Techniques used for determining cure kinetics of rubber compounds

Controlling and assuring the quality of the manufacture of high precision engineering rubber components has led to the need to simulate fundamental industrial processes such as compression molding and injection molding using CAE tools. Both compression and injection molding techniques for the fabrication of rubber products involve crosslinking or vulcanization which is invariably assisted by temperature and pressure. Vulcanization is a chemical process and therefore its simulation necessarily involves characterization of kinetic parameters. The kinetics of curing or vulcanization is somewhat complex as it depends upon the compound formulation, temperature and in some cases pressure. The present paper reports and discusses the application and utility of different techniques for characterizing the cure behavior of rubber compounds. Kinetic data has been fitted to various mathematical models in order to see which of the models can best represent the crosslinking behavior of selected rubber compounds. Finally, the kinetic data is used to simulate the injection molding process for relatively simple geometries.     

Effect of rubber on properties of nylon-6/unmodified clay/rubber nanocomposites

Three nylon-6/unmodified clay/rubber nanocomposites with high toughness, high stiffness, high heat resistance and reduced flammability were studied in this paper, on basis of three compound powders of ultra-fine full-vulcanized powdered rubber (UFPR)/montmorillonite (UFPRM). It was found that all of the three UFPRs used in the study can help the silicate layers without organic treatment to be exfoliated in the nylon-6 matrix, despite some differences in compatibilities between them and nylon-6. Accordingly, the clay in different UFPRMs at the same loading content can lead to a similar improvement in stiffness and heat resistance of nanocomposites. In other words, UFPRs having different compatibilities with nylon-6 do not affect the stiffness and heat resistance of nanocomposites largely. However, the nylon-6 nanocomposites, modified with different UFPRMs, show different superior properties. Butadiene styrene vinyl-pyridine UFPRM (VP-UFPRM) is more effective in improving toughness of nylon-6. Nylon-6/silicone UFPRM (nylon-6/S-UFPRM) nanocomposite exhibits more reduced flammability, good flowability and high thermal stability. As for nylon-6/acrylate UFPRM (nylon-6/A-UFPRM) nanocomposite, it shows high toughness and thermal stability. Furthermore, the mechanism of unmodified clay exfoliation during the melt compounding and the effect of different UFPRs on the properties of the nylon-6/UFPRM nanocomposites are also discussed.     

Quantification of rubber in high impact polystyrene by Raman spectroscopy. Comparison of a band fitting method and chemometrics

An analytical method for the detection and the quantification of polybutadiene (rubber) in high impact polystyrene is described. The percentage of this product in high impact polystyrene pellets influences many of its properties, more the concentration is great, and more the mechanical resistance is high. The analytical method currently used to estimate the proportion of polybutadiene in high impact polystyrene pellets is nuclear magnetic resonance. Nevertheless, the application of Raman spectroscopy to polymers becomes more popular because of its sensitivity to the CC vinyl bond. This technique offers various advantages such as the absence of sample preparation. Raman spectroscopy is furthermore non destructive, and is a reproducible method. Information about conformations of polybutadiene can be easily accessible. Two different quantitative procedures were compared to evaluate which one is the best to estimate the percentage of polybutadiene in high impact polystyrene pellets. The first conventional method was based on the bands fitting of Raman spectra, and yielded a good prediction with a R² regression coefficient equal to 0.96. The second was based on chemometric techniques with a 0.98 − R². Consequently, others evaluation factors of the procedures such as the root-mean-square error, the bias, or the number of principal components must have some influence to select the most appropriate quantitative model.     

导电聚苯胺/橡胶复合材料的研究进展

聚苯胺是一种结构型导电高分子,因其特殊的结构和优异的物理化学性能,使它在二次电池、金属防腐、传感器、电容器、电磁屏蔽及抗静电等领域有着广泛而深入的应用前景。本文概述了导电聚苯胺的结构和特性,主要综述了聚苯胺/橡胶基复合材料的制备方法。其制备方法主要有共混法和聚合法,共混法主要有机械熔融共混法、溶液共混法和乳液共混法;聚合法主要包括电化学聚合、原位乳液聚合法、吸附聚合法等,总结了聚苯胺/橡胶基复合材料的研究情况及发展应用。     

Enhancing viscoelastic and mechanical performances of natural rubber through variation of large and small rubber particle combinations

There have been several reports investigating independent properties of large- (LRP) and small rubber particles (SRP). This work envisaged that, when co-existing, they could offer exceptional viscoelastic and mechanical properties from both components. Latex samples of various mixing ratios were prepared and properties of their rubber films were investigated against those of pure LRP and SRP to find that those containing 10–30% SRP were the best in mechanical strength and elasticity. This could be due to the combination of stronger phospholipid linkages in the LRP and void-filling ability of the SRP. The presence of SRP was shown to enhance curability in the vulcanised samples resulting in better mechanical performance of the vulcanisates. The 70/30 (LRP/SRP) blend showed the best thermal aging resistance among the vulcanisates. This suggested that the mixing ratios of the LRP and SRP contents were tunable to improve desirable properties of rubber products of interest, both green and cured.     

A Study on the Ballistic Performance of Composites

The mechanical behaviour and ballistic performance of carbon, glass (E and S type), aramid and polyethylene fabric reinforced composites with different epoxy resins were studied. The specimens – produced by hand lay-up method – were characterized by low velocity (Charpy and drop-weight tests) and high velocity (two different calibre ballistic) impact tests. The energy absorption capacity of the composites was found to be strongly affected by the material properties of the reinforcing fiber, by the type of fabric structure and by the elasticity of resin.     

微波消解-原子吸收光谱法测定橡胶及其制品中镉

建立了橡胶及其制品中镉含量的快速测定方法. 样品采用微波消解, 消解溶液中的镉用火焰原子吸收光谱法测定. 方法的检出限为2.5 mg/kg, 多种代表性橡胶及其制品的镉元素回收率在101.6%～104.4%之间. 对某含镉橡胶样品的10个实验室3次平行测定的结果表明实验室内和实验室间的相对标准偏差分别1.8%和8.2%. 方法适用于各种橡胶材料中镉的快速分析.     

The effect of alkanolamide loading on properties of carbon black-filled natural rubber (SMR-L), epoxidised natural rubber (ENR), and styrene-butadiene rubber (SBR) compounds

The effect of Alkanolamide (ALK) loading on properties on three different types of carbon black (CB)-filled rubbers (SMR-L, ENR-25, and SBR) was investigated. The ALK loadings were 1.0, 3.0, 5.0 and 7.0 phr. It was found that ALK gave cure enhancement, better filler dispersion and greater rubber–filler interaction. ALK also enhanced modulus, hardness, resilience and tensile strength, especially up to 5.0 phr of loading in SMR-L and SBR compounds, and at 1.0 phr in ENR-25 compound. Scanning electron microscopy (SEM) proved that each optimum ALK loading exhibited the greatest matrix tearing line and surface roughness due to better rubber - filler interaction.     

Effect of CTBN rubber inclusions on the curing kinetic of DGEBA-DGEBF epoxy resin

The curing kinetics of an epoxy resin matrix, based on diglycil ether of bisphenol A and F (DGEBA-DGEBF), associated with an anhydride hardener, at different carboxyl-terminated copolymer of butadiene and acrylonitrile liquid rubber (CTBN) concentration (0-10 phr) are studied using a differential scanning calorimetry (DSC) and a stress-controlled rheometer in isothermal and dynamic conditions. The aim of this work is to correlate the presence of the rubber phase with the transition phenomena that occur during the curing process. The CTBN rubber induces a catalytic effect on the polymerization of the pure resin clearly observed by a significant enhancement of the curing rate. Calorimetric and rheological analysis also evidences that gelation and vitrification times take place not punctually but in a wide range of time. Rheological data show that the presence of rubbery phase induces a higher rate of gel formation during the early stages of the reactions, confirming the calorimetric results. Finally the results are compared with theoretical models evidencing a good fitting between experimental and predictive data.     

An energy dissipation approach on complete loading-unloading and dynamic impact predictions with experimental verification for rubber anti-vibration component

Accurate evaluations of a completed loading-unloading cycle and dynamic impact response for rubber anti-vibration components have been very challenging for industry over many years. In this article, we have altered the classic hyperelastic models to predict complete loading-unloading response using an energy dissipation approach. In addition, we proposed NFR (Natural Frequency Region) approach to simulate a dynamic impact event instead of using the usual viscoelastic methodology, as results from different viscoelastic models may vary widely and to avoid complex parameter fitting procedures. The proposed approaches have been validated in laboratory experiments using industrial anti-vibration components. We have also detailed a procedure for engineers to implement this approach in commercial finite element software without writing intricate user subroutines, as simulation based on finite element method has been routinely used in industry to support design of new products. It is suggested that these methodologies could be used for a design stage in engineering applications.     

A novel method for contact analysis of rubber and various surfaces using micro-computerized-tomography

The experimental analysis of the contact state in a tribosystem is of great importance in the study of contact mechanics. In order to make a realistic analysis on the micro scale, it is desirable to keep the tribosystem unperturbed, i.e., without any surface treatment or incorporation of a third body to facilitate the analysis. This study presents the use of a novel technique, micro-computerized tomography (micro-CT), in the investigation of contact between rubber compounds and various counter-surfaces. The goal of this study was to further advance the use of micro-CT in contact mechanics. Specific image analysis techniques were developed in order to process micro-CT images of contact pairs formed by rubber compounds of different hardness levels against counter-surfaces with varying surface roughness and mechanical properties. The micro-CT method has been shown to allow the direct visualization and precise quantification of the real area of contact without altering the original characteristics of the contact pair.     

Nanocomposites based on chloroprene rubber: Effect of chemical nature and organic modification of nanoclay on the vulcanizate properties

The effect of two chemically opposite type of nanofillers, namely montmorillonite (MMT) and layered double hydroxide (LDH), both in pristine and organically modified forms (OLDH and OMMT) on the mechanical properties and crystallization behavior of chloroprene rubber (CR) vulcanizates have been investigated. While the addition of very small amount of pristine clays shows a significant improvement of the physical properties of the CR based nanocomposites, the organic modification improves the reinforcing efficiency of MMT more than that of LDH. MMT is found to enhance the crystallization tendency of CR chains, whereas LDH has a role to resist it as observed from the dynamic mechanical analysis (DMA). The DMA results also show that the presence small amount of nanoclay enhances the storage modulus of CR based vulcanizates, which becomes more pronounced in case of organically modified clays, especially with OMMT. Finally, we report the ‘house of cards’ structure of exfoliated platelets of montmorillonite in the CR matrix which are produced by mechanical shear mixing.     

Fabrication of exfoliated graphite reinforced silicone rubber composites - Mechanical,tribological and dielectric properties

The effect of exfoliated graphite (EG) on the mechanical, tribological and dielectric properties of the silicone rubber (QM) composites has been systematically investigated and analysed. Morphological analysis of the composites helps to understand the interfacial interaction between the filler and the rubber matrix as well as wear mechanism respectively. An enhancement in the mechanical, tribological and dielectric properties was observed with an increase in filler loading and better performance was observed at 7 phr of filler loading. The improvement in performance is attributed to the better interaction between the QM chains and the EG layers as evident from the AFM and TEM analysis. It is also evident from the Kraus plot which supports the reinforcing effect of EG in QM matrix.     

Numerical prediction and experiment on rubber creep and stress relaxation using time-dependent hyperelastic approach

Rubber is an excellent material for anti-vibration components in industry with a long term service. However, its time-dependent behaviour is undesirable in engineering applications. This article presents an engineering approach to evaluate the time-dependent responses, i.e., creep and stress relaxation, for rubber anti-vibration components. A time-dependent damage function was introduced into hyperelastic models. This function can be expressed in three forms. A typical rubber product and a dumbbell specimen were selected to validate the proposed approach. It has been shown that the predictions obtained from this method are consistent with the experimental data. It has also been established that the time-dependent response of industrial products can be predicted based on the responses from simple specimens, e.g., dumbbell specimen. In addition, it is possible to obtain a creep response based on a relaxation response and vice versa (by changing K value only) using the proposed approach, which has also been observed experimentally in the literature. The proposed function can also be easily incorporated into commercial finite element software (e.g., Abaqus). It has been demonstrated that the proposed method may be used at an appropriate design stage. Finally, the readers can select one of the three forms presented to perform assessments on the time-dependent responses evaluations for rubber anti-vibration products.     

Natural rubber/styrene-butadiene rubber blends prepared by solution mixing: Influence of vulcanization temperature using a Semi-EV sulfur curing system on the microstructural properties

Blends of natural rubber (NR) and styrene-butadiene rubber (SBR) were prepared by solution mixing and vulcanized with sulfur and accelerator in a Semi-EV system at 433 K and 443 K in order to study the vulcanization kinetic and the influence of vulcanization temperature on final structure of the blends. The vulcanization kinetic studied through the variation in rheometer curves was analyzed using the Ding and Leonov model, which takes into account the reversion effect during the cure process. The average free nanohole volume and the fractional free volume of samples with different NR/SBR ratio were estimated using positron annihilation lifetime spectroscopy (PALS). Also, the crosslink density was determined by means of swelling tests in a solvent. For all the compounds, a correlation between the free nanohole volume and the delta torque obtained from the respective rheometer curves was established.     

微波萃取-GC/MS联用法测定橡胶及其制品中多环芳烃

建立了微波萃取-GC/MS联用法测定橡胶及其制品中16种多环芳烃(PAHs)的方法,通过实验优化了萃取溶剂、萃取时间、萃取温度等微波萃取条件和16种PAHs的分离和测定条件。用加标回收方法试验确定方法的准确度。结果表明:16种PAHs检出限(S/N=5)为0.002~0.01 mg/L,平均回收率为63.58%~100.5%,RSD为1.9%~9.9%。该方法可以满足橡胶及其制品中多环芳烃的检测要求。     

Rheological study on the cure kinetics of two-component addition cured silicone rubber

The cure kinetics for two-component silicone rubber formed by addition reaction was studied by the rheological method. The influence of reaction temperature (T) on the cure kinetics was explored in detail. It was observed that the data of gel time (t _gel, i.e. the time when the reaction reaches the gel point) or a specific reaction time (t _nc) (defined as the reaction time before which time the influence of confinement of network on the diffusion of reaction components can be neglected) versus T obey certain functional relationship, which was well explained by the cure kinetics model of thermoset network. The cure kinetics for the two-component silicone rubber can be well fitted by the Kamal-Sourour(autocatalyst) reaction model rather than Kissinger model. When the reaction time was before or equal to t _nc, the reaction order obtained by the Kamal-Sourour reaction model was 2, which was consistent with the reaction order inferred from the two components chemical reaction when the diffusion of reaction components was not influenced by the formed cross-linked polymer network. When the reaction time was larger than t _nc, such as to the end of reaction (t _e), the influence of confinement of network on the diffusion of reaction components cannot be neglected, and the reaction order obtained by the Kamal-Sourour reaction model was larger than 2. It was concluded that the confinement effect of network had a greater influence on the cure kinetics of the silicone rubber. The reaction rate constants (k _r) under different temperatures were also determined by Kamal-Sourour reaction model. The activation energy (E) for the two-component silicone rubber was also calculated from the results of lnt _gel, lnt _nc, and lnk _r versus 1/T, respectively. The three values of E were close, which indicated that above analyses were self-consistent.     

A molecular simulation study of the structure and tribology of polymer brushes: Comparison of behavior in theta and good solvents

Implicit solvent Brownian dynamics simulations of the structure and tribology of opposing polymer-brush covered surfaces have been carried out as a function of surface separation and solvent quality. Consistent with experiment, shear forces were found to be greater under theta solvent conditions than in a good solvent at equal relative separations (normalized by the respective height of the brushes in theta and good solvents). Much higher relative compression is required before the onset of significant shear forces in good solvent compared to theta solvent. The dependence of shear force for a given relative separation on solvent quality can be accounted for by differences in interpenetration of the brushes. When compared as a function of absolute surface separation, greater interpenetration and greater shear force are observed at large separations for the brushes in good solvent than in theta solvent, consistent with the greater brush height in good solvent. At shorter separations, corresponding to moderate to high compression, brush-brush interactions result in significant deformation of the brushes. In this regime, greater interpenetration and greater shear forces are observed in theta solvent at a given separation, in qualitative agreement with experiment.     

The correlation of tear deviation and resistance with the bound rubber content in rubber-silica composites

The tear strength (T_S) of rubber-silica composites is inevitably lowered by the reduction of viscoelastic dissipation imparted by the use of bifunctional silanes. It is of interest to find out whether promoting crack tip deviation represented by a slip-stick tearing can compensate for such a loss in the tear strength. Here, the phenomenon of crack growth in terms of the T_S and also the tearing type is considered for both the untreated and silane-treated silica rubber composites to figure out the microstructure parameters affecting the slip-stick tearing. It was realized that within a certain volume fraction of the reinforcing filler, deviation whether in the form of slip-stick or knotty tearing can be found for both cases. Tearing for silane-treated silica is more similar to a slip-stick tearing with an ordered pattern of deviation and re-initiation; whereas tearing in the composites with untreated silica is like a knotty one with random deviation and re-initiation. Interestingly, a dual role was identified between the bound rubber content and the tearing: on one hand, increasing the bound rubber directly augments the viscoelastic dissipation and the value of T_S, and on the other, it inversely suppresses the crack tip deviation. The second part of this work deals with applying strategies to promote crack tip deviation in treated silica systems. By increasing the degree of bonding at the rubber-silica interface and reducing the bound rubber, the tear deviation was successfully promoted. With a slip-stick type of tearing the crack had to proceed through a tortuous path, thereby enhancing the effective tear diameter and the subsequent tear strength. This roughening role of bound rubber is however insufficient to fully compete with the impact of bound rubber on the viscoelastic dissipation, and thus the decreased T_S of composites with treated silica cannot be totally compensated by this strategy.