Carbon Black Rubber Compounds Research Articles

Comparative study of radiation effect on rubber–carbon black compounds

Acrylonitrile butadiene rubber (NBR) and ethylene–propylene diene monomer (EPDM) rubber compounds have been prepared without and with 50phr contents of high abrasion furnace carbon black (HAF). Cure characteristics, namely, minimum (Ml) and maximum torque (Mh), scorch time (ts2), the optimum cure time (tc90) and the cure rate index (CRI) have been investigated. Prepared compounds have been subjected to gamma radiation doses up to 200kGy to induce radiation crosslinking and degradation process under atmospheric conditions. Mechanical and physical properties, namely, tensile strength (TS), elongation at break (Eb), hardness (Sh-A), Flory–Huggins parameter (χ), the crosslink density (ν) and the molecular weight of the rubber between two crosslinks (M‾c) have been followed up as a function of irradiation dose. The morphology investigations of prepared compounds were carried out using SEM micrograph. The results obtained indicate that improvement to irradiation has been attained in different properties of carbon black reinforced NBR and EPDM rubber compounds with respect to unloaded ones.

Rheological Properties of Rubber-Carbon Black and Carbon Black-Oil Compounds Including Measurements at Very Low Shear Stresses

Abstract The rheological properties of binary rubber-carbon black compounds at compositions 5, 20, 30, 40 and 50 volume percent carbon black have been investigated as well as ternary compounds with rubber/carbon black/oil compositions of 70/20/10, 60/20/20 and 50/20/30, respectively. The compounds were investigated using (1) a constant stress creep instrument at very low rates of deformation, (2) a rotational rheometer at intermediate shear rates and (3) a capillary extrusion instrument at higher shear rates. In experiment (1), it was found that below a critical yield stress, the strain becomes saturated and finite. Above this stress the strain becomes unbounded and the compound maintained a steady shear flow. This observation was made for all compounds investigated. The values of the yield stresses obtained using the creep instrument were found to be significantly lower than those obtained from common extrapolations from rotational and capillary rheometers. In the ternary compounds it was also observed that as the oil content increases, not only the viscosity but the yield stress is reduced significantly. This observation is important because it can throw light on the type of interactions between carbon black and the rubber matrix.

Microwave Diagnosis of Carbon Black Rubber Compounds and Porosity Estimation in Composites

ABSTRACTThe results of an in depth study of the dielectric properties of various rubber compounds at different microwave frequencies are discussed. Subsequently, the influence of carbon black volume percentage on the dielectric properties of rubber is studied in a wide frequency range (5 -24 GHz). The results show that the real and imaginary parts of rubber dielectric constant increase as a function of increasing carbon black percentage. Frequencies around 5 GHz show more sensitivity to small changes in the carbon volume content. The presence of curatives in uncured rubber samples is detected, which is an indication of the sensitivity of microwaves to the chemical reaction triggered by these curatives. Similar approach is used to measure the air content in specially prepared model material (plastic microbaloon-filled epoxy) samples with varying degrees of uniformly distributed air inclusion. The results of these measurements for a wide range of frequencies is also reported. Measurement analysis resulted in detecting variation in the air volume fraction of around 1.5%. The results confirm the utility of microwave NDE techniques for local porosity detection and evaluation in dielectric composites.

Rheological models of rubber-carbon black compounds: low interaction viscoelastic models and high interaction thixotropic - plastic - viscoelastic models

The rheological behavior of a gum elastomer (natural rubber) and its carbon black compounds is represented in terms of a series of interrelated models. A distinction is made between those compounds with low interaction (large particles or low loadings of small particles) and those with high interaction (large loadings of small particles). The low interaction compounds are treated as viscoelastic materials with filler loading modified properties. The high interaction compounds are represented as 'thixotropic-plastic-viscoelastic' materials. The basic non-linear viscoelastic model used in this paper is that due to Bogue, but other non-linear viscoelastic formulations could be used.

Investigations of the rheological behavior of rubber-carbon black compounds over a wide range of stresses including very low stresses

The rheological properties of gum and carbon black compounds of an ethylene-propylene terpolymer elastomer at 20, 30, 40, and 50 vol.% carbon loadings have been investigated over a very wide range of stresses and shear rates. This was accomplished using (1) a constant shear stress creep instrument, (2) a rotational rheometer and (3) a capillary extrusion rheometer at higher shear rates. The stresses used in the studies included magnitudes leading to shear flow and stresses below the yield value, where rubber compounds exhibit only finite deformation. Much attention was given to measurements of creep and strain recovery at low stresses. The magnitudes of yield stresses obtained from these low stress and recovery experiments are significantly lower than those obtained using standard extrapolation to zero shear rate of higher stresses from rotational and capillary instruments.

Basic Studies of Extrusion of Rubber Compounds in a Pin Barrel Extruder

Abstract An experimental study of the flow, pumping, and mixing characteristics of three different rubber-carbon black compounds in a model pin barrel extruder is presented. These are a model SBR/BR passenger tire compound, a NR truck tire compound, and a NBR mechanical goods compound. Comparisons are made of the initial extruder without pins or slices/grooves in the screw flights, an extruder containing slices or grooves in its flights, and a pin barrel extruder. It is found for each compound that introducing slices in screw flights improves mixing/homogenization and decreases pumping ability. Introduction of pins improves mixing/homogenization and has little effect on pumping. The homogenization is best for the passenger tire tread compound and worst for the NBR mechanical good compound.

Rheological Changes in the Processing of Rubber-Carbon Black Compounds

This work shows that the apparent viscosity and the effective relaxation time of rubber-carbon black compounds can be used to evaluate the quality of mixing along the mixing-milling-extrusion process. These rheo metric functions allow one to estimate the degree of carbon black dispersion in relation to mechanical degradation of polymer chains along the production line. It is found that the Occluded Rubber Model is consistent with experimen tal results, which are obtained through capillary rheometry.

Extrudate character and post-extrusion shrinkage of rheologically characterized rubber-carbon black compounds and their interpretation

An experimental study of extrudate swell and post-die shrinkage is presented for a series of rheologically characterized butadiene styrene copolymer rubber-carbon black compounds with varying carbon black level and particle size. The compounds with 20 vol.% carbon black exhibit yield values which increase with decreasing particle size. Extrusion was investigated at 100°C. Decreasing particle size and increasing particle loading reduce extrudate swell and improve extrudate quality. The post-die shrinkage of the extrudates at 20°C has been examined as a function of time. It is found that there is little additional shrinkage beyond the initial rapid swell. The delayed shrinkage as well as the instantaneous swell order inversely with carbon black particle size and loading. This is interpreted in terms of the rheological properties of the rubber compounds.

Rheological properties, extrudate swell, and die entry extrusion flow marker experiments for rubber–carbon black compounds

AbstractRheological characterization, extrudate swell measurements, and a flow marker extrusion study for several elastomers and their compounds is reported. The materials included natural rubber (NR), styrene–butadiene rubber (SBR), ethylene–propylene terpolymer (EPDM), and polychloroprene (CR) and their carbon black compounds. The shear viscosity was measured with a sandwich rheometer, a shearing disk viscometer, and a capillary rheometer over a wide range of shear rates. Evidence for yield values is found in compounds with 0.20 and 0.30 levels of carbon black. Empirical equations were fit to the data. Extrudate swell measurements were carried out for slit and capillary dies. Increasing the level of carbon black reduces the level of swell. Flow marker experiments were carried out in the barrel of a capillary rheometer using a wide range of die designs. These indicated roughly radial streamline flows into the capillary or slit land. Recessed parts of a die could accumulate stagnant material. Evidence for wall slippage in the rheometer barrel for compounds with 0.20 and 0.30 volume fractions of carbon black is discussed.

Rheological behavior of rubber carbon black compounds in various shear flow histories

The rheological properties of rubber carbon black compounds are studied in various shear flow histories. In particular we studied (i) stress relaxation, (ii) transient and steady state shear flow, (iii) stress relaxation after steady flow, (iv) sequential shear flow history, (v) storage effects, (vi) programmed step shear histories. At low carbon black concentrations, the rheological response is similar in character to that of unfilled elastomers. For carbon black concentrations of 20 percent by volume and above, the compounds exhibit yield values which increase with carbon black concentration and decreasing particle size. The rubber carbon black compounds exhibit ‘hysteresis loops’ in programmed step shear histories and rheological property growth in storage experiments.

Carbon Blacks for Highly Conductive Rubber

Abstract The mechanism of the conductance of the electric current through a carbon black dispersion is still a problem which has not been completely solved. Rubber is an insulator and forms a homogeneous liquid phase, while carbon black is a semi-conductor and forms a dispersible solid phase. Mixtures of these two show electrical properties ranging from a near insulator to a near semiconductor. The picture which has been generally accepted for the mechanism of conductivity in rubber-carbon black compounds is one based on through-going paths of carbon black particles. These through-going paths are formed by carbon black particles either touching or situated so close to adjoining carbon black particles that the electrons have a reasonable chance to jump across the gap. This concept implies that each carbon particle must practically touch its neighbor or else the continuous chain will be broken. The definition of “touching” is not given in this concept. The number of conducting or through-going paths will be a function of loading and the particle size of the carbon black. In addition to the number of the paths, the intrinsic conductivity of the carbon blacks themselves, which is mainly a contact resistance, is of paramount importance. This picture is useful only if it is consistent with the various characteristics of electrically conductive rubber-carbon black compounds.