Showing papers on "Natural rubber published in 1985"

Rubber‐toughening in polypropylene

Abstract: To deformation and fracture behavior of several polypropylene (PP) and rubber-modified PP materials have been investigated. Plastic deformation mechanisms of these systems depend upon the test rate and temperature with high rates and low temperatures being in favor of crazing. The ductility and toughness of these materials are explained in light of the competition between crack formation and the degree of plastic deformation through crazing and shear yielding. The second phase morphology with smaller average rubber particle diameter D appears to be more efficient than that with larger D in toughening PP. Theoretical calculations indicate that the stresses imposed upon the rubber particles due to volume shrinkage of PP during crystallization are sufficient to compensate for the stresses due to differential thermal contraction in cooling from solidification temperature to end-use temperature. The difference between these two is small, and therefore they provide very little contribution to interfacial adhesion between rubber particle and PP matrix, the adhesion being insufficient for the rubber particles to be effective in controlling craze propagation. The rubber particles, in addition to promoting crazing and shear yielding, can also improve the fracture resistance of PP by varying the crystalline structure of PP (e.g., reducing the spherulite dimensions).

Polymer blends and mixtures

Abstract: 1. Thermodynamic Theory and Experimental Techniques for Polymer Blends.- 2. Glass Transitions and Compatibility Phase Behavior in Copolymer Containing Blends.- 3. Microscopy and other Methods of Studying Blends.- 4. Preparation of Blends.- 5. Light, Neutron and X-Ray Scattering Techniques for Studying Polymer Blends.- 6. Liquid-Liquid Phase Equilibria in Polymer Blends.- 7. Polymer Blend Modification of PVC.- 8. Synthesis of Block and Graft Copolymers.- 9. Block Copolymers Morphological and Physical Properties.- 10. Colloidal Behaviour and Surface Activity of Block Copolymers.- 11. Relationships between Morphology, Structure, Composition and Properties in Isotactic Polypropylene Based Blends.- 12. Rubber-Rubber Blends.- 13. Pure and Applied Research on Interpenetrating Polymer Networks and Related Materials.- 14. Fracture Toughness Evaluation of Blends and Mixtures and the Use of the J Method.- 15. Crazing and Cracking in Glassy Homopolymers.- 16. The Mechanical Properties of Homogeneous Glassy Polymer Blends.- 17. Mechanical Properties of High-Impact Polymers.- 18. Fatigue of High-Impact Polymers.- 19. Yielding and Failure Criteria for Rubber Modified Polymers, Part 1.- 20. Yielding and Failure Criteria for Rubber Modified Polymers, Part 2.- 21. Multiphase Thermosetting Polymers.- 22. Processing and Phase Morphology of Incompatible Polymer Blends.- Seminars.- 1. Pulse-Induced Critical Scattering.- 2. Phase Separation in Polymer Blends.- 3. Thermodynamics of Compatibility in Binary Polymeric Mixtures.- 4. PVC Blending Resins: Properties and Appllications.- 5. Block Copolymers as Homogenizing Agents in Blends of Amorphous and Semicrystalline Polymers.- 6. Study of Copolymer-Homopolymer Blends.- 7. Rubber-Plastics Blends.- 8. Isotactic Polypropylene/Rubber Blends: Effect of Crystallization Conditions and Composition on Properties.- 9. Ethylene-Propylene Rubber and Polyolefin Polymer Blends: Present Situation and Future Trends.

Epoxidized Natural Rubber

Abstract: The mechanical properties of natural rubber (NR) are generally superior to those of synthetic rubbers. However, NR cannot compete with the speciality synthetic elastomers with regard to such properties as gas permeability and oil resistance.

Microbial degradation of natural rubber vulcanizates.

Abstract: An actinomycete, Nocardia sp. strain 835A, grows well on unvulcanized natural rubber and synthetic isoprene rubber, but not on other types of synthetic rubber. Not only unvulcanized but also various kinds of vulcanized natural rubber products were more or less utilized by the organism as the sole source of carbon and energy. The thin film from a latex glove was rapidly degraded, and the weight loss reached 75% after a 2-week cultivation period. Oligomers with molecular weights from 104 to 103 were accumulated during microbial growth on the latex glove. The partially purified oligomers were examined by infrared and 1H nuclear magnetic resonance and 13C nuclear magnetic resonance spectroscopy, and the spectra were those expected of cis-1, 4-polyisoprene with the structure, OHC—CH2—[—CH2—C(—CH3)=CH —CH2—]n—CH2—C(=O)— CH3, with average values of n of about 114 and 19 for the two oligomers.

Process for making diene polymer rubbers

Abstract: A process for making a diene copolymer rubber having improved rebound, which comprises polymerizing a conjugated diene monomer with an aromatic vinyl monomer in a hydrocarbon solvent in the presence of an alkali metal and/or alkaline earth metal initiator, to form a dienyl-metal terminated, conjugated diene-aromatic vinyl copolymer rubber, and thereafter reacting the copolymer rubber with at least one reactant selected from the group consisting of aminoaldehydes, aminoketones, aminothioaldehydes and aminothioketones.

The rubber particle size dependence of crazing in polypropylene

Abstract: The tensile crazing and Charpy impact behavior of polypropylene modified with styrene-butadiene copolymer (SBR) and ethylene-propylene-diene monomer (EPDM) was studied. Various rubber particle size distributions were obtained by varying the relative viscosities between rubbery phase and PP matrix. Transmission electron microscopy and computer-aided image analysis were used to provide particle size information. In general, PP blends with smaller rubber particles are tougher and more ductile than those with larger particles, probably because the former represents a more efficient use of rubbery phase in promoting crazing and/or shear yielding. Samples with average particle diameter D ≥ 0.5 μm were found to exhibit pronounced crazing. Within a given sample, no crazes appeared to develop around individual rubber particles with D < 0.5 μm. The higher the D, the greater the propensity to form crazes. The behavior of samples with D ≪ 0.5 μm appeared to be dominated by shear yielding; very few crazes could be found. That there exists a critical rubber particle size is explained by the requirement that sufficient stress concentration be maintained to a finite radial distance to permit the initiation and growth of a craze, which requires a finite volume. Small particles, inducing smaller stress-enhanced zones, are therefore not effective in initiating crazes.

The viscoelastic properties of rubber–resin blends. I. The effect of resin structure

Abstract: Blends of elastomers with the proper concentration of appropriate low molecular weight resins exhibit performance as pressure sensitive adhesives. Viscoelastic properties, which may be related to adhesive performance, were measured on 1:l blends of rubber and resin using a mechanical spectrometer. Significant differences in viscoelastic properties were observed depending upon the resin structure. On plots of G′ and tan δ vs. temperature, the addition of a compatible resin produces a pronounced shift of the tan δ peak to a higher temperature and reduces the modulus in the rubbery plateau. An incompatible resin results in a minor shift in the tan δ peak of the elastomer along with the appearance of a second peak at higher temperature, attributed to a second phase which is predominantly resin. Also, the modulus is increased in the rubbery plateau. A polystyrene resin, Mw about 900, is shown to be incompatible with natural rubber but compatible with styrene–butadiene rubber. A cycloaliphatic poly(viny1 cyclohexane) resin, Mw about 650, prepared by hydrogenating the polystyrene resin, is compatible with natural rubber, but incompatible with styrene-butadiene rubber. An alkyl-aromatic poly(tert-butylstyrene) resin, Mw about 850, which is intermediate in aromaticity between the aromatic polystyrene resin and the cycloaliphatic poly(viny1 cyclohexane) resin, is compatible with both natural rubber and styrene-butadiene rubber. Therefore, the structure of the resin is very important in adjusting the viscoelastic properties of a rubber–resin blend to achieve pressure sensitive adhesive performance.

Thermoplastic resin composition

Abstract: PROBLEM TO BE SOLVED: To improve an impact strength level of a specific thermoplastic resin more than the previous level. SOLUTION: The thermoplastic resin composition contains 100 pts.wt. of a thermoplastic resin (a) and 0.5-35 pts.wt. of an impact strength improver (b). The thermoplastic resin (a) is at least one selected from among a polycarbonate resin, polyester resin, polyarylate resin, polyacetal resin and alloy of these resins. The impact strength improver (b) contains a graft copolymer (b-1) having a rubber polymer and a rigid shell, a water-soluble polymer compound (b-2) having properties to form a physical gel and a gellant (b-3). Where the ratio of the rigid shell in the graft copolymer (b-1), is 1-20 wt.%, and the content of the water-soluble polymer compound (b-2) having properties to form a physical gel, is 0.01-3.0 pts.wt. to 100 pts.wt. of the graft copolymer (b-1). COPYRIGHT: (C)2008,JPO&INPIT

Water-lubricated rubber bearings, history and new developments

Abstract: Rubber bearings are simple, robust and highly reliable devices, able to perform over long periods and under adverse operating conditions; the Authors review their historical development and describe some recent designs for reducing friction and wear, especially at low journal velocities. These improved characteristics mean that length/diameter ratios can be reduced, or existing lengths can be used to support much larger radial loads. Other developments discussed are a self-aligning mounting ring of rubber around the bearing housing, and using rubber bearings with oil as the lubricant.

Rubber-Thermoplastic Compositions. Part IX. Blends of Dissimilar Rubbers and Plastics with Technological Compatibilization

Abstract: From this work, one can conclude that compositions which have excellent mechanical properties can be prepared by melt-mixing thermoplastic vulcanizates. (A thermoplastic vulcanizate is a composition containing vulcanized rubber particles dispersed in a thermoplastic. Such a composition is usually prepared by vulcanizing the rubber during its melt-mixing with a thermoplastic.) The excellent mixed TPV compositions can be obtained even though the rubbers and plastics are mutually grossly incompatible with respect to thermodynamic considerations. In such cases, however, it appears to be necessary that a compatibilizing agent be present in the mixture to promote the interaction between the thermoplastic materials. Block copolymers whose molecules contain blocks common to each of the thermoplastic blend components are good technological compatibilizing agents (e.g., polypropylene-nylon block copolymers to compatibilize mixtures containing polypropylene and nylon). Compatibilizing block copolymers can f...

Studies on the melt flow behavior of thermoplastic elastomers from polypropylene—Natural rubber blends

Abstract: The melt flow behavior of thermoplastic polypropylenenatural rubber blends has been evaluated with specific reference to the effects of blend ratio, extent of dynamic crosslinking of the rubber phase and temperature, on viscosity, flow behavior index, and deformation of the extrudate. The proportion of rubber in the blend and the extent of dynamic crosslinking of the rubber phase were found to have profound influence on the viscosity of the blends at lower shear stresses. But at higher shear stresses, the effect of blend ratio on viscosity was comparatively less for the uncrosslinked blends than that for the crosslinked blends. At lower shear stress, the viscosity of the blend increased with increase in degree of crosslinking but at higher shear stress, the effect of crosslinking on viscosity was found to vary depending on the ratio of the plastic and rubber components in the blend. The deformation of the extrudates was also very much dependent on both blend ratio and degree of crosslinking.

Relationships between structure and mechanical properties of rubber‐modified epoxy networks cure with dicyanodiamide hardener

Abstract: Epoxy network systems based on DGEBA and dicyanodiamide (DDA) and modified with a low molecular weight rubber (CTBN) were prepared and characterized. The kinetics of the adduct formation is followed using GPC analysis. The phase separation of the rubber phase is evidenced with DSC and SEM for all samples up to 20% CTBN. The GPC analysis of the soluble fraction demonstrates a chemical modification of the network. The mechanical properties and specially the impact strength behavior are enhanced with CTBN, but exhibit a maximum for 15% CTBN. In connection with SEM of fracture surfaces, these results are discussed and both modification of the rubber morphology and decrease in crosslinking density are taken into account.

Penetration-resistant surgical glove

Abstract: A penetration-resistant surgical glove is disclosed which consists of a thin latex of synthetic rubber foundation glove having a front surface overlay of thin, pliable and limp material composed of a large number of tightly interlaced fibers or filaments of high strength adhesively attached to the face or palmar surface of the foundation glove. The surface overlay of thin, pliable and limp material is shaped to conform to the thumb, fingers and palm of the foundation glove and serves to prevent penetration of the glove by a sharp object. The foundation glove with its protective overlay of penetration-resistant material may be provided with an over-coat of rubber in the form of a second glove, as by dipping in liquid latex, drying and vulcanizing in the conventional manner.The over-coat of latex rubber provides a hermetic seal over the surface of the foundation glove and its protective overlay. Any rupture or penetration of the hermetic seal occurring during the course of an operation which enables fluids to reach the protective overlay causes a visible staining of the overlay material, thereby providing an indication that such a rupture or penetration has occurred.

Epoxidation of natural rubber studied by nmr spectroscopy

Abstract: Epoxidation of natural rubber with peroxyacids in homogeneous solution (CHCl3, benzene) and in latex occurs without main chain fission or isomerization of the cis configuration. There are two possible modes of addition of oxygen to the double bond, which gives rise to diastereoisomers in dyad structures, as shown by the occurrence of splitting of 13C NMR resonances in 100% epoxidized rubber. In partially epoxidized rubber the 13C NMR resonances of the methylene carbon atoms have been fully assigned using pulse sequences and lanthanide shift reagents, in terms of triad sequences. Resonances in the olefinic region of the spectrum require assignment in terms of pentad sequences whereas those from the oxirane region are much more closely spaced and are assigned using triads. Intensity measurements on the methylene carbon NMR resonances show that the epoxidation reaction is a random process in both homogeneous solution and in latex particles.

Surface modified synthetic, silicatic filler, a process for its production and its use

Abstract: The invention is directed to the modification of synthetic, silicatic fillers with water insoluble sulfur containing organosilicon compounds. For this purpose, the fillers are converted into an aqueous suspension and treated with the organosilicon compounds, optionally in the presence of an emulsifier. The thus modified filler in vulcanized rubber mixtures results in a clear improvement in the industrial properties of the rubber.

Elastomer Modification of Structural Adhesives

Abstract: An attempt has been made to review the highlights of the chemistry and physical properties of the rubber modification of structural thermosetting polymers that are used as adhesives. The elastomers are added in order to improve the characteristics of these structural thermosets such that they would be more useful as structural adhesives. The addition of an elastomer acts to increase the resistance of the structural thermoset to crack propogation. The resistance to crack propogation is obtained either by plasticization to increase the ductility of the thermoset or by generation of a two-phase system where the structural polymer forms a matrix in which the phase-separated elastomeric particles are imbedded. In the case of flexibilization by plasticization, the increase in peel strength (fracture toughness) is accompanied by a decrease in shear strength (modulus) at high temperatures. In the case of the two phase system, the matrix properties are unaffected for the most part, and increases in peel s...

Enhanced adhesion of rubber to reinforcing materials through the use of phenolic esters

Abstract: There is disclosed a method for adhering rubber to reinforcing materials which comprises embedding a textile fiber or metal reinforcing material in a vulcanizable rubber composition comprising rubber, a vulcanizing agent, reinforcement, a methylene donor, and a phenolic ester as a methylene acceptor.

Thermoplastic elastomer composition

Abstract: A thermoplastic elastomer composition containing in percentages by weight based on the total weight of the composition, about 5% to about 90% vulcanized rubber crumb; about 5% to about 60% polyolefin; about 2% to about 30% uncured rubber or styrene-based thermoplastic elastomer; and about 2% to about 30% vinyl polymer selected from vinyl homopolymers, copolymers and mixtures. The composition in total contains less than 15% styrene block copolymer.

Device for base isolating structures from lateral and rotational support motion

Abstract: The device of the invention comprises a set of flat rings which can slide laterally on each other with a central rubber core and/or peripheral rubber cores. In this base isolator device the interfacial friction force acts in parallel with the elastic force in the rubber. It combines the beneficial effect of friction damping with that of the resiliency of rubber. The rubber cores distribute the sliding displacement along the height of the device and, due to rubber's resiliency, limit the maximum residual displacement at the base to a pre-specified value, thereby eliminating the need for any repositioning operation after earthquakes. Also, the resiliency of the rubber cores aid in reducing the high frequency effects attributed to friction isolators.

Blends of polypropylene, polycarbonate and a saturated styrene-ethylene-butylene-styrene rubber

Abstract: A composition suitable for melt extrusion in film form comprising an intimate thermoplastic blend of: polypropylene, polycarbonate, and a saturated block copolymer of styrene-ethylene-butylene-styrene.

Toughening of polyester resins by rubber modification

Abstract: The toughening effect of reactive liquid rubber additions on two polyester resin systems has been investigated. Fracture toughness and crack propagation behaviour have been studied, using the double torsion test. Toughness, as defined by fracture surface energy for crack initiation, increased with rubber content. The magnitude of the increase was dependent upon rubber-resin compatibility. The most successful system, incorporating an experimental butadiene-acrylonitrile rubber, showed an eight-fold increase in toughness, compared with the unmodified resin. Other proprietary systems showed more modest increases. Modulus and heat distortion temperature were also investigated for the different rubber-resin systems. In all cases, some deterioration in these properties was seen. The experimental rubber caused a reduction in resin modulus comparable with that produced by proprietary rubbers; heat distortion temperature in the experimental system was relatively little affected. The experimental rubber also affected the stress-strain behaviour of the resin. Resin modified with the experimental rubber yielded and deformed plastically, in contrast with the unmodified material, which behaved in a brittle manner.

Pyrolytic decomposition apparatus

Abstract: Apparatus is disclosed for the thermal decomposition or pyrolysis of shredded vehicle tires. Interially of a pyrolysis chamber is mounted a hollow shaft which carries on at least a portion of its outer surface, a conveyor flight and a plurality of partial flights which compact, mix and stir the rubber shreds during the decomposing cycle. Undecomposed rubber, fiberglass, carbon and metal products are collected at the end of the decomposition chamber and the gaseous products of decomposition are separately collected and sent through a fractionator. Externally of the decomposition chamber is a screen type magnetic separator which removes the magnetic susceptible metal particles and the carbon passes through the rotating cylindrical screen. Undecomposed rubber, fiberglass and the like are removed from the screen and separately treated.

Heat shrinkable thermoplastic olefin composition

Abstract: Heat shrinkable thermoplastic compositions are prepared by blending an ethylene copolymer resin with a rubber and dynamically vulcanizing the rubber. The ethylene copolymer resin is a copolymer of ethylene with an alkyl ester of an alpha, beta monoethylenically unsaturated monocarboxylic acid as well as copolymers of ethylene with the acid per se. The preferred copolymer is ethylene-vinyl-acetate copolymer. The preferred rubber is halogenated butyl rubber. Uncured rubber can be included in the composition.

Sound-damping and heat-insulating composite plate

Abstract: A sound-damping composite panel with elastic properties is provided by disposing a prefabricated porous core made from rubber granules or scrap, e.g. rubber tire scrap, between a pair of metal layers or sheets, e.g. of aluminum, and adhesively bonding the metal layers to the core under heat and pressure.

The viscoelastic properties of rubber–resin blends. III. The effect of resin concentration

Abstract: The viscoelastic properties of a rubber–resin blend, which influences performance of the blend as a pressure-sensitive adhesive, depend upon the structure of the resin as well as its molecular weight. The effect of the concentration of a compatible resin in the blend was examined using a mechanical spectrometer. Four types of resins were used. These are the rosin esters, polyterpenes, pure monomer resins such as polystyrene and poly(vinyl cyclohexane), and petroleum stream resins. Each was examined in blends with both natural rubber and styrene–butadiene rubber over a range of concentrations. It is shown that the temperature of the tan δ peak for compatible systems can be predicted by the Fox equation, T = W1T + W2T, where W1 and W2 are the weight fractions of the resin and rubber, respectively, and the Tg's are the tan δ peak temperatures in K. The plateau modulus G for a blend can be identified as the G′ value in the rubbery plateau at the point where tan δ is at a minimum. The relationship between G and G, the plateau modulus for the undiluted elastomer, is shown to be proportional to the volume fraction of the elastomer raised to the 2.3–2.4 power for natural rubber with six different compatible resins. The exponent for styrene–butadiene rubber is 2.5–2.6 with four different resins. Using these relationships, both the tan δ peak temperature and plateau modulus can be predicted for a rubber–resin system from data on the unmodified elastomer and on one typical rubber–resin blend.

Coating formulation for inorganic fiber mat based bituminous roofing shingles

Abstract: An all-weather inorganic fiber mat based roofing shingle is prepared using a novel bituminous coating formulation comprising a partially air blown asphalt combined with a styrenic elastomer and mineral stabilizer, which formulation more particularly comprises about 3 to 80% elastomeric polymer composition, 10 to 87% bituminous composition and 10 to 87% mineral stabilizer. In another embodiment, improved low and high temperature pliability and strength properties are also attained by blending recycled rubber or reclaimed rubber into the basic formulation which thereby comprises about 1 to 74% elastomeric polymer composition, 10 to 83% bituminous composition, 15 to 88% mineral stabilizer and about 1 to 74% recycled or reclaimed rubber.