Aspects of producing hydrogenated nitrile butadiene rubber (HNBR) nanocomposites by melt compounding processing

Industry is constantly demanding for materials with differential properties that explores nanoscale fillers functionality. Unfortunately, most of the papers present processing methods that are hard to scale up. Effects in addition different amounts of multiwall carbon nanotubes (MWCNT) and few-layer graphene (FLG) on cure behaviour, viscoelastic, mechanical and electrical properties of a hydrogenated nitrile butadiene rubber (HNBR) are investigated and compared with those composites having carbon black (CB) as filler. Looking for scale up the produced nanocomposites, rubber composites were produced in a closed mixing chamber by melt mixing with unmodified fillers. Addition of nanotubes reduces curing time. Microstructural analyses indicate that FLG cannot be easily dispersed by this methodology. Significant improvement in mechanical properties is observed with MWCNT addition, with 940% modulus increment regarding to the pure polymer and also, in lower intensity, in HNBR/FLG composites. Moreover, HNBR/MWCNT composites presented a sharp reduction in electrical resistivity at low loading level.     

Structure and mechanical properties of nitrile rubbers modified with iodine

Nitrile rubbers, both common and hydrogenated, revealed some kind of ordering, as detected by WAXS. Strain-induced crystallization is responsible for the enhanced degree of crystallinity for HNBR. In the case of NBR, another mechanism has been proposed, namely specific interactions between carbon-carbon double bonds from butadiene and cyano groups from acrylonitrile monomer units, leading to an EDA complex formation. Iodination reduces the degree of crystallinity of both materials; however, their stiffness increases as the result of modification, probably due to dipole-dipole interactions or hindering effects accompanying introduction of “large” iodine atoms into the macromolecular structure. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 501–512, 1998     

Study on wear,cutting and chipping behaviors of hydrogenated nitrile butadiene rubber reinforced by carbon black and in‐situ prepared zinc dimethacrylate

In this study, the wear (Akron and DIN) and the cutting and chipping (C&C) behaviors of hydrogenated nitrile butadiene rubber (HNBR) reinforced by carbon black (N115) and in‐situ prepared zinc dimethacrylate (ZDMA) were investigated. It was validated that ZDMA was more effective than N115 to enhance the wear and C&C resistance of HNBR composites. The Akron wear resistance of the HNBR/N115 composites increased with the content of ZDMA, and the Schallamach ridges observed on the abraded surfaces became less and less clear. With increasing content of ZDMA, the failure mode of the DIN abraded surface underwent the transition from craters to Schallamach ridges, and finally to scratches. The HNBR/N115 composite reinforced by 10 phr ZDMA had the best DIN wear resistance when Schallamach ridges were the dominant failure mode. The use of 30 phr ZDMA can dramatically enhance the C&C resistance of the HNBR/N115 composites. The C&C resistance was suggested to be related to both the variation of the morphology of the C&C ridges and the direction of crack propagation as a function of the content of ZDMA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Reinforcement effect of nanocellulose on thermal stability of nitrile butadiene rubber (NBR) composites

Poor physical and chemical attraction between nitrile butadiene rubber (NBR) matrix and filler resulted in low thermal properties. Therefore, nanocrystalline cellulose (NCC) as a reinforcement agent was used to increase the heat resistance and thermal stability of NBR composites. The addition of 2 phr NCC increased thermal stability and activation energy of NBR up to 75%. Meanwhile, the storage modulus of composites increased by 12 GPa at the similar loading of NCC. Good interfacial bonds of electrostatic interactions, formation of hydrogen bonds, crystallinity and nanosized of NCC are the main factors contribute to the final properties of NBR/NCC composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46594.     

Continuous process for production of hydrogenated nitrile butadiene rubber using a Kenics® KMX static mixer reactor

A continuous process for hydrogenating nitrile butadiene rubber (NBR) was developed and its performance was experimentally investigated. A Kenics® KMX static mixer (SM) is used in the process as a gas–liquid reactor in which gaseous hydrogen reacts with NBR in an organic solution catalyzed by an organometallic complex such as an osmium complex catalyst. The Kenics® KMX SM was designed with 24 mixing elements with 3.81 cm diameter and arranged such that the angle between two neighboring elements is 90°. The internal structure of each element is open blade with the blades being convexly curved. The dimensions of the SM reactor are: 3.81 cm ID 80 S and 123 cm length and was operated cocurrently with vertical upflow. The NBR solutions of different concentrations (0.418 and 0.837 mol/L with respect to [C?C]) were hydrogenated by using different concentrations of the osmium catalyst solution at various residence times. The reactions were conducted at a constant temperature of 138°C and at a constant pressure of 3.5 MPa. From the experimental results, it is observed that a conversion and/or degree of hydrogenation above 95% was achieved in a single pass from the designed continuous process. This is the first continuous process for HNBR production that gives conversions above 95% till date. Optimum catalyst concentration for a given mean residence time to achieve conversions above 95% were obtained. Finally, a mechanistic model for the SM reactor performance with respect to hydrogenation of NBR was proposed and validated with the obtained experimental results. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Rheological analysis of the degradation of HDPE during consecutive processing steps and for different processing conditions

Using a twin‐screw extruder, HDPE has been processed six times consecutively under a range of processing conditions (changing barrel temperature, screw speed, and feed rate). After each pass, the product has been analyzed in terms of the melt flow index (MFI) and G_C(ω_C), the crossover point of the viscoelastic moduli as a function of the angular velocity at which it occurs. MFI data show changes in the structure of the HDPE after each processing step, but this information is limited in quality and quantity. G_C data show the mechanism for degradation (side‐chain branching and chain scission) and allow us to track relative changes in mean molecular weight (MMW) and molecular weight distribution (MWD). MMW and MWD both increase as a result of continued reprocessing. The apparent changes in MWD are substantial indicating significant chain scission initially, accompanied and followed during subsequent processing by a combination of side‐chain branching and further chain scission. A relative measure of the polydispersity index (PI) of the melt is calculated and the PI increases as the HDPE is further reprocessed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A mixture of buffing dust and chrome shavings as a filler for nitrile rubbers

The incorporation of biopolymers, such as chrome shavings and buffing dust, into rubber blends makes it possible to obtain biodecomposable collagen–elastomer materials with good utility properties. It is the presence of a biopolymer in multicomponent polymeric materials that facilitates enzymatic hydrolysis and results in biodecomposition through the loss of cohesiveness and polymer scattering. The undertaking of such original studies was justified by the benefits resulting from a new generation of polymeric materials and the need for a solution to the problem of growing amounts of wastes by waste management in the tanning industry. In this study, the effect of a mixture of chrome shavings and buffing dust on the properties of nitrile rubbers was examined. The dust and shavings, in a 1:1 proportion, were mixed with 5 parts by weight of zinc oxide and, in this form, was added to the rubber blends. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Influence of molecular parameters on thermal,mechanical, and dynamic mechanical properties of hydrogenated nitrile rubber and its nanocomposites

The present work derives a relationship between structure and properties of hydrogenated nitrile rubber (HNBR) in the presence as well as absence of nanofillers. Four different grades of HNBR were selected to examine the influence of polarity, unsaturation, and molecular weight on thermal, mechanical, and dynamic mechanical properties of the elastomers and particularly their nanocomposites. An increase in thermal stability, tensile strength, modulus at 100% elongation as well as storage modulus of the unfilled rubber was observed with increase in polarity (acrylonitrile content). Different nanofillers, such as montmorillonite, sepiolite, and nanosilica were used to improve the above properties of the unfilled rubber. Interestingly, a reverse trend of thermal properties was observed for the nanocomposites with acrylonitrile variation, although mechanical and dynamic mechanical properties exhibited similar trend to those of the unfilled rubber. These properties, however, gradually deteriorated as the level of unsaturation on the polymer backbone was increased. On addition of the nanofillers, it was found that the improvement in thermal and mechanical properties was higher for the elastomer having 5.5% diene content. The results were explained by X‐ray Diffraction, Atomic Force Microscopy, Energy Dispersive X‐ray mapping, and swelling studies. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Influence of ultraviolet aging on the structure,mechanical and gas permeability properties of hydrogenated nitrile butadiene rubber

The effect of ultraviolet (UV) radiation on the structure and performance of hydrogenated nitrile butadiene rubber (HNBR) was studied in this paper. The HNBR was exposed to UV radiation for various durations (0, 7, 14, 21 and 28 days). The Fourier transform infrared spectroscopy (FTIR) results demonstrated that the surface molecular structures were oxidized to generate oxygenated species under UV radiation. The oxidative degree enhanced with the increase of aging time, resulting in thicker and denser cracks on the surface. The plausible aging mechanism of HNBR was suggested. The free volume of HNBR before and after UV aging was characterized by positron annihilation lifetime spectroscopy (PALS) and their cross-linking density, compression set, mechanical and gas permeability properties were also analyzed. In the first 14 days of UV irradiation, the dominant chain-scission reaction led to a decrease in cross-linking density of HNBR, resulting in the enhancement of free volume and thereby the increase of gas permeability. When the aging time was longer than 14 days, cross-linking reaction played a leading role and the free volume decreased, thus causing the reduction of gas permeability. As the aging time increased, the glass transition temperature (T_g), tensile strength and storage modulus of HNBR initially reduced and then increased, which was in agreement with the changing trend of cross-linking density.     

Effects of medium phases on the thermal degradation of hydrogenated nitrile rubber O‐rings under compression

The degradation of hydrogenated nitrile rubber O‐rings under exposure to either air or hydraulic oil under compression were investigated at elevated temperatures. The physical and chemical changes of the samples aged for various durations were studied by measuring the weight, compression set, tensile strength, elongation at break, crosslinking density, fracture morphology, and attenuated total reflection–Fourier transform infrared (ATR–FTIR) spectroscopy. The results indicate that the weight decreased with exposure time and temperature and that weight loss was greater in oil. Crosslinking and chain scission both occurred during the aging process. The significant changes in the mechanical properties indicate that more severe degradation occurs in air. The fracture morphologies results show that the fracture surfaces aged in oil become rougher and have more defects. The ATR–FTIR results demonstrate that the hydroxyl groups were formed in air and oil, while carboxyl groups were only generated in air. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45864.     

Investigation on the mechanical properties and oil resistance of sulfur cured nitrile rubber/hydrogenated nitrile butadiene rubber blends

Nitrile rubber (NBR)/hydrogenated nitrile butadiene rubber (HNBR) blends with various ratios were compounded with internal mixer and two-roll open mill. Mechanical properties and low-temperature performance (TR10) of the NBR/HNBR blends after aging under different conditions were investigated. Furthermore, equilibrium swelling test and moving die rheometer (MDR) test were used to systematically investigate the effects of HNBR dosage on the crosslink densities and curing behaviors. Vulcanization torque and crosslink densities decreased with an increase in HNBR content. The crosslink density of pure HNBR is higher than that of pure NBR, which is related to the macromolecular structures of the rubber. Compression sets of the NBR/HNBR vulcanizates were correlated with HNBR dosage indicating a linear relationship. Low-temperature performance of the NBR/HNBR blends was improved after being aged in the synthetic hydrocarbon hydraulic oils (SH-1 and SH-2). This work shows that the low-temperature performance and oil resistance could be better balanced by blending NBR with HNBR, while the mechanical properties maintain relatively high level.     

HNBR和NBR不同温度下力学性能的研究

本文主要研究了在常温、高温条件下,不同交联体系、炭黑用量、碳纳米管用量对氢化丁腈橡胶(HNBR)和氢化丁腈橡胶(NBR)的力学性能的影响。实验结果表明,采用硫黄、过氧化物DCP共同交联的NBR体系,在高温力学性能与常温力学性能相比,下降较大。HNBR的硫化体系对性能影响很大,常温条件下,硫黄交联体系的力学性能不如过氧化物交联体系优异;在高温条件的力学性能与常温力学性能相比,综合性能下降较大。     

Effect of network heterogeneities on the physical properties of nitrile rubbers cured with dicumyl peroxide

The scope of this study is to continue our earlier studies on the peroxide curing of diene elastomers. The effect of peroxide content and temperature on the curing and mechanical properties of NBR and H‐NBR rubbers with different acrilonitrile content was evaluated. Experimental evidence indicates that saturated rubbers behave as expected whereas in unsaturated nitrile rubbers abstraction of allylic hydrogen and addition to the double bonds can act as mechanism of crosslinking, the weight of each mechanism is dependent of DCP content and curing temperature. The addition mechanism produces densely crosslinked zones or clusters, generating a heterogeneous network with effect on the vulcanizate properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3377–3382, 2007     

Mechanical properties and thermal aging behavior of styrene‐butadiene rubbers vulcanized using liquid diene polymers as the plasticizer

The mechanical properties of styrene‐butadiene rubber (SBR) vulcanizates prepared using various plasticizers including liquid polybutadiene and styrene‐butadiene copolymers were investigated. The effect of the liquid polymers as the plasticizers on the mechanical properties of the polymers, such as the hardness, tensile storage modulus, tanδ, and the modulus at 100% elongation values, were determined before and after the thermal aging. As a result, it was revealed that the use of these liquid polymers gave less amount of change in the measurement values for the mechanical properties during the aging. The crosslinking density and the amount of free polymers were also determined on the basis of the swelling and extraction data, respectively, using several organic solvents. These results support the fact that the added liquid polymers are fixed to the SBR networks. We revealed the superiority of the liquid styrene‐butadiene copolymers as the plasticizer, which provides sufficient mechanical properties after vulcanization and the excellent maintenance of the properties during the thermal aging process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of shear processing on morphology orientation and mechanical properties of styrene butadiene triblock copolymers

The influence of ram extrusion on structure and mechanical properties of a triblock copolymer consisting of polystyrene (S) outer blocks and poly(styrene–stat–butadiene) (S/B) middle block is studied for a wide range of shear rates. Structural features on the mesoscale (10–100 nm) are investigated by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Transition Moment Orientation Analysis (TMOA) is applied to quantify the orientation on the molecular (segmental) scale (<1 nm). All extruded samples microphase-separate and show a lamellar morphology with periodicities of about 33 nm. Significant orientation is observed on the mesoscale where the surface normals of the lamellae are preferentially perpendicular to the extrusion direction. The corresponding degree of orientation drops slightly at elevated shear rates of about 600 s⁻¹. Interestingly, Chevron-like pattern with two preferred orientations of the lamellae are observed in cross-sections probably due to shear velocity gradients in the rectangular die. In contrast, significant orientation on the molecular scale is absent for styrene and butadiene units indicating basically random orientation of the chain segments. The mechanical properties are, however, strongly anisotropic. Uniaxial tensile tests performed parallel and perpendicular to the extrusion direction reveal higher E_∥ moduli (1.1 – 0.6 GPa) along with yielding but significantly smaller E_⊥ moduli (100−250 MPa) without pronounced yielding. Main trends in both moduli, E_∥ and E_⊥, can be explained based on mesoscale orientation using the analytical composite model. In general, the results demonstrate that orientation effects on the mesoscale have a strong influence on the mechanical properties and must be considered during the optimization of extruded or injection-molded components made from microphase-separated block polymers.     

Influence of structural parameters on the degradation of ultrahigh‐molecular‐weight vinyl‐type network‐polymer precursors during elution through size exclusion chromatography columns

Network‐polymer precursors obtained in various crosslinking monovinyl/divinyl copolymerization systems, including benzyl methacrylate/1,6‐hexanediol dimethacrylate, benzyl acrylate (BzA)/1,6‐hexanediol diacrylate (HDDA), and vinyl benzoate/divinyl adipate, were subjected to degradation during elution through size exclusion chromatography (SEC) columns, although the copolymerizations were conducted under specified conditions where the factors for the greatly delayed gelation from the Flory–Stockmayer gelation theory were reduced. The most remarkable degradation was observed for the BzA/HDDA copolymerization, which provided prepolymers with the most flexible backbone chains. Thus, the BzA/HDDA precopolymers were chosen, and their degradation behavior during elution through SEC columns was explored in detail as one of the representatives of vinyl‐type network‐polymer precursors. The results were correlated with the structural parameters of network‐polymer precursors, including primary polymer chain length, branched structure, and multiple crosslink or network structure. The degradation became more remarkable with decreased primary polymer chain length, that is, the increment of branching, whereas reduced degradation was observed with the incorporation of loop and network structures into the prepolymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 577–582, 2003     

Effects of crosslinking densities on mechanical properties of nitrile rubber composites in thermal oxidative aging environment

The effects of crosslinking densities on mechanical properties of nitrile rubber (NBR) composites before and after thermal oxidative aging are investigated. Tensile strengths of NBR composites are enhanced slightly at the initial aging stage, attributing to moderate increment of crosslinking densities. Continuous decrease with further aging is followed, resulting from over-crosslinking and uneven distribution of crosslinking densities. The digital image correlation method is explored for large-strain deformation measurement by displacement accumulation and establishing strain model, being promising in practical age detection and measurement of mechanical properties in complex environments. Compression sets are gradually increased with aging because of the destruction of the original crosslinking structures. The molecular chains fracture inhibits elastic recoveries of compressive NBR composites and results in residual deformation in thermo-oxidative and compressive environment after unloading. This study provides new ideas for exploring mechanical properties of rubber-based composites before and after thermal oxidative aging.     

Effect of the processing parameters on the surface resistivity of acrylonitrile–butadiene rubber/multiwalled carbon nanotube nanocomposites

In this study, acrylonitrile–butadiene rubber (NBR) was melt‐mixed with multiwalled carbon nanotubes (MWCNTs). Because the electrical conductivity and mechanical properties of composites are strongly influenced by the filler's state of dispersion and the extent of filler breakage during processing, the processing conditions are very important parameters. The effects of the mixing time, rotor speed, cooling rate, and sulfur concentration on the surface resistivity were investigated. Increasing the rotor speed from 20 to 60 rpm at mixing times of 15 and 30 min led to an increase in the surface resistivity from around 10⁴ to 10¹¹ Ω/square. However, at a mixing time of 7 min, the surface resistivity slightly decreased with increasing rotor speed. When slow cooling was applied, a surface resistivity of 10⁴ Ω/square was obtained at around 2‐phr MWCNTs. However, when the fast cooling was applied, a surface resistivity of 10⁶ Ω/square was obtained at 5‐phr MWCNTs. The tensile strength and tensile modulus at 300% elongation were improved with the addition of MWCNTs into NBR. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Real‐time temperature and photon transmission measurements for monitoring phase separation during the formation of poly(N‐isopropylacrylamide) gels

Phase separation during the formation of poly(N‐isopropylacrylamide) (PNIPA) hydrogels was investigated using real‐time photon transmission and temperature measurements. The hydrogels were prepared by free‐radical crosslinking polymerization of N‐isopropylacrylamide (NIPA) in the presence of N,N′‐methylenebisacrylamide (BAAm) as a crosslinker in an aqueous solution. The onset reaction temperature T₀ was varied between 20 and 28°C. Following an induction period, all the gelation experiments resulted in exothermic reaction profiles. A temperature increase of 6.5 ± 0.6°C was observed in the experiments. It was shown that the temperature increase during the formation and growth process of PNIPA gels is accompanied by a simultaneous decrease in the transmitted light intensities I_tr. The decrease in I_tr at temperatures below the lower critical solution temperature of PNIPA was explained by the concentration fluctuations due to the inhomogeneity in the gel network. At higher temperatures, it was shown that the gel system undergoes a phase transition via a spinodal decomposition process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3589–3595, 2002     

Effects of elevated temperature and crude oil on the properties of a hydrogenated nitrile butadiene rubber elastomer

The stability and durability of hydrogenated nitrile butadiene rubber (HNBR) material in crude oil environments are of great importance for petroleum equipment to resist leakage and to ensure reliability. In this paper, an HNBR material was fabricated, and the degradation of the HNBR material was investigated in simulated crude oil environments. One crude oil and three temperatures (50 °C, 75 °C, and 100 °C, based on actual crude oil operations, were used in this study. Weight changes for the HNBR specimens were monitored after exposure to the environments over time. Optical microscopy was used to show the topographical changes on the specimen surfaces. Attenuated total reflection Fourier transform infrared (ATR‐FTIR) spectroscopy was employed to study the surface chemistry of the HNBR material before and after exposure to the simulated crude oil environments at selected times. Mechanical property tests (tensile and compressive stress–strain tests, tear strength test, and compression set test) were conducted to assess the changes in mechanical properties of the HNBR specimens before and after exposure to the environments. The test results show that the physical–mechanical properties of the HNBR material changed significantly. The temperature and the crude oil had a direct effect on the degradation of the mechanical properties. The ATR‐FTIR test results indicate that the surface chemistry changed via chain crosslinking in the material after exposure to the environments over time. The degradation mechanisms of the HNBR material after exposure to the crude oil could be due to the presence of chain crosslinking, chain mobility, and backbone scission. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44012.