Increasing Vinyl Acetate Content Research Articles

Characteristics and Challenges of Poly(ethylene-co-vinyl acetate) Solution Electrospinning.

Poly(ethylene-co-vinyl acetate) (PEVA) is a versatile elastic, durable, and biocompatible copolymer, which can be processed by melt extrusion or solvent casting, while electrospinning has been reported as challenging. Here, a spinnability window should be identified using a total of 10 different PEVA materials with increasing vinyl acetate content (∼12-40 wt %) and molecular weights (∼60-130 kDa). Based on the solubility predictions by calculating Hansen solubility parameters, candidate solvents were experimentally evaluated. Spinning experiments with systematic alteration of solution composition and processing parameters revealed the causes of material deposition at the spraying nozzle and multijet spinning characteristics. By introducing a spinnability score that accounts for product characteristics and reproducibility, the spinnability of PEVA could be rationalized. Overall, it was demonstrated that PEVA solutions with an apparent viscosity of 920-3500 mPa·s can be spun to bead-free fibers of ∼10 μm. This size may allow suspension electrospinning of composite fibers in the future.

Controlled Release of Mangiferin Using Ethylene Vinyl Acetate Matrix for Antioxidant Packaging

This study investigated the use of ethylene vinyl acetate (EVA) matrix in controlled release packaging. Mangiferin, having high antioxidant activity, was incorporated into the EVA matrix with different vinyl acetate (VA) contents. Mangiferin release rate increased with increasing VA content (or decreasing crystallinity). Linear relationship between mangiferin release rate and VA content was observed in the range of 18–40% VA. The diffusion coefficients of mangiferin released from the EVA matrices containing 12%, 18%, 25% and 40% VA were 0.482, 0.512, 2.81 and 2.88 (×10−14 m2/s), respectively. The enhancement factors of about 22-fold and sevenfold were observed in the 12% and 18% VA matrices, respectively, when using triethyl citrate as a plasticizer. EVA film containing 40% VA had the highest antioxidant activity (81.90% radical scavenging capacity, (RSC)) because the highest amount of mangiferin was released in the food simulant (84.66 µg/ml). Addition of mangiferin in the polymer matrices had no significant (p > 0.05) effect on thermal and barrier properties of the films but decreased tensile strength and Young's modulus. The results of this study demonstrated that EVA matrices with varying degree of VA could potentially be used to control mangiferin release rate for antioxidant packaging. Copyright © 2014 John Wiley & Sons, Ltd.

A study of nano‐mechanical and macro‐mechanical properties of ethylene vinyl acetate

AbstractNano‐ and macro‐mechanical properties of ethylene vinyl acetate (EVA) with various amounts of vinyl acetate (VA) have been investigated. Nano‐mechanical properties (modulus and hardness) were obtained using nano‐indentation measurements while macro‐mechanical properties were determined using tensile test measurements. A decrease in Young's modulus and hardness was observed with increasing VA content for both nano‐ and macro‐mechanical measurements. An increase in Young's modulus and hardness was observed as a function of the draw ratio keeping the VA content constant. The difference between macro‐ and nano‐mechanical properties as a function of VA content and draw ratio is explained in terms of crystallinity and chain orientation. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers

Pervaporation characteristics of ethylene–vinyl acetate copolymer membranes with different composition for recovery of ethyl acetate from aqueous solution

The degree of crystallization, surface property and density of ethylene–vinyl acetate (EVA) copolymer membranes with different vinyl acetate (VA) content were measured by differential scanning calorimetry (DSC), contact angle meter and pycnometer. The pervaporation (PV) characteristics of the EVA copolymer membranes for recovery of ethyl acetate (EA) from aqueous EA solutions have been investigated. The separation factor ( α) decreased with increasing VA content from 26 wt.% (EVA26) to 100 wt.% (poly vinyl acetate, PVAc) in EVA copolymer membranes. A maximum EA flux ( J EA,max) of EVA membrane with 38 wt.% VA content revealed for 2.5 wt.% aqueous EA solution at 30 °C, J EA,max reached to 550 g/(m 2 h) and α was to 118. These PV characteristics of EVA membranes were explained in terms of the crystallinity of EVA copolymer and the affinities between EA or water and VA segment in EVA copolymer membrane. Experimental results also show that both α and J EA increased with increasing feed temperature and feed concentration.

Corona discharge treatment of EVAs with different vinyl acetate contents

Four ethylene vinyl acetate (EVA) co-polymers with different vinyl acetate (VA) contents (9–20 wt%) were treated with corona discharge to improve their adhesion to polychloroprene (PCP) adhesive. The thermal properties of the EVAs decreased as their VA content increased, caused by a decrease in crystallinity. The elastic and viscous moduli of the EVAs decreased and the temperature and modulus at the cross-over between these moduli decreased with increasing VA content. Contact-angle measurements (water), infrared spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to analyse the surface modifications produced in the corona-discharge-treated EVAs. The corona discharge treatment produced improved wettability and created roughness and oxygen moieties on the EVA surfaces. The higher the VA content and the higher the corona energy, the more significant modifications were produced on the EVA surface. The VA content also affected the T-peel strength values of treated EVA/polychloroprene + isocyanate adhesive joints, as the values increased with increasing VA content. Mixed failure modes (interfacial + cohesive failure in the EVA) were obtained in the adhesive joints produced with corona discharge treated EVAs containing more than 9 wt% VA. The accelerated ageing of the joints did not affect the T-peel strength values, but the locus of failure in most cases became fully cohesive in the EVA, likely due to the higher extent of curing of the adhesive.

Degradation and stabilisation of poly(ethylene- stat-vinyl acetate): 1 – Spectroscopic and rheological examination of thermal and thermo-oxidative degradation mechanisms

The degradation of ethylene vinyl acetate (EVA) copolymers was compared with low density polyethylene (LDPE), poly(vinyl acetate) (PVAc) and poly(vinyl chloride) (PVC) using FTIR, UV–visible and fluorescence spectroscopy as well as thermal and rheological analyses. Thermal, thermo-oxidative and photo-oxidative studies were conducted. Thermo-oxidation below 180 °C shows more similarities between EVA and LDPE. The luminescence spectra of degraded EVA and LDPE were almost identical but very different to that of PVAc. UV–vis analysis showed that the polyenes present in aged PVC were unlikely to be the same species responsible for the observed colour formation in aged EVA. It is suggested that they are polyconjugated carbonyl products. Rheological analysis also showed the evolution of crosslinking reactions during thermo-oxidation. FTIR studies after thermal degradation in inert conditions 290 °C showed complete loss of the ester functionality and associated lactone formation along with some evidence for ketonic and unsaturated carbonyl groups. Degradation in air at 180 °C, however, revealed that loss of the ester group was not so marked, with PVAc exhibiting the greatest stability. This was in line with the induction time to onset of autocatalytic carbonyl growth at 180 °C; the latter showed an apparent exponential decrease with increasing vinyl acetate content up to 28% w/w. Fluorescence analysis produced trends that complemented those of carbonyl index; the time to decomposition of initial fluorescent α,β-unsaturated carbonyl species coincided with the time to onset of carbonyl growth. Furthermore, the rate of formation of the new fluorescent species produced in EVA, and LDPE was similar to that of carbonyl growth. These new fluorescent species are therefore likely to be di- or tri-carbonyl products.

Molecular orientation of EVA chains adsorbed on chemically controlled surfaces: influence of specific interactions

AbstractMolecular orientation of ethylene–vinyl acetate (EVA) copolymer nanofilms adsorbed on chemically controlled surfaces is studied. Four EVA copolymers with different contents of vinyl acetate (VA) were spin‐coated onto gold, COOH and NH2 functionalized substrates in order to study chain behaviour when adsorbed in a quasi‐two‐dimensional system. Polarization‐modulation infrared reflection–absorption spectroscopy (PM‐IRRAS), a very suitable technique to study thin films, was the key to quantitative calculation of EVA chain orientational angles. Acid–base interactions between carbonyl groups of the chain ramification (vinyl acetate units) and the surface functionalities are evidenced on the basis of infrared spectra. Their incidence on the molecular orientation is also discussed.Our results show a quasi‐parallel orientation of EVA main chains with respect to the surface plane for all adsorption substrates. At the same time, orientation changes of the acetate groups are observed when the EVA copolymer is adsorbed onto functionalized substrates, suggesting that acid–base interactions could influence the orientation of these groups. However, these changes are limited and cannot reorient the main chain axis. Moreover, our results show that increasing VA content in the chain does not lead to more carbonyl functions involved in acid–base interactions with the adsorption surface. This fact also will be discussed. Copyright © 2003 John Wiley & Sons, Ltd.

Induced crystallization of EVA having various VA contents by compressed CO2

AbstractThe crystallization induced by compressed CO2 was investigated for rubbery ethylene‐vinyl acetate copolymer (EVA) containing various amounts of vinyl acetate (VA). The induction of crystallization was demonstrated by appearance of shoulder‐like differential scanning calorimetry (DSC) endotherms at temperatures lower than Tm of polyethylene segments of EVA after CO2 treatments. The intensity of the endothermic shoulders and the degree of crystallinity increased with increasing VA content, suggesting that the interaction of CO2‐carbonyl groups governed the induction of crystallization of EVA upon CO2 treatment. The interaction of CO2‐carbonyl group was found to decrease with increasing temperature as demonstrated by the decreased crystallization enhancement for 37°C as compared with that for 32°C. The enhancement of crystallization did not monotonically increase with increasing CO2 pressure, resulting from the interplay of thermodynamic and kinetic driving forces, both being associated with the CO2 pressure and thus the sorption concentration. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1144–1151, 2003

N-DIOCTADECYL FUMARATE–VINYL ACETATE COPOLYMER: SYNTHESIS, CHARACTERIZATION AND APPLICATION AS FLOW IMPROVER FOR OILS

ABSTRACT Monomer n-dioctadecyl fumarate (DOF), and copolymers (C18FVA) of DOF with vinyl acetate were synthesized. Monomer and copolymers were characterized by IR, 1H-NMR, VPO and DSC. Due to the special structure of DOF, only copolymers containing 45.9%–97.8% (mol) DOF were obtained. The crystalline CH2 numbers on polymer side chain χ were calculated from enthalpy determined by DSC, and it was found that χ slightly decreased with increasing vinyl acetate content. C18FVA can be used as flow improver for viscous oil and residual oil, and the more the crystalline CH2 number on the side chains, the better lattice match between copolymer and wax crystal structure of oils.

Composition and self-irradiation effects on the positron annihilation lifetime properties of poly(ethylene-co-vinyl acetate)

The behavior of the copolymer poly(ethylene-co-vinyl acetate), with different amounts of vinyl acetate (VA) (2, 4.5, 9 and 19 w/w%, respectively), has been studied by performing positron lifetime measurements as a function of temperature. An overall reduction of the ortho-positronium formation probability I 3 with increasing VA content is observed. The copolymers with 2, 4.5 and 9 w/w% VA show a V-shaped I 3 evolution with temperature, caused by positron irradiation induced ionization, whereas the copolymer with 19 w/w% VA has become practically inert to self-irradiation effects.

Structure of Poly(vinyl alcohol) Microfibrils Produced by Saponification of Copoly(vinyl pivalate/vinyl acetate)

High molecular weight specimens of syndiotacticity-rich poly(vinyl alcohol) (PVA) have been prepared by saponification of copolymers of vinyl pivalate (VPi) and vinyl acetate (VAc). VPi and VAc were copolymerized using the low-temperature initiator 2,2‘-azobis(2,4-dimethylvaleronitrile) and saponified in KOH/methanol/water with vigorous stirring, i.e., under shear. The PVAs obtained had number-average degrees of polymerization in the range (5.6−16.5) × 103 and syndiotactic diad (S-diad) contents of 52.8−61.5%. The highest molecular weight and S-diad content were obtained for specimens derived from homopoly(VPi) prepared at low initiator concentration, and these parameters declined progressively with increasing VAc content in the parent copolymers. The structures of these PVAs show a consistent sharp transition between 55 and 56% S-diad content. Specimens with lower S-diad contents have shapeless morphologies, but at 56% S-diad content the polymers were fibrous, with a higher degree of crystallinity and or...

Effect of vinylacetate content on crystallinity and second‐order transitions in ethylene—vinylacetate copolymers

Thermal characteristics of ethylene—vinylacetate (EVA) copolymers having vinylacetate contents ranging from 5 to 40 w/w % are studied by differential scanning calorimetry. It is first shown that EVA copolymers having a vinylacetate content lower than 30 w/w % obey the Flory and Burfield theories of copolymer crystallisation. The minimum sequence length of CH2 ethylenic entities required to participate in a crystalline lamella is also deduced. One can conclude that EVA copolymers represent cases of “total exclusion” of the noncrystallizable comonomer. Moreover, it is observed that when the vinylacetate content is increased, the relative quantity of polyethylene amorphous phase increases and the degree of crystallinity decreases; whereas the β transition temperature of a characteristic-oriented amorphous phase is kept constant. A phase model of ethylene-vinylacetate copolymers, based on an enrichment process of the interlamellar amorphous phase by polyethylene segments originating from the crystalline phase, at increasing vinylacetate content, is proposed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1903–1912, 1997

Effect of vinylacetate content on crystallinity and second-order transitions in ethylene?vinylacetate copolymers

Thermal characteristics of ethylene—vinylacetate (EVA) copolymers having vinylacetate contents ranging from 5 to 40 w/w % are studied by differential scanning calorimetry. It is first shown that EVA copolymers having a vinylacetate content lower than 30 w/w % obey the Flory and Burfield theories of copolymer crystallisation. The minimum sequence length of CH2 ethylenic entities required to participate in a crystalline lamella is also deduced. One can conclude that EVA copolymers represent cases of “total exclusion” of the noncrystallizable comonomer. Moreover, it is observed that when the vinylacetate content is increased, the relative quantity of polyethylene amorphous phase increases and the degree of crystallinity decreases; whereas the β transition temperature of a characteristic-oriented amorphous phase is kept constant. A phase model of ethylene-vinylacetate copolymers, based on an enrichment process of the interlamellar amorphous phase by polyethylene segments originating from the crystalline phase, at increasing vinylacetate content, is proposed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1903–1912, 1997

Compression Moulded Ethylene Homo and Copolymer Foams I. Effect of Formulation

Various foam formulations based on polyethylene and ethylene-vinyl acetate copolymers were investigated. Interactions between crosslinking and blowing agent concentrations were systematically studied for each base polymer using a two-stage compression moulding technique to manufacture the foams and the effects on physical properties were determined. Initial studies progressively increased blowing agent concentration, whilst maintaining a fixed crosslinking agent level, resulting in density and relative density reduction as expected. However, it was observed that at any specific blowing agent concentration, foam density increased with increasing chain branching in polyethylene and with increasing vinyl acetate content in the copolymers. This phenomenon was satisfactorily explained in terms of increasing crosslinking efficiency with increasing tertiary hydrogen concentration in the base polymer by comprehensive studies on gel content, melt strength at the expansion temperature and cell size trends. Surprisingly, cell size increased with vinyl acetate content at any particular gel content suggesting absolute cell size is a function of nucleation in the first stage of the process.

Phase structure and morphological variations induced by straining in injection-moulded samples of PA6/EVA blends: influence of molecular structure of EVA copolymers

The influence of molecular structure and composition of ethylene-co-vinyl acetate (EVA) copolymers, differing in molecular mass and, for a given molecular mass, in vinyl acetate content (wt/wt), on morphological and structural changes undergone by injection-moulded samples of Nylon 6 (PA6)/EVA blends during uniaxial tensile straining at room temperature up to sample rupture and on properties of such materials was studied. Direct correlations between molecular structure and composition of EVA copolymers and the shape and size of domains of dispersed phase and ultimate properties of PA6/EVA materials have been drawn. For the dumb-bell-shaped specimens strained just beyond the yielding point, it was found that the original layered structure was strongly modified by straining. Three layers were, in fact, generated: a skin surface, where no domains of EVA dispersed phase were observed, an outer layer, where the EVA domains were elongated along the draw direction assuming mainly cylindrical shape, and a core where the EVA phase was segregated in ellipsoidal-shaped domains having their major axis oriented along the draw direction. For the samples strained to break it was found that the PA6/EVA fibres showed a single glass transition temperature, whose value is lower than that found for the fibre of plain PA6, but higher than that shown by PA6 phase in the unstrained samples; such a value, moreover, tends to be decreased on increasing the vinyl acetate content along the EVA chain, irrespective of copolymer molecular mass. The calorimetric measurements performed revealed, moreover, a noticeable increase of the observed melting temperature values of EVA phase in PA6/EVA fibres. In the PA6/EVA samples strained to break, only two different layers were seen: an outer skin, free of EVA domains, and a core where the EVA dispersed phase segregated in ellipsoidal-shaped domains. The values of stress at break, σB, and of the elongation at break, ɛB, exhibited by PA6/EVA fibres were found to be lower than those shown by the plain PA6. The trends of σB and ɛB values against the EVA vinyl acetate content showed, moreover, that σB and ɛB values decreased with increasing vinyl acetate content along the copolymer chain.

Molecular structure and melting behaviour of ethylene-vinyl acetate copolymers

A series of ethylene-vinyl acetate copolymers has been examined by 13C-NMR spectroscopy and DSC. These polymers are products of high pressure free radical copolymerizations and contain 1–40% vinyl acetate by weight. Such copolymers are random and almost all the vinyl acetate units are isolated between ethylene units. All copolymers were branched, but total branching decreased with increasing vinyl acetate content. This effect arises mainly because the vinyl acetate residues inhibit the formation of cyclic intermediates that are involved in the productions of short branches. A decrease of about one short branch per 1000 ethylene carbons is observed for every increase of 2 mol% vinyl acetate. About 10% of the vinyl acetate units are branched at main chain carbons. Copolymers that have been cooled slowly from the melt exhibit multiple melting peaks. The lower melting, minor peaks are believed to reflect crystallization of lower molecular weight, branched molecules. The melting temperature of the copolymers is a function of the average sequence length of crystallizable ethylene units, when allowance is made for vinyl acetate units and short branches.

Separation of poly(styrene—vinyl acetate) block copolymers by liquid adsorption chromatography

Poly(styrene—vinyl acetate) block copolymers, prepared by using a polymeric peroxide as an initiador, were characterized by liquid adsorption chromatography (LAC) and size-exclusion chromatography (SEC). The copolymers were separated according to their chemical composition by LAC using silica gel as an adsorbent and a mixture of 1,2-dichloroethane (DCE) and ethanol as the mobile phase with a 20-min linear gradient from DCEethanol (98:2, v/v) to DCEethanol (85:15, v/v). The column temperature was 30°C. The copolymers were separated by LAC according to the composition in order of increasing vinyl acetate content. The copolymers were fractionated by LAC and SEC in order to determine the relationship between the composition and molecular weight. The LAC fractions were subjected to SEC and the SEC fractions to LAC. The range of composition for the copolymers was between 40 and 90% (w/w) styrene regardless of the monomer feed. There are positive trends in the composition and the molecular weight averages that the copolymer fractions containing more styrene have lower molecular weights, although the copolymers have chemical compositions and molecular weight distributions that are independent of each other.

Mechanism of diffusion of compounds through ethylene vinyl acetate copolymers I. Kinetics of diffusion of l-chloro-4-nitrobenzene, 3,4-dimethylphenol and 4-hexylresorcinol

The mechanism of diffusion of drugs through ethylene-vinyl acetate (EVA) copolymers has been studied. The observed permeability coefficients for the phenols, 4-hexylresorcinol and 3,4-dimethylphenol, increase in a non-linear fashion with increasing vinyl acetate content in the copolymer. Furthermore, their partition coefficients vary in a non-linear manner with increasing vinyl acetate content, while the partition coefficient of a non-phenolic compound, 1-chloro-4-nitrobenzene, increases in a linear manner. Since the diffusion coefficients for the two phenols are shown to be independent of vinyl acetate content, the permeability of phenols in EVA membranes depends almost entirely on the partition coefficient. The non-linear partitioning behavior of the phenolic compounds can be attributed to the formation of vinyl acetate-phenol complexes. The linear increase in partition coefficient for 1-chloro-4-nitrobenzene is attributed to a straightforward solubility enhancement.

Vapor‐phase graft copolymerization of binary solid monomers onto poly(ethylene‐co‐vinyl acetate) film by ultraviolet irradiation

AbstractVapor‐phase graft copolymerizations of acenaphthylene–maleimide or acenaphthylene–maleic anhydride binary solid monomers onto poly(ethylene‐co‐vinyl acetate) films were carried out under ultraviolet irradiation. The extent of sorption of single or binary monomers increased with the increasing vinyl acetate content in the backbone polymers. The sorbed binary monomers were mainly composed of acenaphthylene, but the maleimide or maleic anhydride fraction increased with the increasing vinyl acetate content of the films and the composition was little affected by surface hydrolysis. In all series of graft polymerization of single or binary monomers the overall extent of grafting increased with the vinyl acetate content and was suppressed by the surface hydrolysis of the backbone film. The composition of the grafted copolymer, however, differed markedly, depending on the combination of binary monomers. The grafted copolymer in the acenaphthylene–maleimide system was composed mainly of acenaphthylene units, whereas that in the acenaphthylene–maleic anhydride system was composed mainly of maleic anhydride units. The results were compared with those of γ‐ray grafting, and it was suggested that the contribution of a direct supply of monomers from vapor phase and the existence of an acetoxy group on the surface of the film should play an important role in the grafting reaction.

Crystallization of ethylene/vinylacetate random copolymers

AbstractIt may be anticipated that uncrystallizable units, if introduced randomely into a crystallizable polymer chain, might strongly prohibit the chain folding and enhance intermolecular crystallization, which will give rise to the fringed micelle structure. In anticipation of this, crystallization and resultant texture were studied for random copolymers of ethylene (E) and vinyl acetate (VAc) as functions of composition and crystallization temperature. Crystallization was carried out isothermally from solution as well as from melt. DTA melting behavior of the melt‐crystallized samples revealed that two types of crystals with different melting temperatures were formed during the isothermal crystallization of the copolymers. Since the height of the peak appearing at the higher temperature T1 decreased and that at the lower temperature T2 increased with the increasing VAc content and crystallization temperature, the former peak may be assigned to the chain folded crystals and the latter to the bundle‐like crystals. In other words, the transition from the chain folding crystallization to the bundle‐like crystallization did not occur sharply at a given composition as expected but the two types of crystallization coexist in a rather wide range of compositions, depending on the crystallization temperature.It became also apparent that molecular fractionation occurred during the isothermal crystallization with respect to the composition of the copolymer. Electron microscopy could not confirm the existence of the bundle‐like crystals, probably due to the fact that the individual bundle‐like crystal was not large enough to be distinguished from much larger chain‐folded lamellae with more definite shapes. On the other hand, solution grown crystals gave a single melting peak and a single X‐ray long spacing, suggesting only the chain folding crystallization occurred in the whole range of compositions studied. Molecular fractionation was again evident and the material left uncrystallized in the solution increased with the VAc content. These results may imply that the intermolecular bundle‐like crystallization depends strongly on the probability of finding other chain molecules around a given molecule. The X‐ray crystallinity as well as the heat of fusion measured suggest that the thickness of the amorphous surface layer (loose loops) of the solution grown crystals increases with the VAc content.