Showing papers on "Natural rubber published in 1999"

Rubberized Portland Cement Concrete

Abstract: The use of recycled tire rubber in a portland cement concrete (PCC) mixture is investigated as a possible alternative for nonconventional PCC mixtures. This study is focused on the determination of the practicality of producing such mixes and evaluating their engineering properties. An experimental program was developed to use two types of tire rubber (fine crumb rubber and coarse tire chips) in PCC mixtures. A control PCC mix is designed using American Concrete Institute mix design methods, and three groups of rubberized PCC mixes were developed by partially replacing the aggregate with rubber. Eight tire rubber contents were used in each group. Mixes were tested in compressive and flexural strength in accordance to ASTM standards. Results show that rubberized PCC mixes can be made and are workable to a certain degree with the tire rubber content being as much as 57% of the total aggregate volume. However, strength results show that large reductions in strength would prohibit the use of such a high rubber content. It is suggested that rubber contents should not exceed 20% of the total aggregate volume. A characteristic function that quantifies the reduction in strength for rubberized concrete mixes was developed that could be useful for mix design purposes. Rubberized concrete mixes may be suitable for nonstructural purposes such as lightweight concrete walls, building facades, and architectural units. They could also be used as cement aggregate bases under flexible pavements. Fire hazards are of major concern and need to be thoroughly investigated before recommendations for practical implementation are drawn.

Giant Wormlike Rubber Micelles

Abstract: A low molecular weight poly(ethyleneoxide)-poly(butadiene) (PEO-PB) diblock copolymer containing 50 weight percent PEO forms gigantic wormlike micelles at low concentrations (<5 percent by weight) in water. Subsequent generation of free radicals with a conventional water-based redox reaction leads to chemical cross-linking of the PB cores without disruption of the cylindrical morphology, as evidenced by cryotransmission electron microscopy and small-angle neutron scattering experiments. These wormlike rubber micelles exhibit unusual viscoelastic properties in water.

Magnetorheological elastomers : Properties and applications

Abstract: Magnetorhelogical (MR) elastomers are viscoelastic solids whose mechanical properties are controllable by applied magnetic fields. We have developed a family of MR elastomers, comprising micrometer-sized carbonyl iron particles embedded in natural rubber, that can be processed using conventional rubber-mixing techniques. By crosslinking the elastomer in the presence of an applied magnetic field, field-induced interparticle interactions promote the formation of particle chains and columns aligned along the field direction. The resulting composites possess field- dependent of the mechanical properties of MR elastometers enables the construction of controllable elastomeric components, such as suspension bushings, that may prove advantageous in some automotive applications.

Polymer toughness and impact resistance

Abstract: This report is a review of the factors that influence the impact resistance of high polymers, with an emphasis on crystalline polymers. The phenomenology of polymeric fracture is examined, including brittle and ductile failure, and the ductile-brittle transition temperature (DBTT). An in-depth discussion of the effects of crystalline morphology follows, with special attention given to the influence of spherulite size, fillers, processing conditions, transitions/relaxations, and multilayer coextrusion. Next, rubber phase addition is considered, including mechanisms, morphology, rubber type and particle size, and test conditions. Finally, common impact test methods are surveyed, including pendulum, falling weight, tensile impact, and tensile elongation tests.

The role of filler networking in dynamic properties of filled rubber

Abstract: Fillers, when added to polymer systems, are known to cause a considerable change in dynamic properties. For a given polymer and cure system, this paper discusses the impact of the filler network, both its strength and architecture, on the dynamic modulus and hysteresis during dynamic strain. It was found that the filler network can substantially increase the effective volume of the filler due to rubber trapped in the agglomerates, leading to high elastic modulus. The amount of trapped rubber was estimated according to Van der Poel theory. During cyclic strain, while the stable filler network can reduce the hysteresis of the filled rubber, the breakdown and reformation of the filler network would cause an additional energy dissipation resulting in higher hysteresis.

Viscoelastic properties of plasticized PVC reinforced with cellulose whiskers

Abstract: New nanocomposites are processed with a plasticized poly(vinyl chloride) matrix reinforced by cellulose whiskers whose characteristics are a high aspect ratio and a large interface area. Dynamic mechanical analysis performed on samples rein- forced with a filler fraction of up to 12.4 vol % gives the viscoelastic properties of the composite above and below its glass transition temperature. Different theoretical predictions are proposed to describe this behavior, but none of them is found wholly satisfactory for describing the reinforcing effect of these fillers. A model based on the Halpin-Kardos equation, with the assumption of an immobilized phase around the whiskers, is developed to account for significant decrease in the modulus drop, on passing above the glass transition temperature. The small discrepancy between this model and the experimental modulus measured in the rubber plateau is discussed as a possible effect of a percolating whisker network whose crosslinks are assured by chains adsorbed onto the whisker surface. Swelling experiments support this hypothesis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1797-1808, 1999

Prehistoric polymers: rubber processing in ancient mesoamerica

Abstract: Ancient Mesoamerican peoples harvested latex from Castilla elastica, processed it using liquid extracted from Ipomoea alba (a species of morning glory vine), and fashioned rubber balls, hollow rubber figurines, and other rubber artifacts from the resulting material. Chemical and mechanical analyses of the latex and of the processed rubber indicate that the enhanced elastic behavior of the rubber relative to the unprocessed latex is due to purification of the polymer component and to an increase in the strength and number of interchain interactions that are induced by organic compounds present in I. alba. These ancient peoples' control over the properties of latex and processed rubber gave rise to the Mesoamerican ball game, a central ritual element in all ancient Mesoamerican societies.

Rubber composition, method of adding and blending the composition and vehicle tire made from the composition

Abstract: A rubber composition which contains a rubber mixture that can be vulcanized with a vulcanizing agent, which includes at least one rubber component, at least one filler having nucleophilic groups, gel particles comprising a rubber, having a particle size between about 3x10-9 and about 1x 10-6 m and a swelling index in toluene of about 1 to about 15 and whose surface has electrophilic centers, and a substance acting as a coupling agent between tile filler having nucleophilic groups and the additional filler, the substance acting as a coupling agent having the following structure: X - R1 -Si - (R2)3, wherein X is a nucleophilic group, R1 is an alkyl group having up to about 6 carbon atoms or a phenyl group, and R2 may be the same as or different from each other and from R1 and is an alkyl or alkoxy group having up to 6 carbon atoms and at least one of R2 is an alkoxy group. The rubber composition has improved hysteresis behavior in the vulcanized state so that with the use of this rubber composition in tires, the rolling resistance is reduced and the wet slippage behavior is improved in relation to conventional rubber compositions. A method of adding and blending the rubber composition as well as a composition useful for tire treads and vehicle tires containing the composition are disclosed.

Rubber composition, method of formulating and blending the same and article and vehicle tire made therefrom

Abstract: A rubber mixture containing at least one rubber component, at least one filler, and conventional additives that it contain at least one first gel as a filler, which is essentially comprised of a rubber, has a particle size of 3x10 -9 to 1x10 -6 m, and has a swelling index in toluene of 1 to 15, and at least the surface of this gel has acid or base groups, where these groups have not been produced by means of reaction with dithiophosphonic acid, and comprises: a) at least one second gel as an additional filler, which is essentially comprised of a rubber, has a particle size of 3x10 -9 to 1x10 -6, and has a swelling index in toluene of 1 to 15, which is in a position to undergo a neutralization reaction with the acid or base groups of the first gel and/or b) contains at least one substance as an additional additive, which is capable of undergoing a neutralization reaction with the acid or base groups of at least one gel. The rubber mixture demonstrates an improved hysteresis behavior in the vulcanized state so that, with the use of thin rubber mixture in tires, for example, the rolling resistance is reduced and the wet slippage behavior is improved in relation to the conventional rubber mixture. Methods of formulating such rubber mixtures are also provided.

Rubber particles from four different species, examined by transmission electron microscopy and electron-paramagnetic-resonance spin labeling, are found to consist of a homogeneous rubber core enclosed by a contiguous, monolayer biomembrane

Abstract: The physical characteristics of rubber particles from the four rubber (cis-1,4-polyisoprene) producing species Euphorbia lactiflua Phil., Ficus elastica Roxb., Hevea brasiliensis Mull. Arg., and Parthenium argentatum Gray, were investigated using transmission electron microscopy (TEM) and electron-paramagnetic-resonance (EPR) spin labeling spectroscopy. Transmission electron microscopy showed the rubber particles to be composed of a spherical, homogeneous, core of rubber enclosed by a contiguous, electron-dense, single-track surface layer. The biochemical composition of the surface layer and its single-track TEM suggested that a monolayer biomembrane was the surface structure most compatible with the hydrophobic rubber core. The EPR spectra for a series of positional isomers of doxyl stearic acid, used to label the surface layer of the rubber particles, exhibited flexibility gradients and evidence for lipid-protein interactions for all four rubber particle types that is consistent with a biomembrane-like surface. The EPR spectra confirmed that the surface biomembrane is a monolayer. Thus, rubber particles appear similar to oil bodies in their basic architecture. The EPR spectra also provided information on protein location and degree of biomembrane penetration that correlated with the known properties of the rubber-particle-bound proteins. The monolayer biomembrane serves as an interface between the hydrophobic rubber interior and the aqueous cytosol and prevents aggregation of the particles. An unexpected observation for the probes in pure polyisoprene was evidence of an intrinsic flexibility gradient associated with the stearic acid molecule itself.

Coupling system (white filler/diene elastomer) based on polysulphide alkoxysilane, zinc dithiophosphate and guanidine derivative

Abstract: The invention concerns a coupling system (white filler/diene elastomer) for a rubber composition based on diene elastomer reinforced with a white filler, formed by combining a polysulphide alkoxysilane, a zinc dithiophosphate and a guanidine derivative. The invention also concerns a rubber composition useful for making tyres, comprising at least (i) a diene elastomer (ii) a white filler as reinforcing agent, (iii) a polysulphide alkoxysilane, (iv) a zinc dithiophosphate and (v) a guanidine derivative. The invention further concerns a method for preparing said rubber composition. Finally the composition concerns a tyre or semi-finshed product in particular a running tread for tyre comprising said rubber composition.

Rubber composition, method of formulating the composition and vehicle tire made from the composition

Abstract: A rubber composition, which contains a rubber mixture that can be vulcanized with a vulcanizing agent, which includes at least one rubber component, at least one filler, gel particles comprising a rubber, having a particle size between about 3×10-9 and about 1×10-6 m and a swelling index in toluene of about 1 to about 15 and whose surface has electrophilic centers, and a substance which acts as a coupling agent between the gel particles and which has the structure A--R--A, wherein A is a nucleophilic group, and R is a saturated or unsaturated hydrocarbon group. The rubber composition has improved hysteresis behavior in the vulcanized state so that when this rubber composition is used in tires, the rolling resistance is reduced and the wet slippage behavior is improved in relation to the conventional rubber compositions. A method of formulating the rubber composition as well as a composition useful for tire treads and vehicle tires containing the composition are disclosed.

Process and reactor for microwave cracking of plastic materials

Abstract: A process of activated cracking of high molecular organic waste material which includes confining the organic waste material in a reactor space as a mixture with a pulverized electrically conducting material (sensitizer) and/or catalysts and/or “upgrading agents” and treating this mixture by microwave or radio frequency electro-magnetic radiation. Organic waste materials include hydrocarbons or their derivatives, polymers or plastic materials and shredded rubber. The shredded rubber can be the source of the sensitizer and/or catalyst material as it is rich in carbon and other metallic species. This sensitizer can also consist of pulverized coke or pyrolytically carbonized organic feedstock and/or highly dispersed metals and/or other inorganic materials with high dielectric loss which absorb microwave or radio frequency energy.

Dielectric properties of rubber ferrite composites containing mixed ferrites

Abstract: Rubber ferrite composites (RFC) are important since they have useful applications as microwave absorbers and flexible magnets. The mouldability of these composites into complex shapes is another advantage. The evaluation of their dielectric and magnetic properties is important in understanding the physical properties of these composites. Pre-characterized nickel zinc ferrites (Ni1-xZnxFe2O4 where 0 x1 in steps of 0.2) prepared by ceramic techniques were incorporated in to a butyl rubber matrix according to a specific recipe to yield RFCs. The dielectric constant of ceramic Ni1-xZnxFe2O4 and the butyl rubber composites incorporated with Ni1-xZnxFe2O4 are studied as a function of frequency, composition, loading and temperature. The observed data indicates that the dependence of the dielectric constant on frequency follows Maxwell-Wagner interfacial polarization. The compositional (zinc content, i.e. x value) dependence shows that the dielectric constant increases initially and reaches a maximum value for the composition corresponding to x = 0.6 and thereafter it decreases. This can be explained on the basis of porosity and alternating current (AC) conductivity. It was also observed that the dielectric constant of the composite material increases with an increase of the volume fraction of the magnetic filler. These observations satisfy some mixture equations, which correlate the dielectric constant of the matrix, filler and the composites. The temperature dependence of the dielectric constant of the ceramic samples as well as the RFCs shows an increase with an increase of temperature at low frequencies. The dielectric constant of the blank butyl rubber was also determined. It was observed that for a blank sample (without filler) the dielectric constant decreases with an increase of temperature. This is due to the decrease in polymer density with increase in temperature. These results suggest that the magnetic and dielectric properties of RFCs can be manipulated by appropriate loading and a judicious choice of the magnetic filler. The modification of these properties will aid in the design of composite materials for microwave absorbers.

Design, fabrication, and testing of micromachined silicone rubber membrane valves

Abstract: Technologies for fabricating silicone rubber membranes and integrating them with other processes on silicon wafers have been developed. Silicone rubber has been found to have exceptional mechanical properties including low modulus, high elongation, and good sealing. Thermopneumatically actuated, normally open, silicone rubber membrane valves with optimized components have been designed, fabricated, and tested. Suspended silicon nitride membrane heaters have been developed for low-power thermopneumatic actuation. Composite silicone rubber on Parylene valve membranes have been shown to have low permeability and modulus. Also, novel valve seats were designed to improve sealing in the presence of particles. The valves have been extensively characterized with respect to power consumption versus flow rate and transient response. Low power consumption, high flow rate, and high pressure have been demonstrated. For example, less than 40 mW is required to switch a 1-slpm nitrogen flow at 33 psi. Water requires dose to 100 mW due to the cooling effect of the liquid.

Electrical and mechanical properties of conducting carbon black filled composites based on rubber and rubber blends

Abstract: The electrical and mechanical properties of new conductive rubber composites based on ethylene-propylene-diene rubber, acrylonitrile butadiene rubber (NBR), and their 50/50 (weight ratio) blend filled with conductive black were investigated. The threshold concentrations for achieving high conductivity are explained on the basis of the viscosity of the rubber. The electrical conductivity increases with the increase in temperature whereas the activation energy of conduction decreases with an increase in filler loading and NBR concentration in the composites. The electrical hysteresis and electrical set are observed during the heating-cooling cycle, which is mainly due to some kind of irreversible change occurring in the conductive networks during heating. The mechanisms of conduction in these systems are discussed in the light of different theories.

Dielectric properties of isotactic polypropylene/nitrile rubber blends: Effects of blend ratio, filler addition, and dynamic vulcanization

Abstract: The dielectric properties of isotactic polypropylene/acrylonitrile–butadiene rubber blends have been investigated as a function of frequency with special reference to the effect of blend ratio. The dielectric properties measured were volume resistivity, dielectric constant (ϵ′), dissipation factor (tan δ), and loss factor (ϵ″). At high frequencies, a transition in relaxation behavior was observed whereby the dielectric constant of the blends decreased with frequency, whereas the loss tangent and loss factor increased on reaching a maximum. The variation of the dielectric properties with blend composition was correlated with blend morphology, and relationships were established with reference to blend composition. Experimental ϵ′ values were compared with theoretical predictions. The effect of the addition of fillers on the dielectric properties was also investigated for different fillers and filler loadings. It was found that silica filler increases the dissipation factor, whereas carbon black and cork gave a reverse trend. The variation in dielectric properties upon dynamic vulcanization of the rubber phase using different vulcanizing agents (such as sulfur, peroxide, and mixed systems) was also investigated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 255–270, 1999