Ethylene Vinyl Acetate Research Articles

Development of flexible grouting material for cement-stabilized macadam base using response surface and genetic algorithm optimization methodologies

To repair the voids and cracks in the Cement-stabilized macadam base (CSMB), a grouting material with lower elastic modulus, enhanced fluidity and slight expansion called Flexible Grouting Material (FGM) was developed using superfine cement, fly ash (FA), silica fume (SF), vinyl acetate-ethylene (VAE) copolymer emulsion, and polyvinyl alcohol (PVA) fiber. After that, the study optimized the proportion of FGM using Response Surface Methodology (RSM) and Non-dominated Sorting Genetic Algorithm-II (NSGA-II) in Multi-Objective Optimization (MOO). Firstly, to determine the component contents for subsequent experiments, the fluidity, setting time, compressive/flexural strength (1d + 3d), and ratio of compressive strength to flexural strength (C/F, 1d + 3d) were tested. Subsequently, the Response Surface Methodology-Box Behnken Design (RSM-BBD) was employed using VAE content, PVA content, and water-to-cement ratio (W/C) as factors. Additionally, the fluidity, setting time, compressive/flexural strength and C/F (28d), elastic modulus (28d), and drying shrinkage (28d) were considered as responses in RSM-BBD. The VAE content and W/C significantly influenced the response values, while the PVA content had a relatively minor influence. Finally, the NSGA-II was utilized to determine the optimal proportion of FGM. Compared to the control group, the optimal FGM demonstrated 16.53 % increase in fluidity, 37.86 % decrease in elastic modulus (28d), 47.98 % decrease in C/F (28d), 22.22 % reduction in drying shrinkage (28d), and 54.07 % increase in final setting time.

Synergistic P-N charring agents to enhance flame retardancy of ethylene-vinyl acetate (EVA): Insights from experimental and molecular dynamic simulations

Previous charring agents had nonignorable defects, such as a low charring rate and poor compatibility with acid and gas sources in intumescent flame retardants (IFRs), leading to poor flame retardant efficiency. Thus, we designed a novel P-N macromolecule charring agent named poly(piperazinyl phosphamide) (PA) and confirmed the chemical structure of PA. A small amount of 7.5 wt% PA in EVA/ammonium polyphosphate (APP)/PA improved the limit oxygen index (LOI) to 35.7 ± 0.58% from 19.0 ± 0.33% and reached the level of UL-94 V–0. This implies that PA was an efficient charring agent in IFRs. Moreover, the peak heat release rate (PHRR) and total heat released (THR) dramatically declined by 90.73% and 97.70%, respectively. This suggests that the addition of PA further hinders the diffusion of combustible substances, forming a dense and sturdy char layer in the condensed phase. In detail, the decomposition of PA produces many aromatic structures, such as C = N, C = C, P = O, and P–N. Simultaneously, APP can defer the cleavage of C–N bonds for PA and promote the formation process of the benzene ring, which is clearly conducive to charring. To estimate the flame retardant micromechanism of EVA/APP/PA at high temperatures, this work utilized molecular dynamics simulation based on reaction force field (ReaxFF-MD) to research at the atomic scale. The potential energy, decomposition time, main gas products, and free radical products of the materials were simulated, which demonstrated that EVA/APP/PA has better flame retardancy than equal amounts of EVA/APP owing to the addition of PA. Suppressing the generation of combustible gases (CH4, C2H4, C6H6) and facilitating the binding of molecular products into char residues to form organic molecular structures with good stability is consistent with the experimental results. Proving that the PA was the key to boosting the flame retardancy of EVA by hindering the spread of combustible gases. A novel way for analysing and predicting the flame-retardant mechanism of EVA at the atomic level was proposed.

Effect of global damp heat ageing on debonding of crosslinked EVA- and POE-glass laminates

Polyolefin elastomers (POE) have been established as a promising alternative to commonly used peroxide crosslinked ethylene vinyl acetate copolymer (EVA) photovoltaic encapsulation materials. The main objective of this work was to assess the long-term ageing behavior of double-glass laminates based on UV-transparent EVA and POE under damp heat (85 °C, 85 %rh) conditions for up to 10,000h. Ageing induced changes were characterized by microscopy, UV–visible–near infrared (UVVISNIR) spectroscopy, compressive shear testing (CST), differential scanning calorimetry (DSC), macro- and microscopic Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Within the laminates, the formation of birefringent spheric microdomains (maltese-crosses) was confirmed after an exposure time of more than 2,000h. The compressive shear behavior of EVA laminates was not significantly affected by damp heat ageing. Interestingly, the POE laminates revealed an even improved compressive shear performance. Whereas the tested EVA laminates failed in an interfacial manner independent on damp heat ageing time, POE laminates exhibited a failure mode transition from interfacial (unaged) to combined interfacial and cohesive (10,000h). On the interfacially fractured surfaces of EVA and POE laminates, carboxylic acid groups were ascertained. Deprotonated silanol and water bands were discernible on the opposite glass sides. Damp heat exposure of POE laminates for 10,000h resulted in pronounced glass ageing close to the interface associated with a partly cohesive failure within glass. This phenomenon was quite different to EVA and was attributed to the alkaline characteristics of the hindered amine light (HALS) stabilized, less-polar, UV-transparent POE encapsulant.

Effect of crosslinking on EVA-based encapsulant properties during photovoltaic module fabrication process

The key objective of this work is to create a comprehensive comparison between experimental analysis methods for detecting crosslinking reaction in EVA encapsulant material during PV module fabrication process. Several analytical methods, spanning from classical gel content extraction measurements over different thermo-analytic and mechanical approaches to spectroscopic analysis as Thermally Stimulated Current (TSC), have been investigated as to their ability to reveal the crosslinking state of ethylene vinyl acetate (EVA). The basic results show that TSC complements perfectly other thermal analysis methods like as Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analysis (DMTA) to determine fundamental properties of EVA such as molecular mobility characteristics and also to monitor the crosslinking reaction. Exothermic peak as revealed by DSC analysis can be used to estimate the crosslinking rate of EVA during PV module encapsulation process as fast quality control test.

Diverse and high pollution of microplastics in seasonal snow across Northeastern China

Snow scavenging is recognized as one of the major sinks for atmospheric microplastics (MPs). However, little is known about the properties of MPs in large-scale surface snow. Using Nile Red staining and micro-Fourier transform infrared spectroscopy, we identified the shapes, sizes, and polymer components of MPs in seasonal snow across northeastern (NE) China, a major industrial area. The average concentration of MPs was (4.52 ± 3.05) × 104 MPs L−1, and the highest contamination (6.65 ± 3.89) × 104 MPs L−1 was observed in Changbai Mountains, which was the highest concentration observed in surface snow to the extent of literature. The majority of snow MPs were smaller than 50 μm and composed primarily of fragments. Ethylene vinyl acetate and polyethylene were the dominant contributors to their chemical components. Investigation with positive matrix factorization revealed that the MPs were primarily generated by debris from packaging materials, followed by industrial and construction activities. In addition, the winter atmospheric circulation over the northwestern Siberian and Mongolian plateaus likely dominated the wide-range dispersion and deposition of the MPs across NE China. These results provide a first comprehensive perspective of MPs from sources to removal associated with snow in a large geographic region.

Investigation of the Properties of Polyethylene and Ethylene-Vinyl Acetate Copolymer Blends for 3D Printing Applications.

3D printing of polyolefins, such as polyethylene (PE) and polypropylene (PP), is of great practical interest due to the combination of high properties of these materials. However, the use of these materials in 3D printing is associated with many problems due to their high rate of crystallization, which causes shrinkage and warpage of the printed object. In this regard, blends of PE and ethylene-vinyl acetate copolymer (EVA) of various compositions were investigated for 3D printing. It was found that with an increase in the concentration of EVA, an increase in the pseudoplastic effect and amorphization of PE occurs. It has been shown that with an increase in the EVA content, the degree of crystallinity of PE decreases slightly (by 11% at a content of 80% EVA); however, a significant decrease in the rate of crystallization of PE is observed (by 87.5% at the same EVA concentration). It was found that PE and EVA are completely compatible in the amorphous phase and partially compatible in the crystalline phase, which leads to a slight decrease in the melting point of PE. The introduction of EVA also leads to a significant increase in impact strength: the maximum value is achieved at a 50/50 ratio, which is five times the value of the initial PE and two times the value of the initial EVA. At the same time, it was revealed that EVA leads to a gradual decrease in the elastic modulus and strength of PE, the change of which generally obeys the additivity rule. The resulting printing filaments are characterized by a certain ovality due to their shrinkage, which decreases with increasing EVA content and reaches a minimum value at a PE/EVA ratio of 30/70. This composition also demonstrates the lowest shrinkage of the printed sample and higher processability during printing.

Microstructural and polymer film interaction mechanisms: Insights of GO-reinforced polymer-modified cement composites

The effects of graphene oxide (GO) on cement hydration phases and polymer film formation in GO-reinforced polymer-modified cement (GOPMC) composites were investigated by analysing interactions of film chemical structure and cement hydration kinetics towards enhanced engineering performance. Chemical characterisation by FTIR and XRD analyses revealed that alterations of the cement matrix's chemical structure, such as slow Ethylene vinyl acetate (EVA) hydrolysis, increased calcium-silicate-hydrate (C–S–H) and portlandite Ca(OH)2, were more pronounced in GOPMC composites, indicating direct and robust involvement of GO during early-age hydration kinetics. Isothermal calorimetry displayed an increased heat flow of ∼7.2 % for GOPMC compared with the reference PMC composite. Notably, air voids of GOPMC composite revealed polymer film sheets intermingled with cement hydration products to promote elastic interconnections and microstructural uniformity. Accordingly, the GOPMC composite displayed ∼16 % higher tensile strength at 28 days versus the PMC composite, primarily attributable to GO nucleation, due to its seeding effect on cement hydration kinetics thereby inducing marginally slower EVA hydrolysis, increased C–S–H nucleation sites, and smaller-sized CH crystals while mechanically reinforcing polymer films. More significantly, GO reinforced the microstructure of the GOPMC composites with no apparent chemical interference of crucial film-forming properties. This research provides a fundamental understanding of this novel material's characteristic properties and framework of engineering performance optimization for future infrastructure applications.

Ergonomic Sports Mouthguards: A Narrative Literature Review and Future Perspectives

Sports activities can increase participants’ risk of orofacial trauma. Therefore, it is crucial to have a comprehensive understanding of various types of sports mouthguards. This study aims to present a narrative literature review on ergonomic mouthguards, including their indications for use, classifications, materials, manufacturing methods, and the current status of additive manufacturing in their production. Research of the existing literature was performed in the Google Scholar, MEDLINE/PubMed, Web of Science, and ScienceDirect databases to identify the currently available publications on the topic of sports mouthguards from January 1951 to August 2023. The terms used were “sports mouthguard”, “mouthguards and orofacial traumas”, and “mouthguards and additive manufacturing”. A total of 920 articles were found, and 39 articles were selected and included in this review. While consensus exists regarding the significance of using sports mouthguards with optimal attributes, there is a need for standardization in the methodology for manufacturing custom-made mouthguards. These can be fashioned with conventional ethylene vinyl acetate (EVA) copolymer reinforcements. Such standardization would ensure uniform stress distribution and guarantee ample protection for oral tissues, allowing for universal reproducibility among dental practitioners. Additive manufacturing stands as an innovative method for fabricating mouthguards, displaying promising benefits. However, the materials and methodologies employed in this workflow still require refinement and characterization for a safe clinical integration.

Combustion behavior, mechanical performance and application for vinyl acetate–ethylene copolymer emulsion containing melamine amino trimethyl phosphate and sodium lignosulfonate

AbstractAn intumescent‐flame‐retardant vinyl acetate–ethylene copolymer (IFR/VAE) compound has been prepared by blending with a complex of melamine amino trimethyl phosphate (M‐AT) and sodium lignosulfonate (SL). Then, this obtained IFR/VAE polymer was applied as adhesives for producing the flame‐retardant plywood. The IFR VAE sample (VAE/M‐AT3/SL1) with a mass ratio 3:1 (M‐AT to SL) showed an enhanced amount of char residue, limiting oxygen index (LOI) value and tensile strength value to 20.6 wt%, 32 vol% and 19.3 MPa, which have been increased by 796%, 600%, and 56% compared to that of neat VAE. The cone calorimeter result showed that the peak of heat release rate (pHRR) of VAE/M‐AT3/SL1 sample was reduced by 48% compared to the control one. Additionally, the second peak of HRR of sample IFRPW/15 L/15 (containing 15 wt% M‐AT3/SL1 in the plywood adhesive layer) presented a reduction of 29% compared to that of the sample PW/15 L (neat plywood). It is assigned to the formation of phospho‐carbonaceous structure during combustion, thus the flame‐retardancy of plywood has been greatly enhanced. Thus, this work provides an economical and applicable fire‐retardant VAE adhesive formula for producing plywood materials with good performances.

Protective performance of shear stiffening gel-modified foam against ballistic impact: Experimental and numerical study

As one of the most widely used personal protective equipment (PPE), body armors play an important role in protecting the human body from the high-velocity impact of bullets or projectiles. The body torso and critical organs of the wear may suffer severe behind-armor blunt trauma (BABT) even though the impactor is stopped by the body armor. A type of novel composite material through incorporating shear stiffening gel (STG) into ethylene-vinyl acetate (EVA) foam is developed and used as buffer layers to reduce BABT. In this paper, the protective performance of body armors composed of fabric bulletproof layers and a buffer layer made of foam material is investigated both experimentally and numerically. The effectiveness of STG-modified EVA in damage relief is verified by ballistic tests. In parallel with the experimental study, numerical simulations are conducted by LS-DYNA® to investigate the dynamic response of each component and capture the key mechanical parameters, which are hardly obtained from field tests. To fully describe the material behavior under the transient impact, the selected constitutive models take the failure and strain rate effect into consideration. A good agreement between the experimental observations and numerical results is achieved to prove the validity of the modelling method. The tests and simulations show that the impact-induced deformation on the human body is significantly reduced by using STG-modified EVA as the buffering material. The improvement of protective performance is attributed to better dynamic properties and more outstanding energy absorption capability of the composite foam.

Output power enhancement of a bifacial solar photovoltaic with upside down installation during module defects

A bifacial solar photovoltaic (PV) module performs worse if it has any faults that reduce output power, shorten its lifetime, or raise safety and reliability issues. Since they work in constantly changing environments, the PV modules may have a variety of defects, including glass breakage, soiling, Ethylene Vinyl Acetate (EVA) delamination, discoloration, fractures, corrosion, and hotspots. Thermal stress, photo-thermal deterioration, aging, transportation, dust buildup, bird droppings, and partial shadowing by trees, tall structures, or objects are a few of the potential causes. It is necessary to employ appropriate diagnostic techniques or design modifications to eliminate the negative effects of these faults. In this work, the performance of an n-type passivated emitter rear totally diffused (PERT) module is analyzed during faults that reduce the transparency of front glass cover and restrict the level of solar irradiance. The faults such as dust accumulation, glass breakage, EVA delamination, discoloration, and micro cracks are taken into account for the analysis. To overcome the output power reduction brought on by these defects, a new installation method called upside down installation is proposed that enhances the output power. Overall, depending on the fault cases, the proposed upside down installation method enhances the output power by up to 67% when compared to the normal installation method.

The effect of the simulated aging by thermocycling on the elastic modulus of ethylene-vinyl acetate brands and stress/strain development during an impact: An in vitro and 3D-FEA analysis.

Mouthguards are used to prevent dental trauma and orofacial injuries. The aim of this study was to evaluate the influence of ethylene-vinyl acetate (EVA) aging by thermocycling on elastic modulus, stress, strain and shock absorption ability of different ethylene-vinyl acetate brands used for mouthguards. Thirty EVA samples with a dimension of 70 × 10 × 3 mm were obtained from four commercial brands (Bioart®, Erkodent®, Polyshok® and Proform®). Fifteen samples were submitted to 10,000 cycles (5°C-55°C) in a thermocycling machine with an immersion time of 30 s and a transfer time of 5 s. The samples were submitted to a uniaxial tensile test in a universal testing machine to calculate the elastic modulus. Data were statistically evaluated by two-way ANOVA and Holm-Sidak test. A three-dimensional model of the anterior maxilla was created using Rhinoceros 5.0. A 3 mm custom-fitted mouthguard was simulated. The three-dimensional volumetric mesh was generated using the Patran software (MSC Software) with isoparametrics, 4-noded tetrahedral elements and exported to Marc/Mentat (MSC Software) as element number 134. A non-linear dynamic impact analysis was performed in which a rigid object struck the central incisor at a speed of 5 m/s. The stresses were evaluated by the modified von Mises criteria and the strains were also recorded. Statistically significant differences were observed for elastic modulus values (p < .001). Mean and standard deviation values (MPa) without thermocycling were: Bioart (34.5 ± 0.9), Erkodent (15.0 ± 0.4), Polyshok (17.3 ± 0.4), Proform: (20.6 ± 0.8); and with thermocycling: Bioart (25.4 ± 0.8), Erkodent (10.7 ± 0.5), Polyshok (13.3 ± 0.6), Proform (13.1 ± 0.6). The thermocycling process reduced stress and strain levels regardless of the mouthguard materials. Shock absorption ability calculated based on the strain values was increased with thermocycling process. The thermocycling process, regardless of the commercial brand, reduced the stress/strain and increased the shock absorption ability of mouthguards.

Vinyl acetate-ethylene as a potential alternative to fluorine free binders in supercapacitors

Supercapacitors are an environmentally friendly energy storage technology that is in increasing demand. However, the binder materials used in the electrodes of supercapacitors often contain fluorine components, which are ecologically harmful and are the subject of upcoming restrictions. This study presents an ecologically friendly alternative: vinyl acetate/ethylene (VAE) modified carbon materials in aqueous supercapacitors. It describes initial measurements obtained in VAE-based supercapacitors filled with KOH or Na2SO4. The materials and methods used can, however, also be applied to other aqueous capacitors and batteries.

Multi-Functional Ethylene-vinyl Acetate Copolymer Flexible Composite Film Embedded with Indium Acetate-Passivated Perovskite Quantum Dots.

In recent years, all-inorganic cesium lead halide perovskite quantum dots have emerged as promising candidates for various optoelectronic applications, including sensors, light-emitting diodes, and solar cells, owing to their exceptional photoelectric properties. However, their commercial utilization has been limited by stability issues. In this study, we addressed this challenge by passivating the surface defects of CsPbBr3 quantum dots using indium acetate, a metal-organic compound. The resulting CsPbBr3 quantum dots exhibited not only high photoluminescence intensity, but also a remarkably narrow half-peak width of 19 nm. Furthermore, by embedding the CsPbBr3 quantum dots in ethylene-vinyl acetate, we achieved stretchability and significantly enhanced stability while preserving the original luminous intensity. The resulting composite film demonstrated the potential to improve the power conversion efficiency of crystalline silicon solar cells and enabled the creation of excellent white light-emitting diodes with coordinates of (0.33, 0.31). This co-passivation strategy, involving surface passivation and polymer packaging, provides a new idea for the practical application of CsPbBr3 quantum dots.

Electrical and dielectric properties of EVA/modified lead titanate elastomer composites

At first, the modified lead titanate (PWNTO) was synthesised by cost-effective solid-state reaction method.The ethylene–vinyl acetate (EVA)/PWNTO polymer composites with 2.5, 5.0, 7.5 and 10.0 wt% of PWNTO were fabricated by the solution casting method. The present communication highlights the dielectric behaviour, ac conductivity, impedance of these elastomer composite-sheets. As the inorganic filler content increases in the elastomer-system of EVA/PWNTO, the relative dielectric constant increases. The ac-conductivity of the above films also increasing in the frequency 1kHz to 1 MHz. The behaviour of the Nyquist-plot is simulated with an equivalent circuit of (CQR)(CR); from this the parameters like the bulk capacitance (Cb), bulk resistance (Rb) and frequency factor(n) were evaluated.

On the protectiveness of additively manufactured mouthguards

A mouthguard is a piece of equipment worn in sports worldwide to greatly reduce the chance of orodental injuries. This work uses a newly developed method for testing and analysing mouthguards subjected to high impact energies of up to 100 J. This method allows investigation and comparison between the use of additive manufacturing, and current best mouthguard manufacturing technology of thermoforming with Ethylene-vinyl acetate (EVA). The impact experiments are conducted using a drop tower and high-speed images are captured for the further analysis. Important physical parameters such as peak force, impulse and dissipated energy in the mouthguard are determined. The results revealed that the additively manufactured mouthguards made from Arnitel® ID 2045 lead to a peak force and impulse of impact that is on average 10% and 25% lower, respectively, than that experienced when using the EVA mouthguard. A lower peak force and impulse is preferred as it reduces the chance of an orodental injury occurring. The research shows that previously mouthguards have been tested at impact energies far lower than those experienced in impact prone sports such as field hockey. When using impacts with higher energies, the findings show that additive manufacturing provides a viable technology for manufacturing mouthguards, which offers many new benefits.

High-efficient flame retardant ethylene-vinyl acetate composites by incorporating monomolecular IFR and its pyrolysis behavior

Highly efficient flame retardant and excellent mechanical performance was critical for the application of ethylene vinyl acetate copolymer (EVA) composites. Herein, a monomolecular intumescent flame retardant poly(piperazine methylphosphonic acid pentaerythritol ester) defined as PPMPPE was incorporated into the EVA matrix, and the flame retardancy, mechanical performance of EVA composites were investigated. When 21 wt% PPMPPE was incorporated, the limiting oxygen index (LOI) of 1.6 mm EVA/PPMPPE composites was increased from 18.2 % for neat EVA to 27.5 %, and it achieved UL-94 V-0 grate during vertical burning tests. Meanwhile, the cone calorimetry tests indicated that the peak value of heat release rate and total heat release of FR-EVA composites were obviously reduced by 41.1 % and 27 % compared to neat EVA. The analysis of flame-retarded mechanism for EVA/PPMPPE indicated that PPMPPE facilitated the decomposition of EVA and formed an expanding char layer, and it possessed barrier effect in condensed phase. In addition, the PPMPPE could exert free radicals quenching effect and in gaseous phase. Therefore, the PPMPPE endowed the EVA matrix with good flame-retardant efficiency. Meanwhile, the mechanical performance of EVA/21 wt% PPMPPE composites was well maintained, and its tensile strength and elongation at break decreased by 21.9 % and 14.4 %, respectively. This research work provided a feasibility approach for producing EVA composites with excellent flame-retardant and mechanical performance.

Rubber wastes recycling for developing advanced polymer composites: A warm handshake with sustainability

Recycling and management of rubber wastes experiences an early-stage maturity in the quest for sustainable and circular materials. Up to now, solutions proposed for sustainable development of rubber wastes are limited, so that properties and performance features of recycled products are inadequate for practical applications. Herein, an experimental protocol is introduced for manufacturing semi-sustainable polymer composites based on ground tire rubber (GTR) and ethylene-vinyl acetate copolymer (EVA), varying carbon black (CB) content (5–50 phr), CB type, i.e., low-surface area CB (L-CB) and high-surface area CB (H-CB), and EVA/GTR composition (50/50 and 75/25 w/w). Processing (printability potential and fluidity/flexibility), properties (thermal, and mechanical), and performance (fire safety and electrical conductivity) features of the resulting composites are analyzed and interpreted. Highly-loaded 50/50 GTR/EVA systems reveal promising properties and performance. The flexibility of product is promising for additive manufacturing. Tensile strength is independent from CB type and blend composition, while elongation at break change pursuing a percolation threshold for CB ≤ 10 phr and CB > 10 phr depending on CB type. Thermal stability is considerable for 50/50/50 (w/w)/phr GTR/EVA/CB system with high amount of GTR. A long-standing flame retardancy is observed for 50/50/50 GTR/EVA/L-CB and 50/50/25 GTR/EVA/H-CB (w/w)/phr composites. A frequency-independent direct current (DC) branch is appeared by increasing temperature at low-frequency region, characteristic of rubber-like dielectric materials. The DC part is intensified even at low temperatures (<10 °C) when CB content increased, so that percolation thresholds are 5 phr and 10 phr for H-CB and L-CB loaded blends, respectively. This work opens new gates of hope towards development of fully sustainable polymer composites from recycled rubber wastes.

EVA/KH560 synergistically modified recycled concrete mechanical properties - Experiment and molecular dynamics simulations

Considering the long-term working performance of recycled concrete (RC) members, there is a need to compensate for the performance deficiencies of RC. In this study, the mechanical properties of RC were improved by two different modification methods, and the reinforcement effects of RC modified by Silane Coupling Agent (KH560)/Ethylene vinyl acetate copolymer (EVA) and RC modified by EVA alone were compared and analyzed. The effects of separate modification and co-modification on RC were analyzed through multi-scale methods in terms of macro-mechanical properties, microstructure, chemical composition and molecular mechanism, respectively. The results of macroscopic mechanical experiments showed that the compressive and shear strength of EVA/KH560 synergistic modification is higher than that of EVA alone. Scanning Electron Microscope (SEM) data showed that the surface density of the old and new concrete interfaces was higher under EVA/KH560 co-modification. X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) data showed that more cement gel will be produced under EVA/KH560 synergistic modification. Molecular dynamics (MD) simulations show that EVA single modification can produce hydrogen and ionic bonds at the interface of old and new concrete, while EVA/KH560 synergistic modification not only produces them, but also forms a stable Si-O-Si chemical bond.

Pyrolysis mechanism and recycling strategy of end-of-life photovoltaic modules based on the experiment and the density functional theory

Recent advancements in renewable energy have enabled a reduction of fossil fuel usage. However, the so-called energy waste, such as end-of-life (EoL) photovoltaic (PV) modules, has become a simultaneous emerging issue in the field of solid waste management. Debonding of ethylene-vinyl-acetate (EVA) copolymer is critical for recycling EoL PV modules. The separation of organic substances may be done effectively using pyrolysis technology. Therefore, in this work we investigated the pyrolysis characteristic and mechanism of EVA. Based on TG, TG-FTIR, and Py-GC/MS, the pyrolysis products and pyrolysis characteristics of EVA were examined. Activation energies and reaction mechanisms were determined through iso-conversional model-free and model-fitting methods. Combined with density functional theory (DFT) calculations, the pyrolysis mechanism of EVA was discussed. Our research shows that the pyrolysis technology can almost completely decompose EVA without residue and the EVA pyrolysis can be divided into two stages. Combined with DFT calculation, it was found that in the stage Ⅰ, acetoxy was removed to generate acetic acid, and in the stage Ⅱ, the main chain of EVA was broken to generate olefins. The recycling strategy based on two-step pyrolysis of Eol PV modules was accordingly proposed.