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Both Hansen solubility parameter and Flory–Huggins interaction parameter of two EVA [Poly(ethylene-co-vinyl acetate)] copolymers with different vinyl acetate content have been obtained by means of intrinsic viscosity measurements. To calculate this last parameter it was also necessary to determine the theta solvent at different temperatures of the...
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... the Flory-Huggins parameter, Table 6 shows their calculated values following the Stockmayer-Fixman relationship [23], and Table 7 shows their calculated values according to Berry relationship [24]. Both Tables also show the values of the enthalpic [calculated with Eqs. 4 and 5] and entropic (calculated as the difference between the overall value and the enthalpic term) contributions to the FH parameter. ...
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... It should be pointed out that the enthalphy term in Eq. (34) is introduced for the mixing of polymer-solvent system in line with the Flory-Huggins theory. According to Díez, Camacho, Díaz, and Ovejero (2014), the Flory-Huggins parameter can be determined as ...
... EVA is produced by copolymerization of ethylene and vinyl acetate (VA). It is one of the most useful polymers because of its wide range of applications, including pour point depressant (PPD), coating of photovoltaic cells and covering of tires and cables, as a consequence of the different varieties of the material depending on the VA percentage 1 . With increasing proportion of the polar co-monomer VA, the products change from modified PE to rubber-like products. ...
Ethylene–vinyl acetate (EVA) copolymers were chosen for this work because they show different characteristics depending on their vinyl acetate (VA) percentage. EVA has a wide range of applications, including coating of photovoltaic cells and covering of tires and cables, as a consequence of the different varieties of the material depending on the VA percentage. To date, no study has been conducted yet to determine the relationship between VA percentage and the flow ability response of an emulsion. Previous studies commonly highlighted the effect of particle size and emulsifier concentration on the emulsion process, but none of these studies directly discussed the effect of VA percentage of an EVA copolymer on the flow ability response of an emulsion. In this study, correlation between polymer-interaction was studied through measurement of intrinsic viscosity
... Where, ν= number of moles of effectively elastic chains per unit volume of EVA [mol/ml] (crosslink density, V s = molar volume of solvent (xylene) [cc/mol], χ = Flory-Huggins interaction parameter for polymer-swelling agent (about 0.29) at 30°C as obtained from literature. [23,29] V r is the volume fraction of rubber in the swollen network and V r can be expressed as Equation (4): ...
The present study focuses on the variation of the melt rheological characteristics and the creep behavior of both electron beam crosslinked and peroxide cured ethylene vinyl acetate/thermoplastic polyurethane blends. The variation of complex viscosity, complex modulus, storage modulus and loss modulus were evaluated over a wide range of frequency and strain amplitude using RPA and the effect of radiation dose and peroxide concentration was investigated in detail. The creep study using DMA shows that the creep behavior of the blends significantly improves after crosslinking and the creep compliance gradually decreases with increasing radiation dose and peroxide content. An attempt was also made to pursue a comparative rheological and creep study among the peroxide cured, EB crosslinked and the co-agent treated dynamically vulcanized samples.
... The chosen polymers have polarities (χ p ) of 0.083 for PVB and 0.0079 for EVA. These values were calculated using the properties of PVB [36] and EVA [37] and the equations ...
... PVB and EVA have polarities χ p = 0.083 and 0.0079 respectively. These values were calculated using Eq.13.1 and Eq.13.2 and the properties of PVB (215) and EVA (254) as follows: ...
Improving the efficiency of existing photovoltaic (PV) devices was the main motivation of this thesis. For this purpose various material concepts for solution-processable luminescent down-shifting (LDS) layers were designed and developed. They convert incident UV radiation into visible light that PV devices can typically utilize more efficiently. This is achieved through integration of photoluminescent materials into layers. Yet reports on the increase of efficiency of the solar cells varied in numbers and did not provide a general understanding of the advantages and disadvantages of the used materials. The aim of this thesis was to evaluate the potential of different classes of luminescent materials in LDS application for photovoltaics. Analysis of a theoretical numerical model has revealed the major requirements that luminescent materials and LDS layers must fulfill in order to perform successfully with the PV devices of interest. These include: (1) high photoluminescence quantum yield (PLQY) of the luminescent material; (2) high transmittance in the visible light spectral region to avoid any optical losses for the underlying solar cell; and (3) suitable absorption and emission spectra that match with the region of poor/ high response of the cell respectively. The following state-of-the-art luminescent materials from different classes were chosen for LDS layers: luminescent organic dyes, hybrid organo-inorganic luminescent complexes, inorganic semiconductor quantum dots (QDs), and powder phosphors with desired spectral characteristics. For each of the material classes, suitable transparent polymer binders were found that can be processed from solution into layers on glass substrates. A doctor-blade coating process was optimized to prepare coatings with thicknesses of 40 600 µm. Various spectroscopic techniques were applied to characterize the properties of the LDS layers, such as distribution of the luminescent material in matrix, absorptivity, transmittance, absorptance, photoluminescence excitation and emission spectra, and PLQY. Optimized layers were applied onto CIGS and OPV solar cells, and the change in the performance of the devices was measured and analyzed. As powder phosphors contain mainly particles with sizes of a few microns or more, they scatter incident light. Phosphors thereby strongly affect the light propagation processes in and overall performance of LDS layers. Therefore, characterization and further analysis were performed separately for scattering (with powder phosphors) and non-scattering (with all other luminescent materials) LDS layers. To analyze the amount of emitted and transmitted radiation towards the solar cell the terms “optical efficiency” and PLQYTrans were used. It was found that QDs embedded in a matrix lost nearly half of their initial PLQY in solution, leading to a negligible efficiency increase of 0.5 % in the performance of the CIGS solar cell. Although organic dyes V570 and Y083 from Lumogen series have PLQY close to unity, they also have large re-absorption overlaps and small Stokes shifts. This led to a maximal efficiency increase of 3 %. Accelerated stability tests showed that the dyes degrade rapidly in all considered matrix materials. The nanostructured organosilicon luminophores NOL15, a hybrid organo-inorganic complex, showed PLQY similar to the organic dyes, yet the large Stokes shift resulted in a relative efficiency increase of 4.3 % for a CIGS solar cell. Numerical simulations were used to determine the optimal chemical structure of the molecules that can potentially lead to an efficiency increase of up to 5 %. To understand and model the scattering behavior of phosphor particles in LDS layers, a method was developed to determine the complex refractive index of particulate luminescent materials. Novel spectral and angular resolved scattering measurements were used to measure absorptance and PLQY of the layers. The total transmittance, TTot, absorptance, Abs, and PLQY of these layers were studied both numerically and experimentally as functions of the thickness of the layers, particle concentration, difference between the refractive indices of the particles and matrix material, Δn, and particle size distribution, D50. The irregularities of the shape and surface of particles were found to be an additional influential parameter. The maximum measured efficiency increase upon application of optimized scattering layers was 5 % for an OPV cell, and 2.4 % for a CIGS device. The final chapter presents guidelines for choosing the luminescent material for an LDS application in PV. The recommendations are given in the sequence that is suitable for the producers of the solar panels and applicable for both existing and to-be developed in future luminescent materials.
... where, n ¼ number of moles of effectively elastic chains per unit volume of EVA [mol ml À1 ] (crosslink density), V s ¼ molar volume of solvent (xylene) [cm 3 mol À1 ], c ¼ Flory-Huggins interaction parameter for polymer-swelling agent (about 0.29) at 30 C as obtained from literature. 31 V r is the volume fraction of rubber in the swollen network and V r can be expressed as eqn (4): ...
The effects of electron beam radiation (EBR) on the blends of Ethylene vinyl acetate/Thermoplastic Polyurethane (EVA/TPU) at two different blend ratios prepared via melt blending technique were investigated. All the samples were irradiated by using a 2.5 MeV electron beam accelerating energy over a dose range from 25 to 200 kGy. The blends exhibit drastic improvement in the mechanical properties with increasing radiation dose upto an optimum dosage, beyond which the properties began to deteriorate. Modification of the blends via EBR enhances the elastic recovery of the blends resulting significant improvement in tension set behaviour. DSC study shows that electron beam irradiation causes a marginal change in melting temperature (Tm), glass transition temperature (Tg) and crystallization peak temperature (Tc) of EVA/TPU blends. Dynamic mechanical analysis (DMA) was conducted to investigate the change of loss tangent and storage modulus with varying radiation dose. Thermogravimetric analysis (TGA) suggests that irradiation induced crosslinks also help to improve the thermal stability of the blends to some extent. Scanning electron microscopy (SEM) study was performed to explore the changes in morphology before and after irradiation. All the irradiated blends have higher electrical resistivity than the blends without irradiation and the volume resistivity increases upto 150 kGy. The samples were found to exhibit remarkable improvement in oil resistance property after irradiation which is more prominent in EVA/TPU 70/30 blends.
... To determine the cross-linking density, it is necessary to know the parameter χ, that is the Flory-Huggins interaction parameter between solvent and polymer, which can be determined according to Blanks and Prausnitz [36,37] where:χ S is the entropic contribution of this parameter (usually beings 0.34, according to Blanks and Prausnitz);χ H is the enthalpic contribution, obtained from the molar volume of a solvent, V mS, , universal gas constant R, absolute temperature T (K), the Hildebrand solubility parameters of the polymer (δ P ) and solvent (δ S ). ...
The purpose of this work is to present the results of preparing a polymeric composite with enhanced properties based on natural rubber and hemp. Amounts of 10 and 20 phr hemp were used to obtain the composites. The samples have been processed by sulfur vulcanization and characterized by several methods. The mechanical characteristics, gel fraction, cross-link density, rubber-fiber interactions and water uptake have been investigated depending on the hemp content. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) techniques were also employed for characterization. The values of hardness, tensile strength and tearing strength have increased with the fiber content increasing due to the interaction between the fibers and natural rubber. Also, good adhesion between hemp fibers and rubber matrix was observed in SEM micrographs. The gel fraction value was over 95 % for all composites and increased with the increasing of hemp content. The cross-link density was determined on the basis of equilibrium solvent-swelling measurements applying the modified Flory-Rehner equation. It was observed that cross-linking density of composites increased slightly with the increase of amount of hemp but still was lower than that of the natural rubber without hemp. The extent of interaction between rubber and fiber was determined using the Kraus equation. Results of water absorption tests showed that water uptake increased with the increase of fiber content and temperature. The physical and chemical investigations have shown the reinforcing effect of hemp on sulfur vulcanized natural rubber, as well.
In this study, a compatible blend of 85 wt% polylactic acid and 15wt%poly(ethylene vinyl acetate) (PLA85/EVA15) was added with different amounts of Triacetin (TRI) as a plasticizer. The thermal, tensile, rheological, antifungal and morphological properties of the unplasticized blend, plasticized blends (PLA/EVA-TRI) and plasticized PLA (PLA/TRI) were studied. Thermal stability improved as TRI increased up to 20 wt% while crystallinities continuously increased in the presence of 5—25 wt%TRI. The presence of 15 wt% TRI revealed tensile strength reduced to 21.28 MPa but toughness significantly improved when elongation at break increased up to 280%. At a similar amount of plasticizer based on the weight of the compound, PLA85/EVA15-TRI25 showed comparable thermal properties and tensile strength but higher elongation at break compared with PLA80/TRI20 indicating the importance of EVA in improving the properties of plasticized PLA. Antifungal ability against Aspergillus sp., Penicillium sp, and Fusarium sp improved with the increasing amount of TRI.
This research is devoted to the actual problem of the development of damping polymer materials which are effective in a wide range of temperatures and having satisfactory strength characteristics. There are many works devoted to the study of dynamic mechanical properties of filled composites, but most do not take into account the influence of plasticizer on the strength properties of the polymer, as they change its characteristics for the worse. In this respect, the study and comparison of the mechanical properties of the polymer base with the introduction of different types and concentrations of plasticizers is an urgent task. According to the received regularities it was possible to define the type, concentration and boundaries of the polarity of the plasticizer, which reduces the strength characteristics of ethylene-vinyl acetate to a lesser degree.
