Degradation of photovoltaic backsheets: Comparison of the aging induced changes on module and component level

In reliability testing of components for PV modules an always remaining question is about material (in)compatibilities and synergistic effects and thus, how results of singly tested materials correlate with materials aged within PV modules. Testing of single materials would simplify sample preparation, reduce costs and offer more testing options. Therefore the main objective of this study was to compare the aging behavior of single backsheets with that of backsheets incorporated within PV modules. Four different types of backsheets were chosen, all of them comprising of polyethylene terephthalate (PET) core layers, but differing outer protection layers. Test modules using identical components, varying only in the type of backsheet used were produced and damp heat aged (85°C/85% RH ≤2000 h). The results revealed no influence of the PV module lamination on the thermal characteristics of the polymeric backsheets. Even after DH aging, differences between single and module laminated backsheets were negligible. Degradation effects of PET could be detected for all aged sheets by thermal analysis and were confirmed by tensile tests and rheological measurements. Thus, it can be stated that testing of single PET based backsheets under DH aging conditions is a practicable way to investigate the applicability of a new backsheet. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42093.     

一种光伏背板寿命推算的研究

本文针对含PET结构的背板进行了一系列的热氧老化试验,研究了不同老化温度下背板断裂伸长率与老化时间的关系,根据Arrhenius方程推算出背板的使用寿命,为其他结构背板使用寿命的推算提供参考。     

塑料薄膜之光伏背板市场分析

首先介绍了光伏背板的作用、性能要求、常见结构以及国内主要背板生产企业的背板类型、性能和生产规模，然后对背板的原材料聚对苯二甲酸乙二醇酯（PET）基膜、氟膜和胶黏剂的现状进行了分析，最后根据光伏发展的趋势，对背板市场进行了预测，并介绍了新一代背板——透明背板。     

Correlation study of damp heat and pressure cooker testing on backsheets

For photovoltaic (PV) modules, high‐quality backsheets are essential. To verify these qualities, hot and humid tests of up to 1000 h are standard in the PV industry. Damp heat (DH) tests are useful for evaluating material quality and infant failures, especially for materials that are sensitive to hydrolysis. However, shorter test periods are needed. Hence, the objective of this study was to investigate and correlate the aging behavior of hydrolysis‐sensitive polyester [poly(ethylene terephthalate) (PET)] based backsheets after exposure to DH and pressure cooker conditions. The material properties, such as thermal and mechanical parameters, correlated well between the pressure cooker at 120 °C and the DH test, with the qualification that differences in the failure mechanism were seen after 96 and 2000 h, respectively. Nevertheless, it should be acceptable to use pressure cooker tests (PCTs) for fast material testing. The PCT is proposed to significantly reduce the testing time for infant failures and material quality to around 4 days for PET‐based backsheets. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44230.     

不同老化模式对光伏背板中PET结晶度的影响

分别研究了在湿热老化、加速湿热老化、紫外辐照老化模式下,背板力学性能和PET层结晶度的变化,归纳了背板失效与其PET层结晶度的关系,并对几种老化模式进行了比较.结果表明,湿热老化和加速湿热老化时,PET层趋于结晶,为了保证背板不失效,结晶度应该控制在38%以下;紫外辐照老化时,分子结构破坏为主导,通过比较力学性能发现,...     

Development of value-added polyethylene grades with extended service lifetime: Weathering resistant flame retarded materials for outdoor applications

The current article deals with the development of different novel, tailor-made polyolefin formulations exhibiting both low flammability and high weathering resistance, so as to provide value-added polyethylene grades with extended service lifetime. Two low-density (LDPE) and one linear low-density (LLDPE) polyethylene grades were modified via melt compounding with an additive system comprising: (a) a nitrogen-phosphorous intumescent system for flame retardance and (b) a hindered amine light stabilizer and a benzophenone-type UV absorber for UV/heat stabilization, at a total loading of 30–35 wt%. The target was to reach V0 classification in UL94V flammability tests, while to a large extent maintaining the mechanical properties, such as, tensile and impact strength of the investigated polymers, thus ensuring that the additives do not interfere significantly with the material quality. Subsequently, the compounds were subjected to separate artificial UV and heat aging at 100°C for 1500 h; the formulations showed good flame retardance, even after prolonged artificial weathering, but there was an observable, although acceptable, decrease in the mechanical properties. Nevertheless, all the results show that the developed polyethylene compounds are very promising for outdoor applications, such as, irrigation piping and profiles, where long-term weathering stability is important, and where flame retardance is important for safety during storage.     

抗氧剂3114抗氧化老化性能研究

研究了抗氧剂3114在PP树脂中的抗氧化老化性能，并与抗氧剂1010进行了对比。研究结果表明：添加抗氧剂3114的PP树脂具有良好的加工稳定性能和长期热氧稳定性能，并可改善PP树脂机械力学性能。而且其热稳定性能接近于抗氧剂1010，耐侯性能则明显优于抗氧剂1010。     

The effect of accelerated weathering on the degradation of polymeric films

The influence of artificial weathering on three general properties of films of high-impact polystyrene (HIP), poly(ethylene terephthalate) (PET), and poly(vinyl chloride) (PVC) was investigated, Degradation resulting from weathering was investigated in terms of changes in the water vapor permeation, mechanical properties, and optical transmission. The diffusivities and permeabilities of these three materials were significantly altered by weathering at two levels of exposure. Films of HIP were embrittled at both levels of exposure, whereas the PET films were embrittled only at the high level of exposure. Films of PVC showed embrittlement at the highest level of exposure and the lowest test temperature. Changes in the optical properties were less significant, amounting to a relatively small decrease in the transmission of the films in the visible range.     

聚酰胺光伏背板老化性能及机理研究

分别研究了在湿热老化、加速湿热老化、紫外辐照老化模式下,背板的力学性能和聚酰胺熔融焓及黄度指数的变化,分析了老化前后背板的断面形貌和表面形貌变化。结果表明:湿热老化和加速湿热老化聚酰胺趋于结晶以及聚酰胺和玻璃纤维界面作用减弱;紫外辐射老化主要导致酰胺键断开,分子结构破坏。通过比较老化前后力学性能、黄度指数及表面形貌发现,紫外辐照老化对聚酰胺背板的影响较大。     

Effect of gas-phase tortuosity on the mechanical properties of low-density polyolefin open-cell foams at low- and high-strain rates

This paper describes the mechanical behavior in compression, at both low- and high-strain rates, of several low-density open-cell polyolefin-based foams with different gas phase interconnectivities and different levels of gas-phase tortuosity. The mechanical properties of the open-cell polyolefin foams have been compared with two different references: an open-cell low tortuous foam based on flexible polyurethane and closed-cell polyolefin foams. One the one hand, at low-strain rates, it has been observed that the mechanical performance is controlled by the open-cell content and the properties of the polymeric matrix, being the influence of tortuosity small. On the other hand, the influence of the level of tortuosity is critical to high-strain rates. In fact, it has been demonstrated that open-cell polyolefin foams with high tortuosity (HT) present an unexpected mechanical behavior, showing excellent mechanical properties, which are even similar to that of closed-cell polyolefin materials with the same chemical composition. Therefore, low-density polyolefin foams with HT have a unique mechanical performance strongly influenced by the strain rate. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48468.     

Outdoor weathering of polyamide and polyester ropes used in fall arrest equipment

In this work, the effect of natural climatic aging on two ropes made from polyamide 6 (PA6) and poly(ethylene terephthalate) (PET) was evaluated. Samples of rope from both materials underwent a continuous outdoor aging treatment spanning 6 months in Montreal's weather. Tensile tests carried out on aged PA6 ropes showed an increase in ultimate strain and a decrease in breaking force when compared with as‐received values, while PET ropes exhibited a slight increase in ultimate strain as their breaking force remained unchanged. FTIR analyses of aged PET samples revealed a new absorption band in the hydroxyl region ascribed to the ? OH stretching vibrations of carboxylic acid end groups. FTIR quantitative analyses of the absorption bands in the carbonyl region of aged PA6 spectra displayed an increase in intensity that indicates the occurrence of chemical degradation reactions. The degree of crystallinity of PA6, calculated from differential scanning calorimetry data, was found to increase after the weathering treatment, a result confirmed by X‐ray diffraction analyses. The higher crystalline fraction is believed to entail an increase in the density of PA6 fibers, which give rise to the length reduction seen in PA6 ropes after the aging treatment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3058–3065, 2013     

Influence of some additives on the performance of wood flour/polyolefin composites

The main objective of this study was to investigate the effect of different additives, namely, maleic anhydride, alumina trihydrate (ATH), and a mixture of both on wood flour/polyolefin (50/50) composite samples. The polyolefins used were polyethylene (PE), polypropylene (PP), and a mixture of both PE and PP (50/50 w/w). The effects were studied in terms of the percentage water absorption, volumetric swelling efficiency, and mechanical and electrical properties. We found that the absorption of water and volumetric swelling were greatly retarded after 3 weeks in all of the wood flour/polyolefin composite samples containing various additives. It is also clear from the results that the mechanical properties were enhanced. The presence of ATH improved the electrical properties and enhanced the thermal stability of the wood flour composites. Generally, the PE composite samples gave better results compared to the PP ones. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Microstructure and physical properties of open‐cell polyolefin foams

The cellular structure, physical properties, and structure–property relationships of novel open‐cell polyolefin foams produced by compression molding and based on blends of an ethylene/vinyl acetate copolymer and a low‐density polyethylene have been studied and compared with those of closed‐cell polyolefin foams of similar chemical compositions and densities and with those of open‐cell polyurethane foams. Properties such as the elastic modulus, collapse stress, energy absorbed in mechanical tests, thermal expansion, dynamic mechanical response, and acoustic absorption have been measured. The experimental results show that the cellular structure of the analyzed materials has interconnected cells due to the presence of large and small holes in the cell walls, and this structure is clearly different from the typical structure of open‐cell polyurethane foams. The open‐cell polyolefin foams under study, in comparison with closed‐cell foams of similar densities and chemical compositions, are good acoustic absorbers; they have a significant loss factor and lower compressive strength and thermal stability. The physical reasons for this macroscopic behavior are analyzed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Anisotropic character and ultrasonic stiffness changes during the natural weathering of LDPE films

Blown extruded polyethylene films without stabilizers have been exposed outdoors under severe weathering conditions in the Sahara. The chemical aspect of aging has been followed by IR spectroscopy. The mechanical aspect of aging has been monitored by means of a nondestructive method. It consists of measuring velocities and attenuations of ultrasonic waves propagating in several directions in the film plane. Stiffness constants and energy dissipation terms have been calculated. From the results obtained it is shown that stiffening of the material leads to an increase of velocities and a decrease of wave attenuation. Moreover, the stiffness constants as well as the energy dissipation terms vary with aging and show a changing anisotropic character of the films. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 559–564, 2003     

Effects of acid,alkaline, and seawater aging on the mechanical and thermomechanical properties of glass fiber/epoxy composites filled with carbon nanofibers

Owing to the superior corrosion resistance, fiber-reinforced polymer (FRP) composites are the prime choice of structural materials for various marine and chemical industries, where there is a long-term direct contact of the components takes place with corrosive fluids. In this present work, glass fiber/epoxy (GE) composites have been fabricated with and without carbon nanofibers (CNFs), and aging has been carried out in acidic (pH = 1), seawater (pH = 8.2), and alkaline (pH = 13) solutions for 150 days. The resistance of CNF-filled GE composites toward the corrosive fluids has been evaluated in terms of alteration in the mechanical (flexural), microstructural (fractography analysis by field emission scanning electron microscope), and thermomechanical (dynamic mechanical analysis) behavior of the materials. It is revealed that as the immersion time increases, there is a continuous decrement in flexural strength and modulus, and glass-transition temperature (T_g) of all the materials in all these solutions. Compared to the 1% CNF-filled GE composite, control GE composite showed more degradation in the case of alkaline aging and seawater aging. Maximum reduction (56%) in the strength of GE composite was observed due to 150 days of alkaline aging. However, the control GE composite showed better resistance to the acidic solution than that of CNF-filled GE composite. Possible failure modes, changes in the chemistry of the material due to aging have been studied by fractography analysis. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48434.     

Effects of weathering aging on mechanical and thermal properties of injection molded glass fiber reinforced polypropylene composites

The effect of weathering aging on the degradation behavior of injection molded short glass fiber reinforced polypropylene composites (GFPP) is studied. First, the effect of outdoor weathering on mechanical properties of GFPP composite was investigated by tensile, flexural, and impact tests. Furthermore, to clarify the degradation behavior under natural weathering environments, differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) measurements were carried out to analyze the structural and molecular changes during weathering aging. The results show that weathering aging has a significant influence on changes in mechanical properties, melting temperature and the degree of crystallinity of PG6N1 without added carbon black and UV absorbing agent. Those degradations not only occurred on the surface of GFPP but also proceeded to the inner matrix and interface. However, GFPP GWH42 with added carbon black and UV absorbing agent shows excellent weathering stability.     

Effect of Aging on the Mechanical Properties of UV Curable Optical Fiber Coatings

Abstract

A dual-layer urethane acrylate UV-cured coating is widely used to protect optical fibers because of its well-balanced mechanical properties, weathering resistance and rapid curing. The long-term mechanical behavior of fiber coatings is important for the reliability of optical fibers. Long-term exposure of UV-cured polyether urethane acrylate films was carried out in dry air and in water at elevated temperatures. Tensile testing was performed to reveal changes in mechanical properties and dynamic mechanical analysis to determine both the glass transition temperature and the crosslink density. The equilibrium swelling allowed assessment of the crosslink density. Tensile testing and strip force measurements were performed on virgin and aged optical fibers. Initially the fracture strengths of the secondary coatings increased under all aging conditions indicating post-curing reactions and the possible loss of uncrosslinked species. Aging under wet conditions led at a later stage to hydrolytic degradation of the network and to a decrease in the fracture stress. The equilibrium swelling and equilibrium modulus measurements showed good correlation with the changes in strength. The primary coatings showed a decrease in mechanical strength after only 2–4 weeks under all conditions.     

Microindentation into an epoxy composition to assess the influence of aging on mechanical properties

This work aims to apply the microindentation technique for assessing the influence of two aging factors—long‐term weathering and long‐term laboratory aging—on the time‐dependent mechanical properties of an epoxy composition. The linear theory of viscoelasticity was taken as a background for the problem, and the time‐independent Poisson ratio value was assumed to simplify the assessment. Two nano/microindenters were used (Hysitron Triboscan and Nano XP Indenter) at two different laboratories. Four special time‐dependent loading histories were applied: indentation under a step load, indentation under a constant load rate, indentation with a fixed depth of penetration, and indentation under a constant rate of penetration. The short‐term histories of the viscoelastic compliance of a common epoxy composition, affected by 5‐year weathering or laboratory aging, measured using a microindentation technique were compared to the data derived from standard macro measurements. The findings suggest that a qualitative assessment of the influence of the investigated aging effects on mechanical properties can be handled using short‐term microindentation data, but the data has to be freed of possible attendant factors, especially of the influence of polishing procedures accompanying the microindentation techniques, before comparing it with standard measurement data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Extremely enhanced hydrolytic stability of poly(ethylene terephthalate) films

Poly(ethylene terephthalate) (PET) films possessing extremely enhanced hydrolytic stability were developed by combining the improved processes of polymerization, melt extrusion, and biaxial stretching. The PET films obtained from the combined process were better than commercially available PET films with highest hydrolytic stability at present. An accelerated test (at 120°C and 100% relative humidity) was performed to learn the key parameters governing elongation‐based hydrolytic durability of PET films. The results suggested that ultimate hydrolytic stability was because of the combined effects of significant decrease in the content of carboxylic acid terminal groups and enhanced crystallinity. Another reason for this was an increase in ground‐state dimer sites due to intermolecular stacking between terephthalate units. These dimer sites were probably located in the densely packed amorphous regions, as suggested from the intrinsic fluorescence spectrum of PET films. The PET films developed in this study are very useful in outdoor applications such as backsheet materials in solar cell modules. POLYM. ENG. SCI., 58:261–271, 2018. © 2017 Society of Plastics Engineers     

光伏背板用PET老化性能研究

利用湿热老化、热氧老化对PET及使用该PET为基材的光伏背板进行处理,测定了老化后PET及背板的力学性能,并利用红外、DSC、粘度测试等分析方法研究了PET在上述老化过程中官能团、结晶度、分子量以及断裂伸长率的变化情况,并探讨了这些物性的变化与PET微观结构变化之间的联系.