NBR Compounds Research Articles

Effects of trans‐polyoctylene rubber on rheological and green tensile properties of natural rubber/acrylonitrile–butadiene rubber blends

AbstractThe influence of trans‐polyoctylene rubber (TOR) on the flow property, die swell behaviour and green tensile property of NR (natural rubber)/NBR (acrylonitrile–butadiene rubber) blend compound was investigated as a function of TOR loading level. The pure TOR, NR and NBR compounds were also investigated for comparison with the blend compounds. The shear viscosity of TOR strongly depended on the temperature as well as shear rate. The viscosity of the NR/NBR blend compound was even lower than that of the constituent components at relatively lower shear rates, and the viscosity difference became smaller as the shear rate was increased. The viscosity of the NR/NBR blend compounds was strongly affected by the addition of TOR but the effect became negligible with increasing the shear rate. Both the die‐swell ratio and the surface topology of extrudates were also affected by TOR addition; the dependence on shear rate was much stronger for higher TOR level. The NR/NBR blend compound showed much higher green tensile strength and elongation at break than those of the constituent components. Both the green tensile modulus and strength of the NR/NBR blend compound were greatly enhanced, while the elongation at break was reduced with the addition of TOR.© 2002 Society of Chemical Industry

極性ゴムの交流導電度温度依存性の測定と理論的考察

It is important to understand temperature dependence of electrical conductivity for polar rubber, which is utilized for charging members of an electrophotographic apparatus. The temperature dependence measurements of AC conductivity were investigated for NBR compounds. The conditions for the measurements were as follows; the sample was fixed between the electrodes with 40kPa, AC voltage: ±70V at various constant frequencies, temperature: from - 50°C to 100°C at a heating rate of 4°C/min. in a dry N2 stream. AC conductivity was used the reciprocal of the real part of admittance. As a result the conductivity was in proportion to AC frequency around Tg, and direct current conductivity was shown above Tg, which conductivity and its temperature dependence increased with using the additive such as polyoxyethylene oleyl ether, 1, 8-diazabicyclo [5, 4, 0]-7-undecene (phenol resin mixture) and benzyltriethyl ammonium chloride. Furthermore, it was found that the thermal expansion coefficient of free volume fraction that assumed from time-temperature superposition principle of complex modulus gave as good correlation for the temperature coefficient of electrical conductivity defined by the theoretical equation of the jumping model.

Modification of NBR by Addition of Phenol-CNSL Formaldehyde Copolymer

This paper reports the results of employing a Cashew Nut Shell Liquid (CNSL) based resin for modifying the properties of NBR. The resin is a copolymer obtained by condensing a mixture of phenol and CNSL with hexamethylene tetramine (hexa) at a stoichiometric ratio of 1:2.9 between total phenol and formaldehyde generated from hexa. The synthesis procedure, characterization and method of incorporation into the NBR compound are described. Sheets moulded from the compound have been subjected to different aging periods viz. 24 hrs, 48 hrs, 72 hrs and 96 hrs at 100°C and various properties were evaluated. Comparison of the properties of the aged material containing resin with those of NBR specimens not containing the resin show improved aging characteristics with respect to tensile strength, modulus and tear strength at aging periods in excess of 72 hours.

Direct Adhesion between Electroless Nickel-P Plated Metals and NBR Compounds during Curing

Abstract In this study, an examination was made of the various causative factors for the direct adhesion between nickel-P alloy (nickel alloy) and acrylonitrile-butadiene rubber (NBR) compounds during curing. In a high sulfur curing system (SV), direct adhesion was found to depend on time of exposure to air and not to occur after more than 48 h of exposure. In the peroxide curing system (PV), there was no adhesion at all regardless of the exposure time. The addition of triazine thiols to NBR compounds resulted in adhesion between NBR compounds and nickel alloy for exposures exceeding 48 h. Typical curing systems such as SV, low sulfur curing (LSV), sulfurless curing (SLV), and PV gave good NBR-nickel adherends when the NBR compounds contained the monosodium salt of triazine trithiol (TTN). In these system, peel strength in the adherends increased with triazine thiols, to a maximum, and then decreased. This parameter was influenced by the chemical structures of triazine thiols, such as those containing thiol(-SH) and the sodium salt of thiol (-SNa) groups, and by the exposure of nickel alloy to air. Peel strength decreased with the formation of nickel oxides on the surface. When the nickel oxides were removed from the nickel alloy surface, peel strength was recovered. High peel-strength adhesion between NBR compounds with TTN and nickel alloy is due to the formation of interfacial bonds and reinforcement layers at the adhesive interface during curing. Adherends consisting of NBR compounds with TTN and nickel alloy generally showed high heat resistance, oil resistance, and water resistance. The values for these parameters differed accordingly to the curing system and were optimal in the following order: SV < SV with TTN < PV with TTN.

Effect of Ammonium Derivatives of Oligoamidephosphates on the Vulcanization Characteristics and Mechanical Properties of NBR Compounds

This study presents the results of our research on the activity effect of ammonium derivatives, obtained as neutral analogues of oligoamide-phosphates, in NBR compounds. Using such neutral products as a modifying additive without reducing the level of the basic sulphenamide accelerator leads to an additional acceleration - the cure time decreases and the cure rate increases up to more than three times. The addition of the products studied in the first preparation stage is to be preferred. In this case the heat evolution is strongly decreased, the tear resistance is strongly increased and other mechanical parameters are satisfactory. In a double accelerating system with the traditional sulphenamide accelerator Vulkacit CZ, our products show a synergistic effect. The vulcanization rate increases, and some parameters of the vulcanizates, such as tear resistance, wear resistance and heat evolution (heat build-up), improve considerably in the range of sulphenamide/ammonium derivative strength, elongation at break and Shore hardness, do not change significantly. Modulus M 200 only decreases.

Use of Amine Terminated Liquid Natural Rubber as a Plasticiser in Filled NR and NBR Compounds

Abstract Amine Terminated Liquid Natural Rubber (ATNR) was used as a plasticiser in filled NR and NBR compounds replacing oil/DOP. The scorch time and cure time were found to be lowered when ATNR was used as the plasticiser. ATNR was found to improve the mechanical properties like tensile strength, tear strength and modulus of the vulcanizates. The ageing resistance of the vulcanizates containing ATNR was superior compared to the vulcanizates containing oil/DOP.

Modeling the vulcanization of rubbers in an oscillating bicone cell

AbstractThis work studies the evolution of dynamic rheometric functions (dynamic viscosity η′(ω) and storage modulus G′(ω)) with the degree of vulcanization and temperature of well‐characterized SBR and NBR compounds. Experiments are carried out in an oscillating bicone cell, and results are well fitted through a model that considers flow kinematics, heat transfer, curing kinetics, and rheological functions. It is possible to quantify the model parameters and to understand better the evolution of filled rubber compounds toward crosslinked networks or vulcanizates. Conclusions are also obtained on the interplay between rheological functions and molecular parameters (average molecular weight and polydispersity). Experimental evaluations of the ratios between oscillating torques, at different times of the curing process, correlate directly with changes in rheological properties of the samples studied. © 1995 John Wiley & Sons, Inc.

Diffusion and Sorption of Organic Liquids Through Polymer Membranes. III. Polyurethane, Neoprene, SBR, EPDM, NBR, and Natural Rubber Versus Cyclic Compounds, Esters, and Hydrocarbons

Abstract Diffusion and sorption of a variety of organic liquids into six engineering polymers have been investigated over the interval of 25°–60°C by the use of a conventional weight-gain experiment. While the method is laborious and time consuming, it yields reliable diffusion data. The transport mechanism depends, to a great extent, on the type of the solvent molecule and the barrier material. In all the polymer-solvent systems, the activated diffusion mechanism is operative and that the Arrhenius parameters of diffusion prove the conventional wisdom that smaller diffusion coefficients and higher activation energies are observed for the bigger solvent molecules. The diffusion mechanism has been classified to be anomalous. Sorption equilibrium data have been used to estimate the polymer-solvent interaction parameter in addition to molar mass between crosslinks and other thermodynamic quantities such as enthalpy and entropy of sorption. A first-order kinetic model appears to explain satisfactorily the transport of solvent molecules into polymer networks. Furthermore, attempts have been made to generalize, at least in qualitative terms, the polymer-solvent interactions.

Viscoelastic Response and Adhesion Properties of Highly Filled Elastomers

Abstract The viscoelastic response of four highly-filled elastomers has been investigated. Small deformation dynamic testing of these materials reveals thay they are nonlinear viscoelastic, as well as thermorheologically complex. Nonlinear viscoelastic behavior was observed as a pronounced strain dependence in the range of 0.1 to 10%. The degree of this nonlinear response was quantified through a constitutive equation containing a single nonlinear factor; resultant nonlinear factors for the various materials were compared and evaluated. Thermorheologically complex behavior was displayed by slightly different shift coefficients to superpose G'′ and G″ data. An approach for calculating material resilience from the viscoelastic data was also developed and a nomographic technique presented for its application. A composite adhesive joint, consisting of two layers of a filled NBR compound bonded together by a filled putty interlayer, was also studied. It was found that both the adhesive fracture energy and the effect of interlayer thickness could be related to the loss modulus of the putty interlayer. Finally, the effect of contact time on bond strength was evaluated and results presented as a master curve of adhesive fracture energy vs. temperature-reduced contact time.

Stress Relaxation Measurement as a High-Speed Method for Predicting the Long-Term Behavior of Vulcanized Rubber

Abstract Intermittent stress relaxation is well suited for quantifying aging processes in rubber. For NR, the effects of different antioxidants can be measured by the rates at which the modulus falls. In synthetic rubbers (SBR, NBR, and CR), it can be measured through the modulus increases caused by oxygen crosslinking. Equal-value times, e.g., t0.75 for NR and t1.25 for SBR, NBR, and CR, are the times taken by the modulus to decrease or increase to a given percentage of its original level. They are better measures of aging than the modulus change after a given time. For NR, it has been shown that stress relaxation measurements at elevated temperatures and in pure oxygen correlate with the results of conventional aging methods. Thus the testing times can be drastically reduced—from up to 28 days to 1–8 hours. Discontinuous stress relaxation measurements are considerably more accurate and selective than conventional oxygen aging. For the repeatability of a single equal-value time measurement, we obtained a coefficient of variation (s/x) of 5–10% for stress relaxation measurement and about ±20% for oxygen aging. The degree of selectivity for oxygen aging and stress relaxation was found to be 3.6 and 18, respectively. The correlation between the results of stress relaxation measurements and those of the conventional oxygen and hot air aging tests was investigated for a large number of NR compounds and for some SBR, NBR, and CR compounds. The correlation is not very good, but it must be remembered that the equal-value times determined according to the two methods show relatively pronounced variability. With the conventional aging methods, the results also depend on what quantity is measured, e.g., the change in tensile strength or hardness, and on what equal-value time is chosen, e.g., the time taken by the property concerned to decrease to 90 or 75% of its original value. The conclusion of the investigations described above is that intermittent modulus measurement is an interesting high-speed method for the assessment of aging behavior. It will acquire a firm position in the arsenal of rubber testing methods, but will probably supplement, and not completely replace, the aging methods currently used.

NBR Vulcanizates Resistant to High Temperature and “Sour” Gasoline

Abstract NBR compounded in a conventional fuel hose tube formulation is markedly degraded by “sour” gasoline or “sour” ASTM Fuel C within 7 days at 40°C. Furthermore, the conventional NBR compound is not resistant to aging at 125°C. Use of an NBR designed for heat resistant compounding and an appropriate choice of compound greatly improve resistance to fuel which contains hydroperoxides. The preferred system for “sour” gasoline resistance and resistance to long term aging at 125°C is a cadmium oxide activated low sulfur-sulfur donor compound with silica as the principal filler. This vulcanizate is not much more affected after 7 days at 40°C by gasoline of peroxide number 50 than by clean gasoline, and is less affected by gasoline of peroxide number 200 than are other NBR vulcanizates. The balance of high and low temperature properties can be optimized by appropriate choice of plasticizer and acrylonitrile level. Aging resistance is somewhat improved by increase in acrylonitrile content, and fuel permeability is markedly decreased. Permeability to gasoline with 30 aromatic content can be changed appreciably by compounding, but the resistance to Fuel C with 50% aromatic content does not appear to respond to compounding changes. The stability of NBR vulcanizates in “sour” gasoline is reduced by copper salts and, to a lesser extent, by metallic copper. Bound antioxidant NBR does not appear to offer an advantage in “sour” gasoline resistance over heat resistant NBR compounded in a comparable formulation.

Shrinkage of Cured Fluoroelastomers. I. Basic Parameters

Abstract The thermomechanical analyzer (TMA) is eminently suitable for the measurement of the thermal expansion coefficient of rubbers, provided the equipment is calibrated with materials of similar expansion coefficient. FKM or other thermally stable and amorphous polymers (of independently determined thermal expansion characteristics) can be used as calibration standards. The relative simplicity and precision of the TMA method for the determination of the coefficient of isotropic linear expansion, and hence, of volumetric expansion of rubbers, makes this important thermodynamic parameter easily accessible experimentally. Because of the frequently observed anisotropy of molded elastomeric compounds, measurements in all three dimensions are required to define linear, isotropic expansion and shrinkage which, to an excellent approximation, are represented by arithmetic averages of the three unidirectional values. Good agreement has been found between the average (isotropic) shrinkage determined experimentally and that calculated from the average (isotropic) coefficient of linear thermal expansion, α. The effect of fillers, such as carbon black, on α is additive. This makes it possible to predict α and shrinkage of all filled compounds from a single value of α of the unfilled rubber. The linear thermal expansion coefficients of the tested rubbers (FKM, NBR, EPDM) increase linearly with temperature, the increase being generally stronger for FKM than for the other elastomers. The appreciably higher mold shrinkage of FKM relative to NBR is directly due to the higher α of FKM for comparable levels of fillers. This must be kept in mind when expedience dictates the use of the same molds for FKM and NBR compounds.