After being discarded into the environment, the microplastics (MPs) will undergo weathering effects. However, the low degradation rate of MPs in natural processes greatly limits the understanding of ...long-term aging behavior. By critically reviewing 82 articles in Web of Science from 2015 to 2020, the paper summarized different laboratory technologies including light irradiation, chemical oxidation, heat treatment and γ-ray irradiation to simulate and accelerate the aging of MPs, and evaluated the feasibility by comparison with natural processes. The advantages of laboratory technologies are that aging conditions can be artificially controlled and that the labor and time costs can be saved, whereas the laboratory system is too simple to simulate complex aging processes in the environment. We further reviewed the potential impacts of aging process on the risks of MPs (i.e. physical injury, combined toxicity with external pollutants and chemical risk of additives and low-molecular products). The overall risks are seemingly enhanced by aging process due to the high ingestion by organisms, the strong interaction with pollutants and the release of MP-derived organic compounds. Further studies on the aging behavior of MPs should be focused on the laboratory techniques that can simulate multiple processes of natural aging, the long-term fragmentation behavior of MPs, the effect of aging on growth rate of biofilm in MPs and ingestion property by organisms, and the relationship between aging property of MPs and release rate of chemicals in leachates.
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•Natural and laboratory-accelerated aging processes of microplastics were reviewed.•Advantage of laboratory process is artificially-controlled condition and time-cost saved.•Light irradiation is the mostly selected technology to accelerate the microplastic aging.•Aging increases the risks of microplastics from physical, combined and leachate toxicities.•Laboratory technology that can simulate multiple aging factors should be developed.
Although the current transformer is an essential component in the electrical power system and its failure may result in serious consequences, there are no accelerated aging tests for this equipment ...prescribed by technical standards. Life estimation for this equipment is generally made based on field experience, something that cannot be done for new models and/or new manufacturers. In this work, experimental results of life tests performed on mockups, representing high voltage current transformers with oil-impregnated paper insulation, are presented and discussed. The analysis is based on the application of a multi-stress model, which combines Montsinger rule and, Inverse Power Law. The proposed approach considers the existence of threshold values for electrical and thermal stresses, below them electrical and thermal degradation is negligible. An order of magnitude for the electrical stress threshold value ( E 0 ) and for the electrical aging exponent ( n ) is obtained from the application of the test results to the model used in this investigation.
Polymer resins have yellowing issue when subjected to elevated temperatures or UV exposure, which limit their applications in color-sensitive fields. This paper presents an experimental study on the ...yellowing mechanisms of epoxy and vinyl ester resins under thermal, UV and natural aging conditions. Anti-yellowing methods including air isolation, antioxidant, UV absorber are selected and their effectiveness is assessed. The resins before/and after aging are characterized to analyze their yellowing index, surface morphology, weight loss, mechanical properties (i.e. modulus and Vickers hardness), glass transition temperature and FT-IR spectra. The yellowing mechanisms and the influencing factors are discussed. It is found that the resin yellowing is a result of radical oxidation reaction due to aging, which forms chromophores such as carbonyl groups, double bonds and conjugated structures. Vinyl ester has better yellowing resistance than epoxy. Antioxidant and UV absorber are not effective in terms of anti-yellowing effect, but air isolation has the best performance to slow down the yellowing process. Yellowing in natural environment can be more complicated due to other factors like moisture, wet-dry cycles etc. This study provides an experimental evidence for the study of yellowing mechanisms of polymer resins.
•Yellowing mechanisms of epoxy and vinyl ester resins under thermal, UV and natural aging conditions are investigated.•The effectiveness of anti-yellowing methods is assessed including air isolation, antioxidant and UV absorber.•It is found that the resin yellowing is a result of radical oxidation reaction which forms chromophores.•Vinyl ester has better yellowing resistance than epoxy.•Antioxidant and UV absorber are not effective in terms of anti-yellowing effect while air isolation has the best performance.
The determination of the secure working life of polymeric materials is essential for their successful application in the packaging, medicine, engineering and consumer goods industries. An ...understanding of the chemical and physical changes in the structure of different polymers when exposed to long-term external factors (e.g., heat, ozone, oxygen, UV radiation, light radiation, chemical substances, water vapour) has provided a model for examining their ultimate lifetime by not only stabilization of the polymer, but also accelerating the degradation reactions. This paper presents an overview of the latest accounts on the impact of the most common environmental factors on the degradation processes of polymeric materials, and some examples of shelf life of rubber products are given. Additionally, the methods of lifetime prediction of degradable polymers using accelerated ageing tests and methods for extrapolation of data from induced thermal degradation are described: the Arrhenius model, time–temperature superposition (TTSP), the Williams–Landel–Ferry (WLF) model and 5 isoconversional approaches: Friedman’s, Ozawa–Flynn–Wall (OFW), the OFW method corrected by N. Sbirrazzuoli et al., the Kissinger–Akahira–Sunose (KAS) algorithm, and the advanced isoconversional method by S. Vyazovkin. Examples of applications in recent years are given.
The demand and necessity of direct current (DC) has been increasing owing to large capacity and long distance power transmission. DC application of TP (thermal plastic) materials, which can increase ...the power transmission capacity compared to existing insulation materials, has been the primary focus of existing studies. This study presents the development of a highly reliable accelerated aging system that can implement the aging conditions of DC power cables. Moreover, we verify its reliability by testing TP model cables and analyzing the aging characteristics. Accordingly, we developed an accelerated aging system that can simulate thermal, electrical, and mechanical stresses collectively. We used the accelerated aging system to perform an accelerated aging test of the TP model cable for 40 cycles. The control precision of the accelerated aging system during the test was numerically calculated. The system was evaluated by using the conduction current and chemical characteristics of the aged TP model cables. The experimental results show that the precision of accelerated aging system is 1% for 1 cycle. The conduction current of the aged TP model cables was increased by more than 100% before aging, thereby it is verified the performance of the system accelerates the aging of power cables. It is expected that the highly reliable accelerated aging system of power cables can be used to perform long-term reliability tests and as diagnostic technology during the development of DC power cables.
•Polymer oxidation behavior as function of O2 partial pressure has been reviewed.•Oxidation rates were determined for epoxy thermosets up to 4 atm.•Oxidation rates with pressure were fitted with ...existing equation from autoxidation scheme.•Epoxy materials reach saturation rates only at significantly higher O2 partial pressure.•Conducting polymer oxidation at elevated pressure can in principle reduce DLO sensitivities.
Polymer oxidation is usually accelerated with temperature, which is therefore applied in nearly every experimental approach dealing with predictive materials aging. Because of this simple approach, we may tend to neglect that the effective concentration of oxygen also acts as a rate multiplier for oxidation. Increasing the oxygen partial pressure in an aging environment accelerates oxidation, and while there is often a near proportional increase initially, the effect of additional oxygen usually transitions to a saturation level at some elevated pressure. This has been theoretically described in the general autoxidation scheme and is well recognized. However, for many materials the exact rate behavior under moderately increased oxygen concentration remains to be established. We therefore review epoxy oxidation and offer a broader overview of its behavior under increased O2 partial pressure. Experimental data are given for a few thermoset materials demonstrating their rate behavior under O2 partial pressure up to 4 atm, meaning approximately 20 times more than under standard atmospheric conditions. Confirmative evidence suggests that epoxy materials will reach saturation oxidation rates only at significantly higher O2 partial pressure. In such a high-pressure regime it is theoretically possible to not only accelerate oxidation, but to transition into a condition where O2 diffusion can be increased without further accelerating the oxidation rate. This can reduce diffusion limited oxidation effects under specific accelerated aging conditions as a combination of temperature and O2 partial pressure.
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The multifactor accelerated aging test is an important means to predict the lifetime of gas-insulated switchgear (GIS) O-ring seals, while the leakage rate (LR) is a potential index for failure ...evaluation. This article proposed a three-factor accelerated aging test platform and a leakage test system (LTS) for GIS seal rings. The aging factors are thermal, mechanical compression, and pressured SF 6 gas. The pressure aging vessel (PAV) can be filled with various gases to simulate the operating conditions of the GIS and age multiple samples simultaneously. During the aging process, leakage tests are conducted on flange pairs without disassembling and separating the seal rings. After the test, the aging can be continued so as to study the evolution of LR with aging time. In order to analyze the properties of leakage test and validate the platform, a three-factor accelerated aging and a traditional two-factor accelerated aging (thermal and compression) were conducted on GIS O-ring seals of EPDM material. Compression set (CS) and LR were tested. The result showed that a steady inherent LR F 0 exists for the LTS. The LR rose linearly with accumulating time, allowing simplified calculation of LR. The three-factor aged samples had significantly smaller CS than those of the two-factor aged samples, indicating that the working condition of GIS with SF 6 atmosphere significantly slows the aging rate of GIS seal rings. The findings proved that the three-factor accelerated aging test platform and LTS effectively simulate the operating conditions of GIS seal rings and evaluate their properties.
The oil-paper insulation system is a critical component that serves excellent insulation properties in a power transformer. It has high dielectric strength that can withstand high voltages during ...operation. However, both insulation materials will slowly degrade in long-term operation that can cause serious deterioration to the performance of the insulation system in power transformer. Numerous researchers have used accelerated aging tests under laboratory conditions in order to simulate the degradation conditions in oil-filled transformer. This approach can shorten the lifetime of an electrical insulation system, allowing for investigation on the behavior of the insulation material and the prediction of the insulation system's lifespan in power transformers. This paper focuses on a comprehensive review of the accelerated aging procedure under laboratory conditions which includes five crucial elements that need to be considered prior to the aging experiment. These elements include the pre-treatment of insulating liquids, pre-treatment of cellulose papers, preparation of metal catalysts, selection of appropriate aging temperature and determination of the time period for accelerated aging. This review article will provide helpful pointers to researchers engage on accelerated aging in laboratory conditions.
The latest 2011 edition of the IEEE C57.100 standard introduced a new sealed tube accelerated aging test (STAAT) procedure and methodology for evaluating the thermal index (TI) of liquid-immersed ...transformer insulation systems. The application of this standard becomes increasingly important, as new insulating materials (both solid and liquid) have been developed, and their thermal performance shall be qualified. The experimental work presented in this article investigated the effects of different test parameters on the aging test results and data interpretation. The new findings on the dependence of the aging process on the ratio and type of materials in the system, as well as on the selected aging criteria provide a better understanding of the accelerated aging and interpretation of the data along with practical recommendations for the improvement of the test procedure. In parallel, for the first time, the TI of the Transformerboard, as a component of the so-called industry-proven insulation system, was investigated and defined based on the standard industry test. The results confirmed that the Transformerboard's thermal class is, at least, 120 °C; this validates an empirically based application of this material as a part of the 120 °C class insulation system in both power and distribution transformers.
Composite materials are widely used in various applications, but their mechanical and physical properties can be significantly influenced by environmental factors such as temperature, humidity, and ...UV radiation during service life. This study aims to investigate the accelerated aging behavior of glass/epoxy composites under hygrothermal conditions and compare the results with naturally aged samples to understand the reliability of these materials in harsh environments. NOL GFRP samples were fabricated using the filament winding process and subjected to accelerated aging for varying time periods (ranging from 100 to 1200 hours in 50-hour intervals) under hygrothermal conditions. Additionally, naturally aged samples over several years (1, 1.5, 2, 2.5, and 3 years) were compared. Tensile strength measurements were conducted to assess the mechanical properties of the composites. Machine learning models, including linear regression, polynomial regression, Artificial Neural Network (ANN), random forest regression, and Support Vector Regression (SVR), were utilized to predict natural aging times from accelerated aging data.
Hygrothermal aging led to significant matrix deterioration and fiber exposure, resulting in a notable reduction in tensile strength. The study observed a 35.60 % reduction in strength in three-year naturally aged samples and a 37.57 % reduction in 1000-hour accelerated aged samples. Among the machine learning models, the random forest regressor demonstrated the best performance in predicting natural aging times across different accelerated aging periods, while SVR exhibited poorer performance. Polynomial regression and ANN models showed moderate predictive capabilities.
This study contributes to a deeper understanding of the aging process of composite materials, providing insights into the reliability and durability of glass/epoxy composites in various applications. By employing machine learning models, the research offers a novel approach to predicting natural aging times based on accelerated aging data, which can be beneficial for optimizing the design and maintenance of composite structures to enhance their long-term performance and minimize the risk of failure in service.
•Investigated the impact of hygrothermal conditions on the accelerated aging of glass/epoxy composites over various time intervals.•Compared accelerated aging results with natural aging samples spanning multiple years to assess composite degradation.•Identified significant reductions in tensile strength due to hygrothermal aging, highlighting matrix deterioration and fiber exposure.•Employed five machine learning models to predict natural aging times from accelerated aging data, with random forest regression yielding the most accurate results.•Provided valuable insights into the aging behavior of composite materials through correlation analysis between natural and accelerated aging.
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