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Understanding the impact of climate stressors on photovoltaic (PV) backsheet degradation in real-use conditions is critical to improve the accelerated testing exposures, extend the backsheet lifetime, and increase the confidence in PV reliability. In this work, a total of 33 PV module backsheets were retrieved from six climatic zones worldwide with 2 - 28 years of exposure. These modules included five types of backsheet air-side materials (or outer layer): poly(vinylidene fluoride) (PVDF), poly(tetrafluoroethylene-co-hexafluoropropylene-co-vinylidene fluoride) (THV), poly(vinyl fluoride) (PVF), poly(ethylene terephthalate) (PET), and polyamide (PA). Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) was used to identify air-side materials. The degradation induced color change, gloss loss, and chemical material changes analyzed using optical microscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), colorimetry (yellowness index (YI)), and gloss measurements. PVDF, THV, and PVF air-side layer backsheets, in particular PVF, had minimal degradation in the air-side layer appearance and chemical structures after exposure in different climatic zones. The PET air-side backsheets exhibited obvious color increase (22.55 YI units after about 9 years exposure) and the PA/PA/PA backsheets showed large gloss loss (up to 76.4 %) relative to the unexposed backsheets. Severe cracks between cells that penetrated through the entire thickness of backsheets are observed on PA/PA/PA backsheets after 4-6 years of exposure in 6 climatic zones. The current indoor exposure standards were not sufficient to identify this degradation type. However, fluoropolymer based PV backsheets showed lower levels of degradation predictors and increased climatic resistance. Specific samples (PVF) showed little change from baseline after 28 years of outdoor exposure. • Retrieved module backsheet characterization. • Diverse climatic exposure. • Inhomogeneous backsheet degradation. [ABSTRACT FROM AUTHOR]

Dual-layer hydrophobic/hydrophilic PVDF/Ultem® hollow fiber membranes with superior mechanical and water transport properties have been prepared via co-extrusion method for vacuum membrane distillation (VMD) of seawater. To fabricate such high-performance dual-layer hollow fibers consisting of two different materials, one must overcome the issues of delamination between the two polymer layers and dense interface morphology. The former would result in a defective membrane, while the latter could significantly increase the substructure resistance for vapor transport. By properly manipulating dope formulation and spinning conditions, we have overcome the first challenge and produced delamination free dual-layer fibers. The second problem is resolved by the addition of Al 2 O 3 nanoparticles into the inner layer dope, which creates micro-porosity on the outer surface of the inner layer. The resultant dual-layer fibers show good mechanical properties, permeation flux and wetting resistance simultaneously under VMD operations. Comparing to the conventional single layer MD fibers, the newly developed VMD hollow fiber containing 15 wt% Al 2 O 3 has 4.5- fold tensile strength (i.e., about 350% increment) with a VMD flux of 45.8 kg/m 2 -h at 70 °C. This study may provide valuable guidelines in designing superior dual-layer PVDF membranes for practical VMD applications of seawater desalination. [ABSTRACT FROM AUTHOR]

The width tapered beam method for measuring fracture toughness has been contemplated for use in measuring the adhesion of photovoltaic materials, is promoted by it being a viable method for use directly on modules rather than to engineered test specimens. However, precise determination of crack length is often difficult as failure often involves tendril formation, cavitation voids, and other plastic deformation at the crack front in addition to obfuscation by opaque materials. Because fracture energy varies as the square of crack length, imprecise crack tip length results in large measurement uncertainties. In this work, we develop a method to estimate the crack tip length using the relationship between the applied force and the displacement of the load frame. The crack tip is determined for every data point and can be defined from a calibration curve related to the amount of energy put into the beam, or from a theoretically idealized estimation. Once a calibration curve is set up and the equations programmed, the fracture energy as a function of position on the newly formed crack interface can be accurately estimated. The test additionally provides much easier analysis and insight into the joint failure through more precise knowledge of fracture toughness at each de-bonded area. [ABSTRACT FROM AUTHOR]

While membrane technology continues to thrive in seawater desalination, it would defeat the very purpose of saving the environment if toxic solvents are involved in membrane manufacture. As a paradigm of green chemistry, a non-toxic solvent, triethyl phosphate (TEP), was used for the first time to fabricate polyvinylidene fluoride (PVDF) hollow fiber membranes for direct contact membrane distillation (DCMD). The phase inversion kinetics of the PVDF/TEP system was closely investigated and compared with the conventional N-Methyl-2-pyrrolidone (NMP)/PVDF system. The former showed a less abrupt phase inversion rate and produced a more porous sponge-like structure than the latter. The 12/88 wt% PVDF/TEP binary solution produced fibers with promising performance. They not only possessed robust mechanical properties and a liquid entry pressure up to 2.0 bar but also exhibited an average flux of 20 kg/m 2 ·h at 60 °C and a NaCl rejection of 99.99%. In addition, hollow fiber membranes spun from this PVDF/TEP system had porosity of greater than 83% for all conditions studied. Since there were no additives or non-solvents in the dope solutions and no post-treatments involved, the use of TEP as a green solvent could significantly reduce the complexity of membrane fabrication, scale up and commercialization. Clearly, the much safer solvent TEP is able to replace toxic solvents commonly used in membrane manufacture and to produce membranes with highly competitive performance. [ABSTRACT FROM AUTHOR]

Construction of PVDF hollow fiber membranes with antifouling lumen surfaces is of great interest and significance for many industrial applications because the inside-out filtration mode allows good control over module hydrodynamics. For the first time, a zwitterionic polymer was immobilized on the lumen surface of a PVDF hollow fiber membrane via thermal-induced graft copolymerization with an objective to render the PVDF membrane antifouling. The graft copolymerization consists of two steps: ozone-assisted surface pre-activation and grafting of sulfobetaine methacrylate (SBMA). The grafting density and chain length were systematically optimized by manipulating the operational parameters, e.g. ozone treatment and grafting duration. The resultant membranes were studied with respect to their structure, morphology, ultrafiltration (UF) performance, while their fouling behaviors were evaluated by flux recovery ratio and the resistance-in-series model. In comparison to the pristine one, the composite membranes exhibited superior fouling resistance for a 2-h filtration of a 2.0 wt% bovine serum albumin (BSA) solution. Especially, the irreversible fouling-induced resistance was prominently reduced from 53% to 15% due to the outstanding hydration capacity of the polySBMA polymer. Consequently, the flux recovery ratio ( FRR ) increased significantly from 47% to 85%, suggesting the promising prospect of the zwitterion-grafted PVDF hollow fiber membranes for their antifouling properties. Most importantly, the improvement in antifouling was achieved without sacrificing flux or rejection efficiency. This work may provide useful insights about lumen surface nano-structuring of the inner-selective hollow fiber membranes. [ABSTRACT FROM AUTHOR]

Photovoltaic backsheets are exposed to harsh outdoor weathering conditions throughout their service lives that can compromise their protective function, through adhesive debonding between their constituent layers and between the backsheet and the module. A large-scale study on adhesive degradation was conducted on 37 field-exposed modules, that spanned 19 different module manufacturers, that were deployed among six Köppen–Geiger climatic zones, and that were fielded between 0 and 28 years. Six outer layer polymer classes were identified among the backsheets: polyamide (PA), polyethylene terephthalate (PET), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), fluoroethylene vinyl ether copolymer (FEVE), and tetrafluoroethylene hexafluoropropylene vinylidene fluoride copolymer (THV). Two adhesion tests were used to measure the adhesive strength: the wedge test and the width-tapered single-cantilever beam (SCB) test. Adhesion energies were compared across exposure time and Köppen–Geiger climatic zone. Many of the PET-, PVF-, and PVDF-based backsheets experienced degradation of the adhesive layer between the backsheet outer and core layers. A consistent trend of decreasing adhesion energy with exposure time was observed in five out of the six backsheet types. Trends among adhesion energy and climatic zone, while expected, were not observed, possibly due to broad ranges in temperature, humidity, and precipitation defining Köppen–Geiger climatic zones. The cantilever beam measurements produced an upper cutoff of approximately 100 J/m2, above which no modules exhibited field delamination. The results are part of a two-part study quantifying adhesion in both field-weathered and indoor-exposed PV backsheets. • Thirty-seven (37) PV modules were retrieved from various regions around the world • Two adhesion tests were used to characterize backsheet adhesion • Adhesion energy decreased with number of years of field exposure • Backsheets with adhesive tie layers often showed failure in an adhesive layer • Modules with adhesion energies greater than 100 J/m2 showed no field delamination [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) backsheets provide critical moisture, mechanical, and electrical insulation to the backside of PV modules, but their continued functionality depends upon their ability to remain well adhered over years of harsh environmental exposure. A study of adhesive strength was conducted on several PV backsheet types exposed to indoor accelerated weathering. Two adhesion tests – the wedge test and single cantilever beam test – were used to measure adhesion energy in four backsheets: two with fluoropolymer-based outer (airside) layers – polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF) – and two with non-fluoropolymer-based outer layers–polyamide (PA) and polyethylene terephthalate (PET). The effects of changes in temperature, ultraviolet (UV) irradiance, relative humidity, and a periodic water spray were studied. The PET-, PVF- and PVDF-based backsheets all showed instances of debonding in an adhesive layer, which is commonly reported. For the PA-, PET-, and PVDF-based backsheets, adhesion energy dropped fairly rapidly with exposure, reaching very low levels by 4000 h. The PVF-based backsheet was relatively robust to weathering. Pull-off of an outer chalking layer in the PA- and PET-based backsheets suggested a sensitivity to UV. Adhesion in these two backsheets was also highly sensitive to changes in moisture level. Changes in UV irradiance and temperature did not show a statistically significant effect on adhesion loss for the exposure levels used. The present work is part of a two-part adhesion study on both field-weathered and indoor-exposed backsheets, and forms a basis for understanding adhesion degradation across a variety of backsheet types and degradation factors. • Four indoor-exposed backsheet types were adhesion-tested using two different methods. • Adhesion in the PVF-based backsheet was relatively stable. • The PA-, PET- and PVDF-based backsheets exhibited substantial decrease after 4000 hours. • The PA- and PET-based backsheets exhibited sensitivity to changes in moisture level. • The PET-, PVF-, and PVDF-based backsheets all exhibited debonding in an adhesive layer. [ABSTRACT FROM AUTHOR]