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Recent Progress in the Accelerated Aging and lifetime Prediction of Elastomers : A review
... The thermal degradation of NR components depends on a number of variables, including the compound composition, exposure temperature, and nature of the material [11]. The addition of fillers to a rubber matrix has been demonstrated to improve the durability of rubber composites under environmental conditions, widening the range of applications [12]. ...
... Rubber additives act as curing agents in rubber systems to activate vulcanization. ZnO and stearic acid were employed as activators to enhance the effectiveness of the sulfur vulcanization system, and CBS was employed as an accelerator [11]. ...
... Tensile testing is another fascinating method for tracking the impact of thermal aging on the mechanical properties of materials and quantifying the changes to estimate their lifetimes and is frequently employed by researchers [11]. Despite the complexity of the aging process for NR composites, the rate of degradation is widely known to accelerate significantly with aging time. ...
Thermal aging of natural rubber (NR) composites is the long‐term, irreversible alterations in the composition, morphology, and structure caused by exposure to temperatures normally encountered in service. This has a significant impact on the tensile, wear, and friction properties of the composites. This study aims to investigate the effect of thermal aging on the tensile, wear, and frictional properties of pineapple leaf fiber‐reinforced NR composites with added multiwalled carbon nanotubes (MWCNTs). The variations in tensile and wear properties were monitored for 2, 4, and 6 days of aging at 60°C and 80°C. The morphologies of the tensile‐fractured and worn surfaces were investigated using scanning electron microscopy (SEM). Early in aging, the tensile strength and modulus initially increased, then decreased. The frictional force, coefficient of friction (COF), and specific wear rate gradually increased with aging duration and temperature. After the inclusion of MWCNTs, the tensile strength and COF increased up to 3.21 MPa and 0.94, respectively, under aging conditions of 80°C for 6 days. SEM analysis provided evidence that thermal aging exposure can induce surface cracks, leading to a reduction in the tensile properties of the composites. These findings provide valuable insights into material design for a wide range of applications.
... There is a recent bibliography on the aging and changes in the mechanical behavior of the materials used in this study. In this sense, Tayefi et al. [13] show that under accelerated thermal aging, EPDM undergoes oxidation at high temperatures (120-140 • C) that generates hydroxyl and carbonyl groups, reducing its crystallinity and deteriorating its mechanical properties. Likewise, Xin-Yi et al. [14] investigate γ-ray irradiation, finding that it reduces the Mooney viscosity and molecular weight of EPDM, increases the gel content, and raises the glass transition temperature, which modifies its internal structure and processing performance; finally, Shuang-Hong et al. [15] examine the thermo-oxidative aging of EPDM, noting that crosslinking predominates during degradation, which translates into an increase in hardness and tensile strength along with a decrease in permanent deformation. ...
... This research aims to experimentally evaluate how mechanical and environmental deterioration conditions affect the dynamic stiffness of rail pads manufactured from EPDM and EVA materials. Based on the literature review, it has been established that there are existing studies addressing the aging and changes in the mechanical behavior of EPDM and EVA materials under various environmental conditions [13][14][15][16][17], as well as research identifying specific degradation mechanisms in rail pads exposed to the railway environment [7]. However, no specific study has been conducted to quantitatively measure the magnitude of these effects on real components subjected to conditions representative of the railway environment. ...
... Specifically, the distinct chemical structure of each material influences its degradation mechanisms, resulting in different behaviors under identical environmental conditions. In this way, the variations in dynamic stiffness observed in this study reflect the underlying chemical and structural characteristics unique to each polymer [13][14][15][16][17], affecting their performance and durability in real operating scenarios. ...
The railway sector plays a crucial role in sustainable transportation by reducing greenhouse gas emissions while supporting an increasing volume of freight and passenger transport. Rail pads, essential components in railway infrastructure, mitigate vibrations and distribute loads; however, their long-term performance is influenced by environmental and mechanical degradation, affecting track durability and maintenance costs. Despite their significance, the degradation mechanisms impacting the dynamic stiffness of EPDM (Ethylene Propylene Diene Monomer) and EVA (Ethylene Vinyl Acetate) rail pads remain insufficiently characterized. This study examines the effects of mechanical and chemical aging on the stiffness of these materials through 864 dynamic stiffness tests, analyzing three types of rail pads under mechanical cycling (up to 2,000,000 cycles), UV (ultraviolet light) exposure (100–500 h), and hydrocarbon exposure (100–500 h). Mechanical aging increases stiffness across all pads, with Pad C (EVA) exhibiting the most pronounced increase (27%). The effects of UV exposure vary by material, leading to a stiffness reduction of up to 11.5% in Pad B (EPDM), whereas Pad C (EVA) experiences a 9.5% increase under prolonged exposure. Hydrocarbon exposure also presents material-dependent behavior, with Pad A (EPDM) experiencing an 11.5% stiffness reduction at low exposure but partial recovery at higher exposure, while Pad C (EVA) shows a 5% increase in stiffness under prolonged exposure. These findings offer valuable insights into the aging mechanisms of rail pads and underscore the importance of considering degradation effects in track maintenance strategies.
... For example, exposure to high temperatures can accelerate the aging process of elastomers, causing significant changes in their mechanical, physical, and chemical properties. 1 Styrene-butadiene rubber (SBR), created through the copolymerization of styrene and butadiene, contains unsaturated bonds due to the butadiene component. This necessitates the use of additives to protect it against oxygen, ozone, and UV light. ...
... Therefore, understanding the thermal aging behavior of elastomeric compounds is essential for predicting their service life and ensuring the reliability of products that incorporate these materials. 1 As a consequence, during the past 2 years, several works have been done to study and improve the aging properties of the different elastomers. [8][9][10][11][12] Some studies have explored the effects of thermo-oxidative aging on the mechanical and chemical properties of SBR rubber, [13][14][15] revulcanized SBR, 16 and its thermal properties. ...
... 22 Verifying the durability of these materials for specific applications is essential, especially since end-users often do not have access to the exact formulations of rubber compounds provided by suppliers. 1 For instance, there are some articles on the prediction of the lifetime of commercial rubbers, such as O-ring seals, 23-28 rubber insulators of cables used in nuclear power plants [29][30][31] and polymeric binders in solid propellants. [32][33][34][35][36] Due to this importance, the elastomer service life of elastomeric materials has been studied in our previous articles. ...
This work describes the thermal aging behavior of three industrial elastomeric compounds based on styrene–butadiene rubber (SBR) reinforced with carbon black. Samples were exposed to thermo‐oxidative aging at temperatures ranging from 70 to 120°C for durations between 14 and 365 days. The tensile and hardness tests were performed on the samples to determine changes in their mechanical properties. Upon aging, hardness and 100% modulus increased, while elongation at break decreased for all three samples. The results showed a significant decrease in elongation at break and an increase in hardness and modulus with prolonged aging time and higher temperatures. For instance, the elongation at break of the three types of samples decreased by approximately 50% in less than 90 days at 70°C, whereas at 120°C, this same level of degradation occurred in less than 2 days. These significant changes were correlated with increased brittleness and reduced flexibility of SBR composites. Swelling tests confirmed an increase in crosslink density due to aging. Laser scanning confocal microscopy revealed surface roughness and defects, attributed to oxidation, crosslinking, and the evaporation of low molecular weight components. Lifetime prediction methods, including the Arrhenius equation and time–temperature superposition (TTS), were applied to estimate the service life of the materials. The Ahagon plot was utilized to understand the aging mechanisms, revealing a transition from crosslinking‐dominated degradation to chain scission processes at higher temperatures and longer aging times.
Highlights
Thermal aging makes SBR compounds more brittle and less flexible over time.
The hardness and stiffness of SBR compounds increase with aging temperature and time.
Aging increases crosslink density, confirmed by swelling tests.
Increased surface roughness and defects due to oxidation and crosslinking.
The aging mechanism shifts from crosslinking to chain scission at higher temperatures.
... It is also evident that the elongation at break shows a decreasing trend in NBR and all NBR-NCC nano-composites. A decrease in tensile strength and elongation at break after aging is also reported for other elastomers and polymer matrix nano-composites by many researchers [68]. The NBR-NCC nano-composites after aging show a slight increase in hardness as compared to the composites before aging, as shown in Figure 8. ...
... The rubber becomes less elastic and more brittle after aging, ultimately decreasing the tensile strength and elongation at break. This might be due to thermal degradation, an increase in crosslinking density or a loss of additives that occurs due to exposure to temperatures [68]. It is also noted that NBR-NCC nano-composites show a lower decrease in tensile strength when compared to NBR. ...
... It is also evident that the elongation at break shows a decreasing trend in NBR and all NBR-NCC nano-composites. A decrease in tensile strength and elongation at break after aging is also reported for other elastomers and polymer matrix nano-composites by many researchers [68]. ...
The escalating demand for sustainable rubber products has spurred research into alternative reinforcing fillers, driven by concerns regarding the detrimental effects of using conventional fillers like carbon black and silica. In this investigation, nano-crystalline cellulose (NCC), derived from micro crystalline cellulose (MCC), sourced from sugarcane bagasse via acid hydrolysis, serves as a bio-filler to reinforce Nitrile Butadiene Rubber (NBR) matrices. NBR-NCC nano-composites were prepared using a two-roll mill, varying NCC from 1–5 parts per hundred rubber matrices, followed by hot press curing. NCC and NBR-NCC nano-composites were characterized using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), curing characteristics, thermo-mechanical testing, thermal aging and motor oil resistance. Chemical interactions between the NCC and NBR matrix were verified with FTIR. The SEM images of the NCC showed a combination of rod-like and spherical morphologies and a homogenous dispersion of NCC in NBR-NCC nano-composites with some agglomeration, notably at higher percentages of NCC. It is shown that the cure time decreases with increasing NCC loading which mimics a shorter industrial production cycle. The results also showed an increase in tensile strength, hardness, oil resistance and a rise in degradation temperature when compared to NBR at approximately 34%, 36%, 38% and 32 °C, respectively, at 3 phr NCC loading. Furthermore, NBR-NCC nano-composites showed a lower decrease in mechanical properties after aging when compared to NBR. The findings of this research suggest that the NBR-NCC nano-composites may find applications in high oil resistance seals and rubber gloves where higher thermal stability is strictly required.
... These factors can cause ETPU to age, leading to a To fully evaluate the aging properties of ETPU, natural aging and accelerated aging are both essential. Natural aging could reflect the real aging process of polymers, but the very slow reaction rate of natural aging leads to significant limitations in performance testing, which requires the use of an accelerated aging experiment with different conditions to obtain enough data in a much shorter time to predict lifetime [17][18][19]. With the increasing demand for material aging performance evaluation, accelerated aging experiments have been widely adopted by industry and academia [20]. ...
... The results showed that aging deteriorates the appearance, morphology, and mechanical properties of polyurethanes, where the results of foam morphology analysis showed that the aging treatment causes cracking at the edges of the cells, To fully evaluate the aging properties of ETPU, natural aging and accelerated aging are both essential. Natural aging could reflect the real aging process of polymers, but the very slow reaction rate of natural aging leads to significant limitations in performance testing, which requires the use of an accelerated aging experiment with different conditions to obtain enough data in a much shorter time to predict lifetime [17][18][19]. With the increasing demand for material aging performance evaluation, accelerated aging experiments have been widely adopted by industry and academia [20]. ...
Expanded thermoplastic polyurethane (ETPU) is used in a wide range of applications due to its excellent properties, but inevitably, aging deteriorates the material properties and shortens service lifetime. This study conducted aging experiments on ETPU to summarize the deterioration trend and provide reliable data. The ETPU underwent three distinct aging protocols: thermal aging for 28 days in a controlled 80 °C environment; xenon lamp aging under continuous UV irradiation (via xenon lamp) at 80 °C for 28 days; and weathering aging through 671 days of outdoor exposure to real-world weather conditions. After various structural characterization and performance tests on the aged ETPUs, the results showed that thermal aging is not the key factor causing the aging of ETPU; the internal structure of ETPU is damaged and the performance rapidly deteriorates under the combined effect of light, heat, and humidity. The special heterogeneous structure gives the sample different internal aging characteristics, and the bead interface becomes a defective site after aging, affecting the overall mechanical properties of the material. In the natural state, the lifetime of ETPU is about two years. Our work will provide valuable data for the study of the aging properties of ETPU and contribute to the prediction of the lifetime of the material.
... Vulcanizing agents, such as sulfur and accelerators, and their products can undergo changes during thermal aging, which can affect the strength of the bonds between the chains and reduce the resistance of the material. Thermal aging also causes optical and surface changes and the formation of microcracks on the surface [1,2]. ...
... The FTIR spectra of the CNTs before and after functionalization are shown in Figure 4. The pristine CNT spectrum reveals key chemical features: the 1625 cm⁻ 1 band corresponds to C=C stretching, while bands at 2851 cm⁻ 1 Raman spectra are shown in Figure 6. In the high-frequency region of the spectrum of the pristine CNTs, two bands were observed: the G-band (1583 cm −1 ), which is related to the graphitic structure of the CNTs, and the weak D-band (1352 cm −1 ), which is associated with defects in the carbon structure. ...
The incorporation of carbon nanotubes (CNTs) enhances the mechanical performance of rubber composites. This study examines the effect of single-walled CNTs (1–4 phr) on the properties of a natural rubber compound for sealing applications, both before and after thermal aging, as prolonged exposure to elevated temperatures can alter material properties, affecting durability and functionality. The researched nanocomposites were subjected to a series of mechanical tests, dynamic mechanical analysis, and surface investigation using atomic force microscopy (AFM). After adding 4 phr of CNTs, tensile and tear strength increased by 11.73% and 14.64%, respectively, while aging-related strength degradation was reduced by 5%. CNTs also increased complex modulus and hardness but reduced elongation at break and rebound resilience. Residual deformation in tensile and compressive set tests decreased. AFM analysis confirmed improved surface stability after thermal aging compared to the CNT-free compound.
... This degradation occurs as rubber polymers undergo chemical interactions with the surrounding environment. Over time, these interactions can lead to the formation of additional crosslinks or the breaking of molecular backbones and existing crosslinks, leading to a decline in performance [5][6][7]. To illustrate this, some examples of degradation include rubber aging as an irreversible phenomenon, with the rate of deterioration influenced by various factors such as temperature, ultraviolet (UV) light exposure, and humidity, among others [5]. ...
... Over time, these interactions can lead to the formation of additional crosslinks or the breaking of molecular backbones and existing crosslinks, leading to a decline in performance [5][6][7]. To illustrate this, some examples of degradation include rubber aging as an irreversible phenomenon, with the rate of deterioration influenced by various factors such as temperature, ultraviolet (UV) light exposure, and humidity, among others [5]. For instance, nitrile rubber (NBR) tires are prone to cracking due to temperature effects. ...
The degradation of rubber materials under environmental and mechanical stress presents a significant challenge, particularly due to UV (ultraviolet light) exposure, which severely impacts the material’s physical properties. This study aims to enhance the UV stability and longevity of rubber by evaluating the performance of modified polyurethane and silicone coatings as protective stabilizers. Natural rubber—styrene–butadiene rubber (NR-SBR), known for its exceptional mechanical properties, was selected as the base material. To ensure strong adhesion, cold atmospheric plasma treatment was applied, increasing the surface energy by 250%, primarily through an enhancement of the polar component. After treatment, supplier-recommended coatings were applied and tested for adhesion using the pull-out method. Aging tests under UV exposure, water immersion, and high temperatures were conducted to assess durability, with tensile tests used to monitor changes over time. Coatings exhibiting cracking after UV exposure were excluded from further analysis. A silicone coating demonstrating superior moisture resistance and durability under extreme conditions was identified as a promising candidate for future UV stabilization applications. These findings provide a foundation for developing advanced coatings to significantly extend the service life of rubber materials in demanding environments.
... High-temperature accelerated aging testing is a typical method for investigating the long-term storage and usage performances of polymer materials [19]. Tang et al. [20] studied the thermal aging behavior of tightly wrapped PVA hydrogels at 40-70 • C for 360 d and found that the mechanical properties hardly changed during the thermal aging process. ...
... In order to better observe the experimental phenomenon and distinguish the aging stages more reasonably, aluminum bags were used to provide a semi-sealed environment to appropriately slow down the loss of moisture [19,31,32]. The PVA hydrogel materials wrapped in aluminum bags were subjected to high-temperature accelerated aging tests in a WGL-45L high-temperature test chamber. ...
Polyvinyl alcohol (PVA) hydrogels find applications in various fields, including machinery and tissue engineering, owing to their exceptional mechanical properties. However, the mechanical properties of PVA hydrogels are subject to alteration due to environmental factors such as temperature, affecting their prolonged utilization. To enhance their lifespan, it is crucial to investigate their aging mechanisms. Using physically cross-linked PVA hydrogels, this study involved high-temperature accelerated aging tests at 60 °C for 80 d and their performance was analyzed through macroscopic mechanics, microscopic morphology, and microanalysis tests. The findings revealed three aging stages, namely, a reduction in free water, a reduction in bound water, and the depletion of bound water, corresponding to volume shrinkage, decreased elongation, and a “tough-brittle” transition. The microscopic aging mechanism was influenced by intermolecular chain spacing, intermolecular hydrogen bonds, and the plasticizing effect of water. In particular, the loss of bound water predominantly affected the lifespan of PVA hydrogel structural components. These findings provide a reference for assessing and improving the lifespan of PVA hydrogels.
... The attributes of rubber that enable it to be pliable, versatile, strong, and enduring make it necessary for diverse applications. Therefore, it is crucial to obtain precise forecasts regarding elastomers lifespan to facilitate appropriate design planning, maintenance schedules, and risk prevention [6]. ...
... Predicting the service life of elastomers has always been an expensive, timeconsuming task requiring experiments and extrapolations [6,7]. However, recent strides in materials science and computer modeling show promising ways to improve this process. ...
... In the majority of studies, predictions of long-term service life are based on Arrhenius' law, which stipulates a principle of equivalence between a test duration and its temperature, for a given degradation (Tayefi et al., 2023). This empirical approach is based on strong assumptions: only temperature accelerates ageing; the degradation process is unique and characterised by a constant activation energy; the degradation leads to the same microstructural states whether accelerated or natural ageing is performed. ...
Under environmental exposure, elastomers undergo ageing: chemical reactions lead to changes in the macromolecular network, usually resulting in a decrease of mechanical properties. With the development of marine renewable energies, understanding and predicting the durability of these materials in aggressive environments, i.e. their mechanical lifetime, is key to prevent components failure in service.
Despite extensive research on elastomers ageing in the past decades, some dark spots remain to be elucidated. Among them, the reduction of fatigue lifetime is still poorly understood, ageing in a marine environment has not been extensively studied, and the coupling between ageing and other factors like compounding or multiaxiality lacks exploration.
This thesis proposes insights into the oxidative and marine degradation of a carbon-black filled elastomer, through experimental determination of the material’s macromolecular structure and mechanical properties. The common thread uniting the manuscript lies in using the strain energy density and establishing structure - property relationships.
... This testing sets out to mirror long-term effects on materials. These effects stem from environmental factors such as temperature, humidity, UV radiation, salt spray, and chemical exposure [87]. Environmental exposure testing checks a material's ability to endure weathering, corrosion degradation, and other environmental damage. ...
To ensure the quality, dependability, and long life of sustainable biomaterials, we need comprehensive testing methods. These are for use in varied applications. This chapter provides an in-depth examination. It is of both destructive and non-destructive testing techniques. The techniques are for sustainable biomaterials. Recent advancements in testing technologies are also discussed. This includes machine learning and multi-modal imaging. Destructive testing techniques are used. Tensile testing, impact testing, chemical analysis, and accelerated aging evaluations are employed. These gather essential data. The data is regarding properties and performance of materials. In contrast to this, non-destructive testing methods are used. These include ultrasound, infrared spectroscopy, and imaging techniques. They allow for evaluation without causing damage to the biomaterials. Incorporating environmental impact assessments is discussed. It includes life cycle analysis. It underscores the significance of sustainability in evaluating testing procedures. The section focuses on techniques and approaches. These are required to ensure compatibility of materials in various fields. The aim of this chapter is to equip researchers. It is to equip engineers and practitioners with necessary knowledge and resources. The aim is to assess the efficiency and suitability of sustainable biomaterials. The materials are for various applications. This is done by delving into these evaluation techniques.
Graphical abstract
... Hong and co-authors used the Arrhenius equation to predict the lifespan of a polyurethane elastomer when considering the measured tensile strength and elongation at break values from a heat-aging study, and the estimated lifetime based on tensile strength was 12.2 years at room temperature [40]. Although accelerated thermal aging combined with the Arrhenius method is recognized as one of the more reliable approaches for predicting the lifetime of elastomers, there are several mechanisms of degradation for elastomers (e.g., chemical, mechanical, and environmental factors) that should also be considered in future studies to effectively predict long-term performance capability [41]. ...
Due to its ability to achieve geometric complexity at high resolution and low length scales, additive manufacturing (AM) has increasingly been used for fabricating cellular structures (e.g., foams and lattices) for a variety of applications. Specifically, elastomeric cellular structures offer tunability of compliance as well as energy absorption and dissipation characteristics. However, there are limited data available on compression properties for printed elastomeric cellular structures of different designs and testing parameters. In this work, the authors evaluate how unit cell topology, part size, the rate of compression, and aging affect the compressive response of polyurethane-based simple cubic, body-centered, and gyroid structures formed by vat photopolymerization AM. Finite element simulations incorporating hyperelastic and viscoelastic models were used to describe the data, and the simulated results compared well with the experimental data. Of the designs tested, only the parts with the body-centered unit cell exhibited differences in stress–strain responses at different part sizes. Of the compression rates tested, the highest displacement rate (1000 mm/min) often caused stiffer compressive behavior, indicating deviation from the quasi-static assumption and approaching the intermediate rate response. The cellular structures did not change in compression properties across five weeks of aging time, which is desirable for cushioning applications. This work advances knowledge on the structure–property relationships of printed elastomeric cellular materials, which will enable more predictable compressive properties that can be traced to specific unit cell designs.
... Tayefi et al. conducted a review on the process of accelerated aging and lifespan prediction of elastomers. They emphasized the significance of temperature-induced oxidative degradation, which leads to embrittlement and a decrease in elasticity [11]. Research conducted by Song et al. examined the impact of varying viscosities of EPDM on the crystallization behavior and mechanical characteristics of TPVs. ...
This research investigates the impact of sulfuric acid-water solutions on the physico-chemical characteristics of ethylene propylene diene monomer rubber (EPDM), thermoplastic vulcanizates (TPV), and ECO TPV materials. We evaluated the deterioration of these materials by subjecting them to acidic environments and using methods such as differential scanning calorimetry (DSC), volume and weight measurements, hardness measures, and scanning electron microscopy (SEM). The samples were submerged in solutions of H₂SO₄ with concentrations of 1M, 0.1M, and 0.001M at a temperature of 90°C for a duration of 1000 h. The results indicated that EPDM had superior chemical and thermal stability, accompanied by negligible changes in weight and volume. The TPV exhibited moderate stability, however the ECO TPV showed severe deterioration, as seen by major increases in weight and volume, as well as notable changes in DSC profiles. Surface degradation and cracking, especially in ECO TPV samples, were observed using SEM investigation. The hardness results indicated little changes in hardness after exposure to the various chemical aging techniques. The results indicate that EPDM and TPV are better suited for use in acidic conditions, such as fuel-cell systems. However, ECO TPV may need extra stabilization in order to enhance its endurance.
... Thus, the composite materials undergo ageing techniques such as thermal and water ageing. Thus, the aging condition provides a flexible technique for investigating the physical and chemical changes within in the composite [28]. In addition, the term thermal ageing describes how materials change in characteristics when subjected to heat and moisture loads. ...
Increase in usage plastic substance has dominated the effects of global warming by directly burn and dump those PET (Polyethylene terephthalate) like plastic substance in the open atmosphere. This study investigates the mechanical, thermal, and flammability properties of vinyl ester composites reinforced with 30 vol% Areca fruit fiber, cellulose, and a recycled PET bottle waste foam core, with a focus on the effects of silane coupling agents on these properties. The recycled PET bottle waste foam and Areca fruit fiber were surface-modified using a 3-Aminopropyltrimethoxysilane (APTMS) coupling agent to enhance interfacial bonding and improve the composites’ resistance to thermal and water-induced degradation. Post-fabrication, the composites underwent aging under various conditions, including exposure to borewell water, reverse osmosis water (RO), and elevated temperatures of 40 °C and 50 °C for200 hrs. The results demonstrated that silane-treated composites with 30 vol% Areca fibers provided significantly better shear, thermal conductivity, and flammability, drilling properties than their untreated counterparts, even after extensive aging. Silane-treated composites, including B2, C2, D2, and E2, showed significant improvements in mechanical, thermal, and flammability properties under various aging conditions. For composite B2, aged in borewell water for 200 h, rail shear strength increased from 17.18 MPa to 19.2 MPa, lap shear strength from 17.33 MPa to 20.3 MPa, and thermal conductivity from 0.14 W/mK to 0.17 W/mK. Moreover, composite D2, aged at 40 °C, showed improvements in rail shear strength from 16.34 MPa to 18.3 MPa, lap shear strength from 16.2 MPa to 19.2 MPa, and thermal conductivity from 0.12 W/mK to 0.15 W/mK. Furthermore, the SEM analysis of silane-treated vinyl ester composites reveals that the application of silane coupling agents and the inclusion of cellulose significantly enhance interfacial bonding and microstructural integrity. Drilling tests on silane-treated composites with 60 vol% PET foam core, 30 vol% areca fiber, and 3 vol% cellulose filler using 4 mm and 8 mm top drill diameters show reduced kerf widths compared to untreated composites. These findings confirm that the application of silane coupling agents significantly enhances the thermal stability, water resistance, and overall durability of the composites, making them suitable for demanding applications requiring high mechanical strength, effective thermal management, and robust fire resistance, particularly under challenging environmental conditions.
... While these ions are advantageous for FNR latex production and preservation, their potential detrimental effects on NR should not be overlooked (9). The omnipresent thermo-oxidizing environment can degrade the properties of NR products, culminating in product failure (10), a phenomenon termed thermo-oxidative aging (11)(12)(13). During this aging process, oxidative degradation of NR generates oxygen-containing functional groups (14), leading to chain scission (15). ...
Metal ions are crucial in the production and preservation of fresh natural rubber latex. However, they also catalyze the thermo-oxidative aging of rubber products, leading to premature product degradation. This study investigates the use of tannic acid (TA) to chelate metal ions, thereby enhancing the thermo-oxidative aging resistance of natural rubber (NR). The findings indicate that NR treated with a 1.5 g·L⁻¹ TA solution exhibits superior tensile strength, elongation at break, and crosslink density post-thermo-oxidative aging compared to untreated samples. Analysis of ultraviolet–visible absorption spectra, Fourier transform infrared spectra, and X-ray photoelectron spectroscopy confirms that TA’s resistance to thermo-oxidative aging stems from its ability to form stable chelates with metal ions, reducing their catalytic activity and mitigating oxidative degradation. Consequently, TA chelation treatment is proposed as an effective method to enhance the thermo-oxidative aging resistance of NR.
... This trend correlates with the results of pore size distribution analysis by nitrogen adsorption-desorption. The empirical concept of accelerated aging based on the Arrhenius equation for silicone rubber degradation is expected to be applicable to PMSQ aerogels [39,40]. The acceleration factor of aging per hour at each temperature was calculated, and compared to 25°C, it is 4 and 21 times for 40 and 60°C, respectively. ...
Practical aspects of the successful preparation of monolithic poly(methylsilsesquioxane) (PMSQ) aerogels with glasslike transparency via ambient pressure drying (APD) are discussed in detail. Two-step acid-base process starting from methyltrimethoxysilane (MTMS) in the presence of nonionic poly(ethylene oxide)- block -poly(propylene oxide)- block -poly(ethylene oxide) surfactant and the use of strong base as polycondensation catalyst resulted in fine mesoporous structure, showing low density (0.148 g cm ⁻³ ) and glasslike transparency (95% at 10 mm thickness). Cracking and irreversible shrinkage during APD have been prevented by optimized aging and drying processes. In particular, aging in an aqueous alcohol solution containing a low concentration of MTMS under controlled temperature has been found to be crucial in obtaining PMSQ aerogels with crack-free, low-density, glasslike transparency, and monolithic nature. A large-area APD aerogel in 120×120×6 mm ³ , with thermal conductivity of 15.6 mW m ⁻¹ K ⁻¹ , has successfully been obtained due to optimizations of aging and drying conditions. Similar APD aerogels have also been obtained when alkali metal hydroxides, especially lithium hydroxide, are employed as base catalysts. These findings are expected to play important roles in designing industrial productions of monolithic aerogels for thermal superinsulation and other applications.
... The empirical concept of accelerated aging based on the Arrhenius equation for silicone rubber degradation is expected to be applicable to PMSQ aerogels [39,40]. In other words, the properties of aerogels obtained by different aging conditions can be predicted by extending aging duration at 25°C and calculated using "corresponding accelerated days", which is obtained by multiplying actual days of aging by the acceleration factor at the aging temperature of interest defined below. ...
Practical aspects of the successful preparation of monolithic poly(methylsilsesquioxane) (PMSQ) aerogels with glasslike transparency via ambient pressure drying (APD) are discussed in detail. Two-step acid-base process starting from methyltrimethoxysilane (MTMS) in the presence of nonionic poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) surfactant and the use of strong base as polycondensation catalyst resulted in fine mesoporous structure, showing low bulk density (0.148 g cm⁻³) and glasslike transparency (95% at 10 mm thickness). Cracking and irreversible shrinkage during APD have been prevented by optimized aging and drying processes. In particular, aging in an aqueous alcohol solution containing a low concentration of MTMS under controlled temperature has been found to be crucial in obtaining PMSQ aerogels with crack-free, low-density, glasslike transparency, and monolithic nature. A large-area APD aerogel in 93 × 93 × 6 mm³, with thermal conductivity of 15.6 mW m⁻¹ K⁻¹, has successfully been obtained due to optimizations of aging and drying conditions. Similar APD aerogels have also been obtained when alkali metal hydroxides, especially lithium hydroxide, are employed as base catalysts. These findings are expected to play important roles in designing industrial productions of monolithic aerogels for thermal superinsulation and other applications.
Graphical Abstract
... There are references that can be used as examples and help to understand the process of mechanism equivalence evaluation [31,45] and link function construction [46,47]. These refences studied different materials in different environments, including metals [16,17] and coatings [8,48] in both laboratory and field environments. ...
Conventional indoor corrosion test design methods primarily focus on the rapid evaluation of material corrosion resistance, often neglecting the impact of environmental stress levels on the equivalence of corrosion mechanisms. This study introduces a novel indoor corrosion test design method based on the principle of corrosion mechanism equivalence, aimed at improving the accuracy of indoor accelerated corrosion simulations. We define the characteristic of corrosion mechanism equivalence as the Corrosion Mechanism Equivalence Degree (CMed), which quantifies the similarity between corrosion mechanisms in indoor accelerated tests and field tests. Then, modified conventional link function models are defined, integrating the probability distribution of environmental factors to estimate corrosion model parameters more precisely. Finally, an optimization problem is constructed for accelerated corrosion tests based on CMed, incorporating constraints on environmental stress levels and acceleration factors. A case study demonstrates the proposed method’s ability to accurately simulate the actual service environment of materials, determining the appropriate stress levels for indoor accelerated corrosion tests while ensuring the desired acceleration factor and corrosion mechanism equivalence.
... Cured NR is an elastomer that can withstand more ultimate stress than other elastomers and maintain elastic properties at large strains. This is due to unsaturated carbon-carbon bonding (C=C) in the chemical structure of NR [3]. So, NR is one of the main options in designing parts of systems that require suitable mechanical properties. ...
Elastomers have diverse properties that make them suitable for use in many industrial applications. Natural Rubber, in particular, is an attractive elastomer due to its desirable mechanical properties as well as lightweight compared to metals. However, due to the natural rubber structure, these elastomers are susceptible to heat, oxidation, and chemical compounds, which limits their potential use. In this paper, in order to study the behavior of natural rubber under thermo-oxidative aging, experiments, including continuous stress relaxation, creep, and intermittent tensile tests, are carried out on the samples. Based on the experimental results and using dynamic-network model, a mechanical-chemical-diffusion model is proposed to predict the changes in natural rubber properties during thermo-oxidative aging considering the effect of the natural rubber curing system. In the chemical part of the model, the two main process of aging, including chain scission and crosslinking, are modeled by using two internal variables. The proposed model is implemented using the finite element method to simulate experimental tests for the model verification. The comparisons demonstrate the proposed model ability to accurately simulate the various loading states under thermo-oxidative aging of natural rubber.
... Rubber made of styrene and butadiene monomers is known as styrene-butadiene rubber (SBR), and it is a form of synthetic rubber. SBR has a variety of properties, such as good mechanical properties and excellent wear resistance, that qualify it for many applications such as tires, shoe soles, conveyers, seals, and electrical insulators Tayefi, 2023). Many fillers, such as carbon black (Mostafa, 2009), silica (Lei, 2010), carbon nanotubes (Peddini, 2015), graphene oxide (Khan, 2022), clay (Lolage, 2022), and carbon fibers (Andideh, 2022), were used to reinforce SBR resulting in a composite with improved properties. ...
Hydrophobic nanoparticle copolymers of vinyl acetate and different ratios of veova10 were used to coat Pisum sativum L. fibers (PSF). The impact of coating process on the reinforcement efficiency of PSF of styrene butadiene rubber (SBR) was investigated. The morphology study, indicated that, the coating with hydrophobic nanoparticle copolymers improved the interfacial adhesion between the PSF and SBR. The tensile strength (TS) of the composites containing coated fibers recorded the highest tensile properties, the lowest Mullins effect and the highest resistance to water absorption. The coating process improved the TS of PSF/SBR composite up to 35.3% after incorporation of 10 phr of coated PSF. The PSF/SBR composite containing 20 phr of coated fibers recorded water uptake of 14.18% compared to 23.24% for composites containing uncoated fibers. The PSF/SBR composites exhibited more biodegradation rate than that of neat SBR. The results indicated that the PSF coated with the prepared hydrophobic polymers had a beneficial impact on the physicomechanical properties of the PSF/SBR composites.
The mechanical properties of polymer composites under the influence of external agents (heat, temperature, contact fluids) have been investigated in several industrial areas, such as aerospace, automotive, and petroleum. This study aimed to explore the relationship between environmental exposure and mechanical properties, given its impact on the final mechanical performance, service life, and industrial applications of reinforced composites. In the present study, three laminate plates with a polymeric matrix were manufactured, and reinforced with bidirectional E-glass fiber and Kevlar-49 fabric. The laminates were industrially produced using a hand lay-up process and immersed in fluids (crude oil and seawater) to investigate the relationship between fluid immersion and mechanical properties, highlighting the effects observed under the imposed conditions, apparent morphology, the microstructure of post-immersed samples, and final mechanical performance. Comparative results (dry vs wet) demonstrated that fluid contact did not significantly reduce strength, except for the IGK laminate, which showed a 19% reduction when immersed in petroleum and tested under bending, all other values remained below 10%. However, the losses in elastic modulus were more significant, reaching up to 50% rigidity loss in some cases. Morphological analysis showed resin degradation and petroleum impregnation due to chloride ions from seawater and crude oil exposure.
Polymers, ubiquitous in modern life, undergo static and dynamic ageing processes that significantly impact their mechanical, thermal and chemical properties over time. This contribution provides a comprehensive overview of the static and dynamic ageing phenomena observed in polymers, encompassing mechanisms, influencing factors and implications across various industries. The ageing of polymers involves intricate chemical reactions such as oxidation, hydrolysis and photo-degradation, leading to molecular rearrangements, chain scission and the formation of degradation products. Factors influencing polymer ageing include environmental conditions (e.g. temperature, humidity and UV radiation), mechanical stress, chemical exposure and material composition. Understanding the statics and dynamics of polymer ageing is crucial for predicting material behaviour, optimizing product performance, and ensuring safety and reliability in diverse applications. In the automotive sector, for instance, ageing-related degradation can affect the structural integrity of polymer components, impacting vehicle safety and longevity. Similarly, in the packaging industry, knowledge of polymer ageing kinetics is essential for designing sustainable packaging solutions with extended shelf life and reduced environmental impact. Therefore, the computer-based simulation and prediction of polymer ageing with adequate calibrated models is essential. This is the point where this article applies. A one-dimensional thermomechanical consistent model is developed and presented which is able to capture dynamic ageing processes in the frequency and time domains. Meaningful simulations demonstrate the model’s ability to reasonably depict various ageing effects. A brief summary and a comprehensive outlook on the upcoming work complete this contribution.
Rubber materials are extensively used in the industrial sector, where aging is a critical factor affecting the performance of various rubber materials in industrial applications. After aging, rubber surfaces exhibit crazing, a type of crack that currently relies on subjective visual observation. This method suffers from issues such as subjective judgment bias, difficulty in dynamic tracking, and quantification challenges. This study proposes an objective and effective method for identifying and analyzing the degree of erosion of rubber surfaces due to aging. The results of this research provide an automated recognition scheme for a deeper understanding of the rubber material aging process, making it possible to record the dynamic process of crack propagation and establish a relationship between morphology and performance. Furthermore, it provides process data for developing strategies to improve the aging resistance of rubber materials.
This paper introduces a novel methodology for predicting the lifetime of nonmetallic materials exposed to downhole environments, including high and low pH, H2S, H2, CO2, and brines. The methodology was developed based on fundamental material principles, including viscoelasticity, hyperelasticity, and chemical/physical degradation from laboratory aging tests, field data, and finite-element analyses. This paper describes four case studies that show this methodology's effectiveness in defining the operational limits of polymeric materials. They cover 1) a fluoroelastomer O-ring from an oilfield tool; 2) Nitrile rubber (NBR) and Hydrogenated nitrile butadiene rubber (HNBR) sealing elements degraded by H2S from a well testing job; 3) an HNBR permanent element production packer; and 4) the CO2/H2 compatibility and rapid gas decompression (RGD) of typical elastomers for carbon capture and sequestration (CCS), and H2 well storage. The proposed methodology enables a more comprehensive prediction of the sealing perform
The deterioration of organic anticorrosive coating systems not only diminishes the lifetime of underlying metals but also incurs substantial economic losses and the risk of unforeseen catastrophes. Thus, rigorously monitoring and accurately predicting the lifetime of organic anticorrosive coatings are crucial. In this paper, we introduce a new approach for monitoring the electrochemical performance and predicting the durability of organic coatings. Initially, we propose a model grounded in degradation mechanisms that merges an aging kinetic model of the coating with the three-phase Wiener process, accurately representing the degradation trajectory and its inherent uncertainties. We then apply change point detection techniques, utilizing the t distribution test and the Schwarz Information Criterion, to delineate the three distinct phases of coating degradation. By defining new failure criteria based on degradation thresholds and stages, we develop a reliability model for coating systems and apply the Fiducial Inference-Monte Carlo method for numerical solutions and interval estimations. To corroborate the efficacy of our methodology, we designed electrochemical sensors for coatings and executed accelerated degradation experiments in the laboratory. The model parameters derived from the initial three sets of test data successfully predict the behavior of the fourth data set, verifying the effectiveness of the proposed method.
The aging failure process of acrylic resin (AR) coatings widely used in ship anti-corrosion systems is highly complex. Currently, there are no established models or methods for predicting the aging of AR coatings in different marine environments. Therefore, this study proposes a framework for predicting the aging of AR coatings in marine environment based on short-term indoor accelerated tests. Initially, a comprehensive aging evaluation method for AR coatings is developed by integrating three commonly used coating performance evaluation indicators (gloss, color difference, and electrochemical impedance) based on the Technique for Order Preference by Similarity to Ideal Solution. Subsequently, an aging severity index is defined to quantify the impact of different environments on the coating aging process. Following this, 14 sets of indoor accelerated aging tests for AR coatings under various environmental conditions are conducted. Based on the test results, a comparative analysis of the predictive performance of three environmental effect models, namely multiple linear regression model, generalized Eyring model, and genetic algorithm-back-propagation model, is performed. Finally, utilizing the environmental effect models and global marine environmental data, the aging severity index of AR coatings in global marine environments is predicted and extrapolated.
To investigate the aging performance and storage lifetime of rubber materials used in flexible joint elastomers for solid rocket engines, a compression permanent deformation was used as the performance evaluation index to conduct aging tests on the elastic specimens of joint rubber materials at different temperatures. The results showed that the compression permanent deformation increased with the aging time and temperature, and the value of compression permanent deformation was greater in the initial stage of aging than in the later stage. Based on the regularity of material aging performance, the storage lifetime of rubber materials at room temperature of 25°C is extrapolated to be approximately 17.35 years through the linear equation of aging kinetics. Given that the aging mechanism remains unchanged, the calculation based on the principle of time-temperature equivalence reveals that as the aging temperature of the rubber material increases, the accelerated aging time to reach the regular storage lifetime becomes faster. Aging for 11.25 days at 140°C is equivalent to storing for this rubber material 15 years at 25°C. This research provides references for the future design, manufacturing, maintenance, and storage reliability of flexible joints.
The antioxidant N-isopropyl-N′-phenyl-p-phenylenediamine (4010NA) was dissolved in ethanol and impregnated into silica aerogel (SAG) via vacuum-pressure cycles, yielding composite particles (A-N) with enhanced sustained-release and reinforcing capabilities. The effect of A-N on the mechanical properties and thermal-oxidative aging resistance of styrene-butadiene rubber (SBR) vulcanizates was investigated. TGA and BET assessments indicated that the loading efficiency of 4010NA in SAG reached 14.26% within ethanol’s solubility limit. Incorporating A-N into SBR vulcanizates significantly elevated tensile strength by 17.5% and elongation at break by 41.9% over those with fumed silica and free 4010NA. Furthermore, A-N notably enhanced the thermal-oxidative aging resistance of SBR. After aging for 96 h at 100 °C, the tensile strength and elongation at break of SBR with A-N sustained 70.09% and 58.61% of their initial values, respectively, with the retention rate of elongation at break being 62.8% higher than that of SBR with fumed silica and free antioxidant. The study revealed that A-N composite particles significantly inhibited the crosslinking in SBR’s molecular chains, reducing hardening and embrittlement during later thermal-oxidative aging stages.
This paper delves to improve the upper‐limit temperature of hydrogenated nitrile rubber (HNBR) through regulation of the vulcanization process, filler system and cross‐linking additive. The tensile test and scanning electron microscope images showed that the aging at 180°C significantly accelerated the deterioration in the property of HNBR compared with 150°C aging. The results showed that a higher dosage of bis(1‐(tert‐butylperoxy)‐1‐methylethyl)‐benzene curing agent reduced the compression set of HNBR without sacrificing its tensile strength. Carbon black N539‐filled HNBR exhibited high tensile strength, while carbon black N774‐filled HNBR showed high heat resistance and low compression set. When the HNBR sample was reinforced with 20 phr of N539 and 20 phr of N774 carbon black, it achieved low compression set, high tensile strength, and heat resistance simultaneously. Then, N,N′‐bismaleimide‐4,4′‐diphenylmethane (BMI) was introduced into the HNBR composite as a cross‐linking assistant agent. The residual strength of BMI‐modified HNBR was 20.3 MPa (the retention rate of 92.3%), and its compression set was as low as 19.2% after aging at 180°C for 72 h. Even after aging the composite at 180°C for 168 h, its strength retention rate remained at 83.2% (18.3 MPa). The approach provided here increased the upper‐limit temperature range of HNBR to 180°C.
Environmental aging induces a slow and irreversible alteration of the rubber material’s macromolecular network. This alteration is triggered by two mechanisms which act at the microscale: crosslinking and chain scission. While crosslinking induces an early hardening of the material, chain scission leads to the occurrence of dangling chains responsible of the damage at the macromolecular scale. Consequently, the mechanical behavior as well as the fracture properties are affected. In this work, the effect of aging on the mechanical behavior up to fracture of elastomeric materials and the evolution of their fracture properties are first experimentally investigated. Further, a modeling attempt using an approach based upon a micro-mechanical but physical description of the aging mechanisms is proposed to predict the mechanical and fracture properties evolution of aged elastomeric materials. The proposed micro-mechanical model incorporates the concepts of residual stretch associated with the crosslinking mechanism and a so-called “healthy” elastic active chain (EAC) density associated with chain scission mechanism. The validity of the proposed approach is assessed using a wide set of experimental data either generated by the authors or available in the literature.
This study investigated the service life prediction of fluorocarbon elastomers that are used in automotive vapor fuel hoses under thermal environments. The changes in mechanical properties such as the tensile strength, elongation, compression set (CS), and hardness according to thermal aging were investigated for two types of ternary fluoroelastomers. Destructive tests of the tensile strength and elongation showed large variations in the mechanical properties under the same condition because there is no continuity of samples. In contrast, nondestructive tests of the CS and hardness showed little variations in the mechanical properties under the same condition. The elongation, CS, and hardness were selected as the physical parameters for service life prediction as they showed a tendency according to the aging temperature, which is an accelerating factor. The effective activation energy derived using each physical parameter was 74.91–159.6 kJ mol⁻¹, and the service life was 17.8–140 × 10³ h based on B10. In this study, hardness, which has a small deviation between samples, is considered appropriate as mechanical parameter for predicting the service lifetime.
The thermal decomposition of brominated butyl rubber under air atmosphere was investigated by thermogravimetry (TG) and derivative thermogravimetry (DTG) at various heating rates. The kinetic parameters were evaluated by TG and the isoconversional method developed by Ozawa. One prominent decomposition stage was observed in the DTG curves at high heating rates, while an additional small peak was observed at low heating rates. The apparent activation energy determined using the TG method ranged from 219.31 to 228.13 kJ·mol⁻¹ at various heating rates. The non-isothermal degradation was found to be a first-order reaction, and the activation energy, as determined by the isoconversional method, increased with an increase in mass loss. The kinetic data suggest that brominated butyl rubber has excellent thermal stability. This study can indirectly aid in improving rubber pyrolysis methods and in enhancing the heat resistance of materials.
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.
In this paper, the applications of thermoplastic, thermoset polymers, and a brief description of the functions of each subsystem are reviewed. The synthetic route and characteristics of polymeric materials are presented. The mechanical properties of polymers such as impact behavior, tensile test, bending test, and thermal properties like mold stress-relief distortion, generic thermal indices, relative thermal capability, and relative thermal index are mentioned. Furthermore, this paper covers the electrical behavior of polymers, mainly their dielectric strength. Different techniques for evaluating polymers’ suitability applied for electrical insulation are covered, such as partial discharge and high current arc resistance to ignition. The polymeric materials and processes used for manufacturing cables at different voltage ranges are described, and their applications to high voltage DC systems (HVDC) are discussed. The evolution and limitations of polymeric materials for electrical application and their advantages and future trends are mentioned. However, to reduce the high cost of filler networks and improve their technical properties, new techniques need to be developed. To overcome limitations associated with the accuracy of the techniques used for quantifying residual stresses in polymers, new techniques such as indentation are used with higher force at the stressed location.
In this study, the combustion characteristics and emission of toxic gases of a non-class 1E cable in a nuclear power plant were investigated with respect to the aging period. A thermal accelerated aging method was applied using the Arrhenius equation with the activation energy of the cables and the aging periods of the cables set to zero, 10, 20, 30 and 40 years old by considering the lifetime of a nuclear power plant. According to ISO 5660-1 and ISO 19702, the cone calorimeter Fourier transform infrared spectroscopy test was performed to analyze the combustion characteristics and emission toxicity. In addition, scanning electron microscopy and an energy dispersive X-ray spectrometer were used to examine the change in the surface of the sheath and insulation of the cables according to the aging periods. To compare quantitative fire risks at an early period, the fire performance index (FPI) and fire growth index (FGI) are derived from the test results of the ignition time, peak heat release rate (PHRR) and time to PHRR (tPHRR). When comparing FPI and FGI, the fire risks decreased as the aging period increased, which means that early fire risks may be alleviated through the devolatilization of both the sheath and insulation of the cables. However, when comparing heat release and mass loss, which represent the fire risk at the mid and late period, fire intensity and severity increased with the aging period. The emission of toxic gases coincided with the results obtained from the heat release rate, which confirms that the toxicity of non-aged cables is higher than that of aged cables. From the results, it can be concluded that the aging period significantly affects both the combustion characteristics and toxicity of the emission gas. Therefore, cable degradation with aging should be considered when setting up reinforced safety codes and standards for cables and planning proper operation procedures for nuclear power plants.
This study examines the influence of various electrical parameters on the volume resistivity of the Viton fluoroelastomer. The transient current, the temperature dependence of volume resistivity, the voltage dependence of resistivity, and the surface morphology of Viton insulators are investigated for new and aged specimens. An accelerated aging process has been employed in order to simulate the natural aging of insulators in service. A detailed comparison between the new and aged samples is presented. The transient effect, which is a challenge to the resistivity measurement of insulators, has been investigated. The first 60 s of the resistivity measurement test showed a significant influence from the transient effect and should be excluded from the data. The volume resistivity of both new and aged samples decreased when the temperature increased. However, the resistivity of the aged sample was lower than the new one at all tested temperatures. When the temperature increased from 35 to 190 °C, resistivity decreased from 4.77 × 10¹⁰ to 6.99 × 10⁸ Ω-cm for the new sample and from 2.6 × 10¹⁰ to 6.68 × 10⁸ Ω-cm for the aged sample under 500 V. Additionally, the results from this study showed that the volume resistivity is inversely proportional to the applied voltage. Finally, scanning electron microscope (SEM) micrographs/images allowed us to closely examine the surface morphology of new and aged Viton samples. The surface of aged samples has been recognized with higher surface roughness and more significant surface cracks leading to poor performance under high voltage applications.
The thermo-oxidation (70–160 °C) of two polymeric materials widely used as electrical insulators in cable systems was studied. The polymers are cross-linked polyethylene (XLPE) and cross-linked ethylene propylene rubber (XLEPR). Characterisation of the aged materials was performed by using FTIR spectroscopy, gel fraction, differential scanning calorimetry and tensile tests. Correlations were observed between the formation of oxidation products, the changes in crystallinity, the variation in gel content and the reduction in mechanical properties in both materials. By using a classical Arrhenius methodology, activation energies of XLPE and XLEPR were calculated in the temperature range 70–160 °C from spectroscopic measurements on 200 μm thick films and from tensile test results on 1 mm thick samples: the average values are 103 kJ mol⁻¹ for XLPE and 102 kJ mol⁻¹ for XLEPR. The results were consistent despite a diffusion-limited oxidation (DLO) effect observed in the 1 mm thick samples.
Acrylonitrile–butadiene rubber (NBR) is an important tribological material that is often used in dynamic sealing pairs (as rubber/metal seal-pairs), but often degrades prematurely because of thermal oxidation ageing. In this work, NBR seals were exposed to an accelerated thermal ageing atmosphere at different temperatures and time periods, and the aged NBRs were evaluated for their mechanical properties, tribological behaviour, and energy dissipation. The results showed that thermal oxidation ageing has a substantial effect on rubber properties. The hardness and bulk modulus of rubber increased, whereas its tensile strength and tear strength decreased remarkably with increasing ageing temperature and time. The evolution trends of rubber ageing can be divided into three regions (A, B, and C) according to different ageing degrees (high elastic state, weakened elastic state, and hardening state). The damage mechanism of each region is obviously different. The wear mechanism gradually changes from adhesive wear to abrasive wear, or fatigue and abrasive wear. Although the average wear rate decreases with the increase of ageing parameters, mechanical properties, such as viscoelasticity, fracture resistance, and tear resistance, were severely reduced or even disappeared. The adhesion and hysteresis characteristics of the rubber during friction were remarkably disturbed because of their ageing degradation. Therefore, different energy dissipation characteristics in friction were presented for various aged rubbers.
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.
Being able to predict the lifetime of elastomers is fundamental for many industrial applications. The evolution of both tensile and compression behavior of unfilled and filled neoprene rubbers was studied over time for different ageing conditions (70 °C, 80 °C and 90 °C). While Young’s modulus increased with ageing, the bulk modulus remained almost constant, leading to a slight decrease in the Poisson’s ratio with ageing, especially for the filled rubbers. This evolution of Poisson’s ratio with ageing is often neglected in the literature where a constant value of 0.5 is almost always assumed. Moreover, the elongation at break decreased, all these phenomena having a similar activation energy (~80 kJ/mol) assuming an Arrhenius or pseudo-Arrhenius behavior. Using simple scaling arguments from rubber elasticity theory, it is possible to relate quantitatively Young’s modulus and elongation at break for all ageing conditions, while an empirical relation can correlate Young’s modulus and hardness shore A. This suggests the crosslink density evolution during ageing is the main factor that drives the mechanical properties. It is then possible to predict the lifetime of elastomers usually based on an elongation at break criterion with a simple hardness shore measurement.
To improve the predictive capability of long-term stress relaxation of elastomers during thermo-oxidative ageing, a method to separate reversible and irreversible processes was adopted. The separation is performed through the analysis of compression set after tempering. On the basis of this separation, a numerical model for long-term stress relaxation during homogeneous ageing is proposed. The model consists of an additive contribution of physical and chemical relaxation. Computer simulations of compression stress relaxation were performed for long ageing times and the results were validated with the Arrhenius treatment, the kinetic study and the time-temperature superposition technique based on experimental data. For chemical relaxation, two decay functions are introduced each with an activation energy and a degradative process. The first process with the lower activation energy dominates at lower ageing times, while the second one with the higher activation energy at longer ageing times. A degradation-rate based model for the evolution of each process and its contribution to the total system during homogeneous ageing is proposed. The main advantage of the model is the possibility to quickly validate the interpolation at lower temperatures within the range of slower chemical processes without forcing a straight-line extrapolation.
O-rings made of HNBR, EPDM and FKM were aged in the compressed and uncompressed state at 150 °C, 125 °C, 100 °C, 75 °C, 60 °C and 23 °C for aging times of up to five years. Hardness was measured and increased with aging time and temperature for HNBR and EPDM, but it remained practically constant for FKM. Indenter modulus measurements were performed on the lateral O-ring surface (that was free of DLO effects) to assess an influence of the compression during aging, but none was detected. The equilibrium compression set (CS) exhibited faster and stronger degradation than hardness and was used for lifetime predictions using the time-temperature superposition (TTS) principle. With an end-of-lifetime criterion of 70% CS, lifetimes of 4.5 years, 50 years and 526 years at 75 °C were estimated for HNBR, EPDM and FKM, respectively. The activation energies derived from an Arrhenius plot of the shift factors from the TTS were 85 kJ/mol, 99 kJ/mol and 78 kJ/mol for HNBR, EPDM and FKM, respectively, revealing that a higher activation energy does not necessarily mean that the material has a higher lifetime at lower temperatures. Furthermore, the measured lifetime of EPDM O-rings at 100 °C (5 years) was compared to that predicted on the basis of the lifetime at 150 °C as well as 125 °C using the corresponding shift factors. The error of the prediction was only ±4%. However, this precise prediction could only be achieved using the five-year long-term aging data. When using only data from aging times up to 0.5 years and 2 years, the lifetime of EPDM O-rings at 100 °C was underestimated by 31% and 22%, respectively.
Determining a suitable and reliable end-of-lifetime criterion for O-ring seals is an important issue for long-term seal applications. Therefore, seal failure of ethylene propylene diene rubber (EPDM) and hydrogenated nitrile butadiene rubber (HNBR) O-rings aged in the compressed state at 125 °C and at 150 °C for up to 1.5 years was analyzed and investigated under static conditions, using both non-lubricated and lubricated seals. Changes of the material properties were analyzed with dynamic-mechanical analysis and permeability experiments. Indenter modulus measurements were used to investigate DLO effects. It became clear that O-rings can remain leak-tight under static conditions even when material properties have already degraded considerably, especially when adhesion effects are encountered. As a feasible and reliable end-of-lifetime criterion for O-ring seals under static conditions should include a safety margin for slight dimensional changes, a modified leakage test involving a small and rapid partial decompression of the seal was introduced that enabled determining a more realistic but still conservative end-of-lifetime criterion for an EPDM seal.
Butyl rubber-based composite (BRC) is one of the most popular materials for the fabrication of protective gloves against chemical and mechanical risks. However, in many workplaces, such as metal manufacturing or automotive mechanical services, its mechanical hazards usually appear together with metalworking fluids (MWFs). The presence of these contaminants, particularly at high temperatures, could modify its properties due to the scission, the plasticization and the crosslinking of the polymer network and thus lead to severe modification of the mechanical and physicochemical properties of material. This work aims to determine the effect of temperature and a metalworking fluid on the mechanical behavior of butyl rubber composite, dealing with crosslinking density, cohesion forces and the elastic constant of BRC, based on Mooney–Rivlin’s theory. The effect of temperature with and without MWFs on the thermo-dynamical properties and morphology of butyl membranes was also investigated. The prediction of service lifetime was then evaluated from the extrapolation of the Arrhenius plot at different temperatures.
In this work the use of polyurethane chemical recycling product (i.e. glycolysis of polyurethane waste realized with the mass excess of polymer) as a plasticizer for natural rubber-based composites was proposed. The effect of plasticizer type (napthenic oil and polyurethane foam glycolysate) and amount (2, 4, 6 or 8 parts per 100 parts of natural rubber) on the processing properties of rubber mixtures and chemical structure, swelling, mechanical and thermo-mechanical properties of natural rubber/carbon black composites was investigated. The effect of applied plasticizer was studied in the context of accelerated thermal aging (thermo-oxidative aging) which was applied for the prepared natural rubber-based composites. The obtained results confirm that the polyurethane foam glycolysate can be successfully used as a plasticizer for the preparation of natural rubber composites. Moreover, it was found that glycolysate acts as a vulcanization accelerator and reduces decreasing of mechanical properties during the accelerated thermal aging.
Low‐density polyethylene (LDPE)/carbon black (CB) composites were fabricated via melt‐compounding technique. The percolation threshold was found to be around 20 wt % CB, and an electrical network formed by conductive CB was proven by scanning electron microscopy investigation. Dielectric responses depicted an interfacial relaxation peak at 20 wt % CB content. LDPE/CB composites showed an electric field‐dependent conductivity as and a hysteresis behavior around the percolation threshold region. The CB particles with high thermal conductivity increased the heat conductance of the LDPE/CB20 up to 56%. The dynamic mechanical analysis of the LDPE/CB composites exhibited a noticeable contribution of CB throughout the composites, increasing the storage and loss modulus. The physical interactions between CB particles in the filler network enhanced the thermal degradation of the LDPE/CB25 composite for more than 76°C. The maximum breakdown strength of the LDPE/CB composites appeared with an approximately 10% improvement for LDPE/CB5 than pure LDPE. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47043.
An HNBR grade (ACN 36%) with carbon black (85 phr) was selected for the investigations. Virgin materials and thermally aged samples were implemented in tensile and dynamic mechanical analysis test methods. Additionally, structural changes and chemical analysis were investigated to identify property changes. Thermal aging was carried out in a recirculating hot air oven according to ASTM E145 standard at 100, 150 and 170˚C for exposure times of 24, 72 and 168 hours each. Mechanical property changes •
Tensile test The tensile properties were tested according to DIN 53504 using a Zwick universal testing machine (Zwick Roell, Test expert, Ulm, Germany). A results graph and the measured parameters are marked in the Fig.2, where σ b and ɛ b are stress at break and elongation at break of the aged samples respectively, and E 50 , E 100 are the stress at 50% and at 100% strain of the aged sample. • DMA test The change of the tensile properties of HNBR1 after ageing at different temperatures (100˚C100˚C, 150˚C150˚C and 170˚C170˚C) and exposure times (24, 72 and 168 hours) as a percentage of the virgin sample properties are shown in Fig.6 a, b and c, where σ 0 and ɛ 0 are stress at break and elongation at break of the un-aged sample respectively. E0 50 , E0 100 are the stress at 50% and 100% strain of the un-aged sample. A clear decrease of the tensile stress was observed after aging� at 170˚C for 168 hours.
An accelerated aging study on silicone rubber exploring the effects of exposure to a functional oil (polyalkylene glycol) at elevated temperature (195°C) is reported in this paper. Variations in mechanical (tensile, tear, hardness) and thermal (conductivity, specific heat capacity) properties were monitored versus aging time while permanent deformation of the rubber was evaluated through creep and recovery measurements. Morphology and surface chemistry of the aged rubber were also investigated through scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy, respectively. Aging had a significant impact on the mechanical properties with the ultimate tensile strength and elongation at break decreasing from 7.4 MPa and 2250% in unaged samples to 1.5 MPa and 760% in 6-week aged samples, respectively. The tear strength and hardness exhibited an initial increase during the early stages of aging, followed by a decreasing trend. In contrast, the thermal properties did not change significantly and FTIR did not detect any changes in the surface chemistry of the rubber with aging. SEM however, provided evidence of an increase in brittle behavior from the morphology of the fractured surfaces.
Incorporation of nanofillers into the organic coatings might enhance their barrier performance, by decreasing the porosity and zigzagging the diffusion path for deleterious species. Thus, the coatings containing nanofillers are expected having significant barrier
properties for corrosion protection and reduce the trend for the coating to blister or delaminate.
On the other hand, high hardness could be obtained for metallic coatings by producing the hard nanocrystalline phases within a metallic matrix.
This article presents a little review on recent development of nanocomposite coatings, which provides an overview of nanocomposite coatings in various aspects dealing with the classification, preparative methods, the nanocomposite coating properties and characterization methods.
It covers potential applications in areas such as the anti-corrosion, anti-wear, superhydrophobic, self-cleaning, antifouling/antibacterial, electronics. Finally, conclusion and future trends will be also reported.
Herein, we presented a novel biodegradable copolymer via the chain extending reaction of poly(p-dioxanone)-co-poly(2-(2-hydroxyethoxy) benzoate) (PPDO-co-PDHB) prepolymer with hexamethylene diisocyanate (HDI) as a chain extender. The structures and molecular weights of PPDO-co-PDHB prepolymer and PPDO-co-PDHB-PU chain-extended copolymer are characterized via hydrogen nuclear magnetic resonance spectroscopy (¹H NMR) and viscosity test. The relationship between the molecular structures and properties of the chain-extended copolymers is established. The PPDO-co-PDHB-PU copolymers possess a better thermal stability comparing with the PPDO homopolymer. The study of mechanical properties shows that the elongation-at-break of PPDO-co-PDHB-PU are much higher than that of PPDO. The investigation of hydrolytic degradation behaviors indicates the degradation rate of PPDO can be controlled by adjusting the PDHB compositions, and proves that chain-extended copolymers exhibit an excellent hydrolytic stability being better than that of PPDO.
The effect of Machine Direction Orientation (MDO) processing on the photostabilization of LLDPE samples containing Tinuvin® 770 was studied. The amount of Tinuvin® 770 in the processed samples was deliberately chosen at a level higher than the reported solubility at ambient temperature for two main reasons: the first reason was to assess the equilibrium between the soluble and nonsoluble forms of this additive and the impact of the MDO process, and the second was to demonstrate the role of a higher temperature in accelerated artificial photoaging on the protective role played by the nonsoluble part. The results reported in this article show that at room temperature, a nonnegligible amount of Tinuvin® 770 precipitates at the surface, which is commonly termed blooming. However, the additive that bloomed at the surface can be dissolved within the polymer with increasing temperature, which is the case in the conditions of accelerated artificial photoaging but not the case of natural outdoor weathering. Such physical phenomena are responsible for a possible bias brought by temperature during accelerated photoaging, which can affect aging tests. This questions the representativeness of accelerated aging at higher temperatures for polymers containing a blooming stabilizer.
Hydrogenated nitrile butyl rubber (HNBR) elastomers are highly resistant to chemicals and degradation, and they are good candidates to be adopted in aggressive environmental conditions of high temperature and pressure. As these service parameters are common in oil and gas applications, HNBR is popular in applications such as elastomer packers in wellhead installations. This study investigated the thermal ageing behaviour of HNBR elastomers to better predict the long-term sealing performance of the packers. Elastomer compounds were thermally aged and FTIR-ATR and differential scanning calorimetry techniques were used to indicate dominant chemical reactions during ageing. Furthermore, the mechanical performance of the aged compounds were studied to investigate the effect of dominant ageing reactions on performance. It was indicated that crosslinking reaction was dominant in the ageing process of HNBR compounds up to 150 °C. This resulted in increased stiffness and alleviated elongational strains at the break. However, compounds behaved brittle at ageing temperatures above 150 °C, and from the thermal analysis, it was concluded that at those temperatures chain scission reactions overtook the ageing mechanism. Finally, an approach for life-long prediction of mechanical characteristics of the specimens showed while long-term ageing promotes elastic failure, ageing temperatures above 150 °C facilitate rupture because of the brittle response of the compounds.
It is often necessary to assess the effect of aging at room temperature over years/decades for hardware containing elastomeric components such as oring seals or shock isolators. In order to determine this effect, accelerated oven aging at elevated temperatures is pursued. When doing so, it is vital that the degradation mechanism still be representative of that prevalent at room temperature. This places an upper limit on the elevated oven temperature, which in turn, increases the dwell time in the oven. As a result, the oven dwell time can run into months, if not years, something that is not realistically feasible due to resource/schedule constraints in industry. Measuring activation energy (Ea) of elastomer aging by test methods such as tensile strength or elongation, compression set, modulus, oxygen consumption, etc. is expensive and time consuming. Use of kinetics of weight loss by ThermoGravimetric Analysis (TGA) using the Ozawa/Flynn/Wall method per ASTM E1641 is an attractive option (especially due to the availability of commercial instrumentation with software to make the required measurements and calculations) and is widely used. There is no fundamental scientific reason why the kinetics of weight loss at elevated temperatures should correlate to the kinetics of loss of mechanical properties over years/decades at room temperature. Ea obtained by high temperature weight loss is almost always significantly higher than that obtained by measurements of mechanical properties or oxygen consumption over extended periods at much lower temperatures. In this paper, data on five different elastomer types (butyl, nitrile, EPDM, polychloroprene and fluorocarbon) are presented to prove that point. Thus, use of Ea determined by weight loss by TGA tends to give unrealistically high values, which in turn, will lead to incorrectly high predictions of storage life at room temperature.
Regarded as a strategically crucial material, natural rubber (NR) plays an essential role in our daily life. However, the corresponding rubber products have been facing the problem of aging in which the ozone aging of natural rubber accounts for a crucial position. Based on the concern, the related mechanism of ozone aging for natural rubber was systematically studied in this work. Besides, to deeply understand the mechanism of ozone aging, we selected squalene, a small molecular substance with similar structure to natural rubber, to simulate the ozone aging process and analyze the molecular structure changes of natural rubber. After comprehensive characterization, the obtained results showed that the natural rubber molecular network, during the aging process, was destroyed and three newly-discovered free radicals were generated (•H, •O2⁻and •C=C), finally resulting in the weakened mechanical properties. We believe this work can provide a more insightful view toward the relevant research on the ozonolysis mechanism and the relationship of structure and performance as well as new ideas for the design of high-efficiency antioxidants for NR.
Natural rubber (NR) is acknowledged to be a strategically important material, which spans multiple applications from tires to shock absorbers, generally, the antioxidant is indispensable for NR to prolong the service life and improve the long-term reliability. Recent reports demonstrated that the purified carbon dots with the capability of scavenging oxy radicals can be effective antioxidants for rubbers. However, the application of purified CDs is greatly restricted by the multiple tedious, complicated, time-consuming, and expensive post-purification processes. Herein, we first synthesize the amine-passivated crude carbon dots (CCDs) by a facile microwave-assisted pyrolysis method, and we attempt to directly use the CCDs (without any purifications) as a novel and inexpensive antioxidant for NR. To achieve a fine CCDs dispersion within NR matrix, we disperse the CCDs into the NR matrix by the liquid feeding and in-situ compatibilizing. The CCDs fluid was firstly prepared by mixing the CCDs with water, then the CCDs fluid together with the compatibilizer was melt-compounded with NR. The results showed that the well-dispersed CCDs endowed NR with the impressive antioxidative property. Overall, this work extends application scope of CCDs and provides unique inspiration to develop novel and effective antioxidants for elastomers.
Accumulation of plastic wastes has been recently recognized as one of the most critical environmental challenges, affecting all life forms, natural ecosystems and economy, worldwide. Under this threat, finding alternative environmentally-friendly solutions, such as biodegradation instead of traditional disposal, is of utmost importance. However, up to date, there is limited knowledge on plastic biodegradation mechanisms and efficiency. From this point of view, the purpose of this review is to highlight the negative effects of the accumulation of the most conventional plastic waste (polyethylene, polypropylene, polystyrene, polyvinylchloride, polyethylene terephthalate and polyurethane) on the environment and to present their degradability potential through abiotic and biotic processes. Furthermore, the ability of different microbial species for degradation of these polymers is thoroughly discussed. The present review also addresses the contribution of invertebrates, such as insects in plastic degradation process, highlighting the vital role that they could play in the future. In total, a schematic pathway of an innovative approach to improve the disposal of plastic wastes is proposed, with view to establishing an effective and sustainable practice for plastic waste management.
ccumulation of plastic wastes has been recently recognized as one of the most critical environmental challenges, affecting all life forms, natural ecosystems and economy, worldwide. Under this threat, finding alternative environmentally-friendly solutions, such as biodegradation instead of traditional disposal, is of utmost importance. However, up to date, there is limited knowledge on plastic biodegradation mechanisms and efficiency. From this point of view, the purpose of this review is to highlight the negative effects of the accumulation of the most conventional plastic waste (polyethylene, polypropylene, polystyrene, polyvinylchloride, polyethylene terephthalate and polyurethane) on the environment and to present their degradability potential through abiotic and biotic processes. Furthermore, the ability of different microbial species for degradation of these polymers is thoroughly discussed. The present review also addresses the contribution of invertebrates, such as insects in plastic degradation process, highlighting the vital role that they could play in the future. In total, a schematic pathway of an innovative approach to improve the disposal of plastic wastes is proposed, with view to establishing an effective and sustainable practice for plastic waste management.
Plastic waste are introduced into the environment inevitably and their exposure in the environment causes deterioration in mechanical and physicochemical properties and leads to the formation of plastic fragments, which are considered as microplastics when their size is <5 mm. In recent years, microplastic pollution has been reported in all kinds of environments worldwide and is considered a potential threat to the health of ecosystems and humans. However, knowledge on the environmental degradation of plastics and the formation of microplastics is still limited. In this review, potential hotspots for the accumulation of plastic waste were identified, major mechanisms and characterization methods of plastic degradation were summarized, and studies on the environmental degradation of plastics were evaluated. Future research works should further identify the key environmental parameters and properties of plastics affecting the degradation in order to predict the fate of plastics in different environments and facilitate the development of technologies for reducing plastic pollution. Formation and degradation of microplastics, including nanoplastics, should receive more research attention to assess their fate and ecological risks in the environment more comprehensively.
Lifetime prediction of polymers requires accelerated ageing based on an increase in UV light intensity and temperature. However, the representativeness of artificial ageing is still an issue. The relevance of highly accelerated UV-induced weathering raises the question of reciprocity failure depending on the polymer. The influences of irradiance and temperature on the photooxidation kinetics of polyethylene were studied to determine the extent to which increasing light intensity leads to accelerated photooxidation of polyethylene. Polyethylene films were subjected to accelerated photooxidative experiments at various UV light intensities and different temperatures, and the amounts of carbonylated photoproducts were monitored by IR spectroscopy. The results show reciprocity failure for polyethylene photooxidation and the limits of acceleration by UV light.
In this work, the effects of thermo-oxidative ageing at different temperatures and for different exposure durations on the mechanical and the chemical properties of a styrene butadiene rubber (SBR) are presented. Uniaxial tensile tests, hardness measurements, Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR) spectra analysis, and swelling tests are carried out on as-received and aged samples. Accelerated ageing process was conducted at different temperatures (50∘C, 70∘C, 90∘C, and 100∘C) and for different exposure durations (7,14,21,28,35,45 and 60 days).This work confirm that accelerated ageing lead to a decrease of the ultimate mechanical properties and of the molar mass between cross-links in one hand, and an increase of the cross-linking density and of the material hardness, in another hand. ATR-FTIR analysis shows significant changes in the chemical structure of aged SBR samples dominated by the thermo-oxidative process, which is, mainly pronounced at high temperature and long exposure time. The ultimate mechanical properties are related to the average molar mass between cross-links. A threshold value of this property corresponding to a complete degradation of the rubber can be determined. Finally, the time–temperature equivalence principle is applied to build master curves describing the evolution of certain quantities such as molar mass between crosslinks, tensile strength, and strain at break versus the reduced time. A predictive modeling of the stress and strain at break as function of the effective ageing time is proposed which give satisfactory results.
In this paper, silicone rubber (SR) and ethylene propylene-diene monomer (EPDM) rubber used in 110 kV prefabricated joints of XLPE cables were chosen as subjects, and a multi-stress experimental device was set up to simulate the insulation interface. Different mechanical tensions and/or AC electrical stresses were applied to the rubber samples at the interface composed of XLPE and SR/EPDM. After preset times, microscopic observations, together with measurements of mechanical properties, volume resistivity, crosslinking degree, attenuated total reflectance Fourier infrared spectrum and X-ray photoelectron spectroscopy were performed. It is shown that for both materials, molecular chains are partly broken by electron or ion bombardment from the discharges under electrical stress, and micro-molecules and oxides are formed on the sample surfaces. The mechanical stress facilitates this process without changing the reaction essence. The volume characteristic parameters of SR samples degraded with aging, while those of EPDM samples remained relatively stable. It is shown that under the same interfacial electrical-mechanical stresses, SR samples shows degradation of the overall performance; while for EPDM samples, the damage occurs mainly on the surface. This is due to the different chain structures, filler types and content in the materials.
Accelerated degradation test is an effective means for rapid and convenient prediction of rubber life. In the existing research, the influence of rubber hardness on performance degradation is neglected. Thus, the life prediction results are inaccurate. A rubber ageing model considering hardness influence was established on the basis of modified traditional dynamic degeneration trajectory equation, with which the effect of dispersion of the initial hardness of rubber on service life was described. Three types of natural rubber with different hardness were considered as research objects. On the basis of different high-temperature accelerated ageing tests, the deformation trajectory equation was used to model the compression set of each sample. Identification results show the relatively stable power exponential term coefficient and constant term coefficient, whereas there is large fluctuation in the reaction rate term coefficient. To simplify the research, the power exponent term coefficient and constant term coefficient were set as fixed values. Then, the reaction rate coefficient was estimated again. The rationality of parameter re-identification result was verified by the goodness of fit. The Arrhenius and Peck models were introduced in accordance with the obtained reaction rate coefficient identification results to simulate the reaction rate coefficients. Combined with Peck and dynamic models, a modified rubber ageing life prediction model was established, with which Monte Carlo method was employed to analyse the influence of initial hardness dispersion of rubber on service life under natural environment. The effectiveness of the model was verified by comparison with measured natural ageing data. The proposed ageing life prediction model can simultaneously consider the influences of initial hardness and temperature on rubber ageing with high accuracy. This study can provide a reference for the design and reliability evaluation of rubber parts.
Mesoporous silica nanoparticles (MSNs) were firstly utilized as the delivery vehicles of antioxidant 2-mercaptobenzimidazole (MB) to fabricate highly anti-aging styrene-butadiene rubber (SBR) composites. The thermo-oxidative aging behaviour of SBR composites was systematically evaluated by mechanical testing, FTIR and XPS. For the composites with MSNs-MB and free MB, though some of free MB were consumed or migrated to the elastomer surface, the released MB from MSNs-MB steadily migrated to the free rubber phase to ensure a continuous and stable antioxidant supply for a long time. Therefore, the SBR composites with binary protection from MSNs-MB and free MB exhibited superior thermo-oxidative stability than the SBR composites with only free MB. This work proposed a reliable approach to resolve the “blooming” defects of antioxidants and extend the service life of the elastomer products, which may open up a new route for the rational design and construction of highly anti-aging elastomer composites.
A chemo-mechanical model has been developed for predicting the long-term mechanical behavior of EPDM rubbers in a harsh thermal oxidative environment. Schematically, this model is composed of two complementary levels: The “chemical level” calculates the degradation kinetics of the macromolecular network that is introduced into the “mechanical level” to deduce the corresponding mechanical behavior in tension. The “chemical level” is derived from a realistic mechanistic scheme composed of 19 elementary reactions describing the thermal oxidation of EPDM chains, their stabilization against oxidation by commercial antioxidants but also by sulfide bridges, and the maturation and reversion of the macromolecular network. The different rate constants and chemical yields have been determined from a heavy thermal aging campaign in air between 70 and 170 °C on four distinct EPDM formulations: additive free gum, unstabilized and stabilized sulfur vulcanized gum, and industrial material. This “chemical level” has been used as an inverse resolution method for simulating accurately the consequences of thermal aging at the molecular (concentration changes in antioxidants, carbonyl products, double bonds, and sulfide bridges), macromolecular (concentration changes in chain scissions and cross-link nodes), and macroscopic scales (weight changes). Finally, it gives access to the concentration changes in elastically active chains from which are deduced the corresponding changes in average molar mass MC between two consecutive cross-link nodes. The “mechanical level” is derived from a modified version of the statistical theory of rubber elasticity, called the phantom network theory. It relates the elastic and fracture properties to MC if considering the macromolecular network perfect, and gives access to the lifetime of the EPDM rubber based on a relevant structural or mechanical end-of-life criterion. A few examples of simulations are given to demonstrate the reliability of the chemo-mechanical model.
It is still a challenge to achieve simultaneous improvements in aging resistance, mechanical strength, thermal conductivity and dielectric constant of rubber composites via incorporation of graphene obtained by conventional methods. Herein, an effective and green method was proposed to simultaneously reduce and functionalize graphene oxide (GO) with 2-mercaptobenzimidazole (antioxidant MB) via a one-pot method. GO was successfully reduced by MB which was also chemically grafted on the reduced GO (G-MB). G-MB sheets were uniformly dispersed in rubber with strong interfacial interaction, and graphene-graphene conductive paths were formed through intermolecular H-bonding between the grafted antioxidant molecules. Consequently, rubber composites with G-MB showed higher thermal conductivity, mechanical strength and dielectric constant than rubber composites with hydrazine hydrate reduced GO (rGO). Moreover, the thermo-oxidative aging resistance of rubber composites with G-MB was also superior to that of rubber composites with rGO because of the elimination of blooming effect of the grafted MB molecules. Thus, this work may open a new way for the eco-friendly functionalization and reduction of GO and may boost the development of high-performance, functional graphene-elastomer composites.
This paper synergistically addressed the microstructure alteration and the mechanical behavior of rubber during thermo-oxidative aging process from both experimental and numerical modeling aspects. Through the FTIR spectra analysis, equilibrium swelling experiment, low-field NMR measurement and mechanical tests of styrene-butadiene rubber (SBR) samples, a macromolecular network alteration mechanism was introduced. The mechanism is related to the variation of the crosslinking network and dangling chain ends of SBR during aging. A finite deformation based hyper-viscoelastic constitutive model was then established to capture the mechanical behavior of SBR during aging. Based on the interpretation of the microscopic mechanism, the above-mentioned network alterations during aging were considered in the model. After the implementation by means of the finite element simulation software ABAQUS, the accuracy of the established model was checked via the comparison of the numerical results with the corresponding data obtained from mechanical tests. The work is helpful for estimating rubber mechanical performance during aging process.
This paper reviews the material properties of the seal gaskets of shield tunnels. In order to understand the function of sealing gaskets, the significance and structure of gaskets in tunnel segments are briefly introduced. Then, the material types of gasket are presented. Gasket materials include two categories: (i) the traditional elastic gasket and (ii) the hydrophilic composite elastic gasket. The traditional elastic gasket is composed of chloroprene rubber (CR) and ethylene propylene diene rubber (EPDM), in which the sealing function is implemented as a result of the elastic properties of the materials. The hydrophilic composite elastic gasket includes vulcanized water swelling rubber (WSR) and water swelling polyurethane (WSP), in which the sealing function is obtained from both the elastic properties and the water absorption ability of the gasket material. CR and EPDM were the earliest materials used in engineering practice; however, EPDM is the main material of the gasket today. The sealing mechanism of both CR and EPDM is presented at the molecule level. After that, the water absorption process for both WSR and WSP in hydrophilic composite is reviewed. Methods to improve the sealing behavior of WSR are also summarized. Furthermore, the aging of the gasket material is discussed. Finally, perspectives for future developments of new materials or ways to improve the performance of seal gaskets are proposed.
Accelerated lifetime prediction is the key technology to assure the safety and reliability of rubber products in automotive components. In the present study, carbon black (CB), which has been a conventional reinforcing filler in the rubber industry, was partially replaced by graphene in natural rubber (NR) composite system. Due to the superior intrinsic thermal conductivity of graphene, it is getting much attention to reduce heat build-up problem of vibration mount for longer lifetime in its demanding performance. Therefore this study not only focuses on the effect of graphene loading on mechanical properties of NR composites but also on the accelerated lifetime prediction of graphene-reinforced NR composites. Hardness and compressive properties were linearly increased as CB was partially replaced by graphene (1-5 phr; parts per hundred rubber) showing better reinforcing effect. In accelerated lifetime experiments, hardness and compression set were significantly changed after 24 h when the samples were exposed to 85 °C and 70 °C, respectively. From the relationship between thermal aging temperature and lifetime, Arrhenius plot using least square method was drawn to predict the lifetime of NR composites resulting that the activation energy reached at a maximum when 3 phr of graphene was filled in NR composite. Through the accelerated thermal aging test, lifetime prediction of graphene-reinforced NR composites were successfully drawn particularly focusing on compression set property which is one of the most dominant factors for the aging of vibration mount.
During the design stage of a nuclear power plant, the qualification testing is obliged to be conducted on the electrical equipment like cables to ensure the reliability and to predict the service lifetime of them under the operational conditions. Thereinto, thermal and oxidative degradation of the cable insulations and sheaths that are made of polymeric materials is the priority concern, and the renowned Arrhenius model is always referred to, which consequently calls for determination of the imperative kinetic constant - the activation energy. Actually, diverse methods for activation energies have been established by the scientists and applied by the engineers, but consensuses still have not been reached for such a method that is both convenient and conservative, and for such value ranges that are both reasonable and representative. Hence, in this paper, totally five different testing and data processing methods including thermal ageing test, differential scanning calorimetry and thermogravimetry analysis were utilized to determine the activation energies of three domestic polymeric materials that are intended for nuclear cables of the advanced pressurized water reactors in China. The results were then collected and the reasons for the differences among them were discussed, based on which the advantages and disadvantages of these methods were compared, and finally a compromising approach was proposed.
A new type of antioxidant functionalized silica (SiO2-g-MC) was prepared by grafting antioxidant N-(4-aniline phenyl) maleic imide (MC) onto the surface of silica via γ-mercaptopropyl trimethoxysilane (KH590). The effects of SiO2-g-MC on reinforcement and anti-aging for solution-polymerized styrene butadiene rubber (SSBR) were investigated by experimental and molecular simulation methods. It was found that the reinforcement of SiO2-g-MC was much more effective than that of the neat silica (SiO2) in SSBR matrix due to well-dispersion and strong interfacial interaction between SiO2-g-MC and SSBR. Compared with KH590 modified silica (SiO2-KH590) and SiO2, SiO2-g-MC had better vulcanization behavior and could greatly improve thermo-oxidation resistance of SSBR composite. Furthermore, grafting MC onto the surface of silica could not only restrain the migration of free MC, but also reduce the negative influence of free MC on cross-linking density of SSBR composite. Therefore, SiO2-g-MC/SSBR composite exhibited more preeminent mechanical properties than SiO2-KH590/MC/SSBR composites during the thermo-oxidation aging process. These results indicated that SiO2-g-MC could be used as a functional filler for the preparation of high performance SSBR composites, and moreover, the theoretical molecular simulation process can help us gain a better insight into the structure-property relationship for SSBR composite.
We reported newly prepared functionalized nanoparticles ([email protected]) using mesporous silica (MS) with antioxidant intermediate 4-aminodiphenylamine (RT) via the linkage of KH-560. [email protected] was used as a nanofiller to fabricate styrene-butadiene rubber (SBR) composites. Under the condition of equal antioxidant and filler components, functionalized mesoporous silica can greatly enhance the mechanical properties of SBR owing to the uniform dispersion and strong interfacial interaction between SBR and [email protected] Besides, the antiaging behavior of SBR/[email protected] composites was systematically evaluated by thermal oxidation exothermic enthalpies and oxidation induction time before and after solvent extraction. The results indicated that [email protected] showed much better thermal and oxidative stabilities and longer service life than the most commonly used antioxidant N-isopropyl-N′-phenyl-4-phenylenediamine in SBR due to the improved migration resistance of immobilized RT.
A novel antioxidant (HS-s-RT) to improve the mechanical properties and anti-aging performance of styrene-butadiene (SBR) composites was prepared by antioxidant intermediate p-aminodiphenylamine (RT) grafting on the surface of halloysite nanotubes/silica hybrid (HS) via the linkage of silane coupling agent. The analysis of SEM and rubber processing analyzer (RPA) demonstrated HS-s-RT was uniformly dispersed in SBR, and stronger interfacial interaction between HS-s-RT and SBR was formed. Consequently, SBR/HS-s-RT composites have improving mechanical properties. Furthermore, the test of the retention of mechanical properties, Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR), and oxidation induction time (OIT) showed HS-s-RT can effectively improve the anti-aging effect of SBR composites than corresponding low molecular-weight antioxidant N-isopropyl-N′-phenyl-4-phenylenediamin (4010NA). Then, the mechanism of thermo-oxidative aging of SBR/HS composites was also investigated, and the superior antioxidative efficiency is attributed to the uniform dispersion and excellent migration resistance of HS-s-RT. Hence, this novel antioxidant might open up new opportunities for the fabrication of high-performance rubber composites due to its superior anti-aging effect and reinforcement.
The effects of ZnO particle size on crosslinking and thermal aging behavior of natural rubber (NR) were investigated. NR vulcanizates filled with nano ZnO allowed higher crosslink density, lower polysulfide crosslink, and stronger mechanical properties than those filled with micro ZnO. After thermal aging, NR filled with nano ZnO exhibited much more stable chemical and mechanical properties. The high crosslink density as well as the formation of more stable mono- and di-sulfidic crosslinks was attributed to the good dispersion and high surface area of the nano ZnO.
To better understand the effect of rectorite and carbon black (CB) on the aging performance of styrene-butadiene rubber (SBR), SBR/CB, SBR/CB/rectorite and SBR/rectorite nanocomposites with the same total filler loading were prepared. The microstructure of the three SBR nanocomposites was characterized by XRD, TEM and SEM. After thermal aging, oxygen-containing molecules were found to be formed in the SBR nanocomposites, as verified by FTIR analysis. The SBR/rectorite nanocomposite showed the highest aging coefficient and the lowest change rate of tensile strength and stress at 100% strain among the three SBR nanocomposites, indicating that the introduction of nano-dispersed rectorite layers can enhance the thermal aging resistance of the nanocomposites. For the SBR/CB/rectorite nanocomposite, the addition of CB helped to improve the interfacial compatibility between the filler and matrix, resulting in the best crack resistance as the aged SBR/CB/rectorite nanocomposite always demonstrated the least cracks on the surface during either stretching or bending experiments.
Macromolecular antioxidant due to its low physical loss, high thermal stability, and good compatibility has been considered to be a promising candidate to inhibit polymer aging. In this study, thermo-oxidative aging resistance and antioxidative mechanism of a macromolecular hindered phenol antioxidant, namely, polyhydroxylated polybutadiene containing thioether binding 2, 2′-thiobis (4-methyl-6-tert-butylphenol) (PHPBT-b-TPH) for natural rubber (NR) vulcanizate was studied in detail by oxidation induction time and accelerated thermal aging tests. The results showed that the antioxidative efficiency of PHPBT-b-TPH was very high. When the amount of PHPBT-b-TPH was only 1 phr, the NR vulcanizate could exhibit excellent thermo-oxidative aging resistance, obviously higher than that of NR vulcanizate with low-molecular-weight antioxidant TPH. After aged at 100°C for 168 h, the retentions of tensile strength and elongation at break of NR vulcanizate with PHPBT-b-TPH were 43.6% and 58.6%, respectively. However, those of NR vulcanizate with TPH were 35.6% and 54.5%. In addition, it was found that both thioether and urethane groups in PHPBT-b-TPH had antioxidative ability and had synergistic effect with hindered phenol. Through our findings, new strategy to design and synthesize the macromolecular antioxidant with multi-antioxidative groups for rubber materials and other polymer materials could be developed.
Chemical reduction of graphene oxide (GO) by a suitable reducing agent and preparation of elastomer/graphene composites with high aging resistance and thermal conductivity are of great significance for constructing many advanced materials, such as solar cells and light emitting diodes. Herein, a facile and efficient one-step approach was developed to simultaneously reduce and functionalize GO via antioxidant N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (4020). It was found that oxygen-containing groups in GO were effectively removed and sp2 carbon network was restored after reduction. Besides, 4020 molecules (~10 wt%) was chemically bonded onto the surface of reduced GO (G-4020). As expected, G-4020 showed much better antimigratory efficiency than free 4020 in styrene-butadiene rubber (SBR) and endowed SBR composites with excellent long-term thermo-oxidative aging resistance. Moreover, the bonded 4020 molecules prevented the restacking of graphene sheets and improved the compatibility of G-4020 with SBR. Therefore, SBR/G-4020 composites possessed higher thermal conductivity and mechanical strength than SBR composites with hydrazine hydrate reduced GO, attributing to the improved dispersion of G-4020 and enhanced interfacial interaction. One-step reaction and high-efficiency make the approach of using rubber antioxidants a promising strategy for the eco-friendly reduction and functionalization of GO and may offer a new path to construct high performance elastomer/graphene composites.
Aging-resistance is an important property of rubber products for their long-term applications. Antioxidants are widely used in the rubber formula to prevent its oxidative aging. However, the blooming of antioxidants results in loss of aging protection and induces toxicity and pollutions, which limit their amounts in the rubber. Herein, a novel strategy to avoid such a blooming and improve the aging-resistance of polar acrylonitrile-butadiene rubber (NBR) composites was proposed by doping sustainable carbon nanotubes (CNTs) with antioxidants. Phenolic antioxidants, 3,9-bis-{1,1-dimethyl-2[β-(3-tert-butyl-4-hydroxy-5-methylphenyl-)propionyloxy]ethyl}-2,4,8,10-tetraoxaspiro[5,5]-undecane (AO-80) were chemically grafted and then physically absorbed to CNTs, therefore CNTs with rich antioxidants (CNT-AO80) were prepared, whose total loading efficiency of AO-80 reached 10.3 wt%. In CNT-AO80, physical loading amounts of antioxidants were 3.7 wt% and strongly suppressed by those parts from chemically grafting (6.6 wt%), developing a distribution of antioxidant around CNTs. When 20 phr CNT-AO80 were added to NBR, they allowed a good dispersity and reinforcement for the composites. After naturally aging for 1 year and a 60-day thermal-oxidative test at 90 °C, the NBR composite with CNT-AO80 gave a low variation of mechanical property without AO-80 blooming, showing a good oxidative aging resistance. We believe that the design of loading antioxidants to CNTs may provide an effective solution to extend the service lifetimes of the rubber products.
Ethylene-octene copolymer (EOC)/organically modified Montmorillonite (OMMT) nanocomposites were prepared by melt mixing method in an internal mixer. The nanocomposites were then dynamically cross-linked with 0.25, 0.5, 0.75 and 1 wt% dicumyl peroxide (DCP). The results of low angle X-ray diffraction and transmission electron microscopy (TEM) micrographs demonstrated that the OMMT platelets were mainly intercalated by EOC. According to our findings, a mechanism has been proposed for the separation of OMMT layers from each other upon cross-linking. Thermo-gravimetric analysis (TGA) showed that the OMMT incorporation enhanced the thermal degradation of EOC. A schematic diagram was also prepared to show the main steps of EOC and the nanocomposites degradation with temperature under N2 and air atmospheres. Moreover, it was found from the rheological results that all of the cross-linked nanocomposites behaved as shear thinning fluids over the entire range of frequency. The molecular weight between cross-links (Mc) was estimated using James-Guth as well as Mooney-Rivlin theory. The results indicated that Mc decreased with increasing of the curing agent.