Natural rubber nanocomposites with SiC nanoparticles and carbon nanotubes

Single-walled carbon nanotubes (SWNTs) and SiC nanoparticles were dispersed in natural rubber (NR) polymer solution and subsequently evaporated the solvent to prepare NR nanocomposites. Using this technique, nanoparticles can be better dispersed in the NR matrix. The influence of nano-fillers on the mechanical properties of the resulting nanocomposites was quantified.Mechanical test results show an increase in the initial modulus with nanoscale reinforcements for up to 50% strain compared to pure NR. The modulus and strength of natural rubber with 1.5% SiC nanoparticles appear to be superior to those of SWNTs with the same filler content. In addition to mechanical testing, these nanocomposites were studied using the SEM and Raman spectroscopy techniques in order to understand the morphology of the resulting system and the load transfer mechanism, respectively. The Raman spectrum of the SWNT/NR system is characterized by a strong band at 1595 cm⁻¹ (G mode—C-C stretching) and other two bands at 1300 cm⁻¹ (D mode-disorder induced) and 2590 cm⁻¹ (D* band). A shift of the 2590 cm⁻¹ Raman band to the lower wavenumber was observed after subjecting SWNT/NR sample to cyclic stress testing. Ageing SWNT/NR specimen in distilled water for 30 days also provided a similar result. The Raman shift in aged samples indicates internal stress transfer from the natural rubber matrix to the SWNTs implying the existence of bonding at the interface.     

Initial stage of the chlorination of natural rubber

Kinetics of the initial stage of the chlorination of natural rubber(NR), up to chlorine content ⩽1 Cl/C₅, have been investigated using a stop-flow method in CCl₄ at room temperature. The chlorination is very fast and is accelerated by the product HCl. The first orders of the reaction rate relative to NR, Cl₂, and HCl were established. A proposed mechanism includes formation of molecular complexes between polymer units, Cl₂ and HCl; the corresponding kinetic equation described satisfactorily the experimental data. Kinetic characteristics of the chlorination of the model compound 2-methylpentene-2(MP) are the same as for NR. The noncatalytic and autocatalytic rate constants for MP are close to those for NR. Compositional heterogeneity of chlorinated NR(CNR) containing <1 Cl/C₅ has been studied by cross-fractionation. The sample chlorinated by the routine procedure is markedly heterogeneous whereas the sample prepared in the stop-flow unit (where extremely fast mixing is realized) is quite homogeneous. These results lead to the conclusions: (1) high reaction rate is caused by high reactivity of “kinetically independent” NR units, not by a polymeric effect; (2) great compositional heterogeneity of CNR samples prepared by the routine procedure is caused by macrokinetic factors.     

Thermal properties of compatibilized and filled natural rubber/acrylonitrile butadiene rubber blends

The thermal behaviour of natural rubber/acrylonitrile butadiene rubber (NR/NBR) was studied using thermogravimetry (TG) and differential scanning calorimetry (DSC) in terms of blend ratio, crosslinking systems, fillers and compatibilizer (neoprene) were analyzed. The presence of NBR markedly increases the thermal stability of their blends and it lies in between NR and NBR. DSC studies revealed the thermodynamic immiscibility of the NR/NBR blends by the presence of two distinct glass transition temperatures and the immiscibility was prominent even in the presence of a compatibilizer.     

On the degradation and stability of high abrasion furnace black (HAF)/acrylonitrile butadiene rubber (NBR) and high abrasion furnace black (HAF)/graphite/acrylonitrile butadiene rubber (NBR) under cyclic stress-strain

Acrylonitrile butadiene rubber (NBR) compounds filled with 40 phr of high abrasion furnace black (HAF) and HAF (20 phr)/graphite (20 phr) were experimentally investigated. The stress-strain curves of the composites were studied, which are described by applying Ogden's model. The effect of cyclic fatigue and hysteresis was also examined. The dissipation energy that indicates the vibration damping capacity for all samples was determined. A continuum damage model is used to investigate the fatigue damage behavior for elastomers. Experiments on the cyclic fatigue of a carbon-filled NBR rubber and carbon/graphite filled NBR rubber were conducted to determine the relation between the number of cyclic fatigue and the strain amplitude. The results indicate that the theoretical formula for the number of cyclic fatigue as a function of the strain amplitude, derived from the damage model, can describe experimental data for the prepared samples very well.     

Effect of chitosan derivatives as rubber antioxidants for increasing durability

A series of chitosan derivatives, namely polydiethylamino-ethylmethacrylate-chitosan-graft-copolymer (chitosan-g-DEAEMA), polycarboxy-chitosan-graft copolymer (chitosan-g-COOH), polyvinyl alcohol chitosan-graft-copolymer (chitosan-g-VOH), and carboxymethyl-chitosan (CM-chitosan), were synthesized and investigated as antioxidants for natural rubber (NR) and acrylonitrile butadiene rubber (NBR) mixes and vulcanizates to increase their durability. The rheometric characteristics of the rubber mixes were determined using an oscillating disc rheometer. The physico-mechanical properties of the rubber vulcanized were measured before and after exposure to thermal oxidative aging. It was found that the CM-chitosan had an accelerating effect on the curing process of NR and NBR. Also, the investigated polymers enhanced the properties of rubbers (NR and NBR) especially after ageing up to 7 days compared with commercial antioxidants, such as phenyl ß-naphthylamine (PßN) and N-isopropel-Nphenyl-p-phenylene diamine (IPPD) which are used in the rubber industry. After ageing, the retained values of tensile strength, modulus at 100 % strain, and elongation at break were improved. The optimum concentration of the investigated compounds used to give good properties was found to be 1–2 parts per 100 of rubber (phr). In addition, these prepared polymers showed a decrease in the equilibrium swelling of rubber in toluene which is the proper solvent and consequently increases the crosslink density for rubbers.     

共混硫化丁腈橡胶-氯丁橡胶的物理性能

将丁腈橡胶(NBR)和氯丁橡胶(CR)按不同质量分数共混并硫化,研究了硫化橡胶在自然环境、热空气老化、热油老化等条件下的物理性能,并测定了硫化橡胶与镀铜钢丝的粘合性能.结果表明,随着CR质量分数的增大,混炼胶的焦烧时间逐渐缩短.经热空气老化后,NBR的硬度增加幅度比CR的硬度增加幅度大,拉断强度降低幅度则比CR的小得多.此外,NBR的耐油性能优于CR.就物理性能以及与镀铜钢丝的粘合性能而言,单一NBR和单一CR优于共混NBR/CR.     

Effect of cold plasma process on the surface wettability of NBR and the kerosene resistance of NBR/PTFE composites

In this study, first the acrylonitrile‐butadiene rubber (NBR5080) was modified by argon (Ar), air, and oxygen plasma at low temperature, and the effect of plasma process (power, time, and pressure) on the surface properties of NBR5080, the interfacial properties, physical properties, and the mechanical properties of NBR5080/polytetrafluoroethylene (PTFE) composites were investigated. The state contact angle and the surface free energy were applied to characterize the surface wettability of NBR5080. The scanning electron microscope and the atomic force microscope were used to observe the surface morphology of the NBR5080. The chemical changes on the NBR5080 surface were verified by X‐ray photoelectron spectroscopy. The average water contact angle the NBR5080 declined obviously when NBR5080 was treated by Ar (100 W/600 s/30 Pa). The active oxygen groups were introduced onto the surface of NBR5080 by cold plasma treatment and more active group containing oxygen were observed on the samples treated by Ar plasma. The peel strength between the NBR5080 and the PTFE was increased obviously, which increased from 0 to 44.2 N?m^?1 for Ar plasma treatment. The mass and the dimension of NBR5080 increase sharply after immersing in kerosene, whereas the NBR5080/PTFE composites changed a little. The mechanical properties of NBR5080 and NBR5080/PTFE composites decreased as the immersion time in kerosene increased, but the decreased degree of NBR5080 is higher than NBR5080/PTFE composites.     

Effect of mastication time on the low strain properties of short pineapple leaf fiber reinforced natural rubber composites

Pineapple leaf fiber (PALF), used as a reinforcing agent, does not have good adhesion to natural rubber (NR) due to the difference in their polarities. As a result, the degree of reinforcement of NR imparted by PALF remains low compared to that in a polar rubber like acrylonitrile butadiene (NBR). One of the factors that determines the adhesion between the rubber and the reinforcement is the rubber molecular weight. Thus, the aim of this paper is to demonstrate that the stress at very low strains of short pineapple leaf fiber (PALF) reinforced natural rubber (NR) can be significantly increased by lowering the matrix molecular weight. This can be achieved by increasing the matrix mastication time. The composites studied here contain a fixed amount of PALF at 10 part (by weight) per hundred rubber (phr). The PALF fibers were both untreated (UPALF) and sodium hydroxide treated (TPALF). Mastication times of 2, 4, 8 and 16 min were used. Stress-strain curves of PALF reinforced NR prepared with different mastication times were then compared. The most affected region of the curve is in the low strain region. The slopes of the stress-strain curves (moduli) increase with increasing mastication time, indicating better fiber-rubber interaction. The maximum stress achieved at 10% strain is almost 370% that obtained with the usual short mastication time (2 min). The effect remains up to very high strains, although becoming smaller as the strain is increased. Hence, we demonstrate that, by using long enough mastication time, stress-strain curves and stress at low strain of PALF reinforced NR can be improved without the need of any other adhesion promoters.     

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.     

FTIR spectra and mechanical strength analysis of some selected rubber derivatives

Rubber materials have wide range of commercial applications such as, infant diapers, famine hygiene products, drug delivery devices and incontinency products such as rubber tubes, tyres, etc. In the present work, studies on mechanical properties of some selected rubber materials viz., natural rubber (NR), styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR) and ethylene propylene diene monomer (EPDM) have been carried out in three states viz., raw, vulcanized and reinforced. To enhance the quality of rubber elastomers, an attempt is made to prepare new elastomers called polyblends. In the present study an attempt is made to blend NR with NBR and with EPDM. We here report, a novel approach for the evaluation of various physico-mechanical properties such as mechanical strength, tensile strength, elongation and hardness. The method is simple, direct and fast and involves infrared spectral measurements for the evaluation of these properties. With the applications of modern infrared spectroscopy, the mechanical strength of these rubber materials have been analyzed by calculating the internal standards among the methyl and methylene group vibrational frequencies obtained from FTIR spectroscopy. Also the tensile strength measurements carried out by universal testing machine. The results pertaining physico-mechanical properties of the rubber derivatives undertaken in the present study obtained by IR-based method are in good agreement with data resulted from the standard methods.     

Effect of maleic anhydride and liquid natural rubber as compatibilizers on the mechanical properties and impact resistance of the NR‐NBR blend

The degree of compatibilization between natural rubber (NR) and acrylonitrile‐butadiene rubber (NBR) was investigated by two different methods. NBR was chemically modified with maleic anhydride in a screw twin mixer with and without reaction initiator, benzoyl peroxide. Also, the effects of molecular weight of liquid natural rubber (LNR) as a compatibilizer were studied. The degree of compatibilization between NBR and NR is determined indirectly through measurements of mechanical properties and impact resistance. The maleic anhydride and benzoyl peroxide concentrations influence the mechanical properties and impact resistance of the blends. Also, the mechanical properties of the blends showed that the molecular weight of LNR played an important role in determing their performance. Copyright © 2004 John Wiley & Sons, Ltd.     

Prevulcanized natural rubber latex/clay aerogel nanocomposites

Natural rubber latex (NR)/clay aerogel nanocomposites were produced via freeze-drying technique. The pristine clay (sodium montmorillonite) was introduced in 1-3 parts per hundred rubber (phr) in order to study the effect of clay in the NR matrix. The dispersion of the layered clay and the morphology of the nanocomposites were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Cure characteristics, thermal stability, and the crosslink density of thermal and microwave-cured NR and its composites were investigated. XRD patterns indicated that both intercalated and exfoliated structures were observed at loadings of 1-3 phr clay. SEM studies revealed that the clay aerogel structure was formed at 3 phr clay loading. The increment in Shore A hardness of nanocomposites compared with pure NR signified excellent polymer/filler interaction and the reinforcing effect of the clay to rubber matrix. This was supported by an increase in maximum rheometric torque and crosslink density. The crosslink density of clay-filled NR vulcanizate was found to increase with the pristine clay content in both thermal and microwave curing methods. However, microwave-cured 2 and 3 phr-filled NR vulcanizates exhibited higher crosslink density than those which were thermal-cured under the same curing temperature. In addition, thermal stability studies showed that pristine clay accelerated the decomposition of NR by showing a slight decrease in onset and peak decomposition temperatures along with clay content.     

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.     

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.     

Compounding,mechanical and morphological properties of carbon-black-filled natural rubber/recycled ethylene-propylene-diene-monomer (NR/R-EPDM) blends

Blends of natural rubber/virgin ethylene-propylene-diene-monomer (NR/EPDM) and natural rubber/recycled ethylene-propylene-diene-monomer (NR/R-EPDM) were prepared. A fixed amount of carbon black (30 phr) was also incorporated. The effect of the blend ratio (90/10, 80/20, 70/30, 60/40 and 50/50 (phr/phr)) on the compounding, mechanical and morphological properties of carbon-black-filled NR/EPDM and NR/R-EPDM blends was studied. The results indicated that both the carbon-black-filled NR/EPDM and NR/R-EPDM blends exhibited a decrease in tensile strength and elongation at break for increasing weight ratio of EPDM or R-EPDM. The maximum torque (S′M_H), minimum torque (S′M_L), torque difference (S′M_H?M_L), scorch time (ts₂) and cure time (tc₉₀) of carbon-black-filled NR/EPDM or NR/R-EPDM blends increased with increasing weight ratio of virgin EPDM or R-EPDM in the blend. SEM micrographs proved that, for low weight ratios of virgin EPDM or R-EPDM, the blends exhibited high surface roughness and matrix tearing lines. The blends also showed a reduction in crack path with increasing virgin EPDM or R-EPDM content over 30 phr. This reduction in crack path could lead to less resistance to crack propagation and, therefore, low tensile strength.     

Influence of fluorine-containing lubricant on properties of NR/BR rubber

K95 experimental lubricant being a product of fluorine reaction with a blend of mutually soluble poly(fluorine alcohols) and poly(fluorine esters) with molecular weight 240-900 g/mol was studied as an additive for rubber compounds based on blend of NR and BR. It was thermally stable till 270-300 °C. For comparison, it was tested simultaneously with homogenizing agent, Struktol MS40. Lubricant K95 added in a quantity of 0.5 wt% reduced the viscosity of rubber compound; it also improved compound flow in the mold. Mechanical properties of cured rubber not decrease while resistance to abrasion and fatigue increased. K95 participated in forming strong physical junctions (lower molecular weight between junctions of thermally stable network) while Struktol MS40 reduced the networking degree of rubber. As a result, it acts a multifunctional additive for NR/BR rubber.     

Ternary blends based on poly (ethylene-naphthalate)/glass fibers/nitrile rubber: Preparation,properties and effect of dynamic vulcanization

This work studied the possibility of utilizing nitrile rubber (NBR) to modify the impact properties of poly (ethylene-naphthalate) (PEN). The PEN/NBR ratio used changed from 100/0 to 60/40. At the same time, glass fibers (GF), 40% weight of the PEN component, were used to reinforce the blends to compensate for the loss of mechanical properties of PEN by incorporation of NBR. The results showed that the impact strength of the PEN/GF/NBR blend (PEN/NBR = 60/40) was increased up to 27.6J/m, nearly 5 times higher than that of the neat PEN. Meanwhile, the tensile strength and flexural strength were still maintained at as high as 66.1 MPa and 98.2 MPa, respectively. Dynamic vulcanization further improved the mechanical properties of the PEN/GF/NBR blends, which provided routes to the design of new PEN/elastomer blends. Other properties of the PEN/GF/NBR blends were also investigated in terms of morphology of fractured surface, dynamic mechanical behavior, thermal stability and crystallization, by scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively.     

Carbon-based conductive rubber composite for 3D printed flexible strain sensors

Polymeric-based flexible electronic devices are in high demand due to its wide range of applications. Natural rubber (NR) shows a great potential as matrix phase for flexible conductive polymer composites with its high elasticity and fatigue resistance. In this study, a new 3D printable conductive NR (CNR) composite was developed for strain sensor applications. Different contents of conductive carbon black (CCB) were mixed with NR latex to investigate the effect of the filler content on electrical and mechanical properties of the composites. The best-known CNR composite with the CCB content of 12 phr was selected in order to produce the feedstock for the stereolithography process (SLA). The morphological, electrical, and mechanical properties of cast and 3D-printed samples were investigated and compared. Although the 3D-printed CNR sample had slightly lower conductivity than the cast one, it possessed comparable tensile strength and elongation at break, with values of 12.4 MPa and 703%, respectively. In addition, electrical responses of the CNR samples were investigated to demonstrate the electromechanical property of the material as a strain sensor. The 3D-printed CNR sample exhibited the highest electromechanical sensitivity with a gauge factor (GF) of 361.4 (ε = 210%–300%) and showed good repeatability for 500 cycles. In conclusion, the development of this 3D printable functional material with great sensing capability will pave the way for innovative designs of personalized sensing textiles and other smart wearable devices.     

Modification of deproteinized natural rubber via grafting polymerization with maleic anhydride

Modification of natural rubber (NR) via grafting polymerization with maleic anhydride (MA) has received wide attention as it could improve the hydrophilicity of NR and extend its application to a wider application field. However, the grafting efficiency of MA onto NR in either the molten state or solution state is low and is accompanied with undesired high gel content in the grafts. In this work a novel technical route was developed in that a deproteinization operation was conducted before carrying out the grafting process and a differential microemulsion polymerization technique was applied for the grafting reaction. The effects of initiator and monomer concentration, reaction temperature, and reaction time on the grafting efficiency and gel fraction were investigated, and a comparison of the reaction performance was conducted for deproteinized NR (DPNR) and NR. The results indicated that the deproteinization operation could significantly improve the grafting efficiency and reduce the gel content, and a 29% yield of MA grafted onto the rubber backbone could be achieved at a condition of a DPNR:MA:initiator ratio of 85:9:6 (wt%) at 60 °C for 8 h.     

Maleic-anhydride grafted EPM as compatibilising agent in NR/BR/EPDM blends

Incorporation of approximately 30 phr Ethylene-Propylene-Diene rubber (EPDM) into natural rubber (NR)/butadiene rubber (BR) is a means to achieve non-staining ozone resistance for tire sidewall applications. However, due to incompatibility of the elastomers and heterogeneous filler distribution in each of the rubber phases, the mechanical properties deteriorate. In the present work, maleic-anhydride modified EPM (MAH-EPM) is added as a compatibilising agent between NR/BR and EPDM. The addition of 5 phr of MAH-EPM results in significantly improved tensile and tear strength when compared to a straight NR/BR/EPDM blend. These improvements can mainly be attributed to a compatibilising effect of MAH-EPM, resulting in a more homogeneous phase distribution, but in particular a much better homogeneous carbon black distribution over the different rubber phases. In addition, ionic crosslinks are introduced into the blends by interaction of MAH-EPM with zinc oxide.