Ethylene Vinyl Acetate Material Research Articles

Effect of Vinyl Acetate, Glass Fibers Contents, and Buffer Space on EVA's Mechanical Property and Shock Absorption Ability.

The aim of the study was to evaluate the mechanical properties and impact absorption capacity of prototype materials comprising ethylene vinyl acetate (EVA) of different hardness reinforced using different amounts of glass fibers (GFs), considering a buffer space. Six prototype materials were made by adding E-GFs (5 and 10 wt%) to EVA with vinyl acetate (VA) contents of 9.4 wt% ("hard" or HA) and 27.5 wt% ("soft" or SO). Durometer hardness and tensile strength tests were performed to evaluate the mechanical properties of the materials. Moreover, an impact test was conducted using a customized pendulum impact tester to assess the impact absorption capacity (with or without a buffer space) of the specimens. The mechanical properties of the prototypes, namely, durometer hardness, Young's modulus, and tensile strength, were significantly higher in the HA group than in the SO group, regardless of the presence or added amount of GFs. The addition of GFs, particularly in a large amount (10 wt%), significantly increased these values. In terms of the impact absorption capacity, the original hardness of the EVA material, that is, its VA content, had a more substantial effect than the presence or absence of GFs and the added amount of GFs. Interestingly, the HA specimens with the buffer space exhibited significantly higher impact absorption capacities than the SO specimens. Meanwhile, the SO specimens without the buffer space exhibited significantly higher impact absorption capacities than the HA specimens. Moreover, regardless of the sample material and impact distance, the buffer space significantly improved impact absorption. In particular, with the buffer space, the impact absorption capacity increased with the added amount of GFs. The basic mechanical properties, including durometer hardness, Young's modulus, and tensile strength, of the EVA prototype were significantly increased by reducing the amount of VA regardless of the presence or added amount of GFs. Adding GFs, particularly in large amounts, significantly increased the values of aforementioned mechanical properties. Impact absorption was significantly affected by the hardness of the original EVA material and enhanced by the addition of the buffer space. The HA specimen had a high shock absorption capacity with the buffer space, and the SO specimen had a high shock absorption capacity without the buffer space. With the buffer space, impact absorption improved with the amount of added GFs.

The effects of non-Newtonian fluid material midsole footwear on tibial shock acceleration and attenuation.

Introduction: Given the possibility of higher ground temperatures in the future, the pursuit of a cushioning material that can effectively reduce sports injuries during exercise, particularly one that retains its properties at elevated temperatures, has emerged as a serious concern. Methods: A total of 18 man recreational runners were recruited from Ningbo University and local clubs for participation in this study. Frequency analysis was employed to investigate whether there is a distinction between non-Newtonian (NN) shoes and ethylene vinyl acetate (EVA) shoes. Results: The outcomes indicated that the utilization of NN shoes furnished participants with superior cushioning when engaging in a 90° cutting maneuver subsequent to an outdoor exercise, as opposed to the EVA material. Specifically, participants wearing NN shoes exhibited significantly lower peak resultant acceleration (p = 0.022) and power spectral density (p = 0.010) values at the distal tibia compared to those wearing EVA shoes. Moreover, shock attenuation was significantly greater in subjects wearing NN shoes (p = 0.023) in comparison to EVA shoes. Performing 90° cutting maneuver in NN shoes resulted in significantly lower peak ground reaction force (p = 0.010), vertical average loading rate (p < 0.010), and vertical instantaneous loading rate (p = 0.030) values compared to performing the same maneuvers in EVA shoes. Conclusion: The study found that the PRA and PSD of the distal tibia in NN footwear were significantly lower compared to EVA footwear. Additionally, participants exhibited more positive SA while using NN footwear compared to EVA. Furthermore, during the 90° CM, participants wearing NN shoes showed lower PGRF, VAIL, and VILR compared to those in EVA shoes. All these promising results support the capability of NN footwear to offer additional reductions in potential injury risk to runners, especially in high-temperature conditions.

High-quality 3D printing of ethylene vinyl acetate with direct pellet-based FDM for medical applications: Mechanical analysis, energy absorption and recovery evaluation

Ethylene Vinyl Acetate (EVA) is a biocompatible and non-toxic copolymer known for its applications in medicine, drug delivery systems, and energy absorption. This paper presents a novel method for 3D printing EVA using the Fused Deposition Modeling (FDM) technique. By directly utilizing pellet-form EVA material and employing pneumatic pressure for extrusion, we addressed the issue of filament buckling commonly encountered in traditional filament-based printing. A custom-made pellet printer enabled direct feeding of polymer pellets. The mechanical properties, microstructure of the printed EVA parts was analyzed to evaluate the suitability of the direct pellet printing technique for producing high-quality EVA components. The results showed acceptable printing quality and favorable mechanical properties (about 1000% elongation at break and 6.59 MPa tensile strength). Additionally, a cyclic compression test was conducted, subjecting specimens to various strains (30%,80% and 120%) and assessing their compressive and energy absorption properties undergoing significant deformations. Observations reveal a noticeable decline in the mechanical properties after the first compression cycle. The mechanical properties tend to stabilize and reach a steady state from the second cycle onwards until the sixth cycle. Furthermore, a compression cyclic test with various strain rates conducted, investigated the functional performance of the printed EVA components in engineering and biomedical applications, considering the impact of strain rate. Observations indicate that lower strain rates tend to enhance the material's ability to withstand deformation before yielding. This study contributes to expanding the potential of EVA in additive manufacturing, particularly in biomedical and energy absorption systems.

A novel strategy for preparing ethylene‐vinyl acetate composites with high effective flame retardant and smoke suppression performance by incorporating piperazine pyrophosphate and Ce‐MOF

AbstractCerium‐containing metal organic framework defined as Ce‐MOF was prepared and then combined with piperazine pyrophosphate (PAPP) for preparing flame retardant ethylene vinyl acetate (EVA) copolymer composites. The samples of EVA/PAPP/Ce‐MOF achieved UL‐94 V‐0 rating with the limiting oxygen index (LOI) value of 31.3% when 17 wt% PAPP/Ce‐MOF with the mass fraction of 97:3 was introduced. Under the same loading amount of PAPP, the EVA/PAPP only obtained UL‐94 V‐1 rating with the LOI value of 26.9%. Cone calorimeter test confirmed that the total heat release and total smoke production of EVA/PAPP/Ce‐MOF significantly reduced from 132.8 MJ m−2 and 11.5 m2 for EVA/PAPP to 98.8 MJ m−2 and 7.3 m2, with a reduction of 25.6% and 36.5%, respectively. Besides, the maximum smoke density decreased from 488.8 and 375.9 for EVA and EVA/PAPP to 177.5 for EVA/PAPP/Ce‐MOF. It indicated that the addition of Ce‐MOF and PAPP effectively exerted synergistic flame retardant and smoke inhibition effect for EVA. Moreover, the addition of Ce‐MOF enhanced the compatibility of PAPP with EVA matrix, and water resistance of EVA/PAPP/Ce‐MOF was higher than that of EVA/PAPP. The x‐ray photoelectron spectroscopy texts of residual char of EVA composites indicated that the cerium ion complexed with phosphoric acid and polyphosphate generated by the thermal decomposition of PAPP and then more phosphorus elements remained in condensed phase. As a result, the sufficient, crosslinking and dense char layer with excellent intensity was formed, and the heat, combustible gas and smoke were efficiently inhibited. Consequently, the EVA materials were endowed excellent fire safety as well as low heat and smoke release.

Isolated and combined effects of EVA and TPU custom foot orthoses on constant speed, treadmill running kinematics

Introduction: We investigated the isolated and combined (HYB) effects of ethylene-vinyl acetate (EVA) and expanded thermoplastic polyurethane (TPU) custom foot orthoses (CFOs), compared to a control condition (CON; shoes only), on constant speed, treadmill running kinematics.Methods: Twenty (10 male and 10 female subjects) well-trained runners performed four 6-min bouts at the same individualized speed for each bout on a treadmill under four footwear conditions (EVA, TPU, HYB, and CON). Twenty markers and four clusters (four markers each) were placed on lower limbs and the pelvis. Lower limb and pelvis movements were tracked using a three-dimensional motion capture system with 11 cameras (Vicon MX System, Oxford, United Kingdom). Lower limb joint angles and angular velocity were normalized to 100% of the stance phase.Results: Peak ankle eversion (p &amp;lt; 0.001, η2 = 0.72), peak ankle eversion angular velocity (AV) (p &amp;lt; 0.001, η2 = 0.64), peak ankle inversion AV (p &amp;lt; 0.001, η2 = 0.60), and peak ankle internal rotation AV (p &amp;lt; 0.001, η2 = 0.49) demonstrated the largest differences between conditions. Statistical non-parametric mapping analysis revealed that HYB exhibited the largest proportions of change during the total stance phase compared to the CON.Discussion: All CFO materials caused significant reductions in peak angles and peak AVs at the ankle in the frontal plane, with more pronounced effects for harder (EVA) than softer (TPU) materials. These significant reductions occurred during large portions of the total stance phase for the angles and for the AVs. Although some effects could be found in more proximal joints such as the knee and hip, most significant effects were found at the ankle joint. Overall, combining hard EVA material in the heel and soft TPU in the forefoot (HYB) resulted in significant, more favorable changes compared to the CON that lasted for the largest proportion of stance phase when compared to wearing shoes only.

Nonlinear Static Stiffness of Rail Pads for Different Materials and Thicknesses using Finite Element Method

The rail pad located in between the steel rail and base plate provides flexibility to the track and cushions from shocks and vibrations resulting from train operation. This polymeric material has nonlinear behaviour. In this study, the behaviour of the rail pad for different polymeric materials and various thicknesses was investigated. The three different types of rail pads were ethylene propylene diene monomer (EPDM), thermoplastic elastomers (TPEs) and ethylene vinyl acetate (EVA). Three-dimensional (3D) finite element (FE) approach was used to model the fastening system under the static load. The Abaqus software was used for the FE analysis. The thicker rail pad deformed more than the thinner for the same load value. Comparing the thickness, EPDM pad had the highest amount of deformation which had an average difference of 40%, followed by TPE and then EVA with 33% and 23% respectively. The static stiffness of EVA material was the highest followed by TPE and EPDM. For all materials, the rail pad became stiffer as thickness decreased. The reaction force decreased as the thickness of the rail pad increased. EVA, TPE and EPDM showed 15%, 9% and 5% reduction of reaction force respectively as the rail pad thickness increased from 5 mm to 10 mm. Despite that, in term of material, EVA had highest capability to reduce reaction force compared to EPDM and TPE.

Construction and validation of sham insoles used in clinical trials: A systematic review.

Insoles are commonly prescribed to treat pathologies in a variety of patient groups; however, there is limited evidence to guide clinical decision-making. A well-validated sham insole is critical to conducting a double-blind placebo-controlled trial. The aims were to establish: (1) How are sham insoles constructed? (2) What measures are undertaken to ensure adequate blinding? (3) What methods are used to validate the biomechanical effects? A systematic search of the methodology of level I-II therapeutic evidence. Searches were conducted in MEDLINE, Embase, Cumulative Index of Nursing and Allied Health Literature, and Cochrane Central Register of Controlled Trials. Inclusion criteria were placebo-controlled clinical trials, sham insoles used, treatment insoles alter biomechanics, treatment insoles meet the ISO definition of foot orthotics, sham and treatment insoles tested in normal walking, and article available in English. The search generated 270 results. Twenty-four trials were included. 19% of sham insoles were described sufficiently to be replicated. The most common sham construction characteristics were full length, ethylene-vinyl acetate material, and flat insoles. 58% of studies were double-blinded; however, many did not describe any blinding methods. There is evidence that blinding the intervention details and a similar insole appearance is effective to blind participants. 13% of studies included a shoe-only condition to allow assessment of the biomechanical effects of sham insoles. There is inconsistent construction, blinding, and biomechanical validation of sham insoles. This casts a substantial doubt on the quality and reliability of the evidence base to support the prescription of insoles.

Energy Efficiency Improvement of Vanadium Redox Flow Battery by Integrating Electrode and Bipolar Plate

An integral electrode-bipolar plate assembly, which is composed of electrode, conductive adhesive film (CAF) and bipolar plate, has been developed and evaluated for application with a vanadium redox flow battery (VRB) to decrease contact resistance between electrode and bipolar plate. The CAF, made of EVA (ethylene-vinyl-acetate) material with carbon black or CNT (Carbon Nano Tube), is applied between the electrode and the bipolar plate to enable an integral assembly by adhesion. In order to evaluate the integral assembly of VRB by adhesive film, the resistivity of integral assembly and the performance of single cell were investigated. Thus, it was verified that the integral assembly is applicable to redox flow battery. Through resistance and contact resistance of bare EVA and CAF films on bipolar plate were changed. Among the adhesive films, CAF film coated with carbon black showed the lowest value in through resistance, and CAF film coated with CNT showed the lowest value in contact resistance, respectively. The efficiency of VRB single cell was improved by applying CAF films coated with carbon black and CNT, resulting in the reduced overvoltage in charging process. Therefore, the energy efficiency of both CAF films, about 84%, were improved than that of blank cell, about 79.5 % under current density at 40 mA cm−2. The energy efficiency of the two cells were similar, but carbon black coated CAF improved the coulomb efficiency and CNT coated CAF improved the voltage efficiency, respectively.

Field-Aged Glass/Backsheet and Glass/Glass PV Modules: Encapsulant Degradation Comparison

Ethylene vinyl acetate (EVA) is the predominant encapsulant in crystalline-silicon photovoltaic (PV) modules; however, its degradation is a subject of major concern, which causes significant power loss under field conditions. This article presents a comparison of EVA degradation in field-aged PV modules with glass/backsheet (G/B) and glass/glass (G/G) architectures. Modulelevel characterization included UV fluorescence imaging and I-V measurements. Material analytical techniques, including colorimetry, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and Raman spectroscopy, were performed to correlate the module performance parameters with EVA material properties. An intense EVA discoloration in G/G modules was observed, which was corroborated by higher module Isc and Pmax degradation rates compared with its counterpart G/B modules. Higher power degradation was accompanied by a significant increase in EVA crosslinking, vinyl acetate content, yellowness index, and presence of functional groups containing unsaturated moieties that are linked to degradation products of photothermal reaction, and a higher decrease in the degree of crystallinity. The absence of a polymeric backsheet in hermetically sealed G/G modules, which restricts photobleaching and enhances the entrapment of volatile acetic acid and other degradation by-products, plays a major role in causing higher EVA degradation in G/G modules. This article concludes that EVA might have been a good choice of an encapsulant for the G/B modules over the decades, but it may prove to be an inappropriate choice for the G/G modules because of potential degassing, corrosion, and/or discoloration issues. Ionomers or polyester-based encapsulants like polyolefins could be best suited for G/G modules as it appears to be a current trend in the industry.

Low-frequency elastic wave attenuation in a composite acoustic black hole beam

This study discusses the composite acoustic black hole (ABH) beam structure with low-frequency flexural wave attenuation properties. Band structures show that the proposed structure can overcome the limitation of conventional acoustic black holes, which cannot be applied at low frequency. By introducing an ethylene vinyl acetate (EVA) interlayer, the composite beam structure does not reveal the necessary low local stiffness or high stress concentration, vibration modes indicate that flexural wave attenuation still depends on the ABH. Furthermore, the size of the EVA material only affects the upper boundary of the second flexural bandgap but both boundaries of third flexural BG. Elastic constants of different materials have a great effect on the first three BGs. Vibration experiments prove the effect of the composite ABH beam and validate our results. This research has potential applications for controlling vibration propagation, and may be useful in low-frequency vibration filter design.

Influence of EVA, PVB and Ionoplast Interlayers on the Structural Behaviour and Fracture Pattern of Laminated Glass

Architectural trends increasingly challenge material producers and engineers to create sustainable, renewable and innovative laminated glass products that combine multiple functions as in, for example, glass railings with solar cells, curved laminated glass, floors with light emitting diodes that serve as multimedia screens. All new tendencies require the development of interlayers for laminated glass, which allows laminating electrical parts, solar cells or other objects between two glass plies. For this complex lamination process, the most appropriate interlayer is Ethylene Vinyl Acetate (EVA), because its properties allow for working in low temperatures without autoclave. From the other hand, EVA material has not been defined and discussed entirely in prEN16613 standard as a suitable interlayer material, for example, for structures application like Polyvinyl Butyral (PVB) interlayer. For this reason, EVA interlayer laminates must be investigated and compared with PVB or similar interlayer laminates to evaluate its mechanical behaviour. The research paper gives an idea and compares the structural behaviour and fracture pattern and evaluates laminated glass samples with PVB, Ionoplast and EVA interlayers. Under practical circumstances, glass structures need to be designed to withstand bending stresses which may occur, e.g., due to lateral loading, that means that four-point bending tests is appropriate method for the evaluation of structural behavior. Tests were also modelled in the Finite Element (FE) ABAQUS/CAE software to calculate displacements and evaluate bending stresses. According to current research, the conclusion can be drawn that for samples with EVA interlayer, stiffness is equivalent to PVB interlayer specimens’ results and EVA interlayer can be used in the same cases as PVB material. Moreover, using FE method makes it possible to simulate accurately the mechanical behaviour of laminated glass tested in 4-point bending with high result correlation with error less than 5% while the analytical calculations show error of 10-58%.

Investigation on the effects of process parameters in CNC assisted pellet based fused layer modeling process

A new CNC assisted pellet-based fused layer modeling (FLM) process has been presented. It allows the fabrication of highly flexible parts which is not easily possible through the fused filament fabrication (FFF) process as buckling occurs when the flexible filament is fed into liquefier head. Instead of the filament, the presented FLM process utilizes the material in pellet form. The FLM process is different from the other extrusion based AM processes and has its own characteristics. Therefore, the current paper presents a parametric investigation in the developed FLM process by considering the ethylene vinyl acetate (EVA) material. Experiments have been conducted using the ‘one factor at a time’ (OFAT) approach. The effects of barrel temperature, bed temperature, screw speed, deposition speed, standoff distance between nozzle and bed surface have been studied on the melt flow rate, layer thickness and road width. The obtained results showed that the melt flow rate of EVA is increased with the increase in the screw speed and barrel temperature. A significant variation of approximately 27% was observed in the layer thickness with the change in the deposition speed and standoff distance. A decrease of 42.42% was observed in the road width when the standoff distance was reduced from 2 to 0.8 mm. Based on the investigation, a set of suitable process parameters was obtained to fabricate the flexible parts of the EVA material. The outcomes of the current study showed that the developed FLM process has the capabilities of fabricating parts utilizing a set of suitable process parameters.

The effect of process parameters on tensile behavior of 3D printed flexible parts of ethylene vinyl acetate (EVA)

Fused deposition modeling (FDM) is widely accepted AM process due to its capability of fabricating intricate geometries using filament of thermoplastic materials such as ABS, PLA, etc. Due to the limitations of the filament feed extrusion mechanism, existing FDM systems cannot fabricate flexible parts of soft-elastomers. Instead of filament shape, the material in pellet form has a broad scope for 3D printing of flexible parts. Ethylene vinyl acetate (EVA) material is widely used for the fabrication of flexible objects; however, the potential of this material has not been explored yet using the FDM process. In this study, flexible specimens of EVA material have been printed using a customized pellet based FDM system followed by the investigation on the effect of process parameters on tensile behavior. The effect of process parameters namely barrel temperature, platform temperature, build orientation, raster angle and number of contours have been studied on the tensile properties namely, ultimate tensile strength and % elongation at break. Response surface methodology (RSM) and analysis of variance (ANOVA) techniques have been used to study the effect of process parameters for attaining optimum tensile properties. It was found that barrel temperature, raster angle, and platform temperature affect the tensile behavior of EVA specimens significantly. The maximum obtained values of ultimate tensile strength and elongation at break were 8.83 MPa and 522.34% respectively. The outcome of the current study will help the engineers and designers to predict the tensile behavior of flexible parts for various applications.

Extrusion-based additive manufacturing process for producing flexible parts

The processing of elastomers through fused deposition modeling (FDM) is challenging task due to low column strength and high melt viscosity. Ethylene vinyl acetate (EVA) is an elastomer which is widely used for fabricating flexible objects. However, the potential of this material has not been explored in the FDM process. Pre-fabricated EVA filament cannot be processed in standard filament feed extrusion mechanism of commercial FDM machine due to buckling of the filament. However, development of pellet-based extrusion additive manufacturing (AM) may eliminate the issues caused by elastomer filament. The current study demonstrates the development of pellet-based AM system for processing EVA material. The developed system is compatible with the three-axis CNC milling machine, which provides high precision positioning to the deposition path and required power for screw rotation. Details about hardware and software related to the developed system have been presented. Flexible parts using EVA pellets have been fabricated successfully, which shows the capability of the developed extrusion AM system. Experiments have been performed for tuning process parameters. Further, mechanical characterization has been done to analyze the dimensional accuracy, flexibility, strength and hardness of printed parts. Obtained results show that EVA demonstrates approx. 300–550% higher elongation as compared to ABS and PLA materials, which indicates EVA can be used to make highly flexible parts. The outcome of this study will be helpful to the engineers for the development of low-cost flexible parts for those applications where customized flexible parts are needed in short span of time.

Antimicrobial activity of ethylene-vinyl acetate containing bioactive filler against oral bacteria.

We developed an ethylene vinyl acetate (EVA) containing surface pre-reacted glass-ionomer (S-PRG) filler, as a new mouthguard material for preventing intraoral bacterial infection. We examined its physical properties, antimicrobial activity against a major cariogenic bacterium Streptococcus mutans and a periodontopathogen Porphyromonas gingivalis, and its cytotoxicity toward human gingival epithelial cells. S-PRG filler was added to EVA copolymer at 5, 10, 20, or 40 wt% and was processed into disc-shaped test specimens. Only minor differences between the Shore hardness and rebound resilience properties of EVA materials with and without the S-PRG filler were observed. The specimens with S-PRG filler showed bacteriostatic activity toward S. mutans and P. gingivalis and inhibited S. mutans biofilm formation. No cytotoxicity against the gingival epithelial cells was observed. Our findings show that EVA containing S-PRG filler has antimicrobial activity toward pathogenic oral bacteria and may be an effective material for maintaining the oral health of athletes.

Preparation and Performance Research of New High Toughness EVA Material

The blends of ethylene vinyl acetate (EVA) and thermoplastic polyurethane (TPU) were prepared by means of blending. The mechanical properties of EVA/TPU blends and thermal stability of the extrudates were investigated. The results show that the toughness of EVA/TPU has been improved after adding TPU into EVA, and doesn’t affect the thermal stability of material.

A purely flexible lightweight membrane-type acoustic metamaterial

This paper proposes a purely flexible lightweight membrane-type acoustic structure, wherein one kind of flexible lightweight rubber material takes the roles of mass and stiffness and another type of lightweight flexible EVA (ethylene–vinyl acetate copolymer) or plastic material functions as the localized stiffness for each unit. Because both the scatterers and base are constituted by the same material, this type of structure breaks the limitation that the metamaterials and phononic crystals need different materials with relatively large density and elasticity modulus ratios to play the roles of the scatterers and base respectively. Based on the band structures with different units, mass block shapes and size parameters, it is suggested that the shapes of the mass block can significantly affect the band structure. In addition, this type of structure could not only open a full band gap in the low-frequency range below 500 Hz, but also obtain an ultra-low-frequency bending wave band gap in the range below 100 Hz. Finally, we take into account the semi-infinite medium as a component, and calculate the sound transmission loss (STL) to evaluate the interaction between the structure and air. An experimental validation employing the cylindrical mass structure was developed to directly support the simulation results. Since the structures proposed in this study have achieved a purely flexible lightweight design, there exists an important promotion effect to realize the engineering applications of the acoustic metamaterials in practice.

Encapsulation of PV Modules Using Ethylene Vinyl Acetate Copolymer as the Encapsulant

Ethylene vinyl acetate (EVA) encapsulation materials have attracted a lot of attention due to their extensive applications in solar cells. Nearly 80% of photovoltaic (PV) modules are encapsulated by EVA materials. EVA has lots of advantages, such as good light transmittance and elasticity, low processing temperature, excellent melt fluidity, and adhesive property. In addition, the price is low, which makes it very suitable as a solar cell encapsulation material. However, there are also some problems with EVA. Its damp‐heat aging resistance and ultraviolet aging resistance are not good. It also easily degrades and becomes yellow, reducing the energy conversion efficiency of the solar cell. This article pays special attention to improving the performance of EVA encapsulation films. In addition, it differentiates between different properties, including the aging resistance, adhesive strength and energy conversion efficiency.

Reducing shadowing losses with femtosecond‐laser‐written deflective optical elements in the bulk of EVA encapsulation

AbstractA new approach on decreasing the optical shadowing of the solar cell grid fingers is presented. The approach relies on a local change of the optical properties in the bulk of the photovoltaic module encapsulation material ethylene vinyl acetate (EVA). In particular, scattering and diffractive optical elements are locally generated within the volume of cross‐linked EVA encapsulation material by applying a femtosecond‐laser‐writing process. When these optical elements are located above the metal grid fingers, the optical shadowing of these grid fingers can be decreased. In an experimental proof of concept, the optical performance of this approach is demonstrated. The best results obtained so far indicate a decrease in optical shadowing by 17%. The material characteristics of the volume optics were investigated by applying confocal Raman microscopic characterisation, which indicates that the EVA material partially degraded upon the impact of the laser beam and is partly carbonised. Supplementary optical simulations show that the light deflection is caused by diffraction. However, parasitic absorption substantially deteriorates the optical performance of the deflective volume optics. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Contact-free Determination of Ethylene Vinyl Acetate Crosslinking in PV Modules with Fluorescence Emission

The degree of crosslinking of ethylene vinyl acetate (EVA) is a decisive factor for the photovoltaic (PV) modules reliability. Numerous chemical or physical methods may be applied to determine the extent of crosslinking reaction in the EVA material. The usual and most accurate ones are destructive as they require a sample of material from the module. In this work we present a contactless and non-destructive method for monitoring the crosslinking process of EVA based on fluorescence spectroscopy. We show the correlation of fluorescence emission intensity of EVA when submitted to UV light with its curing grade determined by a rheological method. This approach is of interest for in-line monitoring of the crosslinking during the lamination step and for quality control after production.