Natural Rubber Elastomers Research Articles

Multi-Factor Optimization of Natural Rubber Formula for Friction of Natural Rubber Elastomer Material for Prosthesis Sole Applications

Multi-Factor Optimization of Natural Rubber Formula for Friction of Natural Rubber Elastomer Material for Prosthesis Sole Applications

Design optimization of bridge pier bearings based on material and shape

Elastomer bearings are design efficient and economical, so these are more widely used for bridge construction. Steel bearings were predominantly used before and their performance was good with few disadvantages due to their corrosive nature and high maintenance. Hence elastomer was introduced as a matrix material for steel bearings. In present study, analysis of mechanical properties is carried by changing elastomer material. The results showed that it is better to produce strong and effective reinforced elastomer bearing using material other than natural rubber. The study compares results of bearing elastomer using silicone rubber, PTFE (Polytetrafluoroethylene) with the conventional synthetic natural rubber elastomer bearing. The effect of shape on maximum stress and deformation is also analysed. The bearing used in the case study is designed for forces applicable to metro rail viaduct. The load calculations are done using the specification provided by BMRCL (Bangalore Metro Rail Corporation Limited). The analysis for stress and deformation is performed using ANSYS. The maximum stress, strain and deformation in bearing using new materials as elastomer were found to be lesser than the bearing using neoprene elastomer bearing.

About the elongation at break of unfilled natural rubber elastomers

This paper presents the characterization of the mechanical properties, of the ability to crystallize thermally or under strain, and of the Elastically Active Chains (EAC) network of Natural Rubber elastomer, whose EAC average density and length distribution were modified by thermo-oxidative ageing. EAC length distribution is not a critical parameter for λbreak in elastomers which do not crystallize (as far as the quantity of free and dangling chains stays negligible, which is the case in this study). However, it becomes important in crystallizable materials, since it controls the chains quantity which can be stretched enough to crystallize. When this quantity is large enough, the material can be stretched up to λc, and the crystallization process will enable to increase both λbreakand σbreak. Conversely when it is too low, λbreakis seemingly mainly governed by the average EAC density and a power law then links both quantities.

Mechanical Properties of Silicon Carbon Black Filled Natural Rubber Elastomer

A pyrolyzed ash containing about 50% carbon, named silicon carbon black(SiCB), was prepared by the anoxic pyrolysis of rice husk. Fourier transform infrared spectroscopy(FTIR), thermogravimetric analysis(TGA), Brunauer-Emmett-Teller(BET), transmission electron microscopy(TEM) and universal material testing machine were used to analyze the stress-strain relationship, Mullins effect and static viscoelastic properties of SiCB-filled vulcanized natural rubber(NR), and SiCB was compared with a commercially available semi-reinforcing furnace(SRF) carbon black. The results show that the vulcanized natural rubber filled with SiCB had similar reinforcing properties to those of that filled with traditional SRF, but obvious differences between them exist in stress -strain properties and stress softening resistance. We tried to discuss the related phenomena with the aid of the modified two-layer theory. And it is successfully predicted and verified that SiCB has good compression resistance and obvious stress relaxation advantages in compression stress relaxation.

Reinforcement in Natural Rubber Elastomer Nanocomposites: Breakdown of Entropic Elasticity

We propose an approach based on the combination of different techniques in order to discriminate various reinforcement effects in vulcanized natural rubber elastomers with various cross-link densities, filled with carbon black or silica: mechanical response, independent measurements of the cross-link density by proton multiple-quantum NMR, and measurements of chain segment orientation under stretching by X-ray scattering. We show that, while the modulus measured in dynamical mechanical measurements decreases as the strain amplitude increases (Payne effect), the response of the elastomer matrix in terms of average chain segment orientation under stretching measured by X-ray scattering stays constant. The amplification of average chain segment orientation is comparable to the amplification of modulus measured at medium/large strain amplitude. By analyzing the deviations with respect to the behavior of the pure unfilled elastomer matrix, we show that the contribution due to strain amplification effects in the elastomer matrix can be selectively distinguished. We show that the mechanical response at medium/large strains is essentially driven by strain amplification effects, while, in the linear regime, there is a strong additional reinforcement which is not related to the properties of the elastomer matrix. Hypothesis on the origin of this additional reinforcement are suggested and discussed.

Compliant Natural Rubber Latex Electrodes for Electrostrictive Polyurethane Actuation

Improvement of the electrostrictive polymer with natural rubber (NR) compliant electrodes can potentially offer advantages for enhancement electromechanical efficiency of elastomer actuators. The NR elastomers are capable of advantageous features such as a high productivity, elasticity, and ease of processing. In this work, the NR composites filled with carbon black (CB) nanopowders at high conductivity was used as compliant electrodes on polyurethane electrostrictive polymer. The compliant NR composites electrodes were fabricated by using spin coating technique. The morphology of the NR composites was observed by the scanning electron microscope (SEM). The mechanical, electrical and electromechanical properties of NR composites were investigated. The electric field-induced strain of sample with compliant NR composites electrodes, and comparison with metallic electrodes was determined by using the photonic displacement apparatus. The results show that the thickness strain of polyurethane electrostriction with compliant NR was higher that with metal electrodes, depending not only on compliance between sample and electrodes, but also good conductivity and adhesion of electrodes. Correlation of the electromechanical properties and the mechanically coupled in stretching and compressing to volume incompressibility of polymer are also discussed.

Electrostriction of Natural Rubber Latex/Carbon Black Nanocomposites

The purpose of this paper is to investigate an electrostrictive behavior of natural rubber (NR) and NR composites filled with carbon black (CB) nanopowders below percolation threshold. These NR elastomers present advantageous features such as a high productivity, elasticity, and ease of processing. In addition, such materials also exhibit the high induced strain and low young modulus for electrostrictive materials that can be used as actuators and energy harvesting. The NR and all composites were prepared by using solution casting method. The electrostrictive property of the composites was evaluated at low electric field (E 5 MV/m) by measuring the electric field induced strain Sz with the photonic displacement apparatus. The surface morphology of the samples was observed by the atomic force microscopy (AFM) and their electrical properties were analyzed as function of concentration and frequency in a range of 102105 Hz. The results show that the dielectric constant and the dielectric loss decrease when the frequency was increased. Moreover, the dielectric constant and the electrical conductivity strongly increase with increasing the CB contents, relate to interfacial charge distribution. While the dielectric loss slightly increases with increasing filler concentration. The electrostriction coefficient tended to increase with a higher CB loading. In comparison at CB 1 wt%, it was found that the electrostriction coefficient of NR composites is approximately 7 times larger than the pure NR. The NR nanocomposites thus seem to be very attractive for low frequency electromechanical applications.

Sulfur-Cured Natural Rubber Elastomer Networks: Correlating Cross-Link Density, Chain Orientation, and Mechanical Response by Combined Techniques

We present a combination of independent techniques in order to characterize vulcanized natural rubber elastomer networks. We combine solid state proton multiple-quantum NMR, equilibrium swelling, mechanical experiments, and in-situ tensile X-ray scattering measurements, all of them giving access to the segmental orientation effects in relation to the cross-linking of the systems. By means of the combination of these techniques, we investigate a set of unfilled natural rubber networks with different levels of cross-linking. The relevance of this work is the application of this approach in order to study the reinforcement effect in filled elastomers with nanoparticles in a following work.

Electro-thermo-elastomers for artificial muscles

This paper presents the concept, design and characterization of new type of thermal actuator, which utilizes the entropic properties of natural rubber elastomer. For a stretched elastomer the thermal expansion is negative above its glass transition temperature. The actuator presented in this study comprised an elastomer film and flexible resistive heater realized by photo-etching a Nickel–Silver photosensitized wafer. The results demonstrated that the thermal actuator was able to generate a strain of 5% and a stress of 1MPa for an input electric energy of 25J, i.e. a strain comparable to human muscles mechanical properties.

Effect of Tear Rotation on Ultimate Strength in Reinforced Natural Rubber

We analyze the impact of tear rotation on the tensile strength of reinforced natural rubber elastomers. Vulcanized natural rubber materials reinforced with carbon black or precipitated silica are studied. Single edge notched reinforced samples stretched at constant velocity exhibit an abrupt instability in the direction of propagation of the crack. This phenomenon has been known as tear rotation. The measured apparent tensile strength (in terms of energy at break) may be increased by a factor of 6–8 in some cases. A mechanism is proposed in order to relate the tensile strength of the material to the presence of tear rotations observed in reinforced natural rubber. This large increase in tensile strength associated with the presence of tear rotations is analyzed semiquantitatively, based on energetic arguments, without entering into a detailed description of the elastic strain field in the vicinity of the tear tip. We also show a correlation between the length of a rotation and the stress level at which it appears. The proposed interpretation is based on the idea that tear rotations relax the local strain (or stress) at the tear tip by creating a macroscopic tip radius. Materials reinforced with carbon black or precipitated silica aggregates show similar behavior.

Adhesion of Fibers to Natural Rubber Elastomer using Ring-Opening Metathesis Polymerization (ROMP)

Ring-opening metathesis polymerization is used to investigate adhesion of multifilament fibers (polyester, nylon, Kevlar®) to a natural rubber elastomer through the creation of ROMP polymer coatings on the fiber surfaces followed by encapsulation in pre-cured elastomer. Polymer coated fibers are prepared by 1) physisorption of polynorbornenes which are prepared by solution-phase ROMP and 2) contact metathesis polymerization (CMP) whereby Grubbs' 1st generation catalyst 1 is applied directly to the fiber surface followed by passage of the “activated” fiber through a norbornene monomer bath. Both methods improve adhesion to the elastomer when compared to uncoated control specimens. Catalyst and polymer loading are briefly examined. Although inconclusive, our findings suggest that polymer loading and substrate specificity may affect overall adhesion. ROMP is enabling chemistry for creating an interface to improve fiber adhesion to natural rubber elastomers. Formulated commercial adhesive systems are also included in this study.

A natural rubber drainage tube with antithrombogenic lumen surface

A drainage tube was made by radiation vulcanization of a high polymeric substance based on natural rubber elastomers. Pentosan polysulphate sodium bound to a carrier substance (synthetic type 4A or 13X zeolite) was incorporated in the drainage tube which was then tested for its anticoagulant properties during perfusion with Tris buffer solution, citrated plasma, and blood, resp. The amount of pentosan polysulphate sodium released from the tube walls during perfusion with human citrated plasma in an open circulatory system was sufficient to exert an anticoagulant effect on the streaming plasma. This effect was corroborated by prolonged thrombin times and by unclottability in case of recalcified plasma samples in thrombelastographic studies. The antithrombogenicity test according to Chandler in a closed circulatory system revealed thrombus formation times (TFT) of more than 24 h (control: TFT = 1–3 min in native blood).

Calorimetric study of entropy and energy effects in small deformations of elastomers

Deformation calorimetry was used to determine the energy and heat of uniaxial reversible elongation over the range of small deformation ( λ<1·8) for three natural rubber elastomers, a statistical copolymer of ethylene with propylene containing 45% propylene and polydimethylsiloxane rubber and in the approximation of a Gaussian chain network using the relations obtained a thermodynamic analysis was made of entropy and energy effects accompanying deformation. Overall changes of entropy and internal energy were classified as intra- or intermolecular components and it was shown that the proportion of intramolecular change in entropy and internal energy is independent of deformation and is determined by the molecular structure of the polymer. Intermolecular changes in entropy and internal energy show a marked dependence on deformation and these changes are due to volumetric variation in deformation and offset each other. Volumetric changes in deformation were calculated and thermoelastic inversion of heat and internal energy, analysed.