Nitrile Rubber Vulcanizates Research Articles

Characterization of Blends of Virgin Nitrile Rubber and Compounded Nitrile Rubber Latex Waste Reclaimed with Urea: Part II - Physico-Mechanical Properties

Recycling of rubber waste materials in order to convert these to usable products is one of the main challenges in the rubber industry. Reclaiming of rubber waste and blending it with virgin rubber have increased during the past due to the growing concern on the environment and increase in the prices of synthetic rubbers. Hence, the aim of this study is to partially replace virgin nitrile rubber (NBR) with reclaimed compounded NBR latex waste to develop new rubber blends suitable for special applications. In this study, physico-mechanical properties, ageing performance and swelling behaviour of virgin NBR / reclaimed NBR blend vulcanizates were evaluated and compared with those of the control vulcanizate produced solely with virgin NBR. Results showed that replacement of 50% virgin NBR with reclaimed NBR retained 71-86% of tensile strength, elongation at break and resilience. Hardness and modulus of this blend vulcanizate increased by less than 18%, whereas abrasion volume loss and compression set increased by 27%. Ageing resistance is similar to that of the control vulcanizate. Interestingly, resistance to swelling in toluene and ASTM oil No.3 increased by 14% and 32%, respectively. Hence, the 50:50 virgin NBR / reclaimed NBR vulcanizate would be suitable for oil resistant applications.

Rheological and Mechanical Properties of Silica/Nitrile Butadiene Rubber Vulcanizates with Eco-Friendly Ionic Liquid.

In this paper we designed greener rubber nanocomposites exhibiting high crosslinking density, and excellent mechanical and thermal properties, with a potential application in technical fields including high-strength and heat-resistance products. Herein 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc) ionic liquid was combined with silane coupling agent to formulate the nanocomposites. The impact of [EMIM]OAc on silica dispersion in a nitrile rubber (NBR) matrix was investigated by a transmission electron microscope and scanning electron microscopy. The combined use of the ionic liquid and silane in an NBR/silica system facilitates the homogeneous dispersion of the silica volume fraction (φ) from 0.041 to 0.177 and enhances crosslinking density of the matrix up to three-fold in comparison with neat NBR, and also it is beneficial for solving the risks of alcohol emission and ignition during the rubber manufacturing. The introduction of ionic liquid greatly improves the mechanical strength (9.7 MPa) with respect to neat NBR vulcanizate, especially at high temperatures e.g., 100 °C. Furthermore, it impacts on rheological behaviors of the nanocomposites and tends to reduce energy dissipation for the vulcanizates under large amplitude dynamic shear deformation.

Study on the Synthesis of Castor Oil-Based Plasticizer and the Properties of Plasticized Nitrile Rubber.

A series of new environment-friendly plasticizers was synthesized from castor oil and used to plasticize nitrile rubber (NBR). The test results showed that tensile strength, elongation at break, and tear strength of NBR vulcanizates plasticized by castor oil-based plasticizers were found to be better than that of dioctyl phthalate (DOP). The aging test taken demonstrated that the castor oil-based plasticizers could improve the hot air and oil aging resistance of NBR vulcanizates. The thermal stability test illustrated that castor oil-based plasticizers enhanced the thermal stability of NBR vulcanizates, and the initial decomposition temperatures (T10%) were about 100 °C higher than that of DOP. In general, the studies manifested that EACO and EBCO can replace DOP to plasticize NBR and are used in fields that require high mechanical properties, aging resistance, and thermal stability. This study emphasizes the effects of sustainable, cost-effective, and high-efficiency plasticizers on NBR.

The effect of peroxide crosslinking on the synergistic crosslink of double bond and nitrile group of nitrile rubber in H2S environment

In the H2S environment, the double bonds and nitrile groups of pure nitrile rubber (NBR) are synergistically crosslinked to produce sulfur crosslinks [1]. However, the corrosion of NBR vulcanizate in H2S is unknown. To investigate the effect of crosslinked structure on NBR corrosion, a corrosion test of NBR cured by peroxide crosslinking in H2S is carried out. Researches find out that the vulcanizates are more susceptible to H2S than the raw rubber. The increment of sulfur element in vulcanizate is much higher than that of raw rubber, and the reduction of double bond is more severe than raw rubber, which is attributed to the ɑ-tertiary carbon structure produced by peroxide crosslinking. The ɑ-tertiary carbon greatly activates the double bond and allyl hydrogen (ɑ–H), thereby promoting the reaction of 1,4–polybutadiene (1,4–PB) structural unit with H2S, thus exacerbating the corrosion of NBR, causing a serious decline in its performance.

Assessment of failures of nitrile rubber vulcanizates in rapid gas decompression (RGD) testing: Effect of physico-mechanical properties

Rapid gas decompression (RGD) test is used to evaluate structural failures such as bubbles, blisters, internal and external cracks in rubber vulcanizates exposed to gas environment under high pressure and high temperature (HPHT) conditions. Physico-mechanical properties of vulcanizates may greatly affect the RGD resistance of rubber products. In this study, effect of the most important physico-mechanical properties such as hardness, modulus, elongation at break, tensile strength, tear strength, compression set and crosslink density of nitrile rubber (NBR) samples cured by different sulfur curing systems including conventional system (CV), semi-efficient system (SEV) and efficient system (EV) on RGD resistance has been investigated. Results showed that the type of sulfur curing system and resultant physico-mechanical properties had pronounced effects on RGD resistance. The NBR rubber samples prepared by CV system exhibited highest failures under RGD testing. Moreover, by increasing crosslink density, hardness and modulus of NBR vulcanizates, the internal cracks were increased during RGD test. Furthermore, the RGD resistance was improved at higher tear strength of rubber samples. Also, lower compression set specially in CV curing system and higher tensile strength of NBR samples lead to less structural failures.

The Effect of Acrylonitrile Content on the Abrasion Behavior of Unfilled Nitrile Rubber

Three unfilled nitrile rubber vulcanizates with different acrylonitrile contents (28%, 33%, and 40%) were prepared. The gravimetric wear rate of testing samples increased with increasing acrylonitrile contents. The cross-linking densities of rubbers were studied by the equilibrium swelling method. The measurement of the dissipated energy between tip and rubber surface was also carried out using tapping mode atomic force microscopy and the results suggest that the cross-linking density in local areas is primary responsible to the abrasion performance of unfilled nitrile rubber with reference to the polarity of polymeric matrix.

Reactivity of sulfide-containing silane toward boehmite and in situ modified rubber/boehmite composites by the silane

The silanization reaction between boehmite (BM) nanoplatelets and bis-[3-(triethoxysilyl)-propyl]-tetrasulfide (TESPT) was characterized in detail. Via such modification process, the grafted sulfide moieties on the BM endow reactivity toward rubber and substantially improved hydrophobicity for BM. Accordingly, TESPT was employed as in situ modifier for the nitrile rubber (NBR)/BM compounds to improve the mechanical properties of the reinforced vulcanizates. The effects of BM content and in situ modification on the mechanical properties, curing characteristics and morphology were investigated. BM was found to be effective in improving the mechanical performance of NBR vulcanizates. The NBR/BM composites could be further strengthened by the incorporation of TESPT. The interfacial adhesion of NBR/BM composites was obviously improved by the addition of TESPT. The substantially improved mechanical performance was correlated to the interfacial reaction and the improved dispersion of BM in rubber matrix.

Effect of organo-modified clay on accelerated aging resistance of hydrogenated nitrile rubber nanocomposites and their life time prediction

Organically modified clay – reinforced hydrogenated nitrile rubber vulcanizate was subjected to accelerated heat aging to estimate its long-term thermo-oxidative stability and its useful lifetime was compared with that of the virgin polymer for the first time. Changes in technical properties such as tensile strength, modulus and elongation at break were studied as a function of time and temperature of aging. The infrared spectroscopic analysis of the degraded products revealed that under aerobic hot aging conditions, hydrogenated nitrile rubber (HNBR) compounds undergo cross-linking reactions that lead to embrittlement and ultimately failure. Incorporation of clay filler, however, resulted in significant improvement of the degradation profile of the nanocomposite at elevated temperatures. Loss of ductility during aging of the nanocomposite was also milder, relative to the unfilled polymer, indicating a restricted degradation by the clay filled rubber, thus prolonging the durability. From the scanning electron microscopy and atomic force microscopy studies, it was found that nanofillers protected the elastomer from surface rupture that took place on oxidation. Life prediction of both virgin elastomer and the nanocomposite indicated a three-fold increase in the effective service temperature range of the HNBR using 8 parts organically modified nanoclay.

Reinforcement of nitrile rubber by in situ formed zinc disorbate

Zinc disorbate (ZDS) was in situ formed by the reaction between sorbic acid (SA) and zinc oxide (ZnO) in nitrile rubber (NBR). The effects of SA amount on the curing characteristics, crosslink density and mechanical properties of per- oxide-cured NBR were studied. The results showed that ZDS was generated mainly during the rubber vulcanization, rather than the open mill compounding phase. The results from the crosslink density determinations showed that the formation of ZDS significantly increased the ionic bond content in the vulcanizates. In addition, the formation of ZDS greatly enhanced the mechanical properties of NBR vulcanizates. The modulus, tensile strength, tear strength and hardness were found to be increased with the loading of ZDS. Preheating the compounds before compression moulding was beneficial to the forma- tion of ZDS, and consequently the increases in mechanical properties. At 40 parts per hundred rubber (phr) of SA and 16 phr ZnO, five to six folds of tensile strength and tear strength of the neat NBR vulcanizate were achieved. Transmission electron microscopy (TEM) results confirmed the nano-dispersion structure of the polymerized ZDS in the NBR matrix.

Improvement of the properties of ground tire rubber (GTR)‐filled nitrile rubber vulcanizates through plasma surface modification of GTR powder

AbstractThe surface modification of ground tire rubber (GTR) powder to enhance its adhesion to nitrile rubber (NBR) vulcanizates was investigated. The hydrophobic surface of GTR powder has been transformed to a hydrophilic one through atmospheric pressure dielectric barrier discharge (DBD). The water contact angle dropped markedly from 116 to 0° after being treated for more than 10 s. Attenuated total reflectance Fourier transform infrared spectral (ATR‐FTIR) studies revealed the increase in peak intensity at 3298 and 1640 cm−1 that correspond to OH and CC, respectively, on the surface of the GTR powder. The X‐ray photoelectron spectroscopic (XPS) analysis further confirmed the presence of oxygen containing polar functional groups on the surface of the GTR powder after atmospheric plasma treatment. The improvement in tensile strength and tear strength was observed for the modified GTR‐filled NBR vulcanizates, which is attributed to the enhanced interfacial interaction between modified GTR and NBR matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Studies on the Use of Cardanol as Plasticizer for Silica-Filled Nitrile Rubber

Cardanol is the main ingredient of cashew nut shell liquid (CNSL), an agro-byproduct. Its comparative merits for plasticizing silica-filled nitrile rubber (NBR) is the subject of this paper. Esters like dioctyl phthalate (DOP), polyesters, polyester ethers, polyester polyethers, etc are the conventional plasticizers employed for such compounding requirements. In this study, the mechanical properties, ageing behavior and torque time curves during cure of NBR plasticized by both these materials are compared under identical conditions. It has been established that cardanol when used as plasticizer, gives rise to similar mechanical properties, cure times and superior thermal stability in NBR vulcanizates.

Dynamic mechanical analysis of electron beam irradiated sulphur vulcanized nitrile rubber network—some unique features

Mixed crosslinking system with electron beam irradiation as one of the crosslinkers in rubber has been developed for the first time. This paper describes some unique features of dynamic mechanical properties of the electron beam irradiated nitrile rubber vulcanizates at varying levels of sulphur in the network. Dynamic mechanical thermal analysis (DMTA) was performed on these vulcanizates over a range of temperatures (−80°C to +80°C), frequencies (0.032 to 32 Hz) and strains (0.001 to 10%). The results showed that there were significant changes in tan delta peak temperature and storage modulus on irradiation of these vulcanizates. The vulcanizates containing higher amount of sulphur formed intense crosslinked networks and crosslink rearrangements, which were supported by the increase in the storage modulus and shift in tan delta towards higher temperature as compared to their control counterpart. There is also an increase in the peak height due to chain scission and subsequent plasticization. A concept of network distribution using the plots of the storage modulus ratio divided by frequency against inverse of frequency was introduced. This contravening nature was also affirmed with the help of these curves showing broader network distribution for irradiated samples having lower amount of sulphur. This was also supported from the crossover frequency values estimated from the plot of storage and loss modulii against frequencies observed.

Influence of Electron Beam Irradiation as One of the Mixed Crosslinking Systems on the Structure and Properties of Nitrile Rubber

Abstract The influence of electron beam on the nitrile rubber vulcanizates at varying levels of sulfur is reported. A higher crosslinking density, reduced elongation at break, increased modulus and tensile strength have been observed for the irradiated rubbers, as compared to the control rubber vulcanizates. The vulcanizate containing higher amount of sulfur, tends to form more crosslinkages on impinging with electron beam. This behavior is explained by the formation of monosulphidic linkages and is ascertained with the help of IR analysis (ATR mode), solid-state NMR analysis and chemical probe treatments of the irradiated vulcanizates. The implausible nature of these mixed crosslinking systems with electron beam as an additional crosslinker is explained with a kinetic model using steady state principle. A mechanistic path is suggested for explaining the structural changes on irradiation of these vulcanizates, which is supported by this model.

Structure and properties of nitrile rubber (NBR)–clay nanocomposites by co‐coagulating NBR latex and clay aqueous suspension

AbstractNitrile rubber (NBR)–clay nanocomposites were prepared by co‐coagulating the NBR latex and clay aqueous suspension. Transmission electron microscopy showed that the silicate layers of clay were dispersed in the NBR matrix at the nano level and had a planar orientation. X‐ray diffraction indicated that there were some nonexfoliated silicate layers in the NBR–clay nanocomposites. Stress–strain curves showed that the silicate layers generated evident reinforcement, modulus, and tensile strength of the NBR–clay nanocomposites, which were significantly improved with an increase in the amount of clay, and strain‐at‐break was higher than that of the gum NBR vulcanizate when the amount of clay was more than 5 phr. The NBR–clay nanocomposites exhibited an excellent gas barrier property; the reduction in gas permeability in the NBR–clay nanocomposites can be described by Nielsen's model. Compared with gum NBR vulcanizate, the oxygen index of the NBR–clay nanocomposites increased slightly. The feasibility of controlling rubber flammability via the nanocomposite approach needs to be evaluated further. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3855–3858, 2003

Study of Utilization of Ground EVA Waste as Filler in NBR Vulcanizates

Rubber blends containing nitrile rubber (NBR) and ground ethylene-vinyl acetate copolymer waste (EVAW) from the footwear industry have been prepared over a wide range of composition (up to 90 phr of waste component). The ground EVAW had particle size in the range of 100-350 mm and a gel content of 60±5%. The effect of different amounts of EVA waste on the tensile strength, elongation at break, hardness, tear strength and dynamic mechanical properties was studied. EVAW had a good reinforcing effect on the NBR matrix. A combination of optimum tensile properties, resistance to solvent penetration and dynamic mechanical properties, such as storage modulus and loss tangent was achieved by introducing 50 phr of EVAW in the NBR matrix. This composition also presents a more uniform morphology, as indicated by scanning electron microscopy.

In situ preparation of magnesium methacrylate to reinforce NBR

AbstractMagnesium methacrylate (MDMA) was in situ prepared in nitrile rubber (NBR) by reacting magnesium hydroxide (Mg (OH)2) with methacrylic acid (MAA) during the mixing step. The formation of MDMA in NBR was proved by the wide‐angle X‐ray diffraction analysis (WAXD). The mechanical properties, crosslinking structure, and morphology of the resulting peroxide‐cured NBR vulcanizates were studied. Results showed that Mg (OH)2/MAA mixtures had a great reinforcing effect for NBR, and their amounts and ratio played important roles in influencing the ultimate properties. Both the covalent crosslink density and ionic crosslink density of the vulcanizates were measured. And the nano‐composite morphology of such vulcanizates was also observed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1403–1408, 2002; DOI 10.1002/app.10323

Hybrid filler system for nitrile rubber vulcanizates

Relative efficiency of different types of fillers e.g., phenolic resin, carbon black and carbon black plus phenolic resin hybrid system in nitrile rubber vulcanizates for improvement of physico-mechanical properties, resistance to swelling in oil/fuel and thermal stability has been studied. The hybrid system was always found to offer maximum benefit in strength and dynamic mechanical properties coupled with higher percent of (a) retention of physical properties due to aging and (b) swelling resistance in oil or fuel. Both thermogravimetric analysis (TGA) as well as thermomechanical analysis (TMA) reflect much better thermal stability for the combined filler system compared to the vulcanizates containing either phenolic resin or carbon black.

In situ preparation of zinc salts of unsaturated carboxylic acids to reinforce NBR

Through the neutralization reaction of zinc oxide (ZnO) and methacrylic acid (MAA) or acrylic acid (AA), zinc methacrylate (ZMA) or zinc acrylate (ZA) was in situ prepared in nitrile rubber (NBR). The mechanical properties and crosslinking structure of the resulting peroxide-cured NBR vulcanizates were studied. The results showed that ZnO/MAA (AA) had a great reinforcing effect for NBR, and their amounts and ratio played important roles in influencing the mechanical properties. Such vulcanizate contains both covalent crosslinks and salt crosslinks, and the change in the tensile strength of the vulcanizate was related to the variation of the salt crosslink density. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2740–2748, 2000

Effect of electron beam irradiation on the properties of crosslinked rubbers

Influence of electron beam (EB) irradiation on the mechanical and dynamic mechanical properties of crosslinked fluorocarbon (FKM) rubber, natural rubber (NR), ethylene propylene diene monomer (EPDM) rubber and nitrile rubber (NBR) has been investigated. The modulus, gel fraction, glass transition temperature ( T g) and storage modulus increased, while the elongation at the break and the loss tangent (tan δ) T g decreased. FKM and NBR vulcanizates have been shown to have EB radiation resistance up to 1500 kGy.

In situ preparation of zinc salts of unsaturated carboxylic acids to reinforce NBR

Through the neutralization reaction of zinc oxide (ZnO) and methacrylic acid (MAA) or acrylic acid (AA), zinc methacrylate (ZMA) or zinc acrylate (ZA) was in situ prepared in nitrile rubber (NBR). The mechanical properties and crosslinking structure of the resulting peroxide-cured NBR vulcanizates were studied. The results showed that ZnO/MAA (AA) had a great reinforcing effect for NBR, and their amounts and ratio played important roles in influencing the mechanical properties. Such vulcanizate contains both covalent crosslinks and salt crosslinks, and the change in the tensile strength of the vulcanizate was related to the variation of the salt crosslink density. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2740–2748, 2000