Evaluation and modeling of the mechanical properties of graphite nanoplatelets based rubber nanocomposites for pressure sensing applications

Acrylonitrile butadiene rubber (NBR) compounds filled with different concentrations of graphite nanoplatelets were experimentally investigated. The stress–strain curves of the nanocomposites were studied, which suggest good filler–matrix adhesion. The large reinforcement effect of the filler followed the Guth model for non‐spherical particles. The effect of graphite nanoplatelets on the cyclic fatigue and hysteresis was also examined. The loading and unloading stress–strain relationships for any cycle were described by applying Ogden's model for rubber nanocomposites. With this model for incompressible materials, expressions may be developed to predict the stress–strain relationship for any given cycle. The dissipated energy increased with graphite nanoplatelets concentrations and decrease with number of cycles. The rate of damage accumulation becomes marginal after first ten cycles. The rate of damage increases as the amount of graphite nanoplatelets increase into the rubber matrix. Copyright © 2011 John Wiley & Sons, Ltd.     

Radiation effect on properties of carbon black filled NBR/EPDM rubber blends

Rubber blend of acrylonitrile butadiene rubber (NBR) and ethylene-propylene diene monomer (EPDM) rubber (50/50) has been loaded with increasing contents, up to 100 phr, of reinforcing filler, namely, high abrasion furnace (HAF) carbon black. Prepared composites have been subjected to gamma radiation doses up to 250 kGy to induce radiation vulcanization under atmospheric conditions. Mechanical properties, namely, tensile strength (TS), tensile modulus at 100% elongation (M₁₀₀), and hardness have been followed up as a function of irradiation dose and degree of loading with filler. On the other hand, variation of the swelling number as a physical property, as a function of same parameters, however, in car oil as well as brake oil has been undertaken. In addition, the electrical properties of prepared composites, namely, their electrical conductivity, were also evaluated. The thermal behavior of the prepared composites was also investigated. The results obtained indicate that improvement has been attained in different properties of loaded NBR/EPDM composites with respect to unloaded ones.     

Thermal characterization of nitrile butadiene rubber (NBR)/PVC blends

Summary Nitrile butadiene rubber (NBR) and NBR/PVC blends were produced using 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) or not as antioxidant. Controlled ozone degradation was performed in several samples. Thermal, compositional and morphological analysis was performed by means of differential scanning calorimetry, thermogravimetry, chemical analysis and scanning electron microscopy. Thermogravimetry analysis shows four mass loss processes related to plastizicer, complex rubber degradation and metallic oxides and other additives. In NBR (NBR/PVC blends) the onset temperature of the first degradation process varies between 227-231°C (259-262°C) and the apparent activation energy between 26 and 36 kJ mol^-1 (36-57 kJ mol^-1), the NBR/PVC samples non degraded presents the higher thermal stability.     

High performance hybrid reinforcement of nitrile rubber using short pineapple leaf fiber and carbon black

Rubber composites with very high moduli at low elongation, high elongation at break and high ultimate breaking strength have been developed. The matrix was acrylonitrile butadiene rubber (NBR) and the hybrid (fibrous and particulate) reinforcements were short, fine pineapple leaf fiber (PALF) and carbon black. The amount of PALF was fixed at 10 parts (by weight) per hundred of rubber (phr) while that of carbon black was varied from 0 to 30 phr. Uniaxial NBR composites were prepared. Tensile strength, elongation at break, modulus and tear strength of the hybrid composites were characterized in both longitudinal (parallel to the fiber axis) and transverse (perpendicular to the fiber axis) directions. The addition of carbon black causes the slope of the early part of the stress–strain curve to increase and also extends breaking to greater strains. At carbon black contents of 20 phr and above, the stress–strain relation displays an upturn at high elongations, providing greater ultimate strength. Comparison with the usual carbon black filled rubber shows that the composite behavior at low strains is determined by the PALF, and at high strains by the carbon black. This high performance PALF-carbon black reinforced NBR shows great promise for engineering applications.     

The influence of nano silica particles on gamma-irradiation ageing of elastomers based on chlorosulphonated polyethylene and acrylonitrile butadiene rubber

The goal of this work was to study gamma irradiation ageing of rubber blends based on acrylonitrile butadiene rubber (NBR) and chlorosulphonated polyethylene rubber (CSM) reinforced by silica nano particles. The NBR/CSM compounds (50: 50, w/w) filled with different content of filler (0–100 phr) were crosslinked by sulfur. The vulcanization characteristics were assessed using the rheometer with an oscillating disk. The vulcanizates were prepared in a hydraulic press. The obtained materials were exposed to the different irradiation doses (100, 200, 300 and 400 kGy). The mechanical properties (hardness, modulus at 100% elongation, tensile strength and elongation at break) and swelling numbers were assessed before and after gamma irradiation ageing.     

The physical properties of pressure sensitive rubber composites

Nitrile butadiene rubber, NBR, structural foam of different apparent densities was obtained by using different concentrations of foaming agent, azodicarbonamide, ADC/K. The true stress-strain characteristics, in case of compression, of foamed samples after the application of cyclic stress-strain were measured. The effect of the cyclic stress-strain on strain energy density of ADC/K foaming agent-filled NBR rubber composites was studied. The mechanical parameters were found to depend on the foaming agent concentration and on the pre-cyclic fatigue number. Results also indicated that the strain energy decreased with filler concentration.The effects of the cyclic stress-strain on the conductivity of ADC/K foaming agent-filled NBR rubber composites were studied. The electrical properties were found to depend on the foaming agent concentration, the strain amplitude and the number of stress-strain cycles of pre-strain. This study was assisted by the current-voltage characteristics which were measured under the effect of different compression ratios: 0%, 5%, 10%, 15%, 20%, 25% and 30%. The free current carrier mobility and the equilibrium concentration of charge carriers in the conduction band were produced as functions of compressive strain. Results also indicate that there is a linear variation between pressure and conductivity for all samples, which means that these samples can be used as a pressure sensor.     

Analysis of structure–properties relationship in nitrile‐butadiene rubber/phenolic resin/organoclay ternary nanocomposites using simple model system

The present study deals with the structure–property relationship of organoclay (OC) filled nanocomposites based on rubber blend comprising of nitrile‐butadiene rubber (NBR) and phenolic resin (PH). To obtain a better insight into the characteristics of the NBR/PH/OC hybrid system, a simple model system consisting of NBR/OC nanocomposites is also taken into consideration. A series of NBR/OC and NBR/PH/OC nanocomposites containing a wide range of OC concentrations (2.5–30 phr) are prepared by using traditional open two‐roll mill. Structural analysis performed by X‐ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM) exhibits mixed exfoliated and intercalated morphology at low OC content, below 7.5 phr, and a well‐ordered intercalated morphology at higher OC loading. It is shown that the dispersion of OC is also influenced by mixing time and order of mixing of components. Analysis of the cure characteristics, mechanical, and thermal properties of both the NBR/OC and NBR/PH/OC nanocomposites reveals that the OC is dispersed mainly in the NBR continuous phase, even though some is likely localized in the rubber–resin interface. Copyright © 2009 John Wiley & Sons, Ltd.     

Improving the mechanical properties of short pineapple leaf fiber reinforced natural rubber by blending with acrylonitrile butadiene rubber

This work proposes a simple method for improving the rubber to filler stress transfer in short pineapple leaf fiber-reinforced natural rubber (NR). This was achieved by replacing some of the non-polar NR by polar acrylonitrile butadiene rubber (NBR). The amount replaced was varied from 0% to 20% by weight. The mixing sequence was designed so that the fiber would be coated with polar NBR before being dispersed in the NR matrix. A comparison system in which the mixing was carried out in a single step was also examined. Despite the fact that the two rubbers are immiscible, it was found that significant improvement of the stress transfer in the low strain region can be obtained. The mixing sequence affected the mechanical properties of the resulting composites. It is concluded that frictional stress transfer between the immiscible rubbers contributes more to the total stress transfer than does the frictional stress transfer between non-polar NR and polar cellulose fiber.     

TG-MS analysis of nitrile butadiene rubber blends (NBR/PVC)

Blends of nitrile butadiene rubber (NBR) with polyvinyl chloride (PVC) are widely used in products such as hoses and seals. As part of a project that uses NBR/PVC blends for manufacturing forest fire hoses, blends of NBR/PVC with various inorganic fillers, such as Mg(OH)₂, china clay (organic modified kaolin) and nano clay (organic modified bentonite) were studied by TG-MS. No significant changes were observed to the type of the polymers’ decomposition products, compared to that of NBR/PVC blend without additives. The most remarkable change was the absence of HCl from decomposition products in the presence of the Mg(OH)₂ additive.     

Comparative study of natural rubber and acrylonitrile rubber reinforced with aligned short aramid fiber

The aims of this paper are three-fold. The first is to determine the reinforcement of high performance short aramid fiber in two representative rubber matrices, namely natural rubber and acrylonitrile rubber. The second is to ascertain the effect of rubber polarity on the reinforcement. The third is to establish a pattern of reinforcement for use with less studied fibers. The rubbers were reinforced either with only aramid fiber or with a hybrid of aramid fiber and carbon black. The fiber contents were varied at 0, 2, 5 and 10 parts (by weight) per hundred rubber (phr) while those of carbon black were 0, 10, 20 and 30 phr. Conventional sulfur vulcanization was used. It was found that aramid fiber can reinforce both rubbers in the low strain region effectively, although to a significantly different degree. The hybrid carbon black provides additional reinforcement at low to medium strains and allows high strain stress upturn to occur in both rubber matrices. The findings enable the preparation of rubber composites having a wide, controllable range of mechanical behavior for specific high-performance engineering applications. Significantly, they also serve as a benchmark for developing reinforced systems from alternative fibers, particularly those from natural sources.     

The physical and mechanical properties and cure characteristics of NBR/silica/MWCNT hybrid composites

The main objective of the present study was to investigate the synergistic effect of simultaneous use of two reinforcing fillers in rubber compounds based on acrylonitrile-butadiene copolymer (NBR). Silica was used as reinforcing filler in all samples and the loading content was 25 phr. 3 and 5 phr of multiwall carbon nanotubes (MWCNT) were used as second reinforcing filler in NBR/silica compounds. Melt mixing method was employed for compound preparation. The effects of carbon nanotube/silica hybrid filler on mechanical and vulcanization characteristics of the rubber compounds were investigated. These results revealed that addition of the reinforcing filler, either carbon nanotube or silica, shortened the optimum cure time (t₉₀) and also scorch time (t_s1) of samples compared to that of pure NBR compound. In hybrid compounds, the reduction in optimum cure time and scorch time was higher than that of for silica-filled NBR or CNT-filled NBR compounds. This can be attributed to the synergistic effect between CNT and silica as two reinforcing agents in NBR compounds. Regardless the composition of the reinforcing filler, an increase of the relaxed storage modulus is observed, while the tan δ value is decreased steadily. The dynamic modulus reinforcement of nanocomposites was examined by the Guth Gold and Modified Guth Gold equations. For hybrid samples, the experimental values show a significant positive deviation from model predictions. According to the Barlow’s formula, hybrid compounds show higher burst strength compared to silica or CNT filled NBR compounds.     

Improved resistance to crack growth of natural rubber by the inclusion of nanoclay

The effect of nanoclay on the fatigue crack growth behavior was investigated. Fatigue tests were carried out on edge notched specimens under cyclic tension loadings. A power–law dependency between crack growth rate and tearing energy was obtained. Natural rubber (NR) filled with 5 phr organically modified montmorillonite (OMMT) possessed the lowest value of the exponent, b, and the smallest crack growth rate at a given tearing energy, denoting the strongest resistance to crack growth. Strain‐induced crystallization was probed by synchrotron WAXD experiments, showing earliest occurrence and strongest ability of crystallization in NR with 5 phr OMMT due to the better exfoliation and orientation of clay layers. The study on the viscoelastic property by dynamic mechanical analysis indicated that NR filled with 10 phr OMMT had the largest contribution to tearing energy attributed to the viscoelastic dissipation in the viscoelastic region in front of the crack tip. This revealed that the strain‐induced crystallization played a more important role in the crack growth resistance than the viscoelastic dissipation for clay filled rubber. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermal stability of styrene butadiene rubber (SBR) composites filled with kaolinite/silica hybrid filler

Styrene butadiene rubber (SBR) composites filled with fillers, such as modified kaolinite (MK), precipitated silica (PS), and the hybrid fillers containing MK and PS, were prepared by melt blending. The kaolinite sheets were finely dispersed in the SBR matrix around 20–80 nm in thickness and reached the nano-scale. The SBR composites with fillers exhibited excellent thermal stability compared to the pure SBR. The thermal stability of SBR composites was improved with the increasing of MK mass fraction. When MK hybridized with PS, kaolinite sheets were covered by the fine silica particles and the interface between filler particles and rubber matrix became more indistinct. SBR composite filled by hybrid fillers containing 40 phr MK and 10 phr PS became more difficult in decomposition and was better than that of 50 phr PS/SBR and 50 phr MK/SBR in thermal stability. Therefore, the hybridization of the fine silica particles with the kaolinite particles can effectively improve the thermal stability of SBR composites.     

Anisotropic studies of multi-wall carbon nanotube (MWCNT)-filled natural rubber (NR) and nitrile rubber (NBR) blends

50/50 NR/NBR blends with various MWCNT loadings were prepared by mixing with MWCNT/NR masterbatches on a two-roll mill and sheeted off at the smallest nip gap. Then, the effect of milling direction, machine direction (MD) and transverse direction (TD), on the mechanical and electrical properties of the blends was elucidated. Dichroic ratio and SEM results confirmed that most of the MWCNTs were aligned along MD when MWCNT was less than 4 phr, and the number of agglomerates increased when MWCNT was more than 4 phr. Additionally, anisotropic properties were clearly observed when 4 phr MWCNT was loaded. At 4 phr MWCNT, 100% modulus and tensile strength in the MD were about 1.5 and 1.3 times higher than those in the TD, respectively. Moreover, electrical conductivity in the MD was superior to that in the TD by about 3 orders of magnitude. Results from dynamic mechanical tests also showed that the maximum tan δ in the MD sample was lower than that in the corresponding TD sample. In addition, the storage modulus at 30 °C for the MD sample containing 4 phr MWCNT was 1.15 higher than that of the corresponding TD sample. This stronger reinforcement efficiency resulted from the combination of the greater alignment and dispersion of most MWCNTs in the MD sample.     

The effect of different types of carbon blacks on the rheological and thermal properties of acrylonitrile butadiene rubber

The influence of two types of carbon black filler N330 and N990 (primary particle size 46 nm and >230 nm) on elastomeric composites based on acrylonitrile-butadiene rubber (NBR) have been investigated. The activation energy (E _a) were determined from two high temperature rheokinetic curves (T ₁ = 180 °C and T ₂ = 190 °C). For tensile testing, the compounds with different content of carbon black were vulcanized in a hydraulic press at 150 °C. The stress-strain experiments were performed before and after ageing the specimens in an air-circulating oven at 100 °C for 168 h. The thermal degradation and thermal stability of carbon black filled NBR rubber was investigated by thermogravimetric analysis in a flowing nitrogen atmosphere at a heating rate of 10 °C/min.     

Factors affecting electrical conductivity of carbon black-loaded rubber. I. Effect of milling conditions and thermal-oxidative aging on electrical conductivity of haf carbon black-loaded styrene–butadiene rubber

Styrene–butadiene rubber (SBR-1502) loaded with 50 phr carbon black (HAF) was prepared. The electrical conductivity of rubber vulcanizates was measured. It was found that milling conditions have a marked effect on the temperature dependence of the electrical conductivity σ(T) of test samples. In this case, the resistivity of prepared samples increases with remilling and has a minimum value on the σ(T) curve. Thermal-oxidative aging of such vulcanizates decreases the conductivity of the prepared samples.     

Shape memory properties of dynamically vulcanized poly(lactic acid)/nitrile butadiene rubber (PLA/NBR) thermoplastic vulcanizates: The effect of ACN content in NBR

Morphology structure and interfacial interaction are crucial factors for shape memory thermoplastic vulcanizates. In this study, shape memory thermoplastic vulcanizates based on poly(lactic acid) (PLA) and nitrile butadiene rubber (NBR) were prepared through dynamic vulcanization. The influence of acrylonitrile (ACN) content on the morphology, compatibility, shape memory property, and mechanical property was investigated. A co‐continuous structure was observed. The interfacial compatibilization between PLA and NBR phases occurred, resulting in a significantly improved interface adhesion and interfacial interaction, which was confirmed by Fourier transform infrared spectroscopy. With such a novel structure, the PLA/NBR TPVs owned an excellent shape memory property and further improved with increasing ACN content of NBR, which could be explained that the cross‐linked continuous NBR phase provided a stronger recovery driving force. In the meantime, tensile strength and elongation at break of TPVs increased with increase in ACN content. It is concluded that the preparation of dynamically vulcanized thermoplastic vulcanizate with co‐continuous structure and strong interfacial adhesion is beneficial to obtain outstanding shape memory effect.     

Chlorination and characterization of natural rubber and its adhesion to nitrile rubber

Chlorinated natural rubber (CNR) vulcanized sheets were prepared by immersing the NR sheets in sodium hypochlorite solution for various chlorination times ranging from 0 to 30 min. The degree of chlorination as indicated by X-ray Absorption Near-Edge Spectroscopy (XANES) implied that the chlorine content increases with the chlorination time from 0 to 10 min then levels off. Atomic Force Microscopy (AFM) showed an evolution of the surface roughness and stiffness. These two properties increased gradually with chlorination time. The bond strength between CNR and nitrile rubber (NBR) also increased gradually. The data showed cohesive failure beginning at 1 min and extending throughout the 30 min of the study. The maximum peel strength was found at 1 min of chlorination time and decreased afterwards. The decrease in peel strength was caused by the increase in surface stiffness of NR that acted as weak boundary layer. The surface stiffness governed the peel strength between NR and NBR.     

Investigation of aging behavior and mechanism of nitrile-butadiene rubber (NBR) in the accelerated thermal aging environment

Nitrile-butadiene rubber (NBR) was exposed to an accelerated thermal aging environment produced by an air-circulating oven for different time periods. NBR aging was evaluated by morphology, crosslink density, mechanical properties, chemical changes and thermal stability. The results showed that the surface damage of NBR turned severe and inhomogeneous, and the aging degree was most serious on the edge region of voids. Crosslinking reactions mainly occurred in the aging process. The tensile strength increased with increase in crosslink density up to a maximum value and thereafter decreased with further increase in crosslink density. X-ray Photoelectron Spectroscopy (XPS) and Pyrolysis Gas Chromatography-Mass Spectrometry (Py-GC/MS) analysis demonstrated that hydroxyl groups were formed and the additives migrated from inner to surface of NBR samples. In addition, the thermogravimetric analysis (TGA) indicated that the thermal stability of NBR did not significantly change in the accelerated thermal aging environment.