Types Of Natural Rubber Research Articles

Avaliação de compostos de borracha natural utilizados em equipamentos de segurança

No setor elétrico, a borracha natural (BN) tem sido amplamente utilizada na confecção de ferramentas isolantes. Esses são itens essenciais para a segurança e proteção de trabalhadores da área de manutenção de redes de distribuição de energia elétrica. A boa conservação dessas ferramentas deve ser assegurada com o objetivo de garantir o isolamento elétrico e resistência mecânica adequados, portanto a avaliação dos processos de degradação se torna importante. Neste trabalho duas formulações de borracha natural comerciais, utilizadas na confecção de equipamentos de proteção coletiva (EPC's), foram caracterizadas por envelhecimento térmico, ensaios mecânicos, termogravimétricos, análise termo-dinâmico mecânica, inchamento e extração.

Curing Characteristics, Fatigue and Hysteresis Behaviour of Feldspar Filled Natural Rubber Vulcanizates

Curing characteristics, fatigue, and hysteresis behaviour of feldspar filled SMR L vulcanizates and feldspar filled ENR 50 vulcanizates were studied. Two different types of natural rubber, SMR L and ENR 50 having 0 and 50 mol% of epoxide groups were used. The feldspar filled natural rubber vulcanizates were compared at similar filler loading which were used at 0, 10, 20, and 30 phr of filler loading. The curing characteristics such as scorch time (t 2) and cure time (t 90) slightly increased with increasing feldspar loading for both rubber vulcanizates. Besides t 2 and t 90, maximum torque (M HR) significantly increased for both rubbers with increasing feldspar loading. The fatigue test showed that fatigue life decreased with increasing extension ratio, strain energy and filler loading. As the filler loading increased, the poor wetting of the feldspar by the rubber matrix gave rise to poor interfacial adhesion between filler and rubber matrix. Results also indicate that the vulcanizates with the highest feldspar loading exhibited the highest hysteresis. The feldspar filled SMR L vulcanizates showed higher fatigue life and lower hysteresis compare to feldspar filled ENR 50 vulcanizates.

Study of Fatigue Life and Filler Interaction of Paper Sludge Filled Epoxidized Natural Rubber (ENR) and Maleated Natural Rubber (MNR) Composites

An investigation on the effect of epoxidation and maleated natural rubber (MNR) on fatigue and rubber-filler interaction properties of paper sludge filled natural rubber composites was elucidated. Paper sludge loading was varied from 0 to 40 phr and conventional vulcanisation system was used while compounding was carried out on a laboratory sized two roll mill. Two different types of natural rubber, SMR L and ENR 50 having 0 and 50 mole% of epoxidation were used in order to investigate the effect of epoxidation on the composites. Results indicate that, at a fixed filler loading, ENR 50 vulcanizates exhibit higher fatigue life than SMR L vulcanizates especially at filler loading below 20 phr which might be associated with better rubber-filler interaction. In the case of composites with the addition of maleated natural rubber (MNR), a higher fatigue life was observed due to presence of physical and/or chemical linkages, which increases the interfacial adhesion. Scanning electron microscopy (SEM) micrographs of fatigue fracture surfaces and rubber-filler interaction study supported the observed result on fatigue life.

The Effect of Filler Loading and Epoxidation on Paper-Sludge-Filled Natural Rubber Composites

The effect of filler loading and epoxidation on curing characteristics, dynamic properties, tensile properties, morphology, and rubber-filler interactions of paper-sludge-filled natural rubber compounds have been studied. Two different types of natural rubber, SMR L and ENR 50, having 0% and 50% of epoxidation and conventional vulcanization were used. Paper sludge was used as a filler and the loading range was from 0 to 40 phr. Compounding was carried out using a laboratory-sized two-roll mill. The scorch time for both rubber compounds decreased with filler loading. The cure time was found to decrease with increasing filler content for SMR L vulcanizates, whereas for ENR 50, the cure time seemed to be independent of the filler loading. Dynamic properties, i.e., maximum elastic torque, viscous torque, and tan delta, increase with filler loading in both grades of natural rubber. Results also indicate that both rubbers show increment in tensile modulus but inverse trend for elongation at break and tensile strength. However, for a fixed filler loading, ENR 50 compounds consistently exhibit higher maximum torque, modulus at 100% elongation, and modulus at 300% elongation, but lower elongation at break than SMR L compounds. In the case of tensile strength, ENR 50 possesses higher tensile strength than SMR L at 10 to 20 phr, but the difference is quite small at 30 and 40 phr. These findings might be associated with better rubber-filler interaction between the polar hydroxyl group of cellulose fiber and the epoxy group of ENR 50.

The Effect of Feldspar Loading on Curing Characteristics, Mechanical Properties, Swelling Behavior and Morphology of Natural Rubber Vulcanizates

ABSTRACT Feldspar is being used herein as a filler in natural rubber vulcanizates. Two different types of natural rubber, SMR L and ENR 50 having 0 and 50 mol% of epoxide groups and semi-efficient vulcanization were used. The scorch time, (t2) and cure time, (t90) of both rubber vulcanizates slightly increased with increasing feldspar loading. At a similar feldspar loading, the ENR 50 vulcanizates showed shorter t2 and t90 than SMR L vulcanizates. Besides t2 and t90, maximum torque, (MHR) and torque difference (MHR−ML) were also investigated. Results indicate that MHR and MHR−ML increase for both rubbers with increasing feldspar loading. Swelling test results showed a reduction in the swelling percentage for both rubbers with increasing feldspar loading. At a similar filler loading, SMR L vulcanizates showed lower swelling percentage than ENR 50 vulcanizates. The mechanical properties such as tensile strength (up to certain filler loading), tensile modulus and hardness increased with increasing feldspar loading for both rubbers. However, at a similar feldspar loading, the mechanical properties of SMR L vulcanizates are higher than ENR 50 vulcanizates.

Rheological properties of maleated natural rubber and natural rubber blends

Two types of natural rubber (ADS and STR 5L) were used to prepare maleated natural rubber (MNR). Melt rheological properties of MNRs (i.e. MNR-ADS and MNR-STR) and their blends with the same type of natural rubber were quantified. We found that the Mooney viscosities of MNR-ADS/ADS blends were higher than those of MNR-STR/STR 5L blends. The log additive rule was applied to the Mooney viscosity data. Positive deviation blends (PDB) were observed. A power law model was also applied to the shear flow data at a wide range of shear rates. The pseudoplastic (shear-thinning) behavior for all sets of MNR/NR blends were observed with the power law index, n, lower than 1. According to the log additive rule, plots of the consistency index against MNR levels in the blends also indicated positive deviation blends. Shear viscosity data of the blends also confirmed the shear-thinning behavior and the positive deviation blends. From the rheological property point of view, we therefore concluded that the MNR/NR blends were compatible.

Influence of nonrubber constituents on tack of natural rubber. I. At very short times of contact (pendulum test)

The effect of nonrubber constituents such as proteins and lipids on tack of natural rubber (NR) was studied. Tack or adhesion at short contact time was determined for contact between crosslinked rubbers and glass plates. Various types of natural rubber, with or without nonrubber constituents, were prepared. Synthetic polyisoprene was used as a reference because of its chemical similarity. In this work, the impact pendulum test was carried out to study very short contact times tc of the order of milliseconds. The results show an increase of tack energy with tc for all the rubbers. This is attributed to an increase in true contact area with time and to a modification of the interfacial energy. Furthermore, the natural rubber without lipids and also polyisoprene exhibited the highest tack values while whole natural rubber remained always the less tacky. These results cannot be explained by differences in either the bulk viscoelastic properties of the crosslinked materials or their overall surface energy. The presence of a thin layer of varying composition at the surface of the rubbers appears to be the essential factor that affects the tack properties of the crosslinked materials. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1486–1494, 2000

Effects of palm oil fatty acid on curing characteristics, reversion and fatigue life of various natural rubber compounds

The effects of palm oil fatty acid concentration (0, 1, 3, 5, 7 phr) and epoxidation on curing characteristics, reversion and fatigue life of carbon black filled natural rubber compounds have been studied. Three different types of natural rubber, SMR L, ENR 25 and ENR 50 having 0, 25 and 50 mol% of epoxidation and conventional sulphur vulcanization were used. The cure time t90, scorch time t2, MHR − ML (maximum torque − minimum torque) and fatigue life of all rubbers were found to increase with increasing palm oil fatty acid concentration. However, the reversion of all rubbers decreases with increasing palm oil fatty acid concentration. At similar concentrations of palm oil fatty acid, ENR 50 compounds exhibit the shortest scorch and cure times followed by ENR 25 and SMR L compounds. For reversion, SMR L compounds show the lowest value followed by ENR 50 and ENR 25 compounds, whereas for fatigue life, the highest value is obtained with ENR 50 compounds followed by ENR 25 and SMR L compounds. © 1999 Society of Chemical Industry

The Effects of Multifunctional Additive and Epoxidation in Silica Filled Natural Rubber Compounds

The effects of multifunctional additive (MFA) and epoxidation on physical properties and curing characteristics of silica filled natural rubber compounds have been studied. Three different types of natural rubber, SMR L, ENR 25 and ENR 50 having 0, 25 and 50 mol % of epoxidation and semi-efficient vulcanization were used. The cure time, (t 90) and scorch time, (t 5) of all rubbers decreases with increasing MFA level. At similar MFA level, ENR 50 possessed the shortest scorch and cure times followed by ENR 25 and SMR L vulcanizates. Compared to the control compound (without MFA), the physical properties in all rubbers have been enhanced by the addition of MFA. However at similar MFA level, the physical properties viz. tensile and tear strengths of SMR L vulcanizates is highest followed by ENR 25 and ENR 50 vulcanizates.

Guayule Rubber: Vulcanization Properties of Gum and Filled Stocks

Abstract Guayule rubber has been used both in the resinous and deresinated form for more than sixty years during periods of either scarcity or high prices of hevea rubber. During this time little or no efforts have been made to standardize the individual processes to a point where the products had specifications similar to the “Technically Specified Rubbers”. This lack of specifications consequently left users of the guayule rubbers with various opinions of the capabilities of this type of natural rubber in their commercial products. It was generally believed that the rubber was only good for low-grade products or where guayule was only used as a tackifier for other rubbers. Recent interest in the utilization of arid regions and the increasing need for less dependence on foreign sources has led the Mexican government to develop a modern guayule product. It was the purpose of this study to evaluate Mexican guayule rubber in cooperation with CIQA in an effort to determine processing and vulcanization characteristics of the products prepared in their pilot plant in Saltillo, Mexico.

Determination of degree of crosslinking in natural rubber vulcanizates. Part VII. Crosslinking efficiencies of di‐tert‐butyl and dicumyl peroxides in the vulcanization of natural rubber and their dependence on the type of natural rubber

AbstractThe efficiency with which di‐tert‐butyl peroxide and dicumyl peroxide vulcanize (crosslink) natural rubber depends on the type of natural rubber. Crosslinking efficiencies of the peroxides are increased by acetone extraction of the rubber and by increasing the concentration of peroxide but in no case studied was either peroxide 100% efficient. These findings indicate that the natural rubber samples contain non rubber compounds which compete with the rubber hydrocarbon for reaction with the peroxide. The implications of these findings are: (1) that the values of chemical crosslinks determined by Moore and Watson from the yields of tert‐butyl alcohol and methane formed when an unextracted deproteinized pale crêpe is crosslinked with di‐tert‐butyl peroxide may be overestimated; and, thus, (2) the calibration of Mullins which relates the number of chemical crosslinks in a natural rubber–peroxide vulcanizate to the number of physically manifested crosslinks may require revision.

Viscosity—molecular weight relationship for masticated natural rubber

AbstractIntrinsic viscosity and osmotic molecular weight data are presented for toluene solutions of several types of natural rubber after mastication in air. For [η] < ca. 4 all these data fit the relationship, [η] = 7.11 × 10−7 M̄n1.25. At higher molecular weights deviations from this relation are found, the extent of which depend on the type of natural rubber used. These deviations are attributed to differences in initial molecular weight distribution.

Properties of Ebonite. XXX. Influence on Properties of Ebonite of the Type of Raw Rubber Used, with Special Reference to Purified Rubbers

Abstract Tests have been made on unloaded ebonites prepared from ordinary commercial types of natural rubber, special (deproteinized) rubbers having reduced contents of protein and(or) other water-absorbent substances, and a whole-latex rubber containing relatively large percentages of these substances, to determine to what extent these substances influence the electrical properties of the ebonite and, hence, whether any technically useful improvement can be effected by using specially prepared rubbers. Permittivity and power factor at 106 cycles per second, but particularly power factor, are somewhat improved by using the special rubbers, so that the dielectric loss can be reduced by about 30 per cent. In addition, the increase in dielectric loss caused by exposure to high humidity or by a rise of temperature is in general lessened by the use of these rubbers. Similar, though smaller, improvements in the properties of the ebonite are obtained by washing ordinary commercial rubber (smoked sheet). Although a definite improvement in dielectric loss is obtained, it does not seem probable that purification of natural rubber would lead to ebonites with dielectric properties approaching those of polystyrene, for instance. It seems unlikely that even complete elimination of the water-absorbent impurities would reduce the dielectric loss by more than 50 per cent; the rubber-sulfur compound itself thus appears to be responsible for a fair proportion of the loss normally observed. The large percentages of water-soluble substances present in whole-latex rubber increase the permittivity and especially the power factor of the ebonite made from it. The dielectric properties of ebonite are related, though not closely, to its water-absorbing capacity and that of the raw rubber used, low absorption being in general accompanied by low dielectric loss and reduced sensitiveness to humidity variations. There is only a rough parallelism between the water absorptions of raw rubbers and the corresponding ebonites. Probable reasons for this are indicated. It is concluded that water absorption tests on raw rubber form a useful, though only approximate, guide to its value for making electrical ebonite; electrical tests on the ebonite must be the final criterion. Apart from very impure whole-latex rubber, no correlation can be traced between the inorganic content (ash) of ebonite and its electrical properties. The probable reason for this is indicated. There is evidence that the dielectric loss of ebonite may increase with the passage of time. In view of its obvious theoretical and practical importance, this phenomenon requires further study. No technically useful advantage as regards breakdown strength, volume resistivity, surface resistivity, or stability to light, by the use of the special rubbers, is evident in the present work. The plastic yield characteristics of ebonite are not appreciably altered by using special rubbers. Estimations of uncombined sulfur and also plastic yield tests show that one of the deproteinized rubbers vulcanizes more rapidly than the rest, which differ little among themselves.

Purified Natural Rubbers. Mechanical Aging, Hygroscopic, and Electrical Properties of the Vulcanizate

Abstract The fact that the nonrubber components of crude rubber, especially those of a hygroscopic nature, impair the electrical properties of the vulcanizate has long been known, and the preparation of deproteinized or otherwise purified rubbers for use in electrical insulation had reached the commercial stage before the 1939–1945 war. With the rehabilitation of the plantation industry, the question of what special types of natural rubber should be prepared and marketed has become important, and purified rubbers represent one type that merits careful consideration. Published data on the electrical properties of purified rubbers, both before and after vulcanization, relate entirely to types prepared from solid rubber (crepe or sheet) or ammonia-preserved latex in the consuming country, and there is no published record of experiments on rubber purified during its preparation on the plantation. In 1935 the R.A.B.R.M. began investigations on the use of purified rubbers of the latter type in making electrical ebonite; the results will shortly be published. Examination of soft vulcanizates was began in 1937, but war conditions made it necessary to discontinue the work, for which reason the electrical results are less complete and conclusive than could have been wished. Nevertheless, it is hoped that the results obtained will be of value to the rubber manufacturing and plantation industries. Another use of purified rubbers is in the manufacture of transparent articles that come in contact with water or aqueous solutions. Transparent vulcanizates made from ordinary raw rubber quickly become white and opaque owing to absorption of water, but it would be expected that the use of purified rubber would remove or lessen this defect. This point has accordingly been examined. The thanks of this Association are due to the London Advisory Committee for Rubber Research (Ceylon and Malaya) for arranging for the preparation of special purified rubbers, in Ceylon and Malaya, and for examining the water absorption of the unvulcanized rubbers.