Thermal,rheological, morphological and mechanical properties of high density polyethylene/ethylene vinyl acetate copolymer (HDPE/EVA) blends

Thermal, rheological, morphological and mechanical properties of binary HDPE and EVA blends were studied. The results of rheological studies showed that for given HDPE and EVA, the interfacial interaction in HDPE-rich blends is higher than EVA-rich blends. Using three different rheological criterions, the phase inversion composition was predicted to be in 30 wt% of the EVA phase. This showed good agreement with morphological studies. The tensile strength for HDPE-rich blends showed positive deviation from mixing rule, whereas the EVA-rich blends played negative deviation. These results were in a good agreement with the results of viscoelastic behavior of the blends. The thermal analysis revealed that high co-crystallizaiton in 90/10 composition, which increased the tensile strength and decreased the elongation at break in this composition. Furthermore, the results of thermal behavior of the blends indicated that the melting temperatures of HDPE decrease due to the dilution effect of EVA on HDPE.     

Rheology, morphology and mechanical properties of polyethylene/ethylene vinyl acetate copolymer (PE/EVA) blends

Rheology, morphology and mechanical properties of binary PE and EVA blends together with their thermal behavior were studied. The results of rheological studies showed that, for given PE and EVA, the interfacial interaction in PE-rich blends is higher than EVA-rich blends, which in turn led to finer and well-distributed morphology in PE-rich blends. Using two different models, the phase inversion composition was predicted to be in 45 and 47 wt% of the PE phase. This was justified by morphological studies, where a clear co-continuous morphology for 50/50 blend was observed. The tensile strength for PE-rich blends showed positive deviation from mixing rule, whereas the 50/50 blend and EVA-rich blends displayed negative deviation. These results were in a good agreement with the results of viscoelastic behavior of the blends. The elongation at break was found to follow the same trend as tensile strength except for 90/10 PE/EVA blend. The latter was explained in terms of the effect of higher co-crystallization in 90/10 composition, which increased the tensile strength and decreased the elongation at break in this composition. The results of thermal behavior of the blends indicated that the melting temperatures of PE and EVA decrease and increase, respectively, due to the dilution effect of EVA on PE and nucleation effect of PE on EVA.     

Crystal and phase morphology of dynamic-packing-injection-molded high-density polyethylene/ethylene vinyl acetate blends

The effect of shear stress, provided by so-called dynamic-packing injection molding, on crystal morphology and phase behavior was investigated for high-density polyethylene (HDPE) in blends with ethylene vinyl acetate (EVA) of various viscosities and vinyl acetate (VA) contents, with the aid of differential scanning calorimetry, two-dimensional small-angle X-ray scattering (2D SAXS), and scanning electron microscopy (SEM). A shish-kebab pattern was found in the oriented zones of dynamic samples, and the ratio of shish to kebab increased as a function of the EVA content in the blends up to 20 wt %, regardless of the VA content. This showed that molecules of HDPE could easily be stretched to form a shish structure in the presence of EVA. Moreover, a large increase in the long spacing, characterized by 2D SAXS measurements, was achieved because of the presence of EVA. The SEM results showed an obvious decrease in the domain size of the EVA phase under the effect of shear stress. All these results suggested shear-induced mixing between HDPE and EVA, in that ethylene segments of EVA molecules could be forged in the shish structure during shear and the other fractions of EVA were located in the amorphous regions between the adjacent lamellae of HDPE. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1831–1840, 2004     

Physical blends of PLA with high vinyl acetate containing EVA and their rheological,thermo-mechanical and morphological responses

Rheological, morphological and thermo-mechanical responses of poly(lactic acid) (PLA)/ethylene-co-vinyl-acetate copolymer (EVA) blends at EVA volume fractions varying in the range of 0–0.35 were evaluated. The micro-structural analysis demonstrated dispersive mixing at low content and co-continuous morphology at 30 wt % of EVA in PLA. Dynamic rheology demonstrated enhanced storage modulus and complex viscosity (η*) with increase in frequency of the blends indicated strong phase interaction. Cole-Cole and Han plots indicated partial miscibility and incompatibility between the polymer matrix and the dispersed phase. Dynamic mechanical analysis (DMA) revealed slight increase in damping parameters which indicated interaction or reinforcement in the blends. Additionally, the thermogravimetric analysis (TGA) of the blends showed two step degradation and enhanced thermal stability.     

Irradiation effects on thermal,surface, and physicomechanical properties of ethylene and vinyl acetate copolymer

The structural and thermal transitions for ethylene and vinyl acetate copolymer (EVA) samples irradiated by fast electrons at doses in the range of 2.5–25 Mrad were investigated by DSC and X-ray diffraction analysis. The parameters of chemical bonds in the amorphous phase of copolymer were determined. The change in the degree of crystallinity, melting temperature, and crystallite sizes before and after radiochemical modification were estimated. The obtained results were analyzed and corresponded to the physicomechanical properties of copolymers. The surface energy of copolymers before and after irradiation was defined. The strength of adhesive joints based on EVA from PET substrates and the influence of radiochemical modification of adhesive before joint formation on its strength were analyzed.     

The rheological behavior of ethylene vinyl acetate copolymer/rectorite nanocomposites during the melt extrusion process

To optimize the preparation process for ethylene vinyl acetate (EVA)/rectorite nanocomposites during the melt extrusion, the effect of rectorite on the rheological property of molten polymer has been explored in this paper. The dispersion of rectorite in EVA was probed by X‐ray diffraction, and the rheological behaviors of EVA copolymer and EVA/rectorite nanocomposites during the extrusion process were investigated by means of HAAKE minilab. The positron results reveal that introducing the rectorite in EVA matrix increases the interfaces in composites. And the rheological results indicate that the viscosity of EVA and EVA/rectorite nanocomposites in the molten state was influenced by the processing temperature, processing time and shearing rate. For all the samples, the viscosity increases with increasing the shear rate, and decreases with increasing extrusion temperature. Moreover, compared with the pure EVA, the EVA/rectorite nanocomposite presents a lower viscosity at the same processing condition. Copyright © 2016 John Wiley & Sons, Ltd.     

Miscibility and thermal stability of ethyl vinyl acetate and ethylene-octane copolymer blends

Miscibility and thermal stability of ethyl vinyl acetate (EVA) and ethylene octane (EO) copolymer blends with different compositions were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The degradation behavior by TGA data under dynamic conditions in an inert atmosphere shows the blends to be immiscible. The addition of EO improves the thermal stability of EVA for all composition and temperature ranges. Using the DSC experiment, two single crystallization temperatures (T _c) for the blends were obtained and the crystallization and melting enthalpy with compositions abiding by the additive rules, confirm the immiscibility of the blends. The rate of crystallization seems to be independent of blend compositions. The surface morphology using AFM shows a thin and elongated crystallites of pure EO, and a bulky and random morphology for EVA, where a perfect mixture of aforementioned structures for 50/50 blend, with the immiscible domains of both EO and EVA. The 2D-power spectral density (PSD) analysis shows the surface roughness of 50/50 blends is in between of EO and EVA. Both AFM observations and quantitative PSD results, along the line with DSC and TGA. The experimental data for miscibility and stability by TGA, DSC and AFM techniques reveal that blends of EVA/EO are immiscible in the entire range of compositions.     

Shape memory properties of polyethylene/ethylene vinyl acetate /carbon nanotube composites

The safe operation of electrical equipment relies on advanced polymer insulation to contain electrical pathways. Polymer sheath materials should be mechanically robust and chemically stable in order to protect the internal metal wiring from environmental attack. Polyethylene (PE) and ethylene vinyl acetate (EVA) have often been used as electrical cable jacket materials for electrical power industry. Partially crosslinked PE is able to shrink and wrap tightly around the metal wires upon stimulated by external heat, exhibiting shape memory behaviour. In this work, multiwalled carbon nanotubes (MWCNTs) were introduced to partially crosslinked linear medium density polyethylene (LMDPE) and EVA blend in order to enhance the shape memory performance at lower temperature by promoting the thermal transfer and antistatic properties of the polymer nanocomposite. The morphologies of the partially crosslinked and non-crosslinked composites are analysed. The MWCNTs preferentially resided in the EVA phase while the peroxide crosslinking process drastically altered the morphology and electrical properties. The addition of 3 wt% of MWCNTs resulted in a percolation transition and enhanced the alternating current (AC) conductivity by 10 orders of magnitude for non-crosslinked LMDPE/EVA and by 3 orders of magnitude for crosslinked LMDPE/EVA composites. LMDPE/EVA (80/20) containing 3 wt% MWCNTs possessed excellent shape recovery of 100% and shape fixing of 82%. The addition of MWCNTs can not only promote the shape memory efficiency of the polymer sheath material, but also introduce antistatic properties to avoid electrical shocking or sparking.     

The impact of different antifreeze agents on the thermal properties of ethylene vinyl acetate emulsion

The application of pour point depressants in the form of emulsions provides an alternative to overcoming the problem of handling during applications in cold climate environments. The incorporation of antifreeze agents to these emulsions helps to improve their cold flow properties, without sacrificing much of the other properties. This study considered the effect of the incorporation of different antifreeze agents into ethylene vinyl acetate emulsions that are used as pour point depressants. The results obtained revealed that the ethylene glycol (EG) emulsion system gave the lowest freezing temperature of −45°C, while the propylene glycol emulsion system provided the lowest vitrification temperature of −64°C. The size of the particles in the emulsion was significantly reduced from 359.1 nm to 207.4 to 216.4 nm when an antifreeze agent was used in the emulsion compared to the control sample (pure water). As for the selection of the most suitable antifreeze for the emulsion system, the vitrification performance was a factor that was taken into consideration in the decision to select the EG system due to the fact that this system offered an adequate performance in terms of vitrification efficiency at around −59°C, although it was not as excellent as the vitrification efficiency portrayed in the propylene glycol system. However, the EG emulsion system was the most suitable system for the ethylene vinyl acetate emulsion, as it delivered the best protection against freezing and, at the same time, produced a decent particle size distribution.     

Effect of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of intumescent flame retardant ethylene-vinyl acetate copolymer

Ethylene vinyl acetate copolymer (EVA) flame retarded by ammonium polyphosphate (APP) and pentaerythritol (PER) was cross-linked by electron beam irradiation. The effects of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of EVA composites were investigated. The volatilized products of EVA/APP/PER composites were characterized by thermogravimetric analysis/infrared spectrometry. As VA content increased, the volatilized products increased in the second decomposition step, but decreased in the third decomposition step. For all samples, the increase of irradiation dose could improve both the gel content and the Limit Oxygen Index (LOI, the minimum oxygen concentration by volume for maintaining the burning of a material) values of irradiated composites. The mechanical and thermal properties of the irradiated EVA composites were also evidently improved at appropriate irradiation dose as compared with those of unirradiated EVA composites, whereas these properties decrease at higher irradiation dose because of the electron beam irradiation-induced oxidative degradation or chain scission.     

The effect of gamma irradiation on mechanical, and thermal properties of recycling polyethylene terephthalate and low density polyethylene (R-PET/LDPE) blend compatibilized by ethylene vinyl acetate (EVA)

A study has been made on the compatibility of recycled polyethylene terephthalate (R-PET) and low density polyethylene (LDPE) blend in the presence of ethylene vinyl acetate (EVA) as a compatibilizing agent prepared by extrusion hot stretching process. EVA content in the blend as a compatibilizing agent was an enhancement effect on radiation crosslinking of R-PET/EVA/LDPE blends and the highest radiation crosslinking was obtained when the EVA content was reached at 10 % EVA when irradiated by gamma irradiation. Blends containing different (EVA) ratios were irradiated to different doses of gamma irradiation 25, 50 and 100 kGy. The effect of the compatibilizer and radiation on mechanical, thermal properties of R-PET together with LDPE and morphology has been investigated. It was found that gamma irradiation together with the presence of compatibilizing agent (EVA) has positive effect on the mechanical and thermal properties of R-PET/LDPE blend. The structural properties of R-PET/LDPE modified by gamma irradiation and EVA as compatibilizing agent was examined by SEM. Also, it was found that the optimum concentration of EVA and gamma irradiation dose was found to be 10 % EVA and 100 kGy, respectively.     

Functionalized-graphene/ethylene vinyl acetate co-polymer composites for improved mechanical and thermal properties

The surface functionalization of graphene and the preparation of functionalized graphene/ethylene vinyl acetate co-polymer (EVA) composites by solution mixing are described. Octadecyl amine (ODA) was selected as a surface modifier for the preparation of functionalized graphene (ODA-G) in an aqueous medium. The ODA-G was characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, which confirm the modification and reduction of graphite oxide to graphene. Atomic force microscopy shows that the average thickness of ODA-G is ca. 1.9 nm. The ODA-G/EVA composites were characterized by X-ray diffraction and transmission electron microscopy, which confirms the formation of ODA-G/EVA composites. Measurement of tensile properties shows that the tensile strength of the composites (with 1 wt.% ODA-G loading) is ∼74% higher as compared to pure EVA. Dynamic mechanical analysis shows that the storage modulus of the composites is much higher than that of pure EVA. The thermal stability of the composite with 8 wt.% of ODA-G is ∼42 °C higher than that of pure EVA. The electrical resistivity has also decreased in the composites with 8 wt.% of ODA-G.     

Shrinkability of ethylene vinyl acetate/polyurethane blends and their characterization

Heat shrinkability of the polymer, which depends on the elastic memory, is being utilized in various applications, mainly in the field of encapsulation. The elastic memory is introduced into the system in the form of an elastomeric phase. Here the blends of ethylene vinyl acetate and polyurethane were studied with reference to their shrinkability, introducing crosslinking in both the phases. It is found that with increase in elastomer content the shrinkage increased to a certain level and then decreased. With increase in cure time shrinkage is decreased. It is seen that high‐temperature (HT) stretched samples showed higher shrinkage than room temperature (RT) stretched one. Generally, the crystallinity of the HT stretched sample is higher than that of low‐temperature stretched sample, which is again higher than that of original sample. From high temperature differential scanning calorimetry it is found that with increase in PU content stability towards oxygen is increased and further high temperature processing decreases the initial degradation temperature but enhances the rate of degradation. From scanning electron microscopy it is seen that an HT stretched sample is more elongated than an RT stretched one. Copyright © 2000 John Wiley & Sons, Ltd.     

Layered double hydroxides intercalated with borate anions: Fire and thermal properties in ethylene vinyl acetate copolymer

Fire and thermal properties of ethylene vinyl acetate (EVA) composites prepared by melt blending with layered double hydroxides (LDH) have been studied. Two types of LDHs intercalated with borate anion were prepared using the coprecipitation method and the metals Mg²⁺, Zn²⁺ and Al³⁺. Characterization of the LDHs and the EVA composites was performed using X-ray diffraction, thermogravimetric analysis, and cone calorimetry. Thermal analyses show that the addition of LDHs improves the thermal stability of EVA. Fire properties evaluated using the cone calorimeter were significantly improved in the EVA/LDH composites. The peak heat release rate was reduced by about 40% when only 3% by weight of the LDH was added to the copolymer. Comparison of the fire properties of the LDHs with those of aluminum trihydrate (ATH), magnesium hydroxides (MDH), zinc hydroxide (ZH) and their combinations at 40% loading, reveal that the LDHs were more effective than when MDH and ZH are used alone.     

Adhesion of grafted polyethylene to an ethylene/vinyl alcohol copolymer

Modern developments in polymer technology include the use of multimaterials. Two or more polymers are fashioned together to produce a composite with a desired combination of properties. However, the success of such materials depends on the quality of the adhesion between the various phases. In this study, we considered the adhesion between a grafted polyethylene and an ethylene/vinyl alcohol copolymer with various peel test geometries. The principal, L‐peel, test was employed with various peel angles. Using elastoplastic analysis, we found that the effective peel energy, increasing with the peel angle, may be corrected for bulk energy dissipation, leading to a relatively constant local value for intrinsic peel resistance, independent of geometry. Effects of the peel rate and temperature may be combined to give a master curve, apparently a novelty for thermoplastics, although well known for elastomers. At a (corrected) peel rate, a jump in adhesion energy, apparently related to a change to a stick–slip peel regime, was observed. This jump appeared to be absent for some other peel geometries. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2843–2851, 2001     

Blending and barrier properties of blends of modified polyamide and ethylene vinyl alcohol copolymer

The blending and barrier properties of the MPAEVOH blends of modified polyamide (MPA) and ethylene vinyl alcohol copolymer (EVOH) were systematically investigated in this study. After blending MPA in EVOH resin, a noticeable “negative deviation” was found on the plot of the oxygen permeation rate versus MPA content when the MPA contents present in MPAEVOH resins reach about 80 wt %. The peak temperatures associated with the main melting endotherm of MPA and EVOH reduce significantly with increasing the EVOH and MPA contents present in MPAEVOH resins, respectively. The melting endotherm and X‐ray diffraction peak associated with EVOH crystal phases disappear gradually as the MPA contents present in MPAEVOH increase. In fact, the melting endotherm and X‐ray scattering peak corresponding to EVOH crystals almost disappear as the EVOH contents present in MPAEVOH specimens are less than 20 wt %. Further Fourier‐Transform Infrared (FT‐IR) investigations indicate that the strengths of intermolecular hydrogen bonds of MPAEVOH specimens reduce significantly as the MPA contents increase, wherein the self‐associated hydroxyl‐hydroxyl bonds within EVOH resins almost disappear as the EVOH contents reduce to be less than about 20 wt %. As expected, the average sizes of the free volume holes of MPAEVOH specimens increase significantly as the MPA contents increase. However, somewhat surprisingly, a clear negative deviation was found on the plot of the numbers and fractional free volumes of free volume holes against the MPA contents as the EVOH contents are close to about 20 wt %. The interesting barrier properties of the MPA, EVOH, and MPAEVOH specimens were investigated in terms of the free volume and intermolecular interaction properties in the amorphous phases of MPAEVOH specimens described above. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 511–521, 2005     

Investigation of the curing state of ethylene/vinyl acetate copolymer (EVA) for photovoltaic applications by gel content determination,rheology, DSC and FTIR

The cure behaviour of a specific ethylene vinyl acetate material as used for encapsulation of photovoltaic modules was analysed by rheometer, differential scanning calorimetry and Fourier transform infrared spectroscopy to test for a suitable replacement for the laborious determination of gel content.The results show that all applied methods are capable of describing the effects of the cross-linking process. Some provide results very similar to those yielded by analysis of the insoluble content, but the question remains as to whether indirect methods should be preferred over the direct measurement of physical properties, e.g. as performed by the curemeter.A material stored for one year was also tested to demonstrate the effect of extended storage on cure behaviour and how this is detected by different methods. This complements the other methods, which were clearly able to detect the different cure behaviour of the aged EVA, whereas determination of the gel content could not.     

Radiothermoluminescence of irradiated mixtures of polyethylene with ethylene/vinyl acetate copolymers

The effect of composition and accelerated electrons on the glass-transition temperature (Tg) of irradiated mixtures of polyethylene containing up to 30 mass % of ethylene/vinyl acetate copolymer (EVAC) has been studied. It has been established that the temperature position of the luminescence maximum depends on the EVAC concentration. The appearance of a maximum over the range of temperatures corresponding to the Tg of the initial polymers indicates the compatibility of the initial components.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 5, pp. 633–637, September–October, 1989.     

Electret properties of blends of high-density polyethylene and polystyrene

Corona-electrets based on heterogeneous blends of high-density polyethylene and polystyrene were studied. The observed double-maximum composition dependence of the electret properties of polymer blends was explained in terms of the concept of their colloid structure and electrical conductivity.     

Oxygen permeability in blends of a vinyl alcohol/ethylene copolymer and a metallocenic ethylene/1‐octene copolymer

This work describes the preparation, characterization, and evaluation of the oxygen permeability of blends based on a polyolefin synthesized with a metallocene catalyst (ethylene/1‐octene copolymer) and a vinyl alcohol/ethylene copolymer in an attempt to establish the corresponding relationships between the composition, morphology, and transport properties to design materials with optimized and enhanced agricultural and food packaging performances. Moreover, microhardness measurements have been used to analyze the mechanical response of these blends and to obtain information about the dispersion of the two immiscible components within the blends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3766–3774, 2004