required vertical and horizontal shifts, proportional to (a_T)^?1 and (a_T)^.53, respectively, where a_T is the shift factor. With the incorporation of carbon black, the viscous response is non-Newtonian exhibiting a yield stress at increasing filler concentration and surface area. Master curves of viscosity against shear rate were generated at fixed filler loadings and surface areas by using a single horizontal shift factor.     

Processing and mechanical behavior of carbon black graded rubber compounds

Functionally graded rubber compounds (FGRCs) were prepared by construction based method. The matrix used was natural rubber (NR). Amorphous carbon black (N‐330) was used as grading material. The gradation of nanoparticles in a rectangular geometry comprised the variation of particle volume fraction along thickness direction. Its performance was evaluated for structural application through various mechanical and surface properties like tensile strength, modulus, tear strength, elongation at break, hardness, fracture surface by scanning electron microscopy, etc. At the same percentage of nanofiller loading, FGRCs show enhanced properties, i.e., modulus and tear strength (in some grades) compared to uniformly dispersed rubber compounds (UDRCs). Modulus of FGRCs, for a given particular stacking sequence of the layers, increases as much as by 275% compared to UDRCs. The ultimate properties like tensile strength and elongation at break made up for the modulus enhancement that decreases to as minimum as 50 and 80%, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Nonlinear viscoelastic behavior of butadiene–acrylonitrile copolymers filled with carbon black

Various viscoelastic measurements including dynamic mechanical measurements in tension at 110 Hz from ?60° to 160°C, tensile stress relaxation measurements with 100% elongation at 25°, 54°, and 98°C, capillary flow measurements at 70°, 100°, and 125°C, and high-speed tensile stress–strain measurements carried to break at 25°, 56°, and 98°C were performed on four samples of carbon black-filled butadiene–acrylonitrile copolymers. All the data were treated with the same equation for time–temperature conversion. The capillary viscosity–shear rate curves were significantly lower than the complex viscosity–angular frequency curves, indicating “strain softening” with extrusion. The viscosity was estimated from the stress–strain relationship at the yield point. The viscosity as a function of the strain rate is significantly higher than the complex viscosity as a function of angular frequency, indicating “strain hardening” with extension. The strain softening and strain hardening are attributable to the structural changes upon deformation of the carbon black-filled elastomers. With the unfilled elastomers, neither strain softening nor strain hardening were observed in similar measurements.     

Crystallization behavior and mechanical properties of polypropylene/modified carbon black composites

Carbon black (CB) modified with small organic molecules was filled in polypropylene (PP) matrix. The crystallization behavior and mechanical properties of PP/modified CB (MCB) composites were investigated. Compared with the original CB, MCB could be dispersed uniformly in smaller particle sizes in PP matrix, and MCB could act as a more effective nucleating, toughening, and reinforcing agent when it was filled in PP at low concentrations. Further increasing of MCB particles in PP matrix resulted in the decrease of impact and tensile strength of PP/MCB composites. It was inferred from DSC results that the existence of CB vand MCB in PP matrix could result in the decrease of crystallite size and degree of perfection of PP. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

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.     

Electrical conductivity and rheological behavior of multiphase polymer composites containing conducting carbon black

Multiphase polymer composites of carbon black (CB), polypropylene (PP) and low density polyethylene (LDPE) were prepared by melt‐mixing method to reduce the amount of CB in the conductive composites. SEM images showed that CB preferably located in LDPE phase and formed electrically conductive path. The measurement of conductive properties showed that the ternary materials possessed lower percolation than binary composites of CB/PP or CB/LDPE, the former was ～6 wt% and the latter was 9–10 wt%. Positive temperature coefficient (PTC) effects of the binary and ternary composites were investigated, indicating that the latter exhibited a relatively high PTC intensity. A rheological percolation estimated by a power law function is 2.66 wt% of CB loading, suggesting an onset of solid‐like behavior at low frequencies. This difference between the electrical and rheological percolation thresholds may be understood in terms of the smaller CB–CB distance required for electrical conductivity as compared with that required to impede polymer mobility. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Dynamic mechanical study of polycarbonate-based block copolymers

The dynamic-mechanical properties of some multi-ABA-type block copolymers were studied using the Rheovibron viscoelastometer. Records of tan δ, loss moduli, and storage moduli were obtained over the temperature range of ?100°C to 200°C (or the upper glass transition temperature) for samples cast from different solvents. Separate glass transitions were apparent when there was phase separation. Under the test conditions, the soft segment or block formed the continuous phase and the associated glass transition was independent of the solvent used. The hard-segment phase was either continuous or discretely aggregated, depending on the solvent used. For hard segments from large monomer molecules, the discretely aggregated phase displayed a greater modulus. The reverse was true when the monomer molecules were small.     

Dynamic rheological behavior of high‐density polyethylene filled with carbon black

The dynamic rheological behavior of high‐density polyethylene (HDPE) composites filled with carbon black (CB) was studied by controlling periodic small shear strains at constant temperatures. The results shed light on the relationship between the behavior of dispersed fillers and polymeric matrix systems. At sufficiently high filler concentration a structural skeleton seems to appear, which significantly raises the modulus at the low frequency region. High structure, finer size acetylene black raises the modulus significantly more than does the low structure and larger size one (e.g., N550). Oxidized CB increases the modulus in the whole frequency region for the enhanced interaction between polymer matrix and CBs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3527–3531, 2002     

Electrical conductivity of polymers containing carbon black

Changes in volume resistivity with temperature of carbon-black-filled polymers and a random copolymer of styrene and butyl methacrylate were measured. For polystyrene containing 20 wt % carbon black, of surface area 24 m²/g, the resistivity changes abruptly from 10¹³ to 10⁶ ohm-cm above 150°C. Poly(butyl methacrylate) did not show well-defined changes in resistivity on heating. The random copolymer containing 16.7 or 28.6 wt % carbon black, of surface area 24 m²/g, showed a resistivity exceeding 10¹³ ohm-cm, that decreased to about 10⁷ ohm-cm on heating above 120°C. This Copolymer containing 16.7 wt % carbon black, of surface area 625 m²/g, shows a resistivity of about 108 ohm-cm that decreases sharply to 10³ ohm-cm by 150°C. Decreases in resistivity on increasing the temperature in the quiescent state are correlated with the observation of a yield stress at low shear rates in rheological studies. It is suggested that carbon black agglomerates at elevated temperature and forms an independent conductive network that prevents flow.     

溶聚丁苯橡胶/炭黑/短纤维多相复合材料的动态力学性能

研究了短纤维用量和黏合水平、测试温度及频率对溶聚丁苯橡胶（SSBR）／炭黑／短纤维复合材料（SFRC）动态力学性能的影响。结果表明,SFRC的储能模量（E’）随短纤维用量的增加而增大;填充预处理短纤维的SFRC的E’大于填充同种未处理短纤维的SFRC,损耗因子（tanδ）则是后者大于前者（填充20份尼龙短纤维的SFRC除外）。与相同填充量的纯炭黑硫化胶相比,短纤维部分取代炭黑后,硫化胶在大于15℃时的E’增大（填充未处理聚酯短纤维的SFRC除外）,tanδ减小;SFRC的E’和tanδ随频率的增加而增大,但频率为50～100Hz时,随着温度的升高,短纤维用量越高,SFRC的E’减小,且E。和tanδ受频率的影响越小。     

Dynamic mechanical behavior of carbonized black cherry wood (prunus serotina ehrh.)

Dynamic mechanical properties from 100 to 300°K have been determined for black cherry specimens carbonized up to 1200°K in a nitrogen atmosphere. It was found that the modulus of carbonized black cherry decreases and then begins to increase as a function of heat-treatment temperature. Modulus values appear to be at a minimum after carbonization to near 600°K. It is demonstrated that the internal friction (100 to 300°K) of the specimens after carbonization is complex.     

Cationic photopolymerization of epoxides containing carbon black nanoparticles

The active centers responsible for cationic photopolymerizations are essentially non-terminating, and continue to propagate after the illumination is ceased. In this contribution, the mobility of the long-lived cationic active centers is investigated for the cure of epoxides containing carbon black nanoparticles. Concentration profiles for the cationic active centers produced during illumination were coupled with an analysis of the active center reactive diffusion during the post-illumination period, revealing that migration of the active centers leads to cure beyond the illuminated depth. A kinetic analysis yielded predicted cure times for coatings of varying thickness and carbon black loading, showing good agreement with experimental results obtained for photopolymerizations of cycloaliphatic diepoxide coatings containing a monodisperse carbon black with mean hydrodynamic radius of 29.2 nm. These results indicate that the long lifetimes and reactive diffusion of cationic active centers may be used for effective curing of coatings containing carbon black nanoparticles. This comprehensive approach could be applied to other opaque nanocomposite systems.     

Dynamic mechanical and thermomechanical properties of silicone-polycarbonate block copolymers

Representative random, alternating block copolymers of polydimethylsiloxane (PDMS) and bisphenol-A-polycarbonate (BPAPC) were studied by thermomechanical and dynamic mechanical techniques. Data on glass transition temperatures (T_g), heat-deflection temperatures (T_d), Vicat softening temperatures (T_s), coefficients of linear expansion (α), stress-strain, and stress relaxation for four PDMS-BPAPC block co-polymers are presented. The effect of casting films from mixed n-hexane-methylene chloride solution on the thermomechanical and dynamic mechanical properties was also studied.     

Dynamic mechanical study of molecular dynamics in ethylene-norbornene copolymers

Dynamic mechanical studies of molecular dynamics have been performed for two ethylene-norbornene copolymers. The analysis of data indicates the existence of three relaxation processes: a primary (α) and two secondary (β and γ) ones. It was found that the secondary processes β and γ are connected with the local motions of ethylene and norbornene groups, respectively and that their rates follow the Arrhenius relation. Moreover, the β process was recognized as the Johari-Goldstein process acting as the precursor of the cooperative structural α-relaxation. Contrary to γ and β processes, the motional rate of α-one follows the Vogel-Fulcher-Tammann equation indicating the cooperative nature of motions involved in this process. An increase in norbornene content in copolymer slows down the molecular dynamics of both norbornene fragments and whole chains, and in consequence shifts these relaxation processes into higher temperatures. Using the Havriliak-Negami formalism the motional parameters for the processes mentioned above were estimated.     

Dynamic mechanical properties of carbon fibers

We have determined the dynamic mechanical properties in a low frequency range (0.01–10 Hz) of carbon and graphite fibers at different temperatures and evaluated the influence of fiber stretching. The results, showing frequency and extension dependent losses and changes in Young's moduli, indicate the presence of relatively large, independently mobile fiber constituents, which appear to correspond to the slowly undulating ribbons recognized earlier as the basic carbon fiber components.     

Effect of carbon black on the mechanical and dielectric properties of rubber ferrite composites containing barium ferrite

Fine particles of barium ferrite (BaFe₁₂O₁₉) were synthesized by the conventional ceramic technique. These materials were then characterized by the X‐ray diffraction method and incorporated in the natural rubber matrix according to a specific receipe for various loadings of ferrite. The rubber ferrite composites (RFC) thus obtained have several applications, and have the advantage of molding into complex shapes. For applications such as microwave absorbers, these composites should have an appropriate dielectric strength with the required mechanical and magnetic properties. The N330 (HAF) carbon black has been added to these RFCs for various loadings to modify the dielectric and mechanical properties. In this article we report the effect of carbon black on the mechanical and dielectric properties of these RFCs. Both the mechanical and dielectric properties can be enhanced by the addition of an appropriate amount of carbon black. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 769–778, 2003