The Effect of Oil‐Extension on the Properties of TPI and TPI/SBR Vulcanizates

Trans‐1,4‐polyisoprene (TPI) with a Mooney viscosity of 120 was filled with 37.5 phr aromatic oil to prepare oil‐extended trans‐1,4‐polyisoprene (OETPI) by a dry oil‐extending process. The curing characteristics of TPI gum, OETPI gum, and TPI/SBR compounds were studied and the mechanical properties of vulcanizates were also investigated. The experimental results showed that the Shore A hardness, Mooney viscosity, and mechanical properties of OETPI gum decreased, compared with that of TPI gum. The modulus at 100% elongation, Shore A hardness, and tensile strength of OETPI vulcanizates also decreased, while the abrasion loss, compression heat build‐up, and compression set increased. Compared with TPI/SBR, the dispersibility of carbon black in OETPI/SBR compounds was improved. The mechanical properties of OETPI/SBR vulcanizates changed little, while the wet skid resistance and fatigue resistance was greatly improved.     

Insights into the Reinforcement of Butyl Rubber by Carbon Black and Silica with the Aid of Their Dynamic Properties

Carbon black (N234) and silica (Vulksail N) with a silane coupling agent Si-69 were chosen as reinforcing fillers in butyl rubber (IIR). The rheological behavior of the IIR compounds and the dynamic mechanical properties of IIR vulcanizates were investigated with a rubber processing analyzer and dynamic mechanical analysis (DMA) to examine the filler dispersion in the rubber matrix and the interaction between filler and matrix. The data indicated that the N234 filled IIR compounds had more filler networks than those filled with silica. Filler networks first appeared at 30 phr N234 and 45 phr silica with silane coupling agent Si-69. The interaction between N234 and IIR was far stronger than that between silica and IIR. However, the silica Vulksail N filled IIR had better wet-grip and lower rolling resistance compared to the carbon black-filled IIR should IIR be chosen as a substitute of styrene-butadiene rubber (SBR) in tire tread. The reinforcing factor, R, R (related to the difference in tan d peak height at T_g for the filled and nonfilled rubbers), also demonstrated that the N234-IIR interaction was stronger than for the silica. IIR with 30 phr N234 exhibited the largest tensile strength, 20.1 MPa, for those vulcanizates examined. The tensile and tear strengths of N234 filled IIR were higher than those of IIR with similar amounts of silica. Thus, it was concluded that N234 is a more active reinforcing filler in IIR than silica (Vulksail N) even with a silane coupling agent (Si-69).     

Styrene Butadiene Rubber/Silicone Rubber Blends Filled With Dough Moulding Compound

Blends of styrene butadiene rubber (SBR)/methyl-vinyl silicone rubber (MVQ) filled with dough molding compound (DMC) were prepared and the effects of various amounts of the SBR, as a compatibilizer of MVQ and DMC, on the mechanical properties and the oxygen index of the DMC filled SBR/MVQ blends were investigated. Dynamic mechanical analysis (DMA) and infrared spectrum analysis (IR) of the DMC/SBR/MVQ blends were also investigated. The results showed that the mechanical properties of the DMC filled MVQ blends were improved when SBR was used as a compatibilizer; the best mass ratio was 60 phr (parts per hundred total rubber) DMC, 25 phr SBR and 75 phr MVQ. The volume electric resistivities of the DMC filled SBR/MVQ blends with various DMC mass ratios were all above 5.8?×?10¹² Ω?m; i.e., the electrical insulating property of the blends was excellent. Compared with the blends without DMC and the blends without SBR, the energy storage modulus and the peak area of the loss factor tan δ of the DMC reinforced SBR/MVQ blends were largest; the addition of DMC and SBR improved the thermal properties of the blends.     

Interactions Between an Ionic Liquid and Silica,Silica and Silica,and Rubber and Silica and Their Effects on the Properties of Styrene-Butadiene Rubber Composites

An investigation of the effect of an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMI), on the properties of silica reinforced styrene-butadiene rubber (SBR), aimed to correlate the interactions between the ionic liquid and silica, silica and silica, and silica and rubber with the macro-properties and microstructure of SBR and SBR/silica vulcanizates is described. The interaction between the ionic liquid and silica was characterized by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR), the interaction between silica and silica was characterized by a rubber processing analyzer (RPA), and the interaction between rubber and silica was characterized by the bound rubber content. The FTIR analysis revealed that BMI can react with the hydroxyl groups on the surface of silica, improving the compatibility between the rubber and silica. The RPA and bound rubber testing indicated that the interactions between silica and silica particles were weakened and the interaction between silica and rubber increased with the incorporation of BMI into the SBR rubber. The bound rubber content showed a maximum with a BMI content of 3 phr. At the same time, the dispersion of silica in SBR was improved with the incorporation of BMI. With the increase of BMI content, the curing rate was greatly improved and the crosslink density increased. BMI also increased the tensile strength and abrasion resistance of the SBR vulcanizates. Most important, the BMI significantly improved the dynamic properties of the rubber composites, especially the wet-skid resistance and rolling resistance. However, excessive BMI (beyond 3 phr) acted as a plasticizer and was detrimental to the mechanical properties, resulting in a decrease of tensile strength and abrasion resistance.     

Influence of Carbon Black on Crosslink Density of Natural Rubber

Vulcanization and reinforcement are two important factors contributing to the properties of vulcanized rubber. In order to investigate the influence of carbon black (CB) on chemical crosslinking, three groups of samples with different crosslink densities were prepared. In each group with the same crosslink density, different amounts of CB were introduced. Data fitting showed that delta torque (ΔM = M _H–M _L, the difference between the highest and lowest torques during curing) in the cure curves of each group had a good linear relationship with CB load and extrapolation of the fitting lines almost intercepted the x coordinate at the same value, which indicated that CB had no influence on the chemical crosslinking of the rubber. To verify the above result, a series of nonfilled natural rubber (NR) vulcanizates with different crosslink densities were studied using equilibrium swelling and the swelling ratios were compared with those of corresponding CB filled rubbers with the same sulfur and accelerator amount. The results of both the equilibrium swelling and NMR relaxation parameter measurements showed that CB filled vulcanizates had higher apparent crosslink densities than those of unfilled ones due to the strong interaction between rubber molecules and the surface of the CB particles. The swelling ratios of filled rubbers had a parallel relationship with those of the unfilled ones which indicated that CB had little influence on chemical crosslink density introduced by chemical vulcanization.     

Styrene Butadiene Rubber/Epoxidized Natural Rubber (SBR/ENR50) Nanocomposites Containing Nanoclay and Carbon Black as Fillers for Application in Tire-Tread Compounds

Nanocomposite vulcunizates based on a SBR/ENR50 (50/50%wt) rubber blend containing nanoclay (5 or 10 phr) with and without carbon black (CB 20 phr) were prepared by melt blending in an internal mixer. The compound containing 35 phr carbon black (only) was prepared as a reference sample. Microstructure of nanocomposite samples was investigated by using X-ray diffraction (XRD), melt rheo-mechanical spectroscopy (RMS), and scanning electron microscopy (SEM). The XRD patterns revealed that the distance between the clay layers were increased by adding CB to the nanocomposite samples; they caused better diffusion of chains between the layers and resulted in an intercalated structure. The RMS results also indicated the formation of the filler-filler networks. SEM images of fracture surfaces showed the presence of much roughness in the samples containing both nanoclay and CB compared to the other samples. The results obtained from application of the Flory–Rhener equation showed a high crosslink density for the sample with 10 phr nanoclay and 20 phr CB. Dynamic mechanical behavior, mechanical properties, and abrasion resistance of the nanocomposites were evaluated. The results indicated that the sample containing 10 phr nanoclay and 20 phr CB had an increased dynamic elastic modulus, reduced maximum loss factor (tanδ)_max,, and an improved tensile strength and abrasion resistance compared to the reference sample. Also, this sample showed the lowest maximum loss factor, at 50–60°C, so it can be a candidate for tire-tread application.     

Chemical hardness-based prediction of the surface tension and enthalpy changes of sublimation for alkali halides

A new theoretical route employing the concept of chemical hardness has been developed to predict the surface tension γ and the changes of the standard enthalpies (CSEs) of sublimation Δ_sH⁰ of alkali halides. The values of these quantities have been calculated by means of the ratios η_M/V^1/3_m where η_M and V_m are the molecular hardness and molecular volume, respectively. The obtained results have been compared with those of previous theoretical models as well as with experimental data.     

Study of stress-strain characteristics of SBR and blended NR/SBR rubber

The effect of temperature and carbon black (CB) on the mechanical characteristics of styrene-butadine rubber (SBR) and natural rubber (NR) was studied at various temperatures. The relation obtained between true stress and true strain for both types of rubber showed three regions at room temperature and two regions at high temperature. The optimum CB concentration was found to be 95 phr for the unblended samples as it increases the stiffness of the SBR rubber materials at a maximum value. It was also found that the addition of NR to SBR increases the elasticity in the plastic region. The activation energy at the fracture of SBR samples decreased from about 2.7×10^–20 to 1.8×10^–20 J while for the blended samples NR/SBR it increased from 8×10^–20 to 10.1×10^–20 J with increasing CB concentration.     

Influence of Crosslink Density on Mechanical Properties of Natural Rubber Vulcanizates

Crosslink density is an important structural parameter for cured rubber. Natural rubber (NR) vulcanizates with different crosslink densities were obtained through using different sulfur and accelerator amounts and different accelerator types. The crosslink density was characterized by an ¹ H-NMR technique and its influence on mechanical properties, such as Shore A hardness, 300% modulus, tensile strength, and elongation at break, of NR vulcanizates was investigated. The results showed that both the sulfur amount and the accelerator type and amount had an influence on the crosslink density of the NR networks. The relationship between total crosslink density and mechanical properties was also studied. The results, by changing either the sulfur or the accelerator amount, showed that tensile strength of NR vulcanizates reached maximum value when the total crosslink density was around 13.5 × 10^?5 mol/cm³, equivalently the average molecular weight of the intercrosslink chains (Mc) was around 7000 g/mol. The maximum value of tensile strength came from the balance between contributions of crosslink joints and stretch-induced orientation and/or crystallization of intercrosslink chains. The study on influence of total crosslink density on Shore A hardness and 300% modulus of NR vulcanizates showed that they both increased linearly with the crosslink density, the slopes were 2.7 ～ 3.0 cm³/10^?5 mol and 0.27 ～ 0.31 MPa cm³/10^?5 mol for Shore A hardness and 300% modulus, respectively, whether the crosslink density was varied by sulfur or accelerator.     

Prediction of ortho substituent effect in alkaline hydrolysis of substituted phenyl benzoates in aqueous acetonitrile

The second‐order rate constants k (dm³mol^?1s^?1) for alkaline hydrolysis of meta‐, para‐ and ortho‐substituted phenyl esters of benzoic acid, C₆H₅CO₂C₆H₄‐X, in aqueous 50.9% (v/v) acetonitrile have been measured spectrophotometrically at 25 °C. In substituted phenyl benzoates, C₆H₅CO₂C₆H₄‐X, the substituent effects log k_X ? log k_H in aqueous 50.9% acetonitrile at 25 °C for para, meta and ortho derivatives showed good correlations with the Taft and Charton equations, respectively. Using the log k values for various media at 25 °C, the variation of the ortho substituent effect with solvent was found to be precisely described with the following equation: Δlog k_ortho = log k_ortho ? log k_H = 1.57σ_I + 0.93σ°_R + 1.08E_s^B ? 0.030ΔEσ_I ? 0.069ΔEσ°_R, where ΔE is the solvent electrophilicity, ΔE = E_S ? E_H20, characterizing the hydrogen‐bond donating power of the solvent. We found that the experimental log k values for ortho‐, para‐ and meta‐substituted phenyl benzoates in aqueous 50.9% acetonitrile at 25 °C, determined in the present work, precisely coincided with the log k values predicted with the equation (log k^X)_calc = (log k^H_AN)_exp + (Δlog k^X)_calc where the substituent effect (Δlog k^X)_calc was calculated from equation describing the variation of the substituent effect with the solvent electrophilicity parameter, using for aqueous 50.9% CH₃CN the solvent electrophilicity parameter, ΔE = ?5.84. In going from water to aqueous 50.9% CH₃CN, the ortho inductive term grows twice less as compared with the para polar effect. Copyright © 2013 John Wiley & Sons, Ltd.     

Carbon Black–Filled Styrene Butadiene Rubber Masterbatch Based on Simple Mixing of Latex and Carbon Black Suspension: Preparation and Mechanical Properties

An improved process was developed for the production of carbon black (CB)–filled styrene butadiene rubber masterbatch (SBR-CB-MB) using a simple latex/CB mixing technology; the improvement comprised processing the CB as an emulsifier-free aqueous suspension by high-rate shearing. Tensile and tear strength, dynamic compression behaviors, the Payne effect, equilibrium swelling and bound rubber of the SBR-CB-MB and dry mixing CB filled SBR (SBR-CB-DM), covering a wide range of CB loading (45–70 phr), were investigated and compared. It was found that the tensile and tear strength, heat buildup and compression set, abrasion volume loss, and the Payne effect of the SBR-CB-MB were lower than those of the SBR-CB-DM, while the bound rubber content were higher, indicating good CB/rubber interaction in the SBR-CB-MB. SEM analysis showed that no free CB could be found on the surface or inside of the granular SBR-CB-MB particles, indicating good CB dispersion in the rubber matrix.     

类金刚石薄膜力学特性的分子动力学模拟

基于Brenner的REBO势函数,利用分子动力学方法模拟了含氢量不同的类金刚石薄膜的纳米压痕过程,依据得到的加载卸载曲线,计算了薄膜的刚度、硬度以及弹性模量.结果表明:类金刚石薄膜的硬度由氢含量和sp³键含量两个因素共同决定;当薄膜中氢含量小于39% 时,薄膜硬度主要取决于sp³键含量,sp³键越多,硬度越高;当薄膜中氢含量达到52%,薄膜硬度则显著下降,此时氢的作用占据主导地位. 关键词： 类金刚石薄膜 分子动力学模拟 纳米压痕 硬度     

Investigation on Three-Dimensional Solubility Parameters for Explanation and Prediction of Swelling Degree of Polydimethylsiloxane Pervaporation Membranes

Using polydimethylsiloxane (PDMS) as a basic matrix to prepare ethanol and butanol permselective pervaporation membranes is a vibrant field. Many studies have verified that the three-dimensional Hansen solubility parameters (HSP) theory offers a valid explanation for the swelling performance of ethanol and butanol in PDMS. Five parameters (δ_D, δ_P, δ_H, δ_t, and R_a) are defined in HSP theory which can be individually used to explain the interaction strength between a solvent and a polymer. However, for the above five parameters, which one is the most effective parameter for deciding the swelling degree still needs to be determined. In this study, a commonly used hydroxy-terminated PDMS precursor was adopted to prepare the PDMS network. The HSP of the chosen PDMS precursor was measured by an advanced “solubility-rating” method. The special software package HSPiP (4.1.03), purchased from the HSPiP team, was used to process the “solubility-rating” results. The equilibrium swelling degree (Q value) of the PDMS network in water, ethanol, butanol, and toluene was measured and the relationships between the five HSP parameters of the solvents and the logarithmic equilibrium swelling degree, log(Q), were discussed. It was found that the measured polar parameter, δ_P, of PDMS was 0.12 MPa^0.5. The measured hydrogen bonding parameter, δ_H, was larger than δ_P, attaining a value of 8.6 MPa^0.5, because the hydroxy groups directly contributed to the hydrogen bonding solubility parameter, δ_H. With respect to the relationships between log(Q) and δ_D, δ_P, δ_H, δ_t, and R_a, linear relationships existed after plotting log(Q) vs. δ_P and log(Q) vs. δ_H. The linear relation degree of the fitted lines was 0.995 and 0.989, respectively. Their standard deviations were 0.149 and 0.232, respectively. Therefore, a better linear relationship existed between log(Q) and δ_P than the other solubility parameters. This indicated that the polar interaction was the main effect for deciding the swelling degree of the PDMS network in water and alcohol systems.     

A diffusion model of chain-branching reaction of the explosive decomposition of heavy metal azides

A diffusion model of a solid-phase chain reaction of explosive decomposition of heavy metal azides was developed. The dimensional effects of initiation of the reaction were examined: the dependence of the critical fluence of initiation on the microcrystal size H(R) and on the irradiated zone diameter H(d). It was demonstrated that the diffusion model of the chain reaction closely describes the measured H(R) dependence at diffusion coefficients of D ∼ 0.2–0.3 cm²/s, values that correspond to experimentally measured mobility of electronic charge carriers of μ ∼ 10 cm²/(V s). To account for the measured H(d) dependence and the reaction front propagation velocity (V = 1.2 km/s), it is necessary that the diffusion coefficient be three orders of magnitude higher than the experimentally determined value. That the H(R) and H(d) dependences cannot be quantitatively described simultaneously is indicative of the underlying mechanisms of energy transfer being different.     

Bulk Viscous Bianchi Type I Barotropic Fluid Cosmological Model with Varying <Emphasis Type="Bold">Λ</Emphasis> and Functional Relation on Hubble Parameter

Bianchi Type I bulk viscous barotropic fluid cosmological with varying Λ is investigated. We have also assumed a functional relation on Hubble parameter as H(R)=a(R ⁻ⁿ +1), n>1, a>0, H the Hubble constant, R being scale factor and H = [(R)\dot]/RH = \dot{R}/R. The physical and geometrical aspects of the model related with astronomical observations are discussed.     

The concentration dependence of the proton chemical shift and the deuterium quadrupole coupling parameter for binary solutions of ethanol

Concentration dependent experimental measurements of the ethanol hydroxyl proton chemical shift σ_H for binary solutions were carried out. The solvents used were carbon tetrachloride (CCl₄), benzene, chloroform, acetonitrile, acetone and dimethylsulphoxide (DMSO). The chemical shift values range from 0.69 ppm (relative to TMS) for dilute ethanol (extrapolated to infinite dilution) in CCl₄ to 5.34 ppm for neat liquid ethanol. Ab initio calculations of the ethanol-solvent hydrogen bond energies show a correlation with the values for the chemical shift. The hydrogen bond energies for ethanol-solvent dimers range from 0.63 kcal mol^?1 for ethanol-CCl₄ to 9.34 kcal mol^?1 for ethanol-DMSO. Theoretical calculations show a linear correlation between the deuterium quadrupole coupling parameter XD ^ar d the isotropic proton chemical shift σ_H: X_D(kHz) = 291.48 ? 14.96 σ_H, where σ_H is the proton chemical shift in ppm relative to TMS (R ² = 0.99). Using the concentration dependent chemical shift data and this equation, X_D ia observed to range from 280 kHz for very dilute concentrations in CCl₄, where the primary species is ethanol monomer, to 210 kHz for the neat liquid that is comprised primarily of cyclic pentamers.     

Effect of montmorillonite on abrasion resistance of SiO2-filled polybutadiene

The effect of organically modified montmorillonite (OMMT) and silane coupling agent on the abrasion resistance of SiO₂-filled butadiene rubber (BR) vulcanizates has been investigated. Various amounts of OMMT are added into SiO₂-filled BR vulcanizates. A silane coupling agent, bis-(3-triethoxysilyl propyl) tetrasulfide (Si69), is used to modify OMMT during the masterbatch preparation for evaluating the influence of surface treatment on the abrasion resistance. Incorporation of OMMT into BR results in deterioration of the abrasion resistance as compared to unfilled BR vulcanizate due to poor dispersion of OMMT and insufficient interfacial adhesion between OMMT and BR matrix. The use of Si69 improves dispersion of OMMT particles and rubber/OMMT adhesion, resulting in abrasion resistance enhancement of BR/OMMT vulcanizates. By using similar compounding conditions as those for BR/OMMT vulcanizate, nanodispersion of OMMT in BR/SiO₂/OMMT vulcanizate has been achieved as judged by the high viscosity of the SiO₂-filled BR compound. This improved dispersion leads to better abrasion resistance of the BR/SiO₂/OMMT than that of the BR/SiO₂ composite. Utilization of Si69 slightly affects the DIN volume loss of BR/SiO₂/OMMT vulcanizates and the abrasion pattern.     

Wet Sliding Abrasion of Natural Rubber Composites Filled with Carbon Black at Different Applied Loads

The wet sliding abrasion and abrasion behavior of carbon black (CB)-filled natural rubber (NR) composites were investigated using a Deutsche Industrie Normen (DIN) abrader and compared to their dry abrasion resistance. The results showed that water tended to lubricate the contact between the rubber and the abrader and thus the abrasion loss was reduced. At different applied loads, the abrasion mechanism of the filled vulcanizates was different. When the applied load was below the turning point, the rubber abrasion was mainly fatigue abrasion and the main factor to influence the abrasion was the dynamic loss factor tanδ of the rubber. When the applied load was above the turning point, the rubber abrasion was mainly pattern abrasion and the main factors to influence the abrasion were the mechanical properties, in particular tensile and tear strength.     

Counting operator analysis of the discrete spectrum of some model Hamiltonians

The first step in the counting operator analysis of the spectrum of any model Hamiltonian H is the choice of a Hermitean operator M in such a way that the third commutator with H is proportional to the first commutator. Next one calculates operators R and R^† which share some of the properties of creation and annihilation operators, and are such that M becomes a counting operator. The spectrum of H is then decomposed into multiplets, not determined by symmetries of H, but by those of a reference Hamiltonian H_ref, which is defined by H_ref=H−R−R^†, and which commutes with M. Finally, we introduce the notion of stable eigenstates. It is shown that under rather weak conditions one stable eigenstate can be used to construct another one.