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.     

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.     

Adhesive properties of ethylene and vinyl acetate copolymers

Surface properties of ethylene and vinyl acetate copolymers (EVAs) are considered depending on their composition and history of surface formation. The kinetics of structural transformations in the near-surface layers of copolymers is investigated. Relaxation times and the equilibrium state of the EVA surface are determined. The orrelation dependence between the surface energy of copolymers and their adhesive properties for substrates of different natures is constructed.     

Effect of EVA copolymer containing different VA content on the thermal and rheological properties of bio-based high-density polyethylene/ethylene vinyl acetate blends

The effect of ethylene vinyl acetate (EVA) concentration and vinyl acetate (VA) content of EVA on the mechanical, morphological, and rheological properties of bio-based high-density polyethylene (BioPE)/EVA blends was investigated. The blends were characterized by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and rheological measurements under oscillatory shear flow. The degree of crystallinity of BioPE decreased with the increase in the EVA concentration and was unaffected with the increase in the VA content. DMTA results showed a decrease in the storage modulus (E′) with the increase in EVA content and that the BioPE/EVA19 blends showed higher E′ values than BioPE/EVA28 blend. The impact strength substantially increased with the addition of EVA concentration above 5 mass% and was higher for the blends containing the highest VA content. The blends containing a higher content of VA exhibited the higher EVA dispersed phase domain size, which increased with the increase in EVA concentration. The complex viscosity increased with the increase in the EVA content, being higher for the BioPE/EVA blends containing higher VA content. The storage modulus increased, at low frequencies, with the increase in the EVA content and can be ascribed to the increase in the EVA dispersed phase domain size.

     

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.     

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.     

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.     

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.     

Adhesive properties of ethylene and vinyl acetate copolymer. Deformation strength characteristics: Contribution of plastic deformation work

The deformation-stress curves of ethylene and vinyl acetate copolymer (EVA) are determined by traditional methods with respect to composition at various rates of deformation. The residual deformations after relief are estimated. The deformation work is calculated and the effect of copolymer composition on the value of plastic deformation is evaluated. According to the previously suggested model, the contribution of deformation characteristics of EVA adhesive to the adhesive joint fracture energy is estimated.     

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.     

Gas permeation properties of ethylene vinyl acetate–silica nanocomposite membranes

The effect of silica nanoparticles on the gas separation properties of ethylene vinyl acetate (EVA) copolymer containing 28% vinyl acetate has been investigated. The EVA and hybrid EVA–silica membranes were prepared via thermal phase inversion method. Silica nanoparticles prepared by hydrolysis of tetraethylorthosilicate (TEOS), through the sol–gel mechanism. The prepared membranes were characterized using FT-IR, SEM, DSC and XRD methods. FT-IR and SEM results indicated the nanoscale dispersion of silica particles in polymer matrix. As confirmed by XRD and DSC analyses, increasing the silica content enhances the amorphous regions significantly. Gas permeation of EVA–silica nanocomposite membranes with silica contents of 5, 6 and 10 wt.% was studied for N₂, O₂, CO₂ and CH₄ single gases at pressures of 4, 6 and 8 bar. The obtained results suggest a significant increase in permeability of all gases and an increase in CO₂/N₂ and CO₂/CH₄ gases selectivities upon increasing the silica content. The possible reasons for such behavior were stated and discussed. The pressure dependence of the gas permeabilities of the membranes was also investigated.     

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     

Carbon-13 NMR of poly(vinyl acetate) and ethylene–vinyl acetate copolymer

Carbon-13 nuclear magnetic resonance spectra of atactic poly(vinyl acetate) and ethylene–vinyl acetate copolymers are reported and analyzed. Carbon spectra at 22.6 and 62.9 MHz together with use of shift reagents have permitted a more complete assignment than previously reported; in some cases the published assignments are found to be in error.     

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.     

Structure property relationship of ethylene vinyl acetate copolymer grafted with triallyl cyanurate by electron beam radiation

Electron beam (EB) initiated grafting of triallyl cyanurate (TAC) onto ethylene vinyl acetate (EVA) containing 12% vinyl acetate has been carried out over a range of irradiation doses (20–200 kGy) and concentrations of TAC (0.5–5%). The grafting level, as determined from IR spectroscopy, does not change with the radiation dose at 0.5% TAC. With increase in TAC level the grafting level increases at 50 kGy dose. The gel content increases with radiation dose in the initial stage, whereas it changes marginally with the TAC level. With the increase in radiation dose or TAC level, the crystallinity decreases. The interplanar distance or the interchain distance of the grafted polymer does not change with dose or TAC level. The tensile strength is maximum at 0.5% TAC level and at the 50 kGy dose. The dielectric loss shows a maximum at 50 kGy dose and at 0.5–1.0% TAC level due to changes of polarity and the carrier chain mobility.     

Phase relations in blends of poly(vinyl chloride) with copolymer of ethylene-vinyl acetate and the effects of thermal stabilizers

Further investigations of the system PVC-EVA, with wide line NMR, have shown that the phase relations differ for graft-polymerized samples and non-grafted samples prepared by milling the polymer components together. The phase relations of the grafted products are not appreciably changed by different types of processing and heat treatments. In the non-grafted samples, considerable phase separation is observed by heat treatment at the normal temperatures of processing. It is also shown that the metal-laurates, normally used for thermal stabilization, have good solubility in the PVC-phase and that co-stabilizers of phosphites and epoxides show considerable solubility in the EVA-phase. By heat treatment of milled products at the processing temperature, the co-stabilizers are to some degree transferred from the PVC- to the EVA-phase.     

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.     

Effect of solvent on the copolymerization of ethylene and vinyl acetate

The ethylene (M₁)–vinyl acetate (M₂) copolymerization at 62°C and 35 kg/cm² with α,α′-azo-bisisobutyronitrile as initiator has been studied in four different solvents, viz., tert-butyl alcohol, isopropyl alcohol, benzene, and N,N-dimethylformamide. The experimental method used was based on frequent measurement of the composition of the reaction mixture throughout the copolymerization reaction by means of quantitative gas chromatographic analysis. Highly accurate monomer reactivity ratios have been calculated by means of the curve-fitting I procedure. The observed dependence of the r values on the nature of the solvent is surprisingly large and can be correlated with the volume changes (= excess volumes) observed on mixing vinyl acetate (VAc) with the relevant solvent. An increased hydrogen bonding or dipole–dipole interaction through the carbonyl moiety of the acetate side group of VAc, induces a decreased electron density on the vinyl group of VAc, which in turn leads to a decreased VAc reactivity. The differences among the overall rates of copolymerization in the various solvents can be interpreted in terms of a variable chain transfer to solvent and the rate of the subsequent reinitiation by the solvent radical. In the case of benzene, complex formation is believed to play an important part.     

Thermal degradation of ethylene (vinyl acetate)

Ethylene (vinyl acetate), EVA, is a copolymer which is thermally degraded at high temperatures, with acetic acid release at approximately 620 K. This release can be studied by using thermal methods, and in particular thermogravimetric analysis.The present work was focused on establishing the polymer weight loss with temperature in order to calculate the activation energy of the overall deacetylation process. To obtain the final results, a Mettler TC50 instrument coupled with a Mettler TC11 microprocessor was used.The activation energies of four different industrial EVA formulations were calculated. The results obtained by applying different kinetic methods reported in the literature agreed reasonably well; they were compared in order to select the best method of reporting EVA deacetylation results.The authors wish to express their appreciation to DGICYT (Spain), Project AMB 94-107, for financial support of this study.