Volume Fraction Of Rubber Research Articles

Effect of zinc oxide nanoparticles as cure activator on the properties of natural rubber and nitrile rubber

AbstractZinc oxide (ZnO) nanoparticles were synthesized by homogeneous precipitation and calcination method and were then characterized by transmission electron microscopy and X‐ray diffraction analysis. Synthesized ZnO was found to have no impurity and had a dimension ranging from 30–70 nm with an average of 50 nm. The effect of these ZnO nanoparticles as cure activator was studied for the first time in natural rubber (NR) and nitrile rubber (NBR) and compared with conventional rubber grade ZnO with special reference to mechanical and dynamic mechanical properties. From the rheograph, the maximum torque value was found to increase for both NR and NBR compounds containing ZnO nanoparticles. ZnO nanoparticles were found to be more uniformly dispersed in the rubber matrix in comparison with the conventional rubber grade ZnO as evident from scanning electron microscopy/X‐ray dot mapping analysis. The tensile strength was observed to improve by 80% for NR when ZnO nanoparticles were used as cure activator instead of conventional rubber grade ZnO. An improvement of 70% was observed in the case of NBR. The glass transition temperature (Tg) showed a positive shift by 6°C for both NR and NBR nanocomposites, which indicated an increase in crosslinking density. The swelling ratio was found to decrease in the case of both NR and NBR, and volume fraction of rubber in swollen gel was observed to increase, which supported the improvement in mechanical and dynamic mechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Oil Distribution in iPP/EPDM Thermoplastic Vulcanizates

Abstract Scanning Probe Microscopy (SPM) was used to determine the volume fraction of oil-swollen particulate rubber and oil-swollen plastic in thermoplastic vulcanizates (TPVs) produced from iPP and EPDM rubber. Sample preparation and SPM imaging conditions allowed the ratio of the rubber and plastic area imaged for a TPV sample to be equated to the phase volume ratio. The hydrosilylation cured TPVs contained no filler or inorganic components (other than about 1 ppm of platinum catalyst, based on dry rubber) that would decrease the accuracy of the SPM analysis. The accuracy of the SPM method used for TPV phase volume determination was established by analysis of an oil-free TPV of known composition. The densities of the individual TPV components (rubber, oil, crystalline and amorphous plastic phase), which were assumed to be additive in the composite, were used to calculate the oil distribution between the TPV rubber and plastic phase, since the volumes of the individual components (the extent of plastic crystallinity was measured by differential scanning calorimetry) were known. Thus, the amount of oil in the oil-swollen TPV rubber and plastic phase could be quantified. This information, coupled with the Tg of the oil-swollen amorphous plastic phase, indicated that a substantial amount of oil was present as a separate oil phase that is surrounded by the oil-swollen amorphous plastic phase. To date, it has been assumed that the oil in a TPV partitions between the rubber and amorphous plastic phase, with the plastic crystallites being oil free. This work is the first demonstration of the presence of a separate oil phase in TPVs, and the first accurate determination of the oil content in the oil-swollen rubber, miscible oil in the oil-swollen amorphous plastic, and the free oil in TPVs.

Evaluation of the polymer–solvent interaction parameter χ for the system cured styrene butadiene rubber and toluene

One of the most popular cured rubbers used in industrial applications is styrene butadiene rubber (SBR) and frequently its network structure is studied by means of swelling techniques in solvent. Normally, toluene is used as solvent in this test. In order to estimate the crosslink density from the equilibrium volume fraction of rubber in the swollen state, the correct evaluation of the Flory–Huggins interaction parameter χ is necessary. This work covers the swelling behavior of cured SBR in toluene. The rubber was vulcanized with different amounts sulfur and accelerator at 433 K in order to obtain several network structures and crosslink densities. Network characterisations of the compounds were made by swelling measurements in the frame of the Flory–Rehner relationship using the molecular weight of the network chain between chemical crosslinks obtained previously by mechanical tests. A relationship between χ and v r, the polymer volume fraction at equilibrium (maximum) degree of swelling, was established for the cured SBR/toluene system. It was found that χ is not a constant but depends on the crosslink density in the sample. The types of crosslinks in these samples where estimated applying this function to the swelling behavior of the compounds previously treated with the thiol probe method.

Curing and Physical Properties of Natural Rubber/Wood Flour Composites

AbstractNatural rubber based composites were prepared by incorporating Wood flour of two different particle size ranges (250–300 µm) and (300–425 µm) and concentrations (15 and 30 phr) into the matrix, using a Banbury® internal mixer according to a base formulation. Curing characteristics of the samples were studied. Influence of particle size and loading of filler on the properties of the composites was analyzed. Results obtained show that the addition of wood flour to natural rubber increased scorch time and curing time and caused improvement in modulus at 300% strain and in tear properties. However, it decreased tensile strength and elongation at break. The particle size range of 300–425 µm was found to offer the best overall balance of mechanical and dynamic properties (tan δ and viscous torque). Swelling behavior of the composites in toluene was also analyzed in order to determine the rubber volume fraction and crosslinking density. Composites with the bigger particle size wood flour were found to have greater crosslinking density than the ones with smaller particle size, fact that could possibly indicate a better rubber‐filler interaction in the former. Major percentage of filler increased slightly this interaction. Water absorption behavior of the composites with wood flour reached a maximum of 12% w/w when 30 phr of filler were incorporated; nonetheless, particle size did not affect this property. The ageing study in presence of air at 70 °C revealed that natural rubber composites with wood flour maintained the same classification cell with temperature as the pure rubber. A compound with 30 phr of carbon black was prepared for comparative purposes. Results obtained were as expected. Scorch time decreased and higher values of modulus at 300% strain and tensile strength were achieved, due to strongest interaction between filler and elastomer.

Prediction of properties of rubber by using artificial neural networks

AbstractDifferent rubber formulations were designed using nitrile rubber and a mixed crosslinking system consisting of sulfur/accelerator and electron beam radiation. Based on the experimental results, an artificial neural network (ANN) was constructed to simulate the mechanical properties and volume fraction of rubber. The ANN could predict accurately the above properties for a series of nitrile rubber compounds. However, the number of training data played a key role in the ANN predictive quality. In addition, the more complex the nonlinear relation between input and output was, the larger was the number of training dataset required. The predicted results were further validated using another mathematical model. The constructed ANN was verified with a completely different styrene butadiene rubber system. The prediction was found to be extremely good. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2227–2237, 2006

Effect of curing temperature, fibre loading and bonding agent on the equilibrium swelling of isora-natural rubber composites

Isora fibre-reinforced natural rubber (NR) composites were cured at 80, 100, 120 and 150°C using a low temperature curing accelerator system. Composites were also prepared using a conventional accelerator system and cured at 150°C. The swelling behavior of these composites at varying fibre loadings was studied in toluene and hexane. Results show that the uptake of solvent and volume fraction of rubber due to swelling was lower for the low temperature cured vulcanizates which is an indication of the better fibre/rubber adhesion. The uptake of aromatic solvent was higher than that of aliphatic solvent, for all the composites. As the fibre content increased, the solvent uptake decreased, due to the superior solvent resistance of the fibre and good fibre–rubber interactions. The bonding agent improved the swelling resistance of the composites due to the strong interfacial adhesion. Due to the improved adhesion between the fibre and rubber, the ratio of the change in volume fraction of rubber due to swelling to the volume fraction of rubber in the dry sample (Vτ ) was found to decrease in the presence of bonding agent. At a fixed fibre loading, the alkali treated fibre composite showed a lower percentage swelling than untreated one for both systems showing superior rubber–fibre interactions.

The interrelation among network structures, molecular transport of solvent, and creep behaviors of TiB2 ceramic containing butyl rubber composites

AbstractSwelling of polymer composites in solvents has become one of the major problems in the use of polymer composites exposed to petroleum products. As a possible solution to the problem, this experimental study was conducted to examine the potential application of TiB2 ceramic in butyl rubber (IIR) composites. The effect of TiB2 content on the curing kinetics of IIR composites was studied using a torque rheometer technique. The effect of TiB2 on the network structure was investigated in terms of the crosslinking density, interparticle distance between conducting particles, surface tension, glass transition temperature, degree of crystallinity, scanning electron microscopy, and X‐ray analysis. Moreover, the effect of TiB2 content on the molecular transport of solvent (kerosene) was examined by means of degree of swelling, solvent interaction parameters, volume fraction of rubber, interparticle distance after swelling, penetration rate of solvent, mean diffusion coefficient, cohesive energy density of polymer, standard entropy, standard enthalpy, and standard free energy of IIR composites. It was ascertained that with increasing TiB2 content the degree of swelling shifts to a lower value. The main reason was interpreted as the introduction of good interface adhesion of TiB2 with rubber matrix, which tends to block the diffusion of solvent molecules. The effect of TiB2 content on hardness, tensile strength, Young's modules, and elongation at break is discussed. An apparent steady‐state creep of butyl rubber IIR/TiB2 composites is evident under different constant stresses at room temperature. The strain rate of steady‐state creep showed a dependence on stress and TiB2 volume fraction. The stress sensitivity parameter, viscosity coefficient, and activation volume for samples loaded with different content of TiB2 were estimated. It is apparent that these new composites should be very useful for solvent permeation resistance at high TiB2 loading level with good mechanical properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2226–2235, 2005

Cure characteristics and mechanical properties of short nylon fiber‐reinforced nitrile rubber composites

AbstractAcrylonitrile butadiene rubber (NBR)‐based composites were prepared by incorporating short nylon fibers of different lengths and concentration into the matrix using a two‐roll mixing mill according to a base formulation. The curing characteristics of the samples were studied. The influence of fiber length, loading, and rubber crosslinking systems on the properties of the composites was analyzed. Surface morphology of the composites has been studied using Scanning Electron Microscopy (SEM). Addition of nylon fiber to NBR offers good reinforcement, and causes improvement in mechanical properties. A fiber length of 6 mm was found to be optimum for the best balance of properties. It has been found that at higher fiber loadings, composites show brittle‐type behavior. Composites vulcanized by the dicumyl peroxide (DCP) system were found to have better mechanical properties than that by the sulfur system. The swelling behavior of the composites in N,N‐dimethyl formamide has been analyzed for the swelling coefficient values. Composites vulcanized in the DCP system were found to have higher rubber volume fraction than that in the sulfur system, which indicates better rubber–fiber interaction in the former. The crosslink densities of various composites were also compared. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1023–1030, 2004

Investigation on interfacial adhesion of short sisal/coir hybrid fibre reinforced natural rubber composites by restricted equilibrium swelling technique

Interfacial adhesion of sisal/coir hybrid fibre reinforced natural rubber (NR) composites has been characterized by restricted equilibrium swelling technique with special reference to the effects of fibre loading, orientation and bonding agent. The swelling parameters of NR composites with and without bonding agent were evaluated with three aromatic solvents, namely; benzene, toluene and xylene, by a sorption gravimetric method. As fibre content and penetrant size increase, the solvent uptake has been found to decrease due to the increased hindrance and good fibre–rubber interaction. The bonding agent added mixes showed enhanced restriction to swelling and it is seen that the ratio of change in volume fraction of rubber before and after swelling to the volume fraction of rubber before swelling (V 0 – V r/V 0) is lower for bonding agent added composites, when compared to an unbonded one. The anisotropic swelling studies were carried out to analyse the extent of fibre alignment and fibre–matrix interaction. In strongly bonded composites, the swelling has been mainly observed to take place in the thickness direction, as attested by optical photographs. The rubber–fibre interaction has also been examined by Lorenz–Parks and Kraus equations.

Effects of Accelerator Type and Curing Temperature on Crosslink Distributions and Tensile Properties of Natural-Acrylic Rubber Blends

Abstract Effects of curing temperature and accelerator type on tensile properties of natural-acrylic rubber blends (NR:ACM) were investigated. Three different types of accelerators namely, MBT, ZDEC and DPG, were separately compounded with the rubber blends (50/50, % w/w) along with stearic acid, ZnO, sodium stearate, and sulfur (S) on a two-roll mill. The compounded blends were vulcanized to their optimum cure time in a hydraulic press at 150 and 170 °C. Morphology and tensile properties of the rubber blends were determined by using a scanning electron microscope and a universal testing machine, respectively. Crosslinking characteristics of both NR and ACM phases in the rubber blends were investigated by using a swollen state 1H-NMR and a differential swelling technique. From the tensile test, it was found that strength and strain of the blend vulcanized with the S/ZDEC curing system were remarkably lower than those of the blends vulcanized with the S/MBT and S/DPG systems. The superior tensile properties of the two latter blending systems were accompanied by greater chain mobility of both of the NR and ACM molecules, along with a lower volume fraction of rubber in swollen gel (Vr) of the both NR and ACM phases. These changes were discussed in the light of various possibilities including curative distribution, which were affected by the accelerator type. In term of the effects of curing temperature, it was found that Vr and tensile properties of the blends did not significantly change with the temperature.

Use of χ As a Function of Volume Fraction of Rubber to Determine Crosslink Density by Swelling

Abstract A technique is described allowing a relatively simple determination of χ as a function of vr from swelling in heptane. A good measure of the true νe of the cured elastomer at all values of vr was demonstrated by substituting this relationship for χ in the Flory-Rehner (F-R) equation. The relationship was established over a wide range of vr values by using samples that had the νe of the cured elastomer determined by tensile retraction (TR). Applying this function to samples treated using the thiol probe method of Campbell gave an improved measure of the types of crosslinks present in sulfur-cured stocks. An identical equation describing χ as a function of vr in heptane was obtained with NR, EPDM and SBR containing up to a 0.31 volume fraction of carbon black (CB) and other fillers. The presence of up to 10 % of clay, talc, silica, resins or metal oxides in the CB had no noticeable effect on the relationship measured. However, when the filler contained about 50% silica a distinctly different slope in the relationship was found. The percent S1, S2 and Sx distribution measured was contrasted between measurements made by 13C NMR, swelling with χ = constant or χ as a function of vr.

Criteria for cavitation of rubber particles: Influence of plastic yielding in the matrix

The principles of the cavitation criteria for rubber particles in polymeric matrices are briefly reviewed. Although these criteria are based on a linear elastic analysis, it is shown that it is possible to extend them to take into account the elastic-plastic behaviour of the matrix. In this objective, the representative volume element of a periodic material was meshed and computations were performed using a finite element method. The results reported in this paper focus mainly on cavitation under uniaxial tension and examine the influence on the hydrostatic stress in the rubber particles of different parameters such as the volume fraction of rubber, the plastic behaviour of the matrix or the ratio of the elastic moduli. In all cases, plastic yielding in the matrix leads to saturation of the hydrostatic stress in the rubber phase. It is also shown that the history of cavitation barely influences the progression of plasticity in the matrix.

New double negative and positive temperature coefficients of conductive EPDM rubber TiC ceramic composites

In this paper, we have successfully prepared ethylene–propylene-diene monomer (EPDM)/TiC composites as thermistors, with new double negative and positive temperature coefficients of conductivity (NTCC/PTCC). EPDM composites loaded with 50 phr HAF carbon black and different concentrations of TiC were prepared. This study focuses on the effect of TiC content on the vulcanization process, the network structure and the electrical and thermal properties of EPDM/TiC composites. The effect of TiC on the network structure was evaluated e.g. the curing process, the characteristic time constant during vulcanization, the volume fraction of rubber, gel fraction, interparticle distance between conductive particles, the extent of TiC reinforcement in the rubber matrix and molecular weight between cross-linking through experimental and affine–phantom models. The effects of TiC content on the percolation theory, electrical conductivity, conducting mechanism of conductivity, conducting hysteresis and I– V characteristics were also studied, as well as its TiC on the (NTCC/PTCC), thermoelectric power, dielectric constant and thermal conductivity. Stability and reproducibility of the thermal cycles for heating element applications was tested. Specific heat and the amount of heat transfer by radiation and convection as a function of TiC content was calculated using both the calorimetric technique and a theoretical model. It was proved that TiC improves the network structure, electrical and thermal properties of EPDM composites for practical applications.

Optimization of physical and mechanical properties of rubber compounds by a response surface methodological approach

Response surface methodology was used for optimizing the ratio of vegetable oil and carbon black and occluded volume fraction of rubber in the compound. Central composite design for two variables was chosen as the experimental design. The data obtained from measurement of properties was fitted as a two variable second-order equation, and were plotted as contours using software developed from MATLAB v.5.1. From contours it is observed that at the ratio of 0.06 of vegetable oil and carbon black, there is maximum coupling, and a further increment in vegetable oil and carbon black ratio shows less coupling and more plasticizing effect. The ultimate failure properties like tensile and tear strength and elongation decreases with an increase in occluded volume fraction, reaches a minima at the central region, followed by an increase, whereas 300% modulus and hardness decreases throughout.© 2001 John Wiley & Sons, Inc, J Appl Polym Sci 82: 997-1005, 2001

Optimization of physical and mechanical properties of rubber compounds by a response surface methodological approach

AbstractResponse surface methodology was used for optimizing the ratio of vegetable oil and carbon black and occluded volume fraction of rubber in the compound. Central composite design for two variables was chosen as the experimental design. The data obtained from measurement of properties was fitted as a two variable second‐order equation, and were plotted as contours using software developed from MATLAB v.5.1. From contours it is observed that at the ratio of 0.06 of vegetable oil and carbon black, there is maximum coupling, and a further increment in vegetable oil and carbon black ratio shows less coupling and more plasticizing effect. The ultimate failure properties like tensile and tear strength and elongation decreases with an increase in occluded volume fraction, reaches a minima at the central region, followed by an increase, whereas 300% modulus and hardness decreases throughout.© 2001 John Wiley & Sons, Inc, J Appl Polym Sci 82: 997‐1005, 2001

Joule heating treatments of conductive butyl rubber/ceramic superconductor composites: a new way for improving the stability and reproducibility?

The present paper describes the effect of superconductors on the sintering process, apparent cross-linking density, sintering factor, hardness and volume fraction of butyl rubber (IIR) composites. Electrical conductivity and I– V characteristics at various processing conditions of IIR with different concentrations of superconductor were measured. The stability and reproducibility of IIR composites were tested. Also, the conduction mechanism of electrical conductivity is discussed. Specific heat and the amount of heat transferred by radiation and convection were calculated via the proposed model and calorimetry as a function of superconductor content. It was found that superconductor accelerates the driving force during the sintering process and the characteristic time constant during sintering decreases while the sintering factor, the apparent cross-linking density, hardness and volume fraction of rubber increases as the content of superconductor increases. In addition, it was proved that the superconductor and Joule heating effect improves the electrical and thermal properties of IIR.

Influence of solvent transport on physico-chemical properties of crosslinked butyl rubber filled with TiC ceramic

Understanding the vulcanization and swelling behavior of polymers is potentially important for composite materials, since vulcanization and swelling may significantly influence the electrical and mechanical properties. This work investigates the effect of TiC content on vulcanization reaction and on network structures like the characteristic time constant of vulcanization, vulcanization factor, volume fraction of rubber, extent of filler and interparticle distance between conductive particles. The crosslinking density of the rubber was calculated by the Flory–Rehner equation. The affine and phantom models for physical crosslinks were used to predict the nature of crosslinks. The experimental results were compared with the theoretical predictions. Sorption and diffusion of kerosene were investigated through butyl rubber (IIR) composites reinforced with different concentration of TiC ceramic. Effect of TiC concentration and temperature on solvent uptake and mechanism of diffusion were studied in detail and the experimental diffusion data compared with theoretical predictions. Concentration profiles of the kerosene were calculated to predict the applicability of these composites under extreme service conditions. The apparent activation energy of diffusion and some useful thermodynamic parameters like enthalpy, entropy, Gibbs free energy and heat of sorption were calculated. An abrupt increase in electrical resistivity appears after a characteristic time of swelling. Mechanical properties increase with the addition of TiC reinforcing filler, and decrease after swelling with kerosene (compared with that before swelling with kerosene). In conclusion, it was found that TiC improves the network structure and slows the diffusion of kerosene into the polymer by acting as a barrier.

Interfacial adhesion in sisal fiber/SBR composites: an investigation by the restricted equilibrium swelling technique

Short sisal fiber-reinforced styrene butadiene rubber (SBR) composites were prepared and characterized by the restricted solvent swelling technique. The solvent swelling characteristics of SBR composites containing untreated and bonding agent-added mixes were investigated in a series of aromatic solvents, such as benzene, toluene, and xylene. The diffusion experiments were conducted by the sorption gravimetric method. The adhesion between the rubber and short sisal fibers was evaluated from the restricted equilibrium swelling measurements. The anisotropy of swelling of the composite was confirmed by this study. The effect of fiber orientation in controlling the anisotropy of restricted swelling was also demonstrated. As the fiber content increased, the solvent uptake decreased, due to the increased hindrance and good fiber-rubber interactions. Bonding agent-added mixes showed enhanced restriction to swelling, due to the strong interfacial adhesion. The bonding system containing hexa-resorcinol in the mix produces an in-situ resin, which binds the fiber and the rubber matrix firmly. In addition, as the penetrant size increases from benzene to xylene, the uptake decreases. The swelling index values of the composites support this observation. Due to the improved adhesion between the short sisal fiber and SBR, the ratio of the volume fraction of rubber in the dry composite sample to the swollen sample (V T) decreases. The extent of fiber orientation of the composites was also analysed from the restricted swelling method. SEM studies of the composite revealed the orientation of short fibers. The sorption data support the Fickian diffusion trend, which is typical in the case of cross-linked rubbers.

Effects of interfacial adhesion on the rubber toughening of poly(vinyl chloride) Part 2. Low-speed tensile tests

The influence of interfacial adhesion on the tensile properties, including toughness, of poly(vinyl chloride) (PVC)–nitrile rubber (NBR) blends with the morphology of well-dispersed rubber particles has been investigated using two types of blends. The first type, which contains NBR26 (NBR with 26wt% acrylonitrile (AN)), has a higher interfacial adhesion strength than the second type that contains NBR18. The secant modulus and yield stress of the blends were found to be independent of interfacial adhesion. On the other hand, the elongation-at-break and toughness (defined as the area under the stress–strain curve to break) depend strongly on the interfacial strength. The effects of rubber particle size, size distribution and rubber volume fraction on the tensile properties have been combined into the effect of a single morphological parameter, the matrix ligament thickness T. Both the elongation-at-break and toughness increase as T decreases. At T<0.06μm the blends with stronger interfacial adhesion (PVC–NBR26) have much higher elongation-at-break and toughness. Stress whitening was observed in all deformed PVC–NBR18 blends. For PVC–NBR26 blends, however, stress whitening occurred only at T>0.06μm. Transmission electron microscopy studies revealed that debonding at the PVC–NBR interface is the sole microvoiding mechanism that causes stress whitening.

Electron beam modification offilled fluorocarbon rubber

The effect of electron beam irradiation on the properties of carbon black-, silica-, and clay-filled fluorocarbon rubber has been studied over a range of radiation doses, loadings, and nature of the fillers. Compared to the unfilled irradiated rubber, the tensile strength and modulus improve with a decrease in the particle size of the carbon black filler. Similar improvement in these properties is observed with an increase in both the radiation dose and the amount of the filler upto a certain level. The dynamic mechanical analysis reveal an increased glass transition temperature (Tg), a reduced value of the mechanical loss factor at Tg. and an enhanced dynamic storage modulus for the filled samples. The results are explained with the help of sol-gel analysis and volume fraction of rubber. It is observed that higher reinforcement in the case of the filled vulcanizate is obtained by electron beam modification, as compared to that using the conventional curing system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2016–2025, 2000