Performance improvement of EPDM and EPDM/Silicone rubber composites using modified fumed silica,titanium dioxide and graphene additives

In this work, a polymeric composite was prepared from ethylene propylene diene monomer (EPDM) and silicone rubber (S) with additives of modified fumed silica (MFS), titanium dioxide (TiO₂) and graphene. The dielectric and thermal performances of the EPDM-based composites were studied. An increase in the dielectric constant and AC dielectric breakdown strength was observed for the EPDM rubber composites containing MFS, TiO_2, and graphene additives. In addition, the incorporation of the additives resulted7in a significant increase in the thermal stability (~30–50 °C) and thermal conductivity (~7–35%) of the composites. The combination of these various improvements gives suitable performance advantage to the polymeric composite for use in insulating applications.     

Thermogravimetric and wide angle X-ray diffraction analysis of thermoplastic elastomers from nylon copolymer and EPDM rubber

Nylon copolymer (PA6, 66) and ethylene propylene diene (EPDM) blends with and without compatibilizer were prepared by melt mixing using Brabender Plasticorder. The thermal stability of nylon copolymer (PA6, 66)/ethylene propylene diene rubber (EPDM) blends was studied using thermogravimetric analysis (TGA). The morphology of the blends was investigated using scanning electron microscopy (SEM). In this work, the effects of blend ratio and compatibilisation on thermal stability and crystallinity were investigated. The incorporation of EPDM rubber was found to improve the thermal stability of nylon copolymer. The kinetic parameters of the degradation process were also studied. A good correlation was observed between the thermal properties and phase morphology of the blends. By applying Coats and Redfern method, the activation energies of various blends were derived from the Thermogravimetric curves. The compatibilization of the blends using EPM-g-MA has increased the degradation temperature and decreased the weight loss. EPM-g-MA is an effective compatibilizer as it increases the decomposition temperature and thermal stability of the blends. Crystallinity of various systems has been studied using wide angle X-ray scattering (WAXS). The addition of EPDM decreases the crystallinity of the blend systems.     

EPDM/PP热塑性弹性体在循环应力下的老化行为研究

本文研究了动态硫化EPDM/PP热塑性弹性体的动态疲劳老化行为,考察了其力学性能的变化,并分析了产生力学性能下降的原因。实验结果表明,随着疲劳时间的延长、疲劳振幅的增大,材料的断裂强度降低,并认为疲劳过程中完全硫化的EPDM橡胶粒子和热塑性塑料PP界面处的分子链断裂、滑移导致了断裂强度的降低;紫外光的加入,加速了材料在疲劳过程的分子链断裂、滑移速率,使材料的断裂强度有更大程度的降低;在机械疲劳老化单独作用下,材料体系几乎没有发生氧化反应,而紫外光的加入,促使了机械疲劳老化过程中氧化反应的发生。     

The effect of p-tert-butylcalix[n]arene on γ-radiation degradation of polypropylene

The γ-radiation effect of polypropylene was investigated in the presence of three kinds of p-tert-butylcalix[n]arene (n=4, 6, 8) in air at ambient temperature. The influence of radiation dose and store time upon the mechanical properties of the irradiated PP sheets were measured. The results showed that the radiation stabilization was reduced with the increase of the ring size of calixarenes. Based on the mass spectra and the analysis of post-irradiated product, the mechanism of radiation degradation of p-tert-butylcalix[4]arene has been proposed.     

Synthesis of green CdSe/chitosan quantum dots using a polymer-assisted γ-radiation route

Chitosan-coated CdSe quantum dots (CdSe/CS QDs) were successfully synthesized in aqueous system through a γ-radiation route at room temperature under ambient pressure. The diameter of the resulting QDs was about 4 nm with narrow size distribution. The synthesized QDs exhibited an absorption peak at 460 nm and an emission peak at 535 nm. These QDs were cubic zinc blende CdSe in core structure and coated with chitosan on surface, with fine solubility in water.     

Significant effects of sodium acetate, an impurity present in poly(vinyl alcohol) solution on the radiolytic formation of silver nanoparticle

A silver nanoparticle (AgNPs) stabilizer, polyvinyl alcohol (PVA) generally contains a relatively large amount of sodium acetate (NaOAc) as an impurity (up to several weight percentages) as a result of a base-catalyzed hydrolysis of poly(vinyl acetate) (PVAc). In this study, the effects of NaOAc on the radiolytic formation of AgNPs in PVA solutions were studied by using UV/vis spectroscopy. Several AgNPs were prepared by γ-ray irradiation using ⁶⁰Co source at various doses in the presence of various amounts of NaOAc. The UV data of the AgNPs observed at around 410 nm show that more AgNPs are generally produced as the NaOAc concentration in the PVA solution increases. Furthermore, no significant absorption band of the AgNPs was observed when the purified PVA containing a very small amount of NaOAc (less than 3×10⁻⁴ M) was applied with 1×10⁻³ M AgNO₃ up to 10 kGy. These results reveal that NaOAc present as an impurity in PVA, plays an important role in the radiolytic formation of AgNPs.     

Accelerated aging and aging mechanism of acrylic sealant

One-component acrylic latex sealants with different moduli were subjected to accelerated aging tests, heat aging at different temperatures, xenon arc and UV exposure. The effects of various aging factors on sealant properties were studied by reviewing the appearance and mechanical properties. The aging mechanism was evaluated by thermal analysis, FTIR and solvent swell. The results show that a good relation exists among mechanical properties after aging; mild accelerated aging conditions and short aging times are enough to lead to obvious degradation of acrylic sealants with low modulus. Fillers with ingredients within high modulus may resist UV radiation effectively and enhance their durability but the quantity must be proper. The degree of chain breaking caused by UV is larger than that by heat aging. The study also shows that there are the same or similar aging mechanisms for different aging conditions and that the cure reaction by water volatilisation dominates the initial period of aging while degradation will be induced when aging time is longer and it can result in changes of molecular structure.     

Effect of Ionizing Radiation on the Characteristics of EPDM/UHMW-PE Composites

Ultra high molecular weight polyethylene (UHMW-PE) fibers were used in a chopped form and at different concentrations as a reinforcing material in ethylene–propylene–diene terpolymers (EPDM). The effect of radiation dose and fiber concentration on the mechanical properties of the vulcanized rubber composites obtained was measured. It was found that γ-irradiation improves the interfacial adhesion between UHMW-PE fiber (Spectra 1000) and EPDM matrix which was detected by scanning electron microscopy (SEM). In addition, the Young modulus of the composites increases as the irradiation dose increases. Increasing the concentration of the fibers up to 40 phr leads to an enhancement in mechanical properties and swelling resistance of obtained composites, especially in the absence of carbon black. The absolute value of the modulus increased by a factor of at least two with the addition of carbon black. Moreover the tear strength of reinforced and filled EPDM was improved with respect to reinforced rubber. © 1997 John Wiley & Sons, Ltd.     

The effect of gamma irradiation and particle size of CaCO3 on the properties of HDPE/EPDM blends

Mechanical blends formed of 50 wt% of high-density polyethylene (HDPE) and 50 wt% of ethylene–propylene–diene-monomer (EPDM) elastomer have been loaded with 50 wt% of three different particle size of CaCO₃, namely CaCO₃ 300, CaCO₃ 700, and CaCO₃ 2000 whereby the latter has the smallest particle size of ～311, 82 μm. Mechanical, physico-chemical and thermal properties were followed up as a function of irradiation dose for loaded and unloaded blends. The results obtained indicated that the values of tensile strength, tensile modulus at 50% elongation, gel fraction and decomposition temperature increase with increasing irradiation dose. On the other hand elongation at break, permanent set and swelling number were found to decrease with increasing irradiation dose. Moreover, the effect of particle size of CaCO₃ was observed in a limited but apparent upgrading of mechanical, physico-chemical, and thermal properties. The order of semi-reinforcing capacity of three different types of CaCO₃ is as follow: CaCO₃ 2000 > CaCO₃ 700 > CaCO₃ 300 > unloaded blend. Whereby CaCO₃ 2000 has the smallest particle size.     

New double negative and positive temperature coefficients of conductive EPDM rubber TiC ceramic composites

In this paper, we have successfully prepared ethylene-propylene-diene monomer (EPDM)/TiC composites as thermistors, with new double negative and positive temperature coefficients of conductivity (NTCC/PTCC). EPDM composites loaded with 50 phr HAF carbon black and different concentrations of TiC were prepared. This study focuses on the effect of TiC content on the vulcanization process, the network structure and the electrical and thermal properties of EPDM/TiC composites. The effect of TiC on the network structure was evaluated e.g. the curing process, the characteristic time constant during vulcanization, the volume fraction of rubber, gel fraction, interparticle distance between conductive particles, the extent of TiC reinforcement in the rubber matrix and molecular weight between cross-linking through experimental and affine-phantom models. The effects of TiC content on the percolation theory, electrical conductivity, conducting mechanism of conductivity, conducting hysteresis and I-V characteristics were also studied, as well as its TiC on the (NTCC/PTCC), thermoelectric power, dielectric constant and thermal conductivity. Stability and reproducibility of the thermal cycles for heating element applications was tested. Specific heat and the amount of heat transfer by radiation and convection as a function of TiC content was calculated using both the calorimetric technique and a theoretical model. It was proved that TiC improves the network structure, electrical and thermal properties of EPDM composites for practical applications.     

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.     

Cross-linking assessment after accelerated ageing of ethylene propylene diene monomer rubber

The ageing of filled and cross-linked ethylene propylene diene elastomer (EPDM) has been studied under accelerated UV irradiation (λ ≥ 290 nm) at 60 °C, thermal ageing at 100 °C and in nitric acid vapours for different time intervals. Hardness measurements were performed. DSC-thermoporosimetry was used to estimate the mesh size distribution and cross-linking densities for each ageing. The development of functional groups was monitored by ATR spectroscopy. An increase in oxidation with exposure time after the different types of ageing was observed. The thermal stability of EPDM was assessed by TGA and evolved volatile gases were identified using FTIR spectroscopy.     

NMR measurements of gaseous sulfur hexafluoride (SF6) to probe the cross-linking of EPDM rubber

The effects of embedding gaseous SF6 into EPDM rubber were investigated using NMR methods. It was found that observed sorption and desorption processes follow the behavior of the dual mode sorption model. A strong correlation was found between EPDM cross-linking and transversal relaxation time of embedded SF6. EPDM samples with different cross-link densities, preliminarily determined by 1H transversal relaxation using the Gotlib model and Litvinov's method, were investigated using embedded SF6. The sensitivity of the 19F transversal relaxation rate of SF6 to the EPDM cross-link density variation was found to be at least 10 times higher than for 1H in the polymer chain. First experiments on probing the swelling effects in EPDM due to its contact with polar liquids have been performed.     

Accelerated aging and lifetime prediction: Review of non-Arrhenius behaviour due to two competing processes

Lifetime prediction of polymeric materials often requires extrapolation of accelerated aging data with the suitability and confidence in such approaches being subject to ongoing discussions. This paper reviews the evidence of non-Arrhenius behaviour (curvature) instead of linear extrapolations in polymer degradation studies. Several studies have emphasized mechanistic variations in the degradation mechanism and demonstrated changes in activation energies but often data have not been fully quantified. To improve predictive capabilities a simple approach for dealing with curvature in Arrhenius plots is examined on a basis of two competing reactions. This allows for excellent fitting of experimental data as shown for some elastomers, does not require complex kinetic modelling, and individual activation energies are easily determined. Reviewing literature data for the thermal degradation of polypropylene a crossover temperature (temperature at which the two processes equally contribute) of 83 °C was determined, with the high temperature process having a considerably higher activation energy (107–156 kJ/mol) than the low temperature process (35–50 kJ/mol). Since low activation energy processes can dominate at low temperatures and longer extrapolations result in larger uncertainties in lifetime predictions, experiments focused on estimating E_a values at the lowest possible temperature instead of assuming straight line extrapolations will lead to more confident lifetime estimates.     

The photo-oxidation of EPDM rubber: Part III—Mechanistic aspects and stabilization

The kinetics of the photo-oxidation of crude EPDM rubber has been studied in order to propose a mechanism for the sequence of reactions which occurs during the photo-degradation process. The presence of the unsaturation markedly affects the kinetics of the photo-oxidation of EPDM in comparison with that of EPM. We have also studied the stabilization effect of a hindered amine and a hindered phenol on EPDM and compared this with crude EPM rubber. These stabilizers showed poor efficiency, which is explained by the presence of impurities which act as sensitizers for the degradation of the crude rubber.     

Stabilization Effects of Natural Compounds and Polyhedral Oligomeric Silsesquioxane Nanoparticles on the Accelerated Degradation of Ethylene-Propylene-Diene Monomer

In this work the analysis on the stabilization activities of some natural antioxidants (rosemary extract, capsaicin, quercetin or oleanolic acid) is presented. A similar contribution of an inorganic structure—polyhedral oligomeric silsesquioxane (POSS) nanoparticles—is also evaluated. The stabilization effects on the oxidation protection were investigated for several formulations based on ethylene-propylene-diene-terpolymer (EPDM). The samples were examined in pristine state or after γ-irradiation, when the accelerated degradation scission of polymer macromolecules followed by the mitigation of oxidation. Three evaluation procedures: chemiluminescence, FTIR spectroscopy and thermal analysis were applied for the characterization of stability efficiency. The delaying effect of oxidative aging in EPDM matrix is illustrated by the values of activation energy, which are correlated with the type and concentration of embedded compounds. The durability of studied EPDM formulations is discussed for the assessment of material life. The improved behavior of structured hybrids useful for the optimization application regimes is essentially based on the antioxidant properties of polyphenolic components in the cases of natural antioxidants or on the penetration of free radical intermediates into the free volumes of POSS.     

Deterioration of highly filled EPDM rubber by thermal ageing in air: Kinetics and non-destructive monitoring

The effects of air ageing at different temperatures between 110 and 170 °C on cable transit seals based on highly filled EPDM rubber used in nuclear power plants were studied. The changes of the macroscopic mechanical properties (Young's modulus, indentation modulus and strain-at-break) were in accordance with the Arrhenius equation with an activation energy of 110 kJ mol⁻¹. Profiling to assess the structure and property gradients within aged blocks was performed via IR spectroscopy, micro-indentation, gravimetric analysis of n-heptane-extracted samples and non-invasive portable NMR spectroscopy. A previously developed methodology was used to separate the deterioration into three different processes: polymer oxidation that was diffusion-limited at all temperatures, migration of low-molar-mass species to the surrounding media and anaerobic changes to the polymer network. The methodology allowed the assessment of the kinetics (rate as a function of time and temperature) of the different processes. It was noticed that polymer oxidation yielded more crosslinking at higher temperatures than at lower temperatures. The data obtained by both the portable NMR (a non-invasive method) and the indentation modulus profiling showed correlations with strain-at-break data, indicating their usefulness as condition monitoring methods.     

Aging behavior and mechanism of ethylene-propylene-diene monomer (EPDM) rubber in fluorescent UV/condensation weathering environment

Ethylene-propylene-diene monomer (EPDM) rubber was exposed to an artificial weathering environment produced by fluorescent UV/condensation weathering device for different time periods. The surface chemical changes were detected by X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy. The plausible aging mechanism of EPDM was proposed. The surface energy was calculated through contact angles of water and formamide measured by optical contact angle measuring device. The thermal stability was evaluated by thermo-gravimetric analysis (TGA).The results showed that oxygenated species such as C-O-C, CO and O-CO groups were formed in fluorescent UV/condensation weathering environment. EPDM aging occurred from EPDM surface and propagated to EPDM inner body. The surface energy of EPDM increased to a maximum at 36 days of aging and then decreased slowly. Fluorescent UV/condensation weathering environment does not affect the thermal stability of EPDM predominantly.     

Studies on Hydroiodination and Deconjugation of 5—Aryloxy—（thiophenyl）—3—pentyn—2—one

One-pot hydroiodination and deconjugation of 5-aryloxy(or thiophenyl)-3-pentyn-2-one with a reagent system of sodium iodide/trimethylsilyl chloride/water in acetonitrile at 25℃ have been described.The plasuible mechanism was discussed.The reaction provided a simple and useful method for the preparation of (Z)-β-substituted β，γ-enones and (Z)-β-substituted α，β-unsaturated ketones.