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

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.

Review: Mitigation measures to reduce tire and road wear particles

The generation of tire wear is an inevitable outcome of the friction between the road and the tire which is necessary for the safe operation of vehicles on roadways. Tire wear particles form agglomerates with road surface material. These agglomerates are called tire and road wear particles (TRWP). Due to their persistence in the environmental compartments and their potentially harmful effects, research on preventative and end-of-pipe mitigation strategies for TRWP is essential. The major goal of this study is to summarize and assess the state of the art in science and technology of mitigation measures for TRWP as the basis for further research activities. Approximately 500 literature sources were found and analyzed in terms of the efficiency, maturity, implementation, and impact of the mitigation measures. Generally, technological and management mitigation measures to reduce the generation of TRWP are beneficial since they prevent TRWP from entering the environment. Once released into environmental compartments, their mobility and dispersion would increase, making removing the particles more challenging. Technological and management mitigation measures after the release of TRWP into the environment are mainly well established in industrialized countries. Street cleaning and wastewater technologies show good removal efficiencies for TRWP and microplastics. In any case, no individual measure can solely solve the TRWP issue, but a set of combined measures could potentially be more effective. The absence of fully-developed and standardized methods for tire abrasion testing and measuring TRWP in the environment makes it impossible to reliably compare the tire abrasion behavior of different tire types, determine thresholds, and control mitigation actions. Field tests and pilot studies are highly needed to demonstrate the effectiveness of the abatement measures under real conditions.

Performance of Thermal-Oxidative Aging on the Structure and Properties of Ethylene Propylene Diene Monomer (EPDM) Vulcanizates

A thermal-oxidative aging test at 120 °C was conducted on ethylene propylene diene monomer (EPDM) vulcanizates of the semi-efficient vulcanization system. The effect of thermal-oxidative aging on EPDM vulcanizates was systematically studied by curing kinetics, aging coefficient, crosslinking density, macroscopic physical properties, contact angle, Fourier Transform Infrared Spectrometer (FTIR), Thermogravimetric analysis (TGA) and thermal decomposition kinetics. The results show that the content of hydroxyl and carbonyl groups as well as the carbonyl index increased with increasing aging time, indicating that EPDM vulcanizates were gradually oxidized and degraded. As a result, the EPDM vulcanized rubber chains were crosslinked with limited conformational transformation and weakened flexibility. The thermogravimetric analysis demonstrates that the thermal degradation of EPDM vulcanizates had competitive reactions of crosslinking and degradation, and the thermal decomposition curve can be divided into three stages; meanwhile, the thermal stability of EPDM vulcanizates gradually decreased with increasing aging time. The introduction of antioxidants in the system can promote the crosslinking speed and reduce the crosslinking density of EPDM vulcanizates while inhibiting the surface thermal and oxygen aging reaction. This was attributed to the fact that the antioxidant can reduce the thermal degradation reaction level, but it is not conducive to the formation of a perfect crosslinking network structure and reduces the activation energy of thermal degradation of the main chain.

Aspects of the Ageing of Elastomeric Materials

Rising raw materials prices and increasing customer demands for reliability and durability mean that there is huge interest in finding more and more ways of improving the service life of elastomeric products, for economic and environmental reasons, by boosting their resistance under the relevant operating conditions. The material-dependent oxygen absorption capacity and oxygen permeability play an important role in oxidative ageing processes and their modelling. Thus, ageing resistance is substantially dependent on the rate of oxygen diffusion into the bulk of the material in the case of thermo-oxidative attack. To evaluate the resistance of materials to external influences, artificial ageing methods are used in practice. The advantage of these methods is that, as a result of intensifying the test parameters, e.g. temperature and humidity, the ageing processes in the vulcanisate are accelerated. Within the scope of this study, the influence of accelerated ageing on the mechanical and viscoelastic properties of mainly carbon-black-filled natural rubber (NR) vulcanisates was studied in an oxygen atmosphere at elevated temperature and in oxygen with solar radiation. The filler content was varied and the antioxidant IPPD was used. The analyses showed that, as well as mechanical properties such as hardness and tensile strength, the viscoelastic properties are also affected, depending on the ageing time and the type of ageing. In addition to the investigation of mechanical properties, a direct evaluation of the material change was carried out for selected samples by means of analytical tests. The investigations showed the deterioration of the antioxidant activity.

Accelerated aging for testing polymeric biomaterials and medical devices

Elevated temperature is frequently used to accelerate the aging process in polymers that are associated with medical devices and other applications. A common approach is to assume that the rate of aging is increased by a factor of 2(DeltaT/10), where DeltaT is the temperature increase. This result is a mathematical expression of the empirical observation that increasing the temperature by about 10 degrees C roughly doubles the rate of many polymer reactions. It is equivalent to assuming that the aging process is a first order chemical reaction with an activation energy of 10R/log(e)2, where R is the universal gas constant. A better approach would be to determine the activation energy for the process being considered but this is not always practicable. The simple approach does not depend on the temperature increase, provided that it is not so great that it initiates any physical or chemical process that is unlikely to be involved in normal aging. If a temperature increment theta were to increase a given polymer reaction rate n times, then an elevated temperature would increase the rate of aging by a factor of n(DeltaT/theta).

Durability of crosslinked polydimethylsyloxanes: the case of composite insulators

Most applications of silicones are linked to their hydrophobic properties and (or) their high resistance to ageing (e.g. thermal ageing and photoageing). However, when placed in extreme environments, these materials can fail as in the case of epoxy/fiber glass composite powerlines insulators, where crosslinked polymethylsyloxanes (PDMSs) are used as the protective envelope (housing) of the insulator. We report on the behavior of both pure/noncrosslinked PDMSs and typical formulations used in industrial insulators, i.e. containing peroxide crosslinked PDMS, alumina trioxide hydrated (ATH) and silica. Special attention is paid on both (i) the sources of potential degradation and (ii) the best analytical methods that can be applied to the study of very complex formulations. (i) Aside from conventional types of ageing such as photo-ageing and thermal, hydrolytic, and service life ageings, treatments with acidic vapors, plasma and ozone possibly generating species from the reaction of a high electric field with air were also performed, which allowed to accelerate electrical and out-door ageings and to obtain differently aged materials. (ii) Aside from conventional analytical methods of polymer degradation such as FTIR/ATR spectroscopy and SEC, TG, hardness measurements, more specific methods like photo/DSC, TG/IR, thermoporosimetry, resistivity and density measurements were also performed to characterize the chemical and physical evolutions of polymer materials. In particular, it was found that treatment with nitric acid vapor has detrimental effects on the properties of both fire retardants (e.g. ATH) and PDMSs, affecting the hardness and resistivity of the formulated material.