Showing papers on "Natural rubber published in 1993"

A three-dimensional constitutive model for the large stretch behavior of rubber elastic materials

Abstract: Aconstitutive model is proposed for the deformation of rubber materials which is shown to represent successfully the response of these materials in uniaxial extension, biaxial extension, uniaxial compression, plane strain compression and pure shear. The developed constitutive relation is based on an eight chain representation of the underlying macromolecular network structure of the rubber and the non-Gaussian behavior of the individual chains in the proposed network. The eight chain model accurately captures the cooperative nature of network deformation while requiring only two material parameters, an initial modulus and a limiting chain extensibility. Since these two parameters are mechanistically linked to the physics of molecular chain orientation involved in the deformation of rubber, the proposed model represents a simple and accurate constitutive model of rubber deformation. The chain extension in this network model reduces to a function of the root-mean-square of the principal applied stretches as a result of effectively sampling eight orientations of principal stretch space. The results of the proposed eight chain model as well as those of several prominent models are compared with experimental data of Treloar (1944, Trans. Faraday Soc. 40, 59) illustrating the superiority, simplicity and predictive ability of the proposed model. Additionally, a new set of experiments which captures the state of deformation dependence of rubber is described and conducted on three rubber materials. The eight chain model is found to model and predict accurately the behavior of the three tested materials further confirming its superiority and effectiveness over earlier models.

Some Forms of the Strain Energy Function for Rubber

Abstract: According to Rivlin's Phenomenological Theory of Rubber Elasticity, the elastic properties of a rubber may be described in terms of a strain energy function which is an infinite power series in the strain invariants I1, I2 and I3. The simplest forms of Rivlin's strain energy function are the neo-Hookean, which is obtained by truncating the infinite series to just the first term in I1, and the Mooney-Rivlin, which retains the first terms in I1 and I2. Recently, we proposed a strain energy function which is a cubic in I1. Conceptually, the proposed function is a material model with a shear modulus that varies with deformation. In this paper, we compare the large strain behavior of rubber as predicted by these forms of the strain energy function. The elastic behavior of swollen rubber is also discussed.

Rubber-Tire Particles as Concrete Aggregate

Abstract: Accumulations of worn‐out automobile tires create fire and health hazards. As a possible solution to the problem of scrap‐tire disposal, an experimental study was conducted to examine the potential of using tire chips and crumb rubber as aggregate in portland‐cement concrete. This paper examines strength and toughness properties of concrete in which different amounts of rubber‐tire particles of several sizes were used as aggregate. The concrete mixtures exhibited lower compressive and splitting‐tensile strength than did normal concrete. However, these mixtures did not demonstrate brittle failure, but rather a ductile, plastic failure, and had the ability to absorb a large amount of plastic energy under compressive and tensile loads. A mathematical model is used to describe the effects of rubber aggregate on the compressive and tensile strength reduction of concrete.

Dilatational bands in rubber-toughened polymers

Abstract: A theory is advanced to explain the effects of rubber particle cavitation upon the deformation and fracture of rubber-modified plastics. The criteria for cavitation in triaxially-stressed particles are first analysed using an energy-balance approach. It is shown that the volume strain in a rubber particle, its diameter and the shear modulus of the rubber are all important in determining whether void formation occurs. The effects of rubber particle cavitation on shear yielding are then discussed in the light of earlier theories of dilatational band formation in metals. A model proposed by Berg, and later developed by Gurson, is adapted to include the effects of mean stress on yielding and applied to toughened plastics. The model predicts the formation of cavitated shear bands (dilatational bands) at angles to the tensile axis that are determined by the current effective void content of the material. Band angles are calculated on the assumption that all of the rubber particles in a band undergo cavitation and the effective void content is equal to the particle volume fraction. The results are in satisfactory agreement with observations recorded in the literature on toughened plastics. The theory accounts for observed changes in the kinetics of tensile deformation in toughened nylon following cavitation and explains the effects of particle size and rubber modulus on the brittle-tough transition temperature.

Filler-Elastomer Interactions. Part VII. Study on Bound Rubber

Abstract: SBR compounds were filled with 17 carbon blacks covering the whole range of rubber grades and tested for bound-rubber content. It was found that the bound-rubber content of a polymer at hi...

Does 'jungle rubber' deserve its name? An analysis of rubber agroforestry systems in southeast Sumatra

Abstract: Jungle rubber is a blanced, diversified system derived from swidden cultivation, in which man-made forests with a high concentration of rubber trees replace fallows. Most of the income comes from rubber, complemented with temporary food and cash crops during the early years. Perennial species that grow spontaneously with rubber provide fruits, fuelwood and timber, mostly for household consumption. Jungle rubber enables lower incomes per land unit or man-day than weed-free plantations using selected rubber clones. Yet it requires much less input and labour since wild woody species protect rubber from grass weeds and mammalian predators. With a structure and biodiversity similar to that of secondary forest in its mature phase, jungle rubber belongs to complex agroforestry systems. It has accommodated increasing population densities, while preserving a forest-like environment. Yet farmers' income from jungle rubber is declining due to the exhaustion of forest reserves and reduced land availability. New research and extension options could help in improving the productivity of jungle rubber. Better transportation and marketing are needed for increasing the income from non-rubber output. Short-term, small-scale credit schemes could help farmers adopt high-yielding rubber varieties. Research should participate in creating new management methods for selected rubber based on agroforestry to reduce maintenance costs, enabling smallholders to plant high-yielding rubber at lower cost, and without losing too much of the present biodiversity and economic diversity.

The rubber elongation factor of rubber trees (Hevea brasiliensis) is the major allergen in latex

Abstract: Background: Allergy to latex-containing articles is becoming more and more important because it can result in unexpected life-threatening anaphylactic reactions in sensitized individuals. Methods: A protein of 58 kd with an isoelectric point of 8.45 was purified from raw latex and from latex gloves and identified as the major allergen, completely blocking specific IgE antibodies in the serum of latex-sensitized subjects. The allergen is a noncovalent homotetramer molecule, in which the 14.6 kd monomer was identified, by amino acid composition and sequence homologies of tryptic peptides, to be the rubber elongation factor found in natural latex of the Malaysian rubber tree. Results: Competitive immunoinhibition tests showed that the starch powder covering the finished gloves is the airborne carrier of the allergen, resulting in bronchial asthma on inhalation. The purified allergen can induce allergic reactions in the nanogram range. Conclusion: The identification of the allergen ( Hev b I) may help to eliminate it during the production of latex-based articles in the future.

Rubber mixtures containing polybutadiene gel

Abstract: Mixtures of A) polybutadiene gel and B) other rubbers containing C=C double bonds, the quantity of polybutadiene gel A) , based on the sum of A) + B), being 1 to 70% by weight, show as vulcanizates a favorable combination of the properties hysteresis loss and abrasion resistance.

Reinforcement of rubber by fractal aggregates

Abstract: Rubber is commonly reinforced with colloidal aggregates of carbon or silica, whose structure has the scale invariance of a fractal object. Reinforced rubbers support large stresses, which often grow faster than linearly with the strain. We argue that under strong elongation the stress arises through lateral compression of the aggregates, driven by the large bulk modulus of the rubber. We derive a power-law relationship between stress and elongation λ when λ≫1. The predicted power p depends on the fractal dimension D and a second structural scaling exponent C. For diffusion-controlled aggregates this power p should lie beween 0.9 and 1.1 ; for reaction-controlled aggregates p should lie between 1.8 and 2.4. For uniaxial compression the analogous powers lie near 4. Practical rubbers filled with fractal aggregates should approach the conditions of validity for these scaling laws.

Smallholder rubber and swidden agriculture in Borneo: A sustainable adaptation to the ecology and economy of the tropical forest

Abstract: This is a study of the role of Para rubber cultivation in a system of swidden agriculture in Indonesian Borneo. Such smallholdings produce most of Indonesia’s rubber, which is the country’s largest agricultural generator of foreign exchange. Rubber integrates well into Bornean systems of swidden agriculture: the comparative ecology and economy of Para rubber and upland swidden rice result in minimal competition in the use of land and labor — and even in mutual enhancement — between the two systems. Rubber occupies a distinct niche in the farm economy: it meets the need for market goods, while the swiddens meet subsistence needs. The intensity of production on these smallholdings is, as a result, characteristically low (and may even vary inversely with market prices). This reflects the independence of these smallholders from external economic and political influences, which has been the key to their historical success. The special virtues of such “composite systems” merit greater attention by development planners.

Thread wound golf ball

Abstract: The present invention provides a thread wound golf ball having excellent durability, heat resistance and impact resilience, which comprises a core, a thread rubber layer and an outer layer. A thread rubber constituting the thread rubber layer is obtained from a rubber latex blend containing a depolymerized high-cis polyisoprene rubber latex.

Toughened plastics I : science and engineering

Abstract: Mechanisms of Toughening Thermoset Resins Fracture-Toughness Testing of Toughened Polymers Multiple-Phase Toughening-Particle Morphology: Effects on the Properties of Rubber-Toughened Poly(methyl methacrylate) Toughened Semicrystalline Engineering Polymers: Morphology, Impact Resistance, and Fracture Mechanisms Deformation and Fracture Toughness in High-Performance Polymers: Comparative Study of Crystallinity and Cross-Linking Effects The Damage Zone in Some Ductile Polymers Under a Triaxial Tensile Stress State Additive Effects on the Toughening of Unsaturated Polyester Resins Particle-Matrix Interfacial Bonding: Effect on the Fracture Properties of Rubber-Modified Epoxy Polymers Macroscopic Fracture Behavior: Correlation with Microscopic Aspects of Deformation in Toughened Epoxies Optimization of Mode-I Fracture Toughness of High-Performance Epoxies Using Designed Core-Shell Rubber Particles Toughening of Epoxy Resin Networks with Functionalized Engineering Thermoplastics Epoxy-Rubber Interactions The Synergistic Effect of Cross-Link Density and Rubber Additions on the Fracture Toughness of Polymers Rubber-Modified Epoxies: Analysis of the Phase Separation Process Thermal Shock Resistance of Toughened Epoxy Resins Toughening Epoxy Resin with Poly(methyl methacrylate)-Grafted Natural Rubber Toughening Epoxies Using Rigid Thermoplastic Particles: A Review Preparation of Poly(butylene terephthalate)-Toughened Epoxies Toughening of Epoxy Resins by Epoxidized Soybean Oil Structure-Property Relations of High-Temperature Composite Polymer Matrices Model Multilayer Toughened Thermosetting Advanced Composites Multiphase Matrix Polymers for Carbon Fiber Composites Thermal Characterization of the Cure Kinetics of Advanced Matrices for High-Performance Composites

Ethylene/alpha-olefin/7-methyl-1,6-octadiene copolymer rubber and composition of the same

Abstract: The ethylene/.alpha.-olefin/7-methyl-1,6-octadiene copolymer rubber of the invention is a random copolymer rubber prepared using a Group IVB transition metal type catalyst containing a specific zirconium catalyst component, and in this copolymer rubber, a molar ratio of ethylene to .alpha.-olefin, a diene content, an intrinsic viscosity [.eta.], an intensity ratio D of T.alpha..beta. to T.alpha..alpha. in a 13C-NMR spectrum of said copolymer rubber, a B value which is a measure of distribution of each monomers and a glass transition temperature are all within specific ranges. The rubber composition of the invention comprises the above-mentioned random copolymer rubber and a conjugated diene rubber. The random copolymer rubber has high stereoregularity, narrow composition distribution and excellent low-temperature flexibility, and shows extremely high covulcanizability with the conjugated diene rubber. In addition, this random copolymer rubber is excellent in weathering resistance, ozone resistance and thermal aging resistance.

Linear viscoelasticity in the melt of impact PMMA. Influence of concentration and aggregation of dispersed rubber particles

Abstract: The linear viscoelastic behavior in the melt of PMMA/PS blends and various blends of PMMA containing rubbery latex particles has been characterized by dynamic shear rheometry. For the rubber‐toughened PMMA samples, the influence of rubber content, structure of the latex particles, and aggregation of the particles in the PMMA matrix have been investigated. Morphologies of the dispersed type or of the aggregated type were produced by performing the blending in the melt or in solution. The data for G’ and G‘ have been analyzed in the frame of a rheological emulsion model which is found to account for the behavior of the PMMA/PS blends and of rubber‐toughened PMMA at low rubber content. At high rubber concentrations the model does not predict the secondary plateau in G’ which arises at low frequencies for these systems. Therefore, this plateau cannot be attributed to the deformability of dispersed inclusions as in PMMA/PS blends, but is shown to depend on the extent of aggregation of the dispersed particles, and to be most important in a well dispersed morphology where the particles form a network‐type structure.

Ground rubber tire/thermoplastic composites : effect of different ground rubber tires

Abstract: Thermoplastic composites containing different Ground Rubber Tire (GRT) materials, Linear Low Density Polyethylene (LLDPE) and, in some case, a coupling agent (IB‘E’, an ethylene glycidyl methacrylate copolymer) were prepared by melt blending. The impact energies of all the thermoplastic composites (normally containing 40 wt % GRT) were evaluated using an instrumented impact tester. The effects of the GRT particle-size, particle size distribution and shape, the mode of grinding, and the oxygen surface concentration were analyzed. The wet-ambient-ground GRT based composites show higher surface oxidation and give better impact energy than cryo-ground and normal air-ground GRT based composites. Smaller GRT particle size results in a small increase in the impact property of the composite and a greater influence on the melt processability of the composites. Of the different GRT surface modification techniques studied for improved composite interfacial adhesion and impact properties the composites from ...

Tire with silica reinforced tread

Abstract: The invention relates to a tire with a tread which is quantitatively reinforced with silica where the tread is composed of cis 1,4-polybutadiene rubber, a high vinyl polybutadiene rubber and, optionally a medium vinyl polybutadiene rubber. In one aspect, the tread rubber can also contain a minor amount of cis 1,4-polyisoprene natural rubber.

Elastomer Technology Handbook

Abstract: Analytical Test Methods for Polymer Characterization (N.P. Cheremisinoff, R. Boyko, and L. Leidy). Chemical Characterization in Polymer Analysis (A.B. Hunter). The Use of Thermal Analysis in Polymer Characterization (M.P. Sepe). Tensile Yield in Polymers (D. Hartmann and D. Sudduth). Mechanochemistry of Polymers Deformation and Fracture Processes (C.V. Oprea and M. Popa). Morphology and Mechanical Properties of Natural Rubber/Polyolefin Blends (J. Sunder). Properties Modelling of Viscoelastic Elastomers (H. So and U.-D. Chen). Interpenetrating Polymer Networks (D. Klempner and D. Sophiea). Catalysts for the Copolymerization of Ethylene-Propylene Elastomers (K. Makino). Thermal and Oxidative Stability of Ethylene-Propylene Rubber (G. Mares and P. Budrugeac). The Nature of Sulfur Vulcanization (M.R. Krejsa and J.L. Koenig). Peroxide Crosslinking of EPDM Rubbers (W.C. Endstra and C.T.J. Wreesmann). Properties and Degradation of Nitrile Rubber (S. Bhattacharjee, A.K. Bhowmick, and B.N. Avasthi). Thermoplastic Elastomers: A Rising Star (M.T. Payne and C.P. Rader). Markets for Thermoplastic Elastomers (R.J. School). Degassing of Thermoplastics during Extrusion with Single-Screw and Co-Rotating Twin-Screw Extruders (G. Martin and W. Schuler). Epoxidized Rubbers (S. Roy, B.R. Gupta, and S.K. De). Toughening Concept in Rubber-Modified High Performance Epoxies (H.-J. Sue, E.I. Garcia-Meitin, and D.M. Pickelman). Characterization of Phase Behavior in Polymer Blends (T. Ougizawa and T. Inoue). Compatibilization of Polymer Blends (R.L. Markham). Rubber Mixing Principles (N.P. Cheremisinoff). Rubber Extrusion Principles (N.P. Cheremisinoff). Blown Film Technology (J.D. Culter). Principles of Adhesive Rheology (F.M. Chen). Adhesion between Components of Elastomeric Composite Materials (Y. Kubo). Polymer Applications in the Construction Industry (R. Hussein and N.P. Cheremisinoff). Polymers in Sandwich Construction (R. Hussein). Polymer-Concrete Composites (R. Hussein). Properties of Polymers Suitable for Solar Energy Applications (R. Hussein). Appendices. Index.

Improved Quantitative Determination of Elastomers in Tire Rubber by Kinetic Simulation of DTG Curves

Abstract: A method of identifying and quantifying elastomers and processing oil in tire rubber, called DTG curve simulation method, is proposed. This method is based on DTG (derivative thermogravimetry) analysis of the straight elastomers NR, BR and SBR, which produces a series of decomposition rate data and pairs of kinetic constants. DTG curves of binary elastomer systems NR/SBR, NR/BR and BR/SBR are measured. The samples are qualitatively identified following the shape of their DTG curves. Quantitative determination is achieved by DTG curve simulation using a least squares method. When correct elastomers and proper compound ratio are chosen, minimum simulation error is achieved leading to effective identification. Satisfactory results were obtained when applying the method to elastomer mixtures of known composition and to tire rubbers of unknown composition. The study advanced the capability of the TG-DTG technique for quantitative determination of elastomers and blends.

Filler-Elastomer Interactions. Part VIII. The Role of the Distance between Filler Aggregates in the Dynamic Properties of Filled Vulcanizates

Abstract: Based on the concepts of the occlusion of rubber and random packing of spheres whose volume is equivalent to that permeated by individual aggregates, an equation was deduced to estimate the distance between carbon-black aggregates in filled rubber. It was found that when the interaggregate distance reaches a critical point which is approximately identical for all carbon blacks investigated (furnace blacks), the elastic modulus measured at very low strain deviates from the modified Guth-Gold equation. Tan δ and resilience are mainly determined by the distance between aggregates. These phenomena are related to filler networking which is determined by the attractive potential and the distance between individual aggregates. Since the factor Sf, used to characterize the strength of secondary filler networks in hydrocarbon rubbers and measured by means of inverse gas chromatography, is approximately the same for all furnace blacks, the interaggregate distance seems to determine filler networking. A com...

The use of cryogenically ground rubber tires as a filler in polyolefin blends

Abstract: The effects of cryogenically ground rubber tires (CGT) on some of the mechanical properties of blends with linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) are presented. Precoating the CGT particles with an ethylene-acrylic acid copolymer is shown to overcome most of the deleterious effects of adding CGT to LLDPE, while still retaining composite processability. A blend of 40 wt% EAA coated CGT particles with LLDPE is shown to have impact and tensile strengths that are 90% of those for the pure LLDPE, representing increases of 60 and 20%, respectively, over blends with uncoated particles. Blends of LLDPE with ground tire bladders demonstrate that even better mechanical properties can be obtained with similar large rubber particle size but somewhat better adhesion. For HDPE, however, it is shown that with large rubber particles, moderate adhesion is not sufficient to produce useful composites.

Type IV allergy to rubber additives: A 10-year study of 686 cases

Abstract: Background : Rubber additives, mainly vulcanizers and antioxidants, are increasingly a cause of contact dermatitis. Objective : The aim of the present study was to determine the frequency of type IV allergy to rubber additives. Methods : Seven thousand patients seen during a 10-year period were evaluated. Of them, 4680 were patch tested with the standard series recommended by the Spanish Group for Research of Contact Dermatitis (GEIDC) and a series of individual rubber additives. Results : A total of 686 patients (14.7% of those patch tested) had one or more positive reactions to rubber additives. Of these, 582 (84.8%) were men and 104 (15.2%) were women. The incidence of rubber sensitization was especially high among construction workers (47.0%). Conclusion : Rubber additives are a common cause of occupational contact dermatitis, particularly in construction workers. We postulate that rubber gloves and boots (utilized to avoid contact with sensitizing substances) themselves may be a common cause of contact dermatitis. The high incidence of allergy to some rubber additives, such as thiurams and carbas, indicates that their replacement by other less sensitizing vulcanizers is advisable.

Flexible rubber article and method of making

Abstract: A multi-layer flexible article includes a first layer of natural rubber, a second layer of natural rubber, polyurethane, poly(acrylamide/acrylic acid) and polyethylene oxide and a third layer of acrylic copolymer and fluorocarbon telomer resin. The article is preferably a glove formed by the method of dipping a hand shaped mold into baths containing aqueous emulsions of the components used to form the layers. Gloves manufactured according to the method are substantially wet-hand and dry-hand donnable as compared to powdered latex gloves of similar size. The finished gloved is water washed and wet autoclaved to substantially reduce the protein content from the natural rubber and substantially remove other water extractable allergenic moieties. The washing and autoclaving renders the glove substantially hypoallergenic as compared to gloves not so treated.

Optical characteristics of a ruthenium(II) complex immobilized in a silicone rubber film for oxygen measurement

Abstract: The optical characteristics of tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) perchlorate immobilized in a silicone rubber film were studied for its application to the measurement of oxygen. The luminescence intensity and the degree of quenching of the ruthenium complex by oxygen were shown to be affected by the concentration of the complex in the silicone rubber film. The optimum concentration was found to be about 0.2 mmol dm–3. At this concentration, the silicone rubber film containing the immobilized ruthenium complex emits the highest luminescence intensity and is able to undergo a high degree of quenching of the luminescence by oxygen. The quenching curves for 20 samples containing various concentrations of the ruthenium complex were correlated with high accuracy by using a modified form of the Stern–Volmer equation. The film preparation procedure and the solvent used were found to be critical for performance. The effect of the film thickness on the luminescence intensity and the dynamic response was also studied.

Adhesive rubber compounds

Abstract: Uncured adhesive elastomeric compositions are provided comprising an unsaturated polymeric dicarboxylic acid or derivative adduct and an elastomer. These compositions are capable of adhesion to a broad, general range of materials and are useful for bonding elastomers to other elastomers, to plastic materials, to metal, fabrics, fibers, paper and miscellaneous substrates. These materials can also be bonded to each other using a film or spreadable liquid comprised of a composition of this invention and curing said film or liquid in contact with said substrates.

Anchoring of a tyre carcass

Abstract: A tyre carcass consists of lengths of ply placed side by side forming a single circumferential alignment (30) in the wall. The bead is reinforced with layers (61,62,63) of circumferentially oriented plies. In the bead (2) the carcass plies are divided into two circumferential alignments axially separated (31,32) by the layer of reinforcing plies (62) oriented circumferentially. Between the carcass and reinforcing plies is interposed a rubber compound having a hardness greater than Shore A 70. Tyre carcass prodn. Ensures progressive charge of rigidity to flexing of the tyre wall, bead interface, and allows anchoring of large number of plies and easy mechanical prodn..