Analytical modelling of hysteresis heating in rolling contact of rubber covered rollers

Abstract

In a previous paper, an approximate model for the contact between a rubber covered roller and a rigid roller was developed as analytical functional relationships connecting geometric parameters and material properties of the rubber to nip properties such as maximum contact pressure, etc. in a two-dimensional relationship. The results from that development are used in this work, with the objective to provide a means of estimating the temperature rise due to hysteresis heating. In the heat conduction modelling, one-dimensional steady state heat conduction is assumed. The heat source is a power input coming from internal friction developed during the rolling contact. The power input is expressed by the hysteresis in the rubber represented by a loss angle of the material together with the peripheral speed and some parameters taken from the previously developed contact model. The temperature distribution is calculated in accordance with temperature and heat flow boundary conditions.     

Non-linear mechanical behaviour of carbon black reinforced elastomers: experiments and multiscale modelling

Abstract

Antivibrating parts in automotives are often made of natural rubber reinforced by carbon black. This reinforcement, which comes from the filler–filler and filler–rubber interactions, leads to an increase in the elastic modulus, the tensile strength and the hysteresis. The aim of this work is to develop a micromechanical model within a generalised self-consistent scheme for filled rubber in the moderate elongation range (|?|≤0·5). A complex morphological pattern, representative of the microstructure of the material, and which takes into account the occluded rubber, the bound rubber and a percolating network, is proposed and the effective elastic properties are compared with experimental results obtained in both uniaxial and oedometric compression. The influence of the specific surface of the filler is investigated, using N330 and N650 carbon blacks. The model is extended to the non-linear accommodation of the stress heterogeneities between the phases. Model predictions are compared with experimental values in compression and simple shear.     

Evaluation of compounding techniques for optimising sealing performance of nitrile rubber vulcanisates

Abstract

The minimisation of viscoelastic effects, which give rise to creep, stress– relaxation, hysteresis, and set in elastomers, is highly desirable in engineering applications, particularly in sealing applications. Natural rubber is an important engineering material and as such much work has been carried out to minimise the above properties in an attempt to enhance service life. Consequently, a diverse range of compounding techniques is available for natural rubber. These techniques have been utilised in nitrile rubber mixes primarily in an attempt to minimise compression stress–relaxation and compression set along with other properties, which are considered pertinent to elastomeric materials used as seals and gaskets exposed to hydrocarbon liquids and vapours. The way in which these compounding techniques affect network structure and thus various sealing properties in nitrile rubber vulcanisates is discussed in terms of crosslink concentration, crosslinking efficiency, and mean apparent sulphur rank of crosslinks.     

Measurement and modelling of hollow rubber spheres: surface-normal impacts

Abstract

The performance of natural rubber sports balls under impact conditions is dominated by the material's behaviour under high strain rate conditions dictated by the impact velocity and ball dimensions. To design improved products, sports ball manufacturers need to better understand the physical phenomena associated with ball impact against both rigid and deformable surfaces. This understanding will provide the foundation for performance prediction and optimisation design tools as well as more appropriate product and ultimately material testing techniques. Rebound characteristics of pressurised and pressureless tennis balls and their respective rubber cores subject to normal impacts are presented for a range of incident velocities. High-speed video analysis has been used to measure coefficient of restitution, impact duration and 'whole ball' deformation to validate a surface-normal impact finite element method based predictive model as the first step towards a more comprehensive oblique impact model. Accounting for strain rate dependent stiffness and damping material properties has achieved close correlations between model predictions and observed impact behaviour. The propagation of dominant bending and hoop-strain waves through the ball during the impact is revealed to illustrate the methodology's effectiveness in predicting ball performance associated with difficult to observe impact phenomena.     

Studies on thermal–oxidative degradation behaviours of raw natural rubber: PRI and thermogravimetry analysis

Abstract

Thermal–oxidative degradation behaviours of raw natural rubber (NR) have been investigated by using thermogravimetry analysis in inert and oxidative atmospheres and the plasticity retention index (PRI). The activation energy E_a, was calculated using Horowitz–Metzger and Coats–Redfern methods and compared with PRI. The E_a values obtained by each method were in good agreement with each other. The June samples are the least stable rubbers among the studied ones, whereas February samples exhibited the highest values of activation energy, therefore in agreement with the PRI behaviour, which indicates that the thermo-oxidative stability of the June samples are the poorest during the thermo-oxidative degradation reaction. Natural rubber is a product of biological origin, and thus these variations in the values of thermal behaviour and PRI might be related to the genetic differences and alterations of climatic conditions that act directly on the synthesis of non-rubber constituents, which are generally reflected in latex and rubber properties.     

Autoclaved aerated concrete waste (AACW): An alternative filler material for the natural rubber industry

Material waste from the production of autoclaved aerated concrete, a porous material, should be considered as a valuable byproduct for use as a filler material for the rubber industry. Natural rubber (NR) composites filled with different loading (over the range of 0–60 phr) of autoclaved aerated concrete waste (AACW) as a new eco‐friendly material were produced using two roll mills and then were studied for their cure characteristics, mechanical and aging properties, and morphology, and also compared with commercial fillers, calcium carbonate (CaCO₃), and silica (SiO₂). In most cases, the cure characteristics and mechanical and aging properties of the SiO₂‐filled NR composites were significantly better than those of the AACW‐ and CaCO₃‐filled NR composites. However, these properties for AACW‐filled composites appeared to be higher than CaCO₃‐filled composites. The reason for this could be due to a larger surface area which is both porous and of an irregular shape of the AACW filler used. Scanning electron microscope images showed that the morphology of the rubber filled with SiO₂ was finer and more homogenous compared with the rubber filled with AACW or CaCO₃. Overall results revealed that the reinforcement ability of AACW‐filled NR composites was generally better when compared with CaCO₃‐filled NR composites; therefore, AACW can be used effectively as a cheaper filler for production of rubber products where end‐use properties of a rubber product is specifically required. POLYM. COMPOS., 36:2030–2041, 2015. © 2014 Society of Plastics Engineer     

Effects of interface reactions in compatibilised ground tyre rubber polypropylene elastomeric alloys

Abstract

Compounds of ground tyre rubber (GTR) and polypropylene (PP) were prepared in an internal mixer and characterised by means of mechanical, thermal and morphological testing. Only physical melt mixing could not provide a suitable interface compatibilisation and leads to compounds with poor mechanical properties. However, the application of a reactive melt mixing process, using organic peroxides as radical donators, was found to be suitable to initiate a compatibilisation reaction via interphase grafting. These compatibilised GTR/PP elastomeric alloy (EA) systems exhibit interesting mechanical properties which are close to that of conventional two phase thermoplastic elastomers (TPE) based on dynamically vulcanised ethylene propylene diene monomer (EPDM)/PP blends. Results of the morphology investigations substantiate the occurrence of a compatibilisation reaction between rubber particles and PP matrix during reactive mixing which is most probably responsible for the enhanced material properties of the GTR/PP EA.     

Advanced output of silicone molds in vacuum casting processes by polyamide 12 powder supplementation

ABSTRACT

Vacuum casting of polyurethane in silicone molds is a widely used method for prototype replication and holds great potential for application in small batch production. Products produced in this way offer extremely good shape accuracy even in the nanometer range and high surface quality, as well as flexible material properties that are convenient for serial production. In this work, we present a new method for increasing the feasible output of silicone casting molds in vacuum casting processes. By supplementation of polyamide 12 powder, which is a waste product of the selective laser sintering process, to the silicone rubber the maximum output of the casting molds could be increased by up to 38.5% while the amount of new silicone used has been substituted by up to 20%. Both generic silicone samples and representative silicone molds have shown that with increasing polyamide content, aging characteristics decrease as the output increases. The improvement was quantified by comparative weight, hardness and thermogravimetric measurements. As surface energy and roughness measurements as well as extensive casting experiments have shown, the silicone surface and thus the product surface remains unimpaired.     

Predicting physico-mechanical properties of LLDPE and PDMS rubber blends using ANFIS-based model

Abstract

Blends of linear low density polyethylene (LLDPE) and poly dimethyl siloxane (PDMS) rubber have been identified as a promising material for cable insulation. The influence of processing parameters on the physico-mechanical properties of these blends has been investigated and the same has been optimised for preparing these blends. In practice, it is not possible to carry out several experiments to identify the relationship between the intermediate processing parameters and physical properties. To address this issue, the relationship between the processing parameters and the mechanical properties of the optimised LLDPE and PDMS rubber blends have been mapped using a non-linear system identification technique namely, adaptive-network-based fuzzy inference system (ANFIS) without carrying further experiments, but with the available experimental data. In this model, the effect of the number of fuzzy rules on the model performance has been investigated to predict the properties and to correlate the above relationship. This paper reports the development of ANFIS-based model for predicting the LLDPE/PDMS rubber blends in reducing the experimental trials and its success over the ANN model.     

煤矿井下用阻燃导静电橡胶制品的研制

本文根据阻燃导静电橡胶制品的特性,概述胶料、阻燃剂、导静电剂的选择原则及选用,介绍普通胶料,橡塑并用胶料的生产工艺,产品性能。     

Mechanical and Processing Properties of Polystyrene-(Styrene Butadiene) Blends

Abstract

Blends of Polystyrene-(Styrene Butadiene) rubber copolymers were prepared in a twin screw extruder and then injected. The samples were characterized by various techniques and their properties compared to those of a sample with 0% rubber content. The results show that the morphology of the segregated phases in the blends as well as the chemical architecture of the rubber phase have a definite influence on the mechanical and rheological properties of these materials.     

Mechanical Properties of Impact i-PP/CSM Rubber Blends

ABSTRACT

The impact strength and the tensile behavior of an impact grade of isotactic polypropylene (impact i-pp)/chlorosulfonated polyethylene (CSM) rubber blends are studied at the CSM rubber concentrations 0 to 23.4 vol%. The impact strength, which increased with CSM rubber concentration, has been analyzed on the basis of the interphase adhesion and crazing mechanisms. Tensile modulus and strength decreased whereas breaking elongation increased with increase in CSM rubber content. Predictive models have been used to explain the tensile modulus and strength properties. Scanning electron microscopy has been employed to study the phase structure.     

Temperature and frequency dependent rheological behaviour of carbon black filled natural rubber

Abstract

The temperature and frequency dependent viscoelasticity of carbon black filled rubber is investigated. Temperature sweep and frequency sweep dynamic mechanical analysis tests are performed to investigate the frequency dependent glass transition temperature and to identify the thermorheological nature of the material. The test results show that master curves of dynamical properties can be constructed by horizontal shifts along the frequency axis alone and cover a frequency range of 21 decades, verifying the material’s thermorheological simplicity. This simplicity is confirmed by van Gurp–Palmen and Cole–Cole plots. Moreover, the temperature dependence of the shift factor is modelled well by both the Williams–Landel–Ferry equation and the Arrhenius equation.     

Polymer - phyllosilicate nanocomposites for high-temperature structural application

ABSTRACT

The increasing demand for more weight efficient material systems has called upon for the development of polymer composites for various applications where special properties are anticipated like thermo-physical resistance, bio-compatibility, anti-bacterial, electromagnetic characteristics etc. In recent years, polymeric materials have been explored with wide range of additives to optimize the overall performance of the final composite product. In this review, the authors have tried to comprehend the effect of such modification especially by layered silicates on the mechanical properties and design compatibility of the material.     

Microscopic mechanism of multiaxial fatigue of vulcanised natural rubber

Abstract

Fatigue tests were conducted on two kinds of vulcanised natural rubber with different formulas under uniaxial and multiaxial loading. The results reveal that interfacial adhesion of material A is better, and compared with material B, fatigue life of material A is longer. Under the same engineering strain amplitude, lower fatigue life under tension-torsion non-proportional loading is due to the increase in total hysteresis energy in the torsional direction. Scanning electron microscopy analysis showed that fatigue failure is related to ligaments breakage for material B, while cavitation induced by the decohesion between zinc oxides and rubber matrix is the main cause of the fatigue damage for material A.     

Elastomeric and electrically conductive materials on basis of thermoplastic elastomers and their controlled manufacturing

Abstract

The present work presents a possibility to produce a rubber elastic and electrically conductive polymer material on the basis of dynamic vulcanisates. Thanks to the specific morphology of dynamic vulcanisates and the non-uniform carbon black distribution, carbon black filled dynamic vulcanisates can exhibit a very low percolation threshold of ～4 wt-%. Keeping the carbon black content low, a broad spectrum of resistivity properties can be achieved by variation of material factors like type and content of rubber phase and filler, concentration of cross-linking agent and compatibiliser and technological factors like mixing time respectively. In comparison with thermoplastic elastomers on the basis of block copolymers dynamic vulcanisates show a distinct lower percolation threshold. Up to a carbon black content of ～10 wt-% the mechanical properties of carbon black filled dynamic vulcanisates are not negative influenced essentially. To characterise the development of the carbon black dispersion and distribution processes and the conductivity properties in an internal mixer, the method of online measured electrical conductivity is suited very well for carbon black containing rubber mixtures. It could be shown in pre-investigations that this method promises to be a very useful tool for monitoring the mixing processes of carbon black filled dynamic vulcanisates in continuous mixing processes by means of extruders too.     

Dynamic reaction inside co‐rotating twin screw extruder. I. Truck tire model material/polypropylene blends

Waste ground rubber tire (WGRT) is a complex composite containing various elastomers, carbon black, zinc oxide, stearic acid, processing oils, and other curatives. Most of the waste ground rubber tire is composed of mainly natural rubber (NR) and styrene butadiene rubber (SBR) in varying proportions. Blending it with other thermoplastic materials is difficult due to the inherent thermodynamic incompatibility. But, the compatibility can be increased by making the reactive sites in WGRT with suitable chemicals under optimum condition of shearing inside a twin screw extruder and it is said to undergo a dynamic reaction inside the extruder. To understand the mechanism of dynamic reaction process of a rubber/polyolefin blend, the blending of a truck tire model material rubber with polyolefin was first tried before it was applied to waste WGRT material. It was observed that the blends of a truck tire model rubber material and PP thermoplastic are physical mixture of two incompatible polymers in which a continuous plastic phase is largely responsible for the tensile properties. The rubber particles are the dispersed phase. The large particle size and the poor adhesion of these rubber particles are believed to be liable for the poor tensile properties. In case of blends of truck tire model material with isotactic polypropylene the tensile properties are found to be lower than that of its PP‐g‐MA counterpart which can be attributed to the reaction of the MA with the carbon black particles. A schematic representation of the possible interactions has been proposed. The effect of addition of compatibilizers such as SEBS and SEBS‐g‐MA has also been studied. The tensile and TGA studies indicate that the polarity of SEBS and SEBS‐g‐MA induces an increase in the performance characteristics for both types of polyolefins but the intensity of this increase is higher in the PP‐g‐MA based blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 106: 3193–3208, 2007     

High-Elastic Blood Compatible Material

Abstract

Materials with unique complex of the properties of elasticity and tensile strength processed from the natural rubber latex (NRL) were modified to improve their blood compatibility. ESCA, ATR-IR, UV-spectroscopy and other methods were used for appraisement of the grade of modification, structure and properties of material. Thromboresistancy was studied in in vivo and ex vivo tests. It was shown that blood compatibility is raised after thorough purification of the material from non-rubber components by means of two-stage extraction changing the physical-chemical parameters of the surface. Two different principles were used in the process of modification: 1) coating by thin polyurethane (PU) coverings with improved thromboresistant properties-thus the problem of providing high adhesion interaction of covering with the latex base was solved; 2) heparin surface immobilization-higher efficiency of modification of latex material in gel-form without preliminary protein adsorption was shown. Modification allows to increase blood compatibility of the latex materials preserving at the same time their elasticity and tensile strength.     

Effect of epoxidised liquid natural rubber on nitrile/butadiene rubber based mixes

Abstract

Epoxidised liquid natural rubber (ELNR) constitutes a new family of polymers chemically derived from natural rubber. It is a highly viscous rubber of low molar mass generally used as plasticiser or processing aid, especially during processing of natural rubber and styrene/butadiene rubber stocks.

The effect of incorporating this polymer rather than a standard plasticiser in a nitrile/butadiene rubber based mix has been investigated. The retention in mechanical properties following air and oil aging of the vulcanisates was also studied. Satisfactory processability of compounded stocks, mechanical properties, and aging resistance was maintained following incorporation of ELNR into nitrile/butadiene rubber formulations even at the lowest plasticiser concentrations. The improvement in aging behaviour was more pronounced when 25 mol-% ELNR was used at concentrations above 15 pphr.     

在橡胶加工设备中制备溴化丁基橡胶

选用无溶剂的本体法,以N-溴代琥珀酰亚胺与少量丁基橡胶(IIR)和稳定剂的预混物为溴化剂,在橡胶加工设备中对IIR进行化学改性,制备溴化丁基橡胶(BIIR)。通过红外光谱、核磁共振氢谱对产物BIIR的结构进行分析,并考察反应时间、温度和溴化剂用量等对BIIR硫化特性和物理性能的影响。结果表明:采用该方法可以制得BIIR,没有观察到腐蚀设备的情况,产物BIIR的硫化速率相比原料IIR有明显提高,硫化特性和物理性能达到了商品BIIR的水平;溴化反应温度应在60~100℃范围内,在所考察的范围内,溴化剂用量和反应时间对BIIR的硫化特性和物理性能影响不大。