Showing papers on "Natural rubber published in 1991"

Solid golf ball

Abstract: PURPOSE:To decrease the difference in hardness between the inside and outside of the solid golf ball and to eliminate the indefinite feel of impact by crosslinking and molding a compsn. formed by adding specific materials at specific pts. wt. into a specific butadiene rubber alone or a rubber material formed by blending this butadiene rubber with other rubber and/or plastics. CONSTITUTION:The compsn. formed by adding at least acrylic acid or methacrylic aid, zinc white and an org. peroxide and further 2- mercaptobenzothiazole and/or 2-mercaptobenzothiazole dicyclohexylamine salt to a butadiene rubber alone contg. >=90% cis-1,4-polybutadiene or a rubber material formed by blending this butadiene rubber with the other rubber and/or the plastics, at 0.1 to 3.0 pts.wt. per 100 pts.wt. rubber material is crosslinked and molded to form the solid gold ball. Namely, the above-mentioned materials are added to the compsn. to attempt the suppression of the effect of the org. peroxide and the internal hardness of the golf ball is increased by the crosslinking and molding. The solid golf ball which lessens the difference in the hardness between the inside and the outside and has the excellent performance is obtd.

Crosslink Density and Fracture Toughness of Epoxy Resins.

Abstract: A series of networks of diverse crosslink density were prepared using bifunctional epoxide prepolymers of different molecular weight, crosslinked with diamine diphenyl sulphone, and their fracture behaviour investigated. The same set of resins was also modified with a reactive rubber. The fracture toughness regularly decreased on increasing the crosslink density for all formulations. The addition of the rubber gave rise to a marked increase in toughness, though it magnified the influence of the molecular weight of the prepolymer. Tests performed with blunt notches showed that the fracture toughness was maximum at medium crosslink densities. A dispersion of rubber particles caused a toughness increase through the formation of microcavities ahead of the crack tip. Failure was preceded by a rapid volume increase caused by void coalescence.

Diffusion and sorption of organic liquids through polymer membranes. 5. Neoprene, styrene-butadiene-rubber, ethylene-propylene-diene terpolymer, and natural rubber versus hydrocarbons (C8-C16)

Abstract: Diffusion and sorption of four long-chain hydrocarbons, namely, 2,2,4-trimethylpentane, dodecane, tetradecane, and hexadecane, through four commercial polymer membranes has been studied in the temperature interval of 25-60°C by conventional weight gain experiments. The diffusion results have been analyzed in terms of the simple Fickian model. The slightly anomalous transport behavior of the polymer-solvent systems has been attributed to a slow leaching out of the indigenous elastomer compounds and/or additives during solvent immersion

Fracture mechanics and cavitation in rubber-like solids

Abstract: Conditions for propagation of a pressurized crack within a rubber-like solid are derived in terms of the elastic properties of rubber, the fracture energyGc and the initial radiusro of the crack. A previously proposed criterion, that the critical internal pressurePc for crack growth is given by 5E/6, whereE is the tensile (Young) modulus of elasticity, is shown to be inadequate both for small cracks, when the stiffening of rubber at high strains must be taken into account, and for large cracks, when the critical degree of inflation is so small that the assumptions leading toPc=5E/6 do not apply. However, this simple criterion is found to remain a useful guide for cracks having initial radii lying in an intermediate range, such thatroE/Gc lies between about 0.0005 and 1. For representative rubber-like solids, this corresponds to the rangero=0.5 μm to 1 mm.

Rubber‐modified epoxies. II. Influence of the cure schedule and rubber concentration on the generated morphology

Abstract: The morphology of a system consisting of a bisphenol A digrycidylether (DGEBA) based epoxy, cured with a cycloaliphatic diamine (4,4'-diamino-3,3'-dimethyldicyclohexylmethane, 3DCM), in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration

Diffusion and sorption of organic liquids through polymer membranes. II. Neoprene, SBR, EPDM, NBR, and natural rubber versus n‐alkanes

Abstract: Diffusion and sorption of n-alkanes (C6–C10) through commercial polymer membranes such as neoprene, styrene butadiene rubber, ethylene propylene diene terpolymer, nitrile butadiene rubber, and natural rubber have been studied from 25 to 60°C. The diffusion results have been explained in terms of the size of liquid molecules and the diffusion mechanism was found to follow the Fickian trend. Nitrile butadiene rubber and neoprene showed much smaller values of diffusivities and sorption constants than the other polymer membranes. Arrhenius parameters for the activated diffusion process and the thermodynamic quantities for the process of equilibrium sorption have been estimated.

Hydrophobic behavior of insulators coated with RTV silicone rubber

Abstract: Room temperature vulcanizing (RTV) silicone rubber coatings are applied to electrical insulators to improve their subsequent insulation strength, particularly under wet conditions. Under prolonged wetting the hydrophobicity of the coating is reduced temporarily and the insulator protection is lost. After a dry period, a recovery of the hydrophobicity takes place. To investigate this phenomenon, the surface was subjected to various wetting conditions with and without electrical stress. Measurements of the contact and the sliding angles were used to determine the state of the surface. Using water, the surface free energy of the RTV was calculated from the contact angle measurements as a function of time of exposing the surface to salt-fog. The surface free energies due to London dispersion and hydrogen bonding forces on the surface of RTV coatings were calculated from the contact angle measurements using both water and methylene iodide. Good agreement was obtained with the literature value for a virgin RTV surface. The chemical changes of the surface are shown to be responsible for the loss of hydrophobicity. >

Surface structural changes of naturally aged silicone and EPDM composite insulators

Abstract: In a long-term outdoor test with high direct and alternating voltages, silicone and ethylene propylene diene monomer (EPDM) rubber composite insulators have, at the beginning, shown a performance superior to that of glass and porcelain insulators. In the long-term test, however, the silicone rubber composite insulator has, in spite of the aging of both insulator types, kept its good performance, while the performance of the EPDM rubber composite insulator was drastically deteriorated. In order to get a better insight into the results obtained, the wettability and the surface structural changes of the insulators were studied by the drop deposition method using a goniometer and by advanced techniques such as scanning electron microscopy, electron spectroscopy for chemical analysis, Fourier-transform infrared spectroscopy, and secondary ion mass spectrometry. The results show that the differences in performance are related to the differences in the surface structural changes and in the dynamic ability of the surface to compensate the aging. Silicone rubber insulators have higher repellency than the EPDM insulators, especially when aged. The reason seems to be low silicone polymer diffusion from the bulk which covers the insulator surface, embeds the pollutants, and keeps the surface hydrophobic. Porcelain insulators with silicone elastomer coatings show lower water repellency than insulators with massive silicone rubber sheds. When aged, EPDM insulators do not, however, seen to possess the same dynamic recovery of their surface, thus becoming hydrophilic. >

On Compression of Rubber Elastic Sphere Over a Large Range of Displacements—Part 1: Theoretical Study

Abstract: This paper presents one general theory of large elastic deformations of a rubber sphere in simple compression, as the removal of restrictions of the constant Young modulus and small deformation in the prevailing Hertzian theory in contact of elastic bodies. It derives a set of five equations associated with approach, radii of contact surface without and with lateral extension of free surface, the lateral extensive displacement on the contact surface and the position of the contact surface in a very large range of applied forces, on the basis of the Hertz theory (half-space elastic body model) with an extensive term, in consideration of the rubber-elastic nonlinear elasticity, the lateral extension and the symmetry of the deformed shape of the rubber sphere. In Part 2 it is shown that results calculated by the set of the equations fit experimental data for a rubber sphere.

Study of rubber-modified brittle epoxy systems. Part II: Toughening mechanisms under mode-I fracture

Abstract: The toughening mechanisms in grafted-rubber concentrate (GRC), dispersed acrylic rubber (DAR), and Proteus rubber-modified brittle epoxy (i.e., highly crosslinked) systems are examined using scanning electron microscopy, optical microscopy and transmission electron microscopy techniques. The toughening of the GRC-modified brittle epoxy system is found to be due to cavitation of the GRC rubber particles, followed by formation of limited shear yielding when the crack propagates. Crack bifurcation and crack deflection are also observed in this system. Only crack bifurcation, crack deflection, and possibly crack/particle bridging mechanisms are operative in the DAR-modified brittle epoxy system. In the case of the Proteus rubber-modified system, the rubber appears to be rigid (Tg ≈ 28°C). As a result, the crack/particle bridging mechanism is not observed. Only crack deflection and crack pinning mechanisms are found. These observations are in agreement with the toughness measurement results (see Part I), which indicate that the GRC rubber provides the most effective toughening, followed by the DAR rubber, and then by the Proteus rubber. An approach for toughening brittle epoxies is also discussed.

Frequency, spectrum and occupational relevance of type IV allergies to rubber chemicals

Abstract: 3851 consecutive patients patch tested between January 1985 and March 1990 have been analysed for rubber allergies. The incidence of rubber allergy was 3.8% (n = 145). In 80/145 patients (55%), the source of rubber sensitization was occupational, 67 of whom (84%) had acquired allergy from wearing rubber gloves at work. Most of them (36%) were employed in the health services. The most commonly positive rubber-mix in this group was thiuram-mix (72%) followed by carba-mix (25%). 13/80 patients (16%) had occupational rubber allergy from industrial rubber products other than gloves. Patch tests revealed thiuram-mix (62%) as the most commonly positive rubber-mix but, in contrast to the group with glove-induced rubber allergy, black-rubber-mix came second (38%). In 47/145 patients (32%), the source of rubber sensitization was non-occupational; in 18/145 (13%) the origin remained unknown.

Carbon black filled natural rubber. 1. Structural investigations

Abstract: The effects of solvent extraction of increasing severity on carbon black filled natural rubber are examined. Collated NMR, DSC, and DMTA methods examine the glass transition and motional cooperation in the filled system. DSC is insensitive to the immobilization of small amounts of tightly bound rubber on the surface of carbon black particles. Also examination of component T 2 intensity data as a function of temperature engenders the notion of a range of binding energies between the rubber and the carbon black. The Carr-Purcell pulse train has been used to glean additional insight into the dynamics of molecular motion, and exchange between heterogeneous sites is explored

Epoxidised natural rubber

Abstract: INTRODUCTION As long ago as 1922 natural rubber (NR) was reacted* with a peroxyacid and although the structure of the product was not elucidated epoxidation must have occurred. Since this date a number of conflicting reports have been published on the preparation and properties of epoxidized natural rubber (ENR). A variety of reaction conditions were employed and the products variously described as hard thermoplastic'''' to soft rubbery polymers'-'. The epoxidation of NR and other unsaturated polymers was stated to increase solvent resistance and to improve wear resistance and mechanical properties*-'. However, other publications have reported a reduction in tensile strength properties'-'. A number of epoxidised latices have also been studied--. In the early to mid 1970's there was a renewed interest in the chemical modification of NR to produce other polymeric materials as a result of the oil crises. Epoxidation was an attractive route because of the simple reaction procedure, the reaction can be carried out in the latex phase, and the relatively low cost of the reagents involved.

Carbon blacks modified with organosilicon compounds, method of their production and their use in rubber mixtures

Abstract: Carbon black is reacted with at least one organosilicon compound of the General Formula [R.sup.1.sub.n (RO).sub.3-n Si-(Alk).sub.m -(Ar).sub.p ]q [B](I) R.sup.1.sub.n (RO).sub.3-n Si-(Alkyl) (II) or R.sup.1.sub.n (RO).sub.3-n Si-(Alkenyl) (III), and any excess of said organosilicon compound is extracted with a solvent. The products are useful as active fillers in rubber mixtures, carbon black suspensions and plastic mixtures which can be cross-linked with sulfur or peroxide.

Rubber‐Modified epoxies. IV. Influence of morphology on mechanical properties

Abstract: The mechanical properties of a system consisting of a bisphenol A diglycidylether (DGEBA) expoxy, cured with a cycloaliphatic diamine (4,4′-diamino-3,3 dimethyldicyclohexyl-methane, 3DCM), in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration. Fracture toughness (KIc) and fracture energy (GIc) were increased, while Young's modulus and yield strength decreased slightly with increasing volume fraction of the dispersed phase. We show that there is no significant influence of the precure schedule and of the various observed particle diameters on the mechanical properties for a constant rubber volume fraction. In our case, the main deformation process in the rubber-modified epoxy networks is shear yielding while cavitation is negligible.

Tire tread rubber composition

Abstract: An abrasion-resistant halogenated isobutylene-based rubber composition having good traction characteristics is disclosed. In a preferred embodiment, the composition comprises a halogenated isobutylene rubber, styrene/butadiene rubber and polybutadiene rubber combined with carbon black and a silane-coupled silica filler. In automobile tire treads, tire retreads, and other anti-skid materials, the composition exhibits viscoelastic properties offering excellent traction and good rolling resistance with no loss in tire treadwear.

Rubber blend and tire with tread thereof

Abstract: A pneumatic tire with a tread composed of a blend of 3,4-polyisoprene rubber, cis 1,4 polyisoprene rubber and at least one additional diene based rubber.

The influence of materials of construction on biconical rotor and capillary measurements of shear viscosity of rubber and its compounds and considerations of slippage

Abstract: An experimental study is presented of the flow of elastomers and their compounds in biconical and capillary geometries using rotors and capillaries produced from different materials including aluminum, brass, copper, steel, and stainless steel plus polytetrafluorethylene (PTFE). The rotational rheometer could be operated at various controlled pressure levels. A butadiene–styrene copolymer (SBR) was investigated as well as an SBR compound with 20 vol % carbon black and a second SBR compound with 7% zinc stearate added. It was found in the pressurized rheometer, when the pressure was greater than 0.2 MPa, that the data for SBR and SBR–carbon black was essentially the same for smooth and grooved rotors fabricated from different metals. However when the pressure was reduced the torques were substantially reduced and the data for the grooved rotors were higher than for the smooth rotors. Generally, the copper and brass gave rise to higher shear stresses than the steel or stainless steel. The PTFE yielded the l...

Tin containing elastomers and products having reduced hysteresis properties

Abstract: An anionic polymerization initiator comprising the reaction product of a an organatin halide and lithium in a suitable solvent. Elastomeric polymers prepared with these initiators have tin containing functional groups on substantially every polymer chain and provide vulcanizable rubber compounds exhibiting reduced hysteresis. Articles such as tires, produced with low hysteresis elastomeric polymers have lower rolling resistance. Methods are also provided for preparing the initiators and the elastomers having reduced hysteresis properties.

Thermoplastic elastomer composition

Abstract: Provided is a thermoplastic elastomer composition from which a sheet showing excellent uniform extensibility and embossing retention over a wide range of forming temperatures can be obtained The thermoplastic elastomer composition is obtainable by incorporating (C) 5 to 200% by weight of at least one component selected from an ethylene copolymer resin having a denisty of 094 g/cm 3 or lower and a crystalline propylene polymer resin into a crosslinked polymer (II) obtained by subjecting a composition (I) comprising (A) 10 to 75% by weight of a crystalline propylene polymer resin and (B) 90 to 25% by weight of a propylene-olefin copolymer rubber to a dynamic thermal treatment which is carried out in the presence of an organic peroxide

A method for estimating the Young's modulus of complete tracheal cartilage rings.

Abstract: Cartilage is primarily responsible for maintaining the stability of the large airways; yet very little is known about the mechanical properties of airway cartilage. This work establishes a technique whereby average values for the equilibrium modulus of excised tracheal cartilage rings can be obtained. An apparatus was designed to apply preset deformations to a tracheal segment and to monitor the deforming force. Segments of four human tracheae obtained postmortem and containing three rings were mounted in the apparatus after being stripped of posterior membrane. The load-deformation behavior was analyzed with a model on the basis of thin curved beam theory. Agreement between predicted deformed shapes and those observed was good in three of the four cases and in the case of a short length of longitudinally split rubber tube. The technique is suitable for comparing mechanical properties of cartilage before and after an intervention.

Rubber shaped articles having a finishing layer and a process for production thereof

Abstract: A rubber shaped article having a finishing layer which comprises a main body of rubber shaped article made of EPDM, a finishing layer of a PVC composition formed on the main body, and an adhesive layer formed between the main body and the finishing layer, said adhesive layer comprising 40 to 80% by weight of NBR, 20 to 40% by weight of EPDM and 0 to 35% by weight of SBR; and a process for producing said rubber shaped article. The rubber shaped article of the present invention provides internal and external automotive trims having an improved decorative design, with high productivity.

Method and arrangement for the single-stage continuous production of a rubber base compound and a rubber end compound

Abstract: The invention is directed to a method and an arrangement for continuously producing a rubber base compound and a rubber end compound in a single stage for vehicle tires, drive belts, conveyor belts as well as for industrial rubber products. The rubber base compound and the rubber end compound are produced continuously in one and the same mixing arrangement which includes a twin-screw extruder.

Process for preparing a rubbery terpolymer of styrene, isoprene and butadiene

Abstract: The subject invention relates to a technique for synthesizing rubbery terpolymers of styrene, isoprene and butadiene. These rubbery terpolymers exhibit an excellent combination of properties for utilization in tire tread rubber compounds. By utilizing such terpolymers in tire treads, tires having improved wet skid resistance can be built without sacrificing rolling resistance or tread wear characteristics. The subject invention specifically discloses a process for preparing a rubbery terpolymer of styrene, isoprene, and butadiene having multiple glass transition temperatures and having an excellent combination of properties for use in making tire treads which comprises: terpolymerizing styrene, isoprene and 1,3-butadiene in an organic solvent at a temperature of no more than about 40° C. in the presence of (a) at least one member selected from the group consisting of tripiperidino phosphine oxide and alkali metal alkoxides and (b) an organolithium compound.

Characterization of Dispersions

Abstract: The methods of pigment dispersion analysis have been reviewed in regard to their application to rubber, plastics, and other vehicle systems. The characteristics of dispersions have been divided into three categories: (1) agglomeration (2) microdispersion (networking) and (3) polymer-phase distribution. Stylus roughness measurements on cut surfaces offer the combination of simplicity and speed of operation with high accuracy and precision for measuring pigment agglomeration in elastomer systems of known composition. This method may also be applied to the surface of thin plastic extrudates. However, optical analyses of thin cryosections are preferred for most plastics or unknown rubber compounds containing high loadings of carbon black. X-radiography is generally preferable for the analysis of inorganic agglomeration in most polymeric vehicle systems. The scanning electron microscope is also applicable for this type of analysis and has the added capability of identifying unknown agglomerates by ene...