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Effect of Thermal Treatment on Crystallinity of Poly(ethylene oxide) Electrospun Fibers

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Polymers 2019, 11(9), 1384; https://doi.org/10.3390/polym11091384 - 23 Aug 2019

Cited by 18 | Viewed by 2866

Abstract

Post-process thermal treatment of electrospun fibers obtained from poly(ethylene oxide) (PEO) water and methanol solutions was examined. PEO fibers from methanol solution showed larger diameters as observed by scanning electron microscopy. Fibers both from water and methanol solutions exhibited a significant dimensional stability [...] Read more.

Post-process thermal treatment of electrospun fibers obtained from poly(ethylene oxide) (PEO) water and methanol solutions was examined. PEO fibers from methanol solution showed larger diameters as observed by scanning electron microscopy. Fibers both from water and methanol solutions exhibited a significant dimensional stability and surface cracking during the specific exposure time after thermal treatments at 40, 50, and 60 °C. Changes in crystallinity after the thermal treatment were studied by wide-angle X-ray diffraction. The kinetics of secondary crystallization were positively influenced by the as-processed level of the amorphous phase and temperature of thermal treatment. Samples treated at 60 °C were degraded by thermooxidation within the time. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Cyclic Moisture Sorption and its Effects on the Thermomechanical Properties of Epoxy and Epoxy/MWCNT Nanocomposite

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Tatjana Glaskova-Kuzmina

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Polymers 2019, 11(9), 1383; https://doi.org/10.3390/polym11091383 - 23 Aug 2019

Cited by 11 | Viewed by 2641

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The aim of this work was to reveal the moisture absorption–desorption–resorption characteristics of epoxy and epoxy-based nanocomposites filled with different multiwall carbon nanotubes (MWCNTs) by investigating the reversibility of the moisture effect on their thermomechanical properties. Two types of MWCNTs with average diameters [...] Read more.

The aim of this work was to reveal the moisture absorption–desorption–resorption characteristics of epoxy and epoxy-based nanocomposites filled with different multiwall carbon nanotubes (MWCNTs) by investigating the reversibility of the moisture effect on their thermomechanical properties. Two types of MWCNTs with average diameters of 9.5 and 140 nm were used. For the neat epoxy and nanocomposite samples, the moisture absorption and resorption tests were performed in atmospheres with 47%, 73%, and 91% relative humidity at room temperature. Dynamic mechanical analysis was employed to evaluate the hygrothermal ageing effect for unconditioned and environmentally “aged” samples. It was found that moisture sorption was not fully reversible, and the extent of the irreversibility on thermomechanical properties was different for the epoxy and the nanocomposite. The addition of both types of MWCNTs to the epoxy resin reduced sorption characteristics for all sorption tests, improved the hygrothermal and reduced the swelling rate after the moisture absorption–desorption. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Comparative Study on the Thermal-Aging Characteristics of Cellulose Insulation Polymer Immersed in New Three-Element Mixed Oil and Mineral Oil

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Polymers 2019, 11(8), 1292; https://doi.org/10.3390/polym11081292 - 02 Aug 2019

Cited by 33 | Viewed by 3244

Abstract

Cellulose paper, whose main component is cellulose polymer, has been widely used in oil-immersed power transformer that gradually deteriorates during transformer operation. Thermal aging is the main degradation form for cellulose paper immersed in insulation oil (oil–paper insulation) in a transformer. One of [...] Read more.

Cellulose paper, whose main component is cellulose polymer, has been widely used in oil-immersed power transformer that gradually deteriorates during transformer operation. Thermal aging is the main degradation form for cellulose paper immersed in insulation oil (oil–paper insulation) in a transformer. One of the most challenging issues in oil–paper insulation is inhibiting the aging of cellulose paper and extending its life. In this work, a comparative study was conducted on the thermal-aging characteristics of cellulose paper immersed in a novel three-element mixed insulation oil and mineral oil at 130 °C for 150 days. The key parameters of cellulose paper were analysed, including the degree of polymerization (DP), thermal-aging rate, surface colour, and AC breakdown voltage. The furfural content and acidity of the oil, as well as the AC breakdown voltage of the insulation oil were also analysed. The results show that the cellulose paper immersed in novel three-element mixed insulation oil had much higher DP values than that immersed in mineral oil after the same thermal-aging time. The mixed insulation oil could significantly inhibit the thermal aging of cellulose paper and prolong its life. The thermal-aging rate of the cellulose insulation polymer immersed in mixed insulation oil is significantly lower than that immersed in mineral oil, whether in the process of oil–paper insulation continuous aging or in the process of aging after oil replacement with unused insulation oil. The furfural generated by cellulose degradation in the novel three-element mixed insulation oil was also less than that in the mineral oil. The mixed insulation oil had a higher acidity value during the thermal-aging process, which was mainly due to the natural esters in the components of the mixed insulation oil. However, the AC breakdown voltage of the mixed insulation oil was always higher than that of the mineral oil. This study offers a new perspective in inhibiting the thermal aging of cellulose polymer in insulation oil. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Influence of Reinforcement Structures and Hybrid Types on Inter-Laminar Shear Performance of Carbon-Glass Hybrid Fibers/Bismaleimide Composites under Long-Term Thermo-Oxidative Aging

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Polymers 2019, 11(8), 1288; https://doi.org/10.3390/polym11081288 - 01 Aug 2019

Cited by 11 | Viewed by 2733

Abstract

The effects of reinforcement structures and hybrid types on the inter-laminar shear strength (ILSS) of carbon-glass hybrid fibers/bismaleimide composites under thermo-oxidative aging conditions were investigated. The process resulted in progressive deterioration of the matrix and fiber/matrix interfaces, in the form of chain scissions, [...] Read more.

The effects of reinforcement structures and hybrid types on the inter-laminar shear strength (ILSS) of carbon-glass hybrid fibers/bismaleimide composites under thermo-oxidative aging conditions were investigated. The process resulted in progressive deterioration of the matrix and fiber/matrix interfaces, in the form of chain scissions, weight loss, and fiber/matrix debonding, which significantly led to the decrease of the ILSS of composites. Moreover, the three-dimensional orthogonal woven hybrid composites (3D composites) showed higher ILSS retention rate than those of the laminated orthogonal hybrid composites (laminated composites). No delamination occurred in the aged 3D composites like in the aged laminated composites. This was because the Z-binder yarns in the 3D composites resisted the inter-laminar shear load, although the resin was damaged and the adhesive force between fiber bundles and resin decreased seriously after thermo-oxidative aging. Meanwhile, the ILSS retention rate of the laminated composites with the carbon fiber as intermediate layers was higher than that of the laminated composites with the glass fiber as the intermediate layers. This was because the carbon fiber/bismaleimide interface bonding performance was stronger than that of the glass fiber/bismaleimide at the same thermo-oxidative aging condition. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Scission, Cross-Linking, and Physical Relaxation during Thermal Degradation of Elastomers

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Polymers 2019, 11(8), 1280; https://doi.org/10.3390/polym11081280 - 31 Jul 2019

Cited by 30 | Viewed by 4222

Abstract

Elastomers are susceptible to chemical ageing, i.e., scission and cross-linking, at high temperatures. This thermally driven ageing process affects their mechanical properties and leads to limited operating time. Continuous and intermittent stress relaxation measurements were conducted on ethylene propylene diene rubber (EPDM) and [...] Read more.

Elastomers are susceptible to chemical ageing, i.e., scission and cross-linking, at high temperatures. This thermally driven ageing process affects their mechanical properties and leads to limited operating time. Continuous and intermittent stress relaxation measurements were conducted on ethylene propylene diene rubber (EPDM) and hydrogenated nitrile butadiene rubber (HNBR) samples for different ageing times and an ageing temperature of 125 °C. The contributions of chain scission and cross-linking were analysed for both materials at different ageing states, elucidating the respective ageing mechanisms. Furthermore, compression set experiments were performed under various test conditions. Adopting the two-network model, compression set values were calculated and compared to the measured data. The additional effect of physical processes to scission and cross-linking during a long-term thermal exposure is quantified through the compression set analysis. The characteristic times relative to the degradation processes are also determined. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Open AccessArticle

Effect of Accelerated Ageing on the Mechanical and Structural Properties of the Material System Used in Protectors

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Longina Madej-Kiełbik

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Katarzyna Kośla

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Dorota Zielińska

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Edyta Chmal-Fudali

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Magdalena Maciejewska

Polymers 2019, 11(8), 1263; https://doi.org/10.3390/polym11081263 - 30 Jul 2019

Cited by 6 | Viewed by 3020

Abstract

Currently, there is a wide range of materials for motorcyclists available on the market that have a significant ability to absorb impact energy. Understanding the aging processes of materials is crucial for guaranteeing the long-term durability and safety of a new product. For [...] Read more.

Currently, there is a wide range of materials for motorcyclists available on the market that have a significant ability to absorb impact energy. Understanding the aging processes of materials is crucial for guaranteeing the long-term durability and safety of a new product. For this reason, the effect of accelerated aging on the mechanical and structural properties of the multifunctional materials used in commercial protectors was analyzed. The accelerated aging considered in this study simulated 3 years of use under real conditions. Then, DMTA and FT-IR research, as well as impact tests, were carried out on the commercially available protectors for motorcyclists, before and after the accelerated aging processes. Structural analysis using FT-IR showed no significant changes in the structure of the polymers used for producing the protectors. The DMA test results are consistent with those obtained from the impact study. Both methods showed that the samples maintain their protective properties, after accelerated aging. All of the examined protectors show that an increase in force is transferred through the sample, after the accelerated aging processes, but they still provide protection, according to the ISO standard. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Analysis of O-Ring Seal Failure under Static Conditions and Determination of End-of-Lifetime Criterion

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Polymers 2019, 11(8), 1251; https://doi.org/10.3390/polym11081251 - 29 Jul 2019

Cited by 29 | Viewed by 7932

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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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Towards Novel Fluorinated Methacrylic Coatings for Cultural Heritage: A Combined Polymers and Surfaces Chemistry Study

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Polymers 2019, 11(7), 1190; https://doi.org/10.3390/polym11071190 - 16 Jul 2019

Cited by 17 | Viewed by 2874

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In this work, new co- and ter-polymers of methyl methacrylate (MMA), ethyl methacrylate (EMA), and N-butyl methacrylate (nBuMA), containing just 1% mol × mol⁻¹ of a fluorinated co-monomer, 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-octyl methacrylate (POMA), were synthesized. After an UV accelerated aging test, the photo-chemical [...] Read more.

In this work, new co- and ter-polymers of methyl methacrylate (MMA), ethyl methacrylate (EMA), and N-butyl methacrylate (nBuMA), containing just 1% mol × mol⁻¹ of a fluorinated co-monomer, 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-octyl methacrylate (POMA), were synthesized. After an UV accelerated aging test, the photo-chemical stability of the polymers prepared was determined by ¹H NMR and FT-IR spectroscopy, size exclusion chromatography, differential scanning calorimetry and wettability measurements. The polymers were applied to Botticino tiles to achieve better performances in terms of water repellency and consequently deterioration resistance. One-year prolonged exposure to a real environment was conducted and the properties of the coated materials and their performances were studied using different surface techniques such as water contact angle (WCA) and colorimetric measurements (CIELaB), capillary absorption, permeability (RVP) tests and soluble salts determination. The effectiveness of the fluorinated methacrylic coatings was clearly demonstrated; among all the resins, the co-polymer MMA_POMA seems to be the most performing one. Furthermore, both the UV photo-chemical resistance and the easiness of removal was successfully studied. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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A Novel Universal Approach for Temperature Correction on Frequency Domain Spectroscopy Curve of Transformer Polymer Insulation

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Polymers 2019, 11(7), 1126; https://doi.org/10.3390/polym11071126 - 02 Jul 2019

Cited by 13 | Viewed by 2452

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It is a fact that the frequency domain spectroscopy (FDS) curve at different temperatures can be corrected by the shift factor (α_T) extracted from the master curve. However, the α_T and master curve reported by previous works are distinctive [...] Read more.

It is a fact that the frequency domain spectroscopy (FDS) curve at different temperatures can be corrected by the shift factor (α_T) extracted from the master curve. However, the α_T and master curve reported by previous works are distinctive due to the difference in the construction algorithm. Therefore, it is of great significance to report a universal approach for extracting α_T. In this work, the unaged oil-immersed pressboards with different moisture content (mc%) are firstly prepared and selected as the research specimen. Then, the α_T of FDS curves on the above pressboard is extracted based upon the master curve technique. The influence mechanism under the various test temperature (T) and mc% is therefore analyzed so as to establish a universal model for predicting the α_T. The present findings reveal that the α_T value extracted from FDS curves is both temperature-dependent and moisture-dependent. In addition, the predicted α_T is not only suitable for temperature correction on FDS curve of same type pressboard with different insulation conditions (moisture contents and aging degrees), but also maintains considerable accuracy when applied to different types of pressboard. Therefore, the obtained conclusions will provide a universal method for temperature correction on FDS curve of transformer polymer insulation. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Comparison on the Aging of Woods Exposed to Natural Sunlight and Artificial Xenon Light

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Polymers 2019, 11(4), 709; https://doi.org/10.3390/polym11040709 - 18 Apr 2019

Cited by 23 | Viewed by 3120

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To investigate the relationship between sunlight and artificial light sources on the weathering of wood, three woods, namely, Tectona grandis L.F. (teak), Stereospermum colais (mabberley), and Dicorynia guianensis (basralocus), were tested under natural sunlight for 733 days and artificial xenon light for 180 [...] Read more.

To investigate the relationship between sunlight and artificial light sources on the weathering of wood, three woods, namely, Tectona grandis L.F. (teak), Stereospermum colais (mabberley), and Dicorynia guianensis (basralocus), were tested under natural sunlight for 733 days and artificial xenon light for 180 h, respectively. A comparison between sunlight and artificial xenon light was made based on surface color changes at various intervals. The results showed that the woods suffered from more severe aging in the artificial xenon light exposure than that in the natural sunlight exposure. At the early stage of exposure, very good relationships were found between 70 days under natural sunlight weathering and 60 h under artificial xenon light weathering. Compared with natural sunlight, about a 30 times faster aging process was identified in the artificial xenon light. However, the linear relationship vanished at the later aging stage. It was found that the color change fluctuated in natural sunlight, while it increased steadily in artificial xenon light. The wood species affected the aging of woods. In natural sunlight exposure, the color change decreased in the order of mabberley > teak > basralocus, while in artificial xenon light exposure, color change decreased in the order of mabberley > basralocus > teak due to the easier volatilization of extractives in artificial xenon light than in natural sunlight. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Influence of Various Climatic Conditions on the Structural Changes of Semicrystalline PLA Spun-Bonded Mulching Nonwovens during Outdoor Composting

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Polymers 2019, 11(3), 559; https://doi.org/10.3390/polym11030559 - 25 Mar 2019

Cited by 13 | Viewed by 3217

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This study analyzed the structural changes of semicrystalline polylactide (PLA) in the form of spun-bonded mulching nonwovens, during outdoor composting. The investigation was carried out at the microstructural, supramolecular and molecular levels using scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD) and the [...] Read more.

This study analyzed the structural changes of semicrystalline polylactide (PLA) in the form of spun-bonded mulching nonwovens, during outdoor composting. The investigation was carried out at the microstructural, supramolecular and molecular levels using scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD) and the viscosity method, respectively. The obtained experimental results revealed how the popular outdoor composting method, realized under two different European climatic conditions (in Poland and in Bulgaria), affects the degradation of PLA nonwoven, designed for agriculture use. The results showed the insignificant influence of the climatic conditions and prepared compost mixtures on the molecular and micromorphological structure of PLA spun-bonded mulching nonwovens, with a visible increase in crystallinity after the first year of composting. Significant changes were observed only after the second year of composting, which indicates the resistance of semicrystalline PLA to degradation in outdoor composting conditions. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Water Absorption, Hydrothermal Expansion, and Thermomechanical Properties of a Vinylester Resin for Fiber-Reinforced Polymer Composites Subjected to Water or Alkaline Solution Immersion

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Polymers 2019, 11(3), 505; https://doi.org/10.3390/polym11030505 - 16 Mar 2019

Cited by 28 | Viewed by 3378

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In the present paper, a vinyl ester (VE) resin, potentially used as a resin matrix for fiber-reinforced polymer (FRP) composite sucker rods in oil drilling, FRP bridge cables, or FRP marine structures, was investigated on its resistance to water and alkaline solution immersion [...] Read more.

In the present paper, a vinyl ester (VE) resin, potentially used as a resin matrix for fiber-reinforced polymer (FRP) composite sucker rods in oil drilling, FRP bridge cables, or FRP marine structures, was investigated on its resistance to water and alkaline solution immersion in terms of water uptake, hydrothermal expansion, and mechanical properties. A two-stage diffusion model was applied to simulate the water uptake processes. Alkaline solution immersion led to a slightly higher mass loss (approx. 0.4%) compared to water immersion (approx. 0.23%) due to the hydrolysis and leaching of uncured small molecules (e.g., styrene). Water immersion caused the expansion of VE plates monitored with Fiber Bragg Grating (FBG). With the same water uptake, the expansion increased with immersion temperatures, which is attributed to the increased relaxation extent of the resin molecular networks. Although an obvious decrease of the glass transition temperatures (T_g) of VE due to water immersion (5.4 to 6.1 °C/1% water uptake), T_g can be recovered almost completely after drying. Tensile test results indicate that a short-term immersion (less than 6 months) enhances both the strength and elongation at break, while the extension of the immersion time degrades both the strength and elongation. The modulus of VE shows insensitive to the immersion even at elevated temperatures. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Effects of Freeze–Thaw Thermal Cycles on the Mechanical Degradation of the Gas Diffusion Layer in Polymer Electrolyte Membrane Fuel Cells

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Yanqin Chen

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Chao Jiang

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Chongdu Cho

Polymers 2019, 11(3), 428; https://doi.org/10.3390/polym11030428 - 06 Mar 2019

Cited by 11 | Viewed by 3564

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In this paper, the mechanical degradation of a commercial gas diffusion layer subjected to repeated freeze–thaw thermal cycles is studied. In a fuel cell, the mechanical assembly state directly affects the performance of polymer electrolyte membrane fuel cells. Particularly, the gas diffusion layer [...] Read more.

In this paper, the mechanical degradation of a commercial gas diffusion layer subjected to repeated freeze–thaw thermal cycles is studied. In a fuel cell, the mechanical assembly state directly affects the performance of polymer electrolyte membrane fuel cells. Particularly, the gas diffusion layer repeatedly withstands the complex heat and humidity environmental conditions in which the temperature and humidity are always greatly changed. Studying the three-dimensional mechanical degradation of gas diffusion layers due to orthotropic properties is very useful in extending the lifetime and durability of fuel cells. To investigate this, we first established the standard freeze–thaw thermal cycle and studied the gas diffusion layer’s mechanical degradation performance with up to 400 repeated freeze–thaw thermal cycles. Furthermore, different types of failure in the gas diffusion layer caused by the repeated thermal aging treatment were observed using a scanning electron microscope, to explain the change in the mechanical deterioration. As a result, the different thermal failure plays different roles in the explanation of the gas diffusion layer’s mechanical degradation under different thermal cycles. In particular, the thermal failure that resulted from the first 100 thermal cycles has the greatest effect on the compressive and tensile performance, compared to the shear behavior. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Understanding the Effects of In-Service Temperature and Functional Fluid on the Ageing of Silicone Rubber

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Polymers 2019, 11(3), 388; https://doi.org/10.3390/polym11030388 - 26 Feb 2019

Cited by 9 | Viewed by 3330

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With an organic/inorganic hybrid nature, silicone elastomers are amongst the most versatile engineering materials, exploited in a wide range of applications either as end-products or in manufacturing processes. In many industrial machines, silicone components are exposed to in-service conditions, such as high or [...] Read more.

With an organic/inorganic hybrid nature, silicone elastomers are amongst the most versatile engineering materials, exploited in a wide range of applications either as end-products or in manufacturing processes. In many industrial machines, silicone components are exposed to in-service conditions, such as high or low temperatures, contact with functional fluids, mechanical loading, and deformations, which can adversely affect these components and reduce their lifespan, leading to machine failure in turn. The present study investigates the behaviour of a silicone component of a manufacturing equipment and the variations in the part’s properties due to in-service conditions (temperature, exposure to heat transfer fluid, and mechanical deformation) to develop a monitoring tool. An experimental design was employed to study the main and the interaction effects of temperature (22 °C, 180 °C), medium (air, synthetic heat transfer fluid), and strain (0%, 200%) on the silicone component’s properties. Results showed that while the chemistry of the component remains intact, its thermal and in particular mechanical properties are largely influenced by the in-service conditions. Consequently, leading to a physical rather than a chemical failure of the component and limiting its service life. Statistical analysis revealed that high temperature and the exposure to the heat transfer fluid have the most sever effects. Moreover, these two manufacturing parameters were found to have a significant interaction with one another, whose effect cannot not be neglected. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Fatigue Life Prediction of Reinforced Concrete Beams Strengthened with CFRP: Study Based on an Accumulative Damage Model

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Polymers 2019, 11(1), 130; https://doi.org/10.3390/polym11010130 - 13 Jan 2019

Cited by 9 | Viewed by 3197

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With the prestressed carbon fiber reinforced polymer (CFRP) strengthening technique widely used in reinforced concrete (RC) structures, it is more and more important to study the fatigue performance of RC structures. Since the fracture of a tensile steel bar at the main cracked [...] Read more.

With the prestressed carbon fiber reinforced polymer (CFRP) strengthening technique widely used in reinforced concrete (RC) structures, it is more and more important to study the fatigue performance of RC structures. Since the fracture of a tensile steel bar at the main cracked section is the leading reason for the failure of RC beams reinforced by prestressed CFRP, a fatigue life prediction model of RC beams reinforced by prestressed CFRP was developed based on an accumulative damage model. Moreover, gradual degradation of the performance of the concrete was considered in the fatigue life prediction model. An experimental study was also conducted to research the fatigue behavior of RC beams reinforced by prestressed or non-prestressed carbon fiber laminate (CFL). During the tests, fatigue crack patterns were captured using a digital image correlation (DIC) technique, and the fatigue lives of a total of 30 beams were recorded. The results showed that the predicted main crack propagation curves and the fatigue lives were close to the experimental data. This study also exhibited that the prestressed CFRP could reduce the stress of main steel bars in RC beams and effectively improve the fatigue performance of the RC beams. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Novel Intumescent Flame Retardant Masterbatch Prepared through Different Processes and Its Application in EPDM/PP Thermoplastic Elastomer: Thermal Stability, Flame Retardancy, and Mechanical Properties

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Polymers 2019, 11(1), 50; https://doi.org/10.3390/polym11010050 - 31 Dec 2018

Cited by 15 | Viewed by 4080

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In this work, the ethylene-propylene-diene monomer/polypropylene (EPDM/PP) thermoplastic elastomer filled with intumescent flame retardants (IFR) is fabricated by melting blend. The IFR are constituted with melamine phosphate-pentaerythritol (MP/PER) by compounding and reactive extruding, respectively. The effects of two kinds of MP/PER with different [...] Read more.

In this work, the ethylene-propylene-diene monomer/polypropylene (EPDM/PP) thermoplastic elastomer filled with intumescent flame retardants (IFR) is fabricated by melting blend. The IFR are constituted with melamine phosphate-pentaerythritol (MP/PER) by compounding and reactive extruding, respectively. The effects of two kinds of MP/PER with different contents on the thermal stability, flame retardancy, and mechanical properties of materials are investigated by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94, cone calorimeter test (CCT), and scanning electron microscopy (SEM). FTIR results show that the reactive extruded MP/PER partly generates melamine pyrophosphate (MPP) compared with compound masterbatches. TGA data indicate that the best thermal stability is achieved when the molar ratio of MP/PER reaches 1.8. All the reactive samples show a higher flame retardancy than compound ones. The CCT results also exhibit the same trend as above in heat release and smoke production rate. The EPDM/PP composites filled with 30 and 35% reactive MP/PER exhibit the improved flame retardancy but become stiffer and more brittle. SEM photos display that better dispersion and smaller particle size are obtained for reactive samples. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Molecular Simulation on the Thermal Stability of Meta-Aramid Insulation Paper Fiber at Transformer Operating Temperature

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Polymers 2018, 10(12), 1348; https://doi.org/10.3390/polym10121348 - 05 Dec 2018

Cited by 33 | Viewed by 3728

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The influence of the thermal field of a transformer during operation on the thermal stability of meta-aramid insulation paper was studied through molecular dynamics simulations. Models of the crystalline and amorphous regions of meta-aramid fibers were constructed using known parameters. The model of [...] Read more.

The influence of the thermal field of a transformer during operation on the thermal stability of meta-aramid insulation paper was studied through molecular dynamics simulations. Models of the crystalline and amorphous regions of meta-aramid fibers were constructed using known parameters. The model of the crystalline area was verified by comparing X-ray diffraction results with experimental data. The reasonableness of the simulation results was judged by the variation of energy, temperature, density, and cell size in relation to the dynamic time. The molecular dynamics simulations revealed that the modulus values in the crystalline regions were two to three times higher than those in the amorphous regions at various temperatures. In addition, the incompressibility, rigidity, deformation resistance, plasticity, and toughness of the crystalline regions were obviously higher than those of amorphous regions, whereas the toughness of the amorphous regions was better than that of the crystalline regions. The mechanical parameters of both the crystalline and amorphous regions of meta-aramid fibers were affected by temperature, although the amorphous regions were more sensitive to temperature than the crystalline regions. The molecular chain motion in the crystalline regions of meta-aramid fibers increased slightly with temperature, whereas that of the amorphous regions was more sensitive to temperature. Analyzing hydrogen bonding revealed that long-term operation at high temperature may destroy the structure of the crystalline regions of meta-aramid fibers, degrading the performance of meta-aramid insulation paper. Therefore, increasing the crystallinity and lowering the transformer operating temperature may improve the thermal stability of meta-aramid insulation paper. However, it should be noted that increasing the crystallinity of insulation paper may lower its toughness. These study results lay a good foundation for further exploration of the ways to improve the performance of meta-aramid insulation paper. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Tribological Behavior of Nanocomposites Based on UHMWPE Aged in Simulated Synovial Fluid

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Polymers 2018, 10(11), 1291; https://doi.org/10.3390/polym10111291 - 21 Nov 2018

Cited by 17 | Viewed by 3444

Abstract

Ultra High molecular weight polyethylene (UHMWPE) suffers wear degradation in total joint replacements and it needs to be improved. Thus, we enhanced wear resistance of UHMWPE with carbon nanofiller and paraffin oil and studied its tribological behavior in Simulated Synovial Fluid (SSF) for [...] Read more.

Ultra High molecular weight polyethylene (UHMWPE) suffers wear degradation in total joint replacements and it needs to be improved. Thus, we enhanced wear resistance of UHMWPE with carbon nanofiller and paraffin oil and studied its tribological behavior in Simulated Synovial Fluid (SSF) for 60 days at 37 °C to reproduce the conditions of a real joint. Ageing in biological fluid accelerates the wear action but nanocomposite exhibited a higher wear resistance compared to UHMWPE because of its higher structural homogeneity. Carbon nanofiller closes the porosity of UHMWPE hindering SSF to penetrate inside. Wear resistance of the nanocomposite with 1.0 wt.% of CNF improved of 65% (before ageing) and of 70% (after 60 days in SSF) with respect to pure UHMWPE. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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Criticality of the Self-Heating Effect in Polymers and Polymer Matrix Composites during Fatigue, and Their Application in Non-Destructive Testing

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Andrzej Katunin

Polymers 2019, 11(1), 19; https://doi.org/10.3390/polym11010019 - 23 Dec 2018

Cited by 37 | Viewed by 5025

Abstract

The self-heating effect is a dangerous phenomenon that occurs in polymers and polymer matrix composites during their cyclic loading, and may significantly influence structural degradation and durability as a consequence. Therefore, an analysis of its criticality is highly demanding, due to the wide [...] Read more.

The self-heating effect is a dangerous phenomenon that occurs in polymers and polymer matrix composites during their cyclic loading, and may significantly influence structural degradation and durability as a consequence. Therefore, an analysis of its criticality is highly demanding, due to the wide occurrence of this effect, both in laboratory fatigue tests, as well as in engineering practice. In order to overcome the problem of the accelerated degradation of polymer matrix structures, it is essential to evaluate the characteristic temperature values of self-heating, which are critical from the point of view of the fatigue life of these structures, i.e., the temperature at which damage initiates, and the safe temperature range in which these structures can be safely maintained. The experimental studies performed were focused on the determination of the critical self-heating temperature, using various approaches and measurement techniques. This paper present an overview of the research studies performed in the field of structural degradation, due to self-heating, and summarizes the studies performed on the evaluation of the criticality of the self-heating effect. Moreover, the non-destructive testing method, which uses the self-heating effect as a thermal excitation source, is discussed, and the non-destructivity of this method is confirmed by experimental results. Full article

(This article belongs to the Special Issue Assessment of the Ageing and Durability of Polymers: Procedures and Reliability)

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