Vinyl Acetate Content Research Articles

Rheology, Mechanical Properties and Morphology of Poly(lactic acid)/Ethylene Vinyl Acetate Blends

In this work, the effect of ethylene vinyl acetate (EVA) content on the rheology, mechanical properties, and morphology of poly (lactic acid) (PLA)/EVA blends was investigated. Differential Scanning Calorimetry (DSC) showed that the addition of EVA to PLA decreased the degree of crystallinity of PLA. Dynamic Mechanical Thermal Analysis (DMTA) results showed that the presence of EVA copolymer increased the cold crystallization temperature (Tcc) of PLA. The addition of 10% of EVA to PLA substantially increased the impact strength. Morphology analysis by Scanning Electron Microscopy (SEM) indicated the immiscibility between PLA and EVA phases and an in increase the EVA average dispersed phase domains size with the increase in EVA content. Rheological measurements under oscillatory shear flow showed that storage modulus (G′) increased with the increase in the EVA content at low frequencies and is related to the increase in the EVA dispersed phase domains size, as also observed by relaxation spectrum analysis. Cole–Cole plots of imaginary viscosity (η″) versus real viscosity (η′) and Han plots of storage modulus (G′) versus loss modulus (G″) indicated that PLA and EVA phases are immiscible, as also observed by SEM.

Isothermal Crystallization Kinetics of Poly (3-hydroxybutyrate/ Poly(ethylene-co-vinyl acetate) Blends Enhanced by NH4Cl as a Nucleating Agent

The isothermal crystallization kinetics of poly (3-hydroxybutyrate) (PHB)/NH4Cl composites, PHB/poly(ethylene-co-vinyl acetate), with vinyl acetate contents of 80% (EVA80) blends and PHB/EVA80/1 wt% NH4Cl composites were investigated by using differential scanning calorimetry (DSC). The Avrami approach was applied to estimate the kinetic parameters of the PHB samples under isothermal crystallization conditions. It was found that the values of The Avrami rate constant, of PHB were increased with the incorporation of NH4Cl, declining EVA80 content in the PHB blends, and decreasing crystallization temperature. Moreover, the Avrami exponent, n, remained unchanged in spite of the change in the crystallization temperature, EVA80 content, and presence of NH4Cl. The activation energy, calculated using the Arrhenius equation, for PHB/NH4Cl was much lower than that of pure PHB and PHB/EVA80, suggesting that the NH4Cl induced heterogeneous nucleation. The values for PHB/EVA80/1 wt% NH4Cl increased as the EVA80 content was increased, indicating a retardation effect of EVA80. Furthermore, a modified Lauritzen–Hoffmann treatment (LH) was used to evaluate the nucleation constant, of the PHB samples based on the assumption that U* was 13.8 kJ/mol and the equilibrium melting temperatures were 470 K, intercepts of HL equation, were 25.9 for all PHB samples. The values indicated that the crystallization of PHB in its composites and blends, described here, occurred in regime III. The maximum degradation rate temperatures of the PHB/NH4Cl composites were higher than that of PHB, by 9 oC. No significant change in thermal stability was detected by the addition of EVA80.

Electrospinning of Ethylene Vinyl Acetate/Carbon Nanotube Nanocomposite Fibers.

Nanocomposites, based on an ethylene vinyl acetate (EVA) copolymer with a vinyl acetate content of 34 wt % and varying amounts of multiwall carbon nanotubes (MWCNTs), were prepared by an electrospinning method. The dispersibility of the MWCNTs in the solution was improved by using cholesteryl 1-pyrenecarboxylate (PyChol) as a compatibilizer. The transmission electron microscopy images showed that the MWCNTs were aligned inside of the elastomeric matrix by the electrospinning process. The morphologies of the fibers were evaluated by scanning electron microscopy. When the amount of MWCNTs in the polymer solution reached 3 wt %, fibers with a diameter of 846 ± 447 nm were prepared. The chemical composition of the prepared fibers was investigated by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). FTIR results confirmed the presence of a carboxyl group, originating from the presence of PyChol. XPS results showed that the EVA fibers produced by electrospinning were oxidized in ethylene units, when comparing the spectra of the original EVA granules, but the presence of MWCNTs enhanced the stability of the EVA. The thermal stabilities of the fibers were tested with thermogravimetric analysis. The results confirmed that the presence of MWCNTs inside the fibers enhanced the thermal stabilities of the prepared nanocomposites.

Influenceof Vinyl Acetate Content on the Surface Hydrophobic Recovery of Ethylene Vinyl Acetate Copolymer after Plasma Modification

AbstractIn this paper, two kinds of ethylene vinyl acetate copolymers (EVA) with different vinyl acetate (VA) contents were modified by plasma technique. The surface hydrophobic recovery and the nanostructure of the samples were evaluated by water contact angle measurement and positron annihilation lifetime spectroscopy, respectively. The water contact angle results indicated that higher VA content would result in faster hydrophobic recovery after plasma modification. The positron annihilation results indicated that two kinds of EVA samples exhibited similar o‐Ps lifetime, and EVA with higher VA content showed higher o‐Ps intensity. The results implied that the faster hydrophobic recovery after plasma modification should be contributed to the easier relaxation of chain segments for the EVA with higher VA content.

Thermal and Rheological Behavior of Binary Blends of Poly(hydroxybutyrate‐co‐hydroxyvalerate) and Poly(ethylene‐co‐vinyl acetate) with Different Vinyl Acetate Content

The aim of this study is to investigate the influence of vinyl acetate (VA) content on the thermal and rheological properties of poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV)/poly(ethylene‐co‐vinyl acetate) (EVA) blends. Binary blends of PHBV and EVA containing 65 wt% (EVA65) and 90 wt% (EVA90) VA were prepared by torque rheometry and their thermal properties were studied by differential scanning calorimetry (DSC). Rheograms of PHBV/EVA65 containing up to 40 wt% EVA showed that the torque values decrease as a function of mixing time due to the thermo‐mechanical degradation, which preferentially for PHBV is chain scission. The increase in the EVA65 concentration results in torque stability probably due to the balance between chain scission of the PHBV and chain branching of the EVA65. For PHBV/EVA90 blends, the torque values are stable indicating that the presence of EVA90 decreases the degradation process of the PHBV and hence increases the thermal stability of blends. DSC curves showed that the PHBV cold crystallization temperature (Tcc) increased and cold crystallization (ΔHcc) and melting enthalpies (ΔHm) decreased with the increase in the EVA content, independently of VA content and blend morphology. DSC curves of PHBV/EVA65 showed two glass transition temperatures and clear phase separations, in all studied formulations, typical of immiscible systems. In contrast to it, PHBV/EVA90 blends showed a single glass transition, suggesting total miscibility. Both findings were corroborated by scanning electron microscopy (SEM) analysis.

Poly(lactic acid)/ethylene vinyl acetate copolymer blend composites with wood flour and wollastonite: Physical properties, morphology, and biodegradability

In the present study, poly(lactic acid) (PLA), a biodegradable plastic, was melt‐blended with five weight percentages (10–50 wt%) of ethylene vinyl acetate (EVA) copolymer, a non‐biodegradable plastic, having a vinyl acetate content of 19 wt% and a melt flow index of 530 g/10 min, on a twin screw extruder, followed by an injection molding. The blends at 10 and 20 wt% EVA revealed a noticeably increased impact strength and strain at break over the pure PLA, and the blend at 10 wt% EVA exhibited the highest impact strength and strain at break. The 90/10 (wt%/wt%) PLA/EVA blend was then selected for preparing either single or hybrid composite with wood flour (WF) and wollastonite (WT). The filler loading was fixed at 30 parts by weight per hundred of resin throughout the experiment, and the WF/WT weight ratios were 30/0, 20/10, 15/15, 10/20, and 0/30. The prepared composites were examined for their mechanical and thermal properties, melt flow index, flammability, water uptake, and biodegradability as a function of composition. All the composites showed a filler‐dose‐dependent decrease in the impact strength and strain at break, but an increase in the tensile and flexural modulus (optimal at 0/30 WF/WT) and tensile and flexural strength (optimal at 30/0 WF/WT) as compared with the neat 90/10 (wt%/wt%) PLA/EVA blend. In addition, the melt flow index, char residue, anti‐dripping ability, water uptake, and biodegradability of the composites were also higher than those of the neat blend. J. VINYL ADDIT. TECHNOL., 25:313–327, 2019. © 2019 Society of Plastics Engineers

Quantification of Aerospace Polymer Blends by Thermogravimetric Analysis and Infrared Spectrometry

Ethylene-propylene-diene elastomer (EPDM) is employed as thermal insulation for rocket motors, as well as EPDM blends with ethylene vinyl acetate (EVA) have been used in the aerospace industry. The quantification of these blends is more common using Fourier Transform Infrared Spectrometry (FT-IR) by transmission mode, but without discussing sample preparation and methodology error. Considering this fact, a methodology was developed for determining EVA content in binary blend with EPDM samples, by Universal Attenuated Total Reflection (UATR) technique, associated to thermogravimetric analysis (TGA). This last one, it was applied to determine Vinyl Acetate (VA) content in EVA and to identify differences between EPDM/EVA blends. Samples of the analyzed blends showed two VA contents and five proportions of EPDM/EVA: 90/10, 70/30, 50/50, 30/70, and 10/90. The carbonyl stretching vibration band C=O at 1740 cm–1 was used as analytical band in FT-IR quantification. Finally, the results presented excellent accuracy with a good linear correlation coefficient (R > 0.940) and with relative error values lower than 2%, respecting the precision limits of the FT-IR spectrometer.

Online determination of chemical and physical properties of poly(ethylene vinyl acetate) pellets using a novel method of near-infrared spectroscopy combined with angle transformation

Melt flow rate (MFR) and vinyl acetate content (VAC) are the target parameters for quality control of poly(ethylene vinyl acetate) (EVA) pellets in production processes.

Quantitative Analysis for Estimating the Content Ratio of Ethylene Vinyl Acetate Copolymer (EVA)/Very Low Density Polyethylene (V-LDPE) Blended Foam

Recently, ethylene vinyl acetate (EVA) and very low density polyethylene (V-LDPE) blended foam (EVA/V-LDPE-foam) used in various industrial fields has been studied in order to improve the mechanical properties such as lightness and cushioning. The content ratio of EVA and V-LDPE was one of the important factors to control mechanical properties. The determination of the ratio of the above was desired from the view of quality control. The ratio could be determined through comparison between the content of vinyl acetate of non-linked EVA(VA wt%N) and EVA/polyethylene (PE) foam (VA wt%F). However, it was difficult to determine VA wt%N by the conventional analytical techniques. In this study, a trace amount of non-cross-linked EVA in the cross-linked foam is focused on the determination of VA wt%N. Separation of non-linked EVA was attempted by using solubility-difference between EVA and V-LDPE which were extracted from the foam to 10 vol% acetonitrile in chloroform solution. As a result, non-linked EVA was separated from non-linked components including a trace amount of V-LDPE by elution-time-difference. VA wt%N was estimated by Fourier-transform infrared spectroscopy (FT-IR) and the content ratio was determined through comparison between VA wt%N and VA wt%F.

Evaluation of acoustic and dynamic behaviour of ethylene vinyl acetate panels

AbstractEthylene vinyl acetate panels, with high vinyl acetate content and a closed‐cell structure, were studied through various experimental techniques as a first approach to evaluate the vibrational and acoustic behaviour of ethylene vinyl acetate panels for building applications. Test specimens, with a variety of densities and thicknesses were tested to evaluate the influence of these two parameters on acoustic impedance, sound transmission loss, dynamic stiffness and attenuation of vibrations. The results obtained shows sound transmission loss values for frequencies up to 2500 Hz with a maximum of about 63.7 dB, the dynamic stiffness results presented a wide range, with a maximum value of 350 MN/m3 and a minimum value of 23.3 MN/m3.On the other hand the lack of pore in the surface produce a high acoustic impedance. It can be concluded that ethylene vinyl acetate presents appropriate characteristics, mainly as an acoustic and vibration isolating material, for floorings and light partitions.

Effect of ethylene vinyl acetate content on the performance of VMD using HDPE co-blending membrane

Abstract Membranes were fabricated with high-density polyethylene (HDPE) and ethylene vinyl acetate (EVA) blend through thermally induced phase separation and were then used for vacuum membrane distillation (VMD). The membranes were supported by nonwoven polyester fabric with a special cellular structure. Different membrane samples were obtained by adjusting the polymer concentration, HDPE/EVA weight ratio, and coagulation bath temperature. The membranes were characterized by scanning electron microscopy (SEM) analysis, contact angle test, and evaluation of porosity and pore size distribution. A series of VMD tests were conducted using aqueous NaCl solution (0.5 mol·L−1) at a feed temperature of 65 °C and permeate side absolute pressure of 3 kPa. The membranes showed excellent performance in water permeation flux, salt rejection, and long-term stability. The HDPE/EVA co-blending membranes exhibited the largest permeation flux of 23.87 kg·m−2·h−1 and benign salt rejection of ≥ 99.9%.

Torsional Fiber Actuators from Shape-memory Polymer

ABSTRACT:Humanoid robots, prosthetic limbs and exoskeletons require soft actuators to perform their primary function, which is controlled movement. In this work, we explored whether crosslinked poly[ethylene-co-(vinyl acetate)] (cPEVA) fibers, with different vinyl acetate (VA) content can serve as torsional fiber actuators, exhibiting temperature controlled reversible rotational changes. Broad melting transitions ranging from 50 to 90 °C for cPEVA18-165 or from 40 to 80 °C for cPEVA28-165 fibers in combination with complete crystallization at temperatures around 10 °C make them suitable actuating materials with adjustable actuation temperature ranges between 10 and 70 °C during repetitive cooling and heating. The obtained fibers exhibited a circular cross section with diameters around 0.4±0.1 mm, while a length of 4 cm was employed for the investigation of reversible rotational actuation after programming by twist insertion using 30 complete rotations at a temperature above melting transition. Repetitive heating and cooling between 10 to 60 °C or 70 °C of one-end-tethered programmed fibers revealed reversible rotations and torsional force. During cooling 3±1 complete rotations (Δθr = + 1080±360°) in twisting direction were observed, while 4±1 turns in the opposite direction (Δθr = - 1440±360°) were found during heating. Such torsional fiber actuators, which are capable of approximately one rotation per cm fiber length, can serve as miniaturized rotary motors to provide rotational actuation in futuristic humanoid robots.

Viscoelastic and adhesion properties of hot-melts made with blends of ethylene-co-n-butyl acrylate (EBA) and ethylene-co-vinyl acetate (EVA) copolymers

Several hot-melts (HMAs) were prepared by using blends of ethylene-co-n-butyl acrylate (EBA) and ethylene-co-vinyl acetate (EVA) copolymers - EBA/EVA. HMAs were prepared with mixtures of EVA copolymers with 18 (EVA18) and 27 (EVA27) wt% vinyl acetate contents and EBA copolymer with 27 wt% n-butyl acrylate, polyterpene resin and mixture of microcrystalline and Fischer-Tropsch waxes. HMAs made with EBA/EVA blends showed lower viscosities and reduced shear thinning than the ones made with EBA or EVA due to differences in compatibility, but both the set time and the open time were not affected as they depended mainly on the wax nature and amount. The increase of the vinyl acetate (VA) content in EVA copolymer reduced the crystallinity of the EBA/EVA blends. Even EBA copolymer was more compatible with EVA27 than with EVA18 (the α- and β-transitions shown in DMTA plots were closer) and the compatibility did not vary with the EBA content in the blends. The addition of polyterpene resin and the mixture of waxes decreased the compatibility of the EBA/EVA blends, the higher compatibility was observed for the HMAs made with only one copolymer. The tack of the HMAs depended on their EBA/EVA contents, EBA/EVA27 HMAs showed broader temperature interval with higher tack, while the tack of EBA/EVA18 HMAs blend decreased and the temperature interval with tack was shortened and shifted to lower temperatures. Adhesion to polypropylene film was improved in HMAs made with 75 wt% EBA/25 wt% EVA18 and 50–75 wt% EBA/50-25 wt% EVA27. The adhesion to aluminum film of EBA or EVA hot melts was improved only in the joints made with EBA/EVA 27 HMAs, more noticeably when they contained higher EBA content.

Development and Characterization of Polypropylene/Polyethylene Vinyl Acetate/Micro Cellulose Trays as a Prototype for Chilled Food Packaging Application

Cellulose and polypropylene (PP) were successfully designed as a composite material. To obtain higher efficiency, ethylene vinyl acetate (EVA) with vinyl acetate (VA) content 28 % was integrated as a coupling agent. The presence of EVA improved the composite compatibility and polypropylene matrix toughness under low temperatures. The composite was compounded by twin screw extrusion (TSE) with 30 part of EVA per hundred parts of resin (phr) and varying ratios of cellulose 5, 10, 20 and 30 phr, respectively. The effects of cellulose and EVA on properties of the composite were investigated. Thermal degradation temperature of PP/cellulose composites with and without EVA was higher than pure PP. The impact strength of the composite with EVA was increased compared to composite without EVA. PP/EVA/cellulose-10 phr is the best condition which showed a very high elongation at break and tan δ. In conclusion, the role of cellulose and EVA could improve the thermal stability and flexibility of thermoplastic composites and would be useful in packaging chilled food.

Electrospinning of Ethylene Vinyl Acetate/Poly(Lactic Acid) Blends on a Water Surface.

The electrospinning of an ethylene vinyl acetate (EVA) copolymer with a vinyl acetate content of 28 wt.% is limited due to the solubility of the copolymer in standard laboratory conditions. Poly(lactic acid) (PLA) is a biodegradable polymer that can be electrospun easily. However, PLA has limited applicability because it is brittle. Blends of these polymers are of interest in order to obtain new types of materials with counterbalanced properties originating from both polymeric compounds. The fibers were electrospun on a water surface from a solution mixture containing various weight ratios of both polymers using a dichloromethane and acetone (70:30 v/v) mixture as solvent. The morphologies of the prepared non-woven mats were examined by scanning electron microscopy (SEM), and the chemical composition was investigated by X-ray photoelectron spectroscopy (XPS) and by Fourier Transform Infrared Spectroscopy (FTIR). The fibers’ thermal properties and stability were examined, and the mechanical properties were tested. The results showed that the strength and flexibility of the blend samples were enhanced by the presence of PLA.

Kinetics of Vinyl Acetate Biodegradation by Pseudomonas fluorescens PCM 2123

Abstract The microbial degradation of vinyl acetate (VA) by Pseudomonas fluorescens PCM 2123 strain was studied in both batch and continuous modes. The purpose of the experiments was to determine the kinetic model of the cell growth and biodegradation rate of vinyl acetate (VA), which was the sole carbon and energy source for tested microorganisms. The experiments, carried out in a batch reactor for several initial concentrations of growth substrate in the liquid phase ranging from 18.6 to 373 gsubstrate·m−3 (gs·m−3) made it possible to choose the kinetic model and to estimate its constants. The Haldane inhibitory model with the values of constants: μm = 0.1202 h−1, KS = 17.195 gs·m−3, Ki = 166.88 gs·m−3 predicted the experimental data with the best accuracy. To set the parameters of maintenance metabolism it was necessary to carry out a series of continuous cultures at different dilution rates (0.05 to 0.072 h−1) and concentrations of VA in the liquid supplied to the chemostat ranging from 30.9 to 123.6 gs·m−3. The obtained data-base enabled to determine the coefficient for maintenance metabolism (me = 0.0251 gsubstrate gcell dry weight −1·h−1 (gs·gcdw −1·h−1)) as well as the maximal and observed values of yield coefficients, Yxs M = 0.463 gcdw·gs −1 and (Yxs ) obs = 0.411 gcdw·gs −1, respectively. The developed kinetics was verified by comparison of the computed and obtained in batch experiments profiles of changes in biomass and growth substrate concentrations.

Superhydrophobic EVA copolymer fibers: the impact of chemical composition on wettability and photophysical properties

Fibers of poly(vinyl acetate) (PVAc) homopolymer and ethylene vinyl acetate (EVA) copolymers with varying vinyl acetate (VAc) contents between 25 and 40 wt.% have been prepared to investigate wettability and photophysical properties. At lower VAc contents, it was difficult to prepare fibers without any beads due to the presence of crystalline ethylene groups at higher concentrations. EVA copolymer composition strongly affected the wettability of fibers; all EVA copolymer fibers exhibited superhydrophobic behavior and CA values varied between 150° and 160° depending on copolymer composition while hydrophilic PVAc homopolymer fibers exhibited hydrophobic behavior with a CA of 134°. Photophysical properties of PVAc homopolymer and EVA copolymers were evaluated in terms of transmittance and emission intensity. Emission intensity and transparency of EVA copolymers were decreased with the increase of VAc contents due to its amorphous behavior.

PLA/EVA/Teak Wood Flour Biocomposites for Packaging Application: Evaluation of Mechanical Performance and Biodegradation Properties

Mechanical properties such as tensile modulus and strength, elongation-at-break, and impact strength of poly(lactic acid)/ethylene-co-vinyl acetate copolymer (EVA, vinyl acetate content 18 weight %)/Teak wood flour (TWF) composites were evaluated at TWF volume fractions ranging from Φf = 0.1–0.32. Tensile modulus showed an initial increase up to Φf = 0.25 and the parameter decreased marginally at Φf = 0.32, however, remaining much higher than that at Φf = 0. The increase in modulus was attributed to the generation of mechanical restrains by TWF. This mechanical restrains decreased ductility of the composites which also decreased the impact strength. The composite structure was evaluated by comparing the tensile properties with predictive theories, of two-phase models. TWF decreased the thermal stability of the composite, although char yield enhanced due to decomposition of cellulosic bodies in TWF. Differential scanning calorimetry (DSC) studies indicated decrease in the crystallinity of the crystallizable component PLA in the presence of TWF particles in the polymer blend matrix. The biodegradation studies were undertaken to evaluate the biodegradation of the composite under soil burier condition.

Kinetic modelling and kinetic parameters calculation in the lipase-catalysed synthesis of geranyl acetate

The interest in new natural products used in cosmetic industry has increased the research in order to synthesize those compounds. The aim of this work is to assess the reaction of the transesterification between geraniol and vinyl acetate for the enzymatic synthesis of geranyl acetate, using Novozym® 435 as catalyst, as well as to obtain a kinetic model for the bioprocess and the values of the kinetic parameters. Five experimental series have been performed with variation of: enzyme amount, concentrations of geraniol and vinyl acetate in molar ratio 1:1, stirring rate, temperature and, finally, substrates molar ratio. A conversion of geranyl acetate of 98.4% has been obtained in the best experimental conditions and, also, high conversions were obtained for most of the other conditions assayed. It has been concluded that the catalyst amount is the most significant variable on the reaction kinetics and the reaction yield and that both the stirring rate and the initial substrates concentrations have no significant influence. Finally, a Ping–Pong bisubstrate kinetic model has been applied and its kinetic parameters have been determined by using an improved version of a procedure developed by authors in a previous work. The values obtained for the Michaelis constants show that, for the equal substrates concentrations series, the Ping–Pong model can be simplified to a pseudo-first order kinetic model, which has been confirmed, with high correlation coefficients, by using the “Curve Expert” software.

Ethylene-Vinyl Acetate Copolymer (EVA) and Resin-Stabilized Asphaltenes Synergistically Improve the Flow Behavior of Model Waxy Oils. 3. Effect of Vinyl Acetate Content

Ethylene-Vinyl Acetate Copolymer (EVA) and Resin-Stabilized Asphaltenes Synergistically Improve the Flow Behavior of Model Waxy Oils. 3. Effect of Vinyl Acetate Content