Photo-, thermal and natural ageing of ethylene–propylene–diene monomer (EPDM) rubber used in automotive applications. Influence of carbon black, crosslinking and stabilizing agents

Thermal Oxidative Aging and Service Life Prediction of Commercial Ethylene-Propylene-Diene Monomer Spacer Damping Composites for High-Voltage Transmission Lines

The aging behavior and life prediction of rubber composites are crucial for ensuring high-voltage transmission line safety. In this study, commercially available ethylene-propylene-diene monomer (EPDM) spacer composites were chosen and investigated to elucidate the structure and performance changes under various aging conditions. The results showed an increased C=O peak intensity with increasing aging time, suggesting intensified oxidation of ethylene and propylene units. Furthermore, the surface morphology of commercial EPDM composites displayed increased roughness and aggregation after aging. Furthermore, hardness, modulus at 100% elongation, and tensile strength of commercial EPDM composites exhibited a general increase, while elongation at break decreased. Additionally, the damping performance decreased significantly after aging, with a 20.6% reduction in loss factor (20 °C) after aging at 100 °C for 672 h. With increasing aging time and temperature, the compression set gradually rose due to the irreversible movement of the rubber chains under stress. A life prediction model was developed based on a compression set to estimate the lifetime of rubber composites for spacer bars. The results showed that the product's life was 8.4 years at 20 °C. Therefore, the establishment of a life prediction model for rubber composites can provide valuable technical support for spacer product services.

Filler Influence on H2 Permeation Properties in Sulfur-CrossLinked Ethylene Propylene Diene Monomer Polymers Blended with Different Concentrations of Carbon Black and Silica Fillers

Filler effects on H₂ permeation properties in sulfur-crosslinked ethylene propylene diene monomer (EPDM) polymers blended with two kinds of carbon black (CB) and silica fillers at different contents of 20 phr–60 phr are investigated by employing volumetric analysis in the pressure exposure range of 1.2 MPa~9.0 MPa. A linear relationship is observed between the sorbed amount and pressure for H₂ gas, which is indicative of Henry’s law behavior. The hydrogen solubility of EPDM composites increases linearly with increasing filler content. The magnitude of hydrogen solubility for the filled EPDM composites is dependent on the filler type. The hydrogen solubility is divided into two contributions: hydrogen absorption in the EPDM polymer and hydrogen adsorption at the filler surface. Neat EPDM reveals pressure-dependent bulk diffusion behavior. However, with increasing filler content, the diffusivity for the filled EPDM composites is found to be independent of pressure. The magnitude of filler effects on the hydrogen permeation parameter is measured in the order of high abrasion furnace CB~semireinforcing furnace CB ˃ silica, whose effect is related to the specific surface area of CB particles and interfacial structure. The correlation between the permeation parameters and filler content (or crosslink density) is discussed.

Off-line analysis in the manganese catalysed epoxidation of ethylene-propylene-diene rubber (EPDM) with hydrogen peroxide

The epoxidation of ethylene-propylene-diene rubber (EPDM) with 5-ethylidene-2-norbornene (ENB) as the diene to epoxidized EPDM (eEPDM) creates additional routes to cross-linking and reactive blending, as well as increasing the polarity and thereby the adhesion to polar materials, e.g., mineral fillers such as silica. The low solubility of apolar, high molecular weight polymers in the polar solvents constrains the catalytic method for epoxidation that can be applied. Here we have applied an in situ prepared catalyst comprising a manganese(ii) salt, sodium picolinate and a ketone to the epoxidation of EPDM rubber with hydrogen peroxide (H₂O₂) as the oxidant in a solvent mixture, that balances the need for polymer and catalyst/oxidant miscibility and solubility. Specifically, a mixture of cyclohexane and cyclohexanone is used, where cyclohexanone functions as a co-solvent as well as the ketone reagent. Reaction progress was monitored off-line through a combination of Raman and ATR-FTIR spectroscopies, which revealed that the reaction profile and the dependence on the composition of the catalyst are similar to those observed with low molar mass alkene substrates, under similar reaction conditions. The combination of spectroscopies offers a reliable method for off-line reaction monitoring of both the extent of the conversion of unsaturation (Raman) and the extent of epoxidation (FTIR) as well as determining side reactions, such as epoxide ring opening and further, aerobic oxidation. The epoxidation of EPDM described, in contrast to currently available methods, uses a non-scarce manganese catalyst and H₂O₂, and avoids side reactions, such as those that can occur with peracids.

Epoxidation of ethylene-propylene-diene rubber (EPDM), based on 5-ethylidene-2-norbornene, to epoxidized EPDM (eEPDM) opens routes to cross-linking and reactive blending, with increased polarity aiding adhesion to polar materials such as silica.

Natural Aging of Ethylene-Propylene-Diene Rubber under Actual Operation Conditions of Electrical Submersible Pump Cables

Ethylene-propylene-diene monomer (EPDM) rubbers used in electric submersible pump (ESP) cables were analyzed after being aged in actual operation conditions in oil wellbores. These rubbers constitute the insulation and jacket layers of the ESP cables. EPDM rubbers from four different cables operating during different time intervals (2 and 4.8 years) at different depths (from 760 to 2170 m) below sea level were studied. To verify the effects of the long exposure on the rubber performance, thermal analysis was performed to determine the thermal stability and activation energy of degradation. In addition, structural analysis, through vibrational spectroscopy and crosslinking fraction assessment, was carried out. The mechanical properties of the aged rubbers were inferred through the measurement of hardness, while the absorption of a service fluid was studied by gravimetry. The results showed only minor changes in the thermal, structural, mechanical and barrier properties of the EPDM-based ESP cable layers. It is suggested that the thermo-oxidation mechanism followed by chain scission does not have a role in the degradation of EPDM within the aged ESP cables, and no sign of variation of crosslink fractions has been encountered. Therefore, it was concluded that EPDM-based layers seem not to be weak links in the configuration of modern ESP systems.

Phlogopite-Reinforced Natural Rubber (NR)/Ethylene-Propylene-Diene Monomer Rubber (EPDM) Composites with Aminosilane Compatibilizer

Rubber compounding with two or more components has been extensively employed to improve various properties. In particular, natural rubber (NR)/ethylene-propylene-diene monomer rubber (EPDM) blends have found use in tire and automotive parts. Diverse fillers have been applied to NR/EPDM blends to enhance their mechanical properties. In this study, a new class of mineral filler, phlogopite, was incorporated into an NR/EPDM blend to examine the mechanical, curing, elastic, and morphological properties of the resulting material. The combination of aminoethylaminopropyltrimethoxysilane (AEAPS) and stearic acid (SA) compatibilized the NR/EPDM/phlogopite composite, further improving various properties. The enhanced properties were compared with those of NR/EPDM/fillers composed of silica or carbon black (CB). Compared with the NR/EPDM/silica composite, the incompatibilized NR/EPDM/phlogopite composite without AEAPS exhibited poorer properties, but NR/EPDM/phlogopite compatibilized by AEAPS and SA showed improved properties. Most properties of the compatibilized NR/EPDM/phlogopite composite were similar to those of the NR/EPDM/CB composite, except for the lower abrasion resistance. The NR/EPDM/phlogopite/AEAPS rubber composite may potentially be used in various applications by replacing expensive fillers, such as CB.

HEAT AGING OF A BROMOBUTYL TIRE INNER LINER UNDER AEROBIC AND ANAEROBIC CONDITIONS

A bromobutyl tire inner liner compound was prepared and subjected to aerobic and anaerobic heat aging at a temperature of 100 °C for seven aging times up to 8 weeks. Hardness and mechanical properties were monitored, and the evolution of the crosslink density was followed using equilibrium solvent swell and low field double quantum (DQ) nuclear magnetic resonance (NMR). The hardness and the 300% tensile stress increased with heat aging, while both tensile strength and elongation at break dropped. Both chain scission and crosslinking reactions were taking place. Equilibrium swelling and DQ NMR results confirmed that a larger crosslink density increase was seen under aerobic versus anaerobic aging conditions. The network distribution consisting of a dominant low crosslinking zone and small areas of higher crosslinking slowly broadened and shifted toward higher crosslink densities upon heat aging. The compounds aged heterogeneously. Attenuated total reflectance–Fourier transform infrared spectroscopy confirmed the presence of an oxidized surface layer, and therefore diffusion-limited oxidation effects, but only under aerobic aging conditions. Reaction mechanisms are proposed to explain the net crosslink rise with heat aging.

Stress-Strain Response of Cylindrical Rubber Fender under Monotonic and Cyclic Compression

The study was devoted to the observation and modeling the mechanical behaviors of a hybrid SBR/NR (Styrene-Butadiene/Natural Rubber) hybrid vulcanized rubber fender under monotonic/cyclic compression. In experimental observations of the monotonic compression tests, it was found that lateral deformation occurred on the tested fender and was more significant with increasing the extent of the compressive strain. The relationship between the transmission stress Sc and the compressive strain ec was nonlinear and the absorbed strain-energy-density was increased monotonically with the increment of the compressive strain. Among all cyclic compression tests with strain controlled, the reductions in both the stress range and the absorbed strain-energy-density up to the ten-thousandth cycle were found and then both of the cyclic properties remain approximately constant in the following compression cycles. Two new properties, the softening factor and the energy reduction factor, were introduced to quantify the effect of the strain range on the extent of the reduction in stress range and that on the absorbed strain-energy-density, respectively. It was found that both of the calculated values of the new properties increase with the increment of strain range. In mathematical modeling of the relationship between the transmission stress and the compressive strain, a new approach based on energy-polynomial-function Es(ec) was presented and was successfully used to simulate the monotonic curve and the stable hysteresis loop curves of the tested rubber fender in compression. Essentially, the energy-polynomial-function Es(ec) was obtained by performing a polynomial regression on a large amount of (ec,Es) data. Moreover, the least-square approach was applied to determine the corresponding regression coefficients in Es(ec). Clearly, the stress-polynomial-function in modeling the Sc−ec curve could be obtained from the differentiation of the energy-polynomial-function with respect to the compressive strain. In addition, to provide an adequate estimation of the mechanical properties of the cylindrical rubber fender under compression, the named cyclic stress-strain curve and cyclic energy-strain curve were developed and also modeled in this study.

Monitoring the degradation of physical properties and fire hazards of high-impact polystyrene composite with different ageing time in natural environments

The current study aims at monitoring the role of the different natural environments on the physical properties and fire hazards of HIPS composites ageing in Turpan and Qionghai. The results indicated that the chromatic aberration and degradation of surface appearance intensified with the increasing ageing time. More flame retardants migrated and were eroded for HIPS composites ageing in Qionghai than those ageing in Turpan, which was caused by the combination of sunlight, high temperature and rainwater in Qionghai. After degradation in the natural environments, the HIPS composites possessed the lower thermal stability and char residues, more toxic gases release, higher peak heat release rate and fire hazard. For example, the peak heat release rate in Qionghai increased by 88.9%, which is much higher than that of in Turpan (55.6%). Moreover, the tensile strength and elongation at break decreased by 46% and 59% for HIPS composites ageing in Turpan and reduced by 53% and 67% for HIPS composites aged in Qionghai, respectively. The results demonstrate that more serious degradation of physical properties and higher fire hazard for HIPS composites ageing in Qionghai than those in Turpan due to the different natural ageing environments.

Relaxation behavior of flax-reinforced ethylene–propylene–diene rubber

The molecular dynamics of flax-reinforced ethylene–propylene–diene monomer (EPDM) composites, with increasing quantities of flax (EPDM0–EPDM20), was investigated by dynamic mechanical analysis. Multifrequency experiments were also performed in order to distinguish between the relaxation and the kinetic events. Also the time–temperature superposition was applied to the multifrequency results for obtaining the master curves. They were used to anticipate the behavior of the composites in time and to calculate the activation energies using the Williams–Landel–Ferry equation.

Fabrication of carbon black coated flexible polyurethane foam for significantly improved fire safety

Fire resistant coatings, composed of nanosized carbon black (CB) and polyurethane acrylate (PUA), were synthesized through a facile and low-cost method to improve the fire safety and thermal stability of flexible polyurethane foam (FPU).