Morphology,mechanical, and water transport properties of melt blended EVOH/PVOH films

Herein, we report for the first time the successful preparation of ethylene–vinyl alcohol (EVOH)/poly(vinyl alcohol) (PVOH) blends by a melt blending process for PVOH volume content ranging from 0 to 30%. Thermal stability up to 270 °C was maintained for all blends. The blends morphology consisted in spherical low size PVOH domains homogeneously dispersed in the EVOH matrix with good interfacial properties. An increase of the mean size of the PVOH domains (from 0.3 to 1.2 μm) and of the size distribution was evidenced as the PVOH content increased. The contribution of each phase to the water sorption and diffusion was clearly demonstrated. The impact of water uptake was investigated on the chains mobility by using Gordon–Taylor law and on the mechanical properties of the blends with respect to the reference polymers. It was pointed out that the reinforcing effect of PVOH phase decreased as the water activity increased. However, a significant elongation at break was maintained, underlining the major role played by the EVOH continuous phase at high water activity. Finally, it was shown that adding PVOH to EVOH up to 15 vol % allowed strengthening the material at low water activity and keeping interesting elongation at break and barrier properties at high water activity. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 838–850     

Thermal oxidative stability and effect of water on gas transport and mechanical properties in PA6‐EVOH films

The thermal oxidative stability and the effect of water on gas transport and mechanical properties of blends of polyamide 6 (PA6) with ethylene‐co‐vinyl alcohol (EVOH) and EVOH modified with carboxyl groups (EVOH‐COOH) have been investigated. The presence of EVOH reduces water vapor and oxygen gas permeability of polyamide, as well as small amounts of EVOH‐COOH further improve barrier properties, especially to oxygen. This has been explained in terms of improved interactions of the blend constituents in the amorphous phase, due to ionic linkages between the polyamide amino groups and the carboxyls of modified EVOH. The permeation to gases was found to increase with the amount of sorbed water. The morphology of the samples was found to have an effect on barrier properties, as the presence of EVOH causes the PA6 α crystalline form to increase, lowering the permeability to oxygen and water vapor. Mechanical properties are strongly affected by water sorption, as tensile modulus and strength decrease with increasing water content. Chemiluminescence (CL), infrared spectroscopy (FTIR), and tensile test were employed in order to assess the correlation between chemical composition and the thermal oxidative stability of the films aged at 110 °C in air. CL experiments suggest that the presence of EVOH and EVOH‐COOH efficiently inhibits the formation of peroxidized species during the processing, and increases the thermal oxidative stability of the films. Infrared spectroscopy showed a build‐up of carbonyl absorption in the range 1700–1780 cm^?1, due to the formation of oxidation products, which is greater in the case of the pure polymer. Tensile tests on films revealed a reduction in ductility as a result of ageing for neat PA6, whereas in comparison the blends exhibit a far better long‐term stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 840–849, 2007     

Investigation of polyethylene‐grafted‐maleic anhydride presence as a compatibilizer on various properties of nanocomposite films based on polyethylene/ethylene vinyl alcohol/ nanoclay

High oxygen barrier films were prepared based on low‐density polyethylene (LDPE)/ethylene vinyl alcohol (EVOH)/ nanoclay and polyethylene‐grafted‐maleic anhydride (LDPE‐g‐MA) as a compatibilizer. Box–Behnken statistical experiment design methodology was employed to study the effects of nanoclay, LDPE‐g‐MA, and EVOH presence and their contents on various properties of the final films. The R² parameter varied between 0.89 and 0.99 for all the obtained responses. The morphology of the samples was evaluated. Results of oxygen transfer rate (OTR) test indicated that the addition of EVOH up to 30 wt% to neat LDPE can decrease oxygen permeability significantly. The addition of nanoclay also decreased the permeability of resulting films but, LDPE‐g‐MA reduced the permeability of the films only at an optimal content. Elastic modulus was increased with the addition of nanoclay, EVOH, and LDPE‐g‐MA to the matrix. An increase in EVOH content in the samples improved the tensile strength. Effect of nanoclay on tensile strength was highly dependent on the presence of a compatibilizer. The addition of compatibilizer to the samples and increasing its content enhanced the tensile strength of the specimens. Incorporation of nanoclay, EVOH, and LDPE‐g‐MA to the LDPE matrix and increasing the amount of these components in the samples led to higher storage modulus, zero shear rate viscosity, and shear thinning exponent, but, lowered the terminal slope and the frequency of intersection point of storage modulus (G′) and loss modulus (G″). The only exception was that EVOH increment resulted in a lower shear thinning exponent. Copyright © 2016 John Wiley & Sons, Ltd.     

Blends of starch with ethylene vinyl alcohol copolymers: effect of water,glycerol, and amino acids as plasticizers

Blends of thermoplastic starch with poly(ethylene‐co‐vinyl alcohol) copolymer (EVOH) were melt extruded with water/glycerol as plasticizer and a series of amino acid additives. The biggest factor in end‐use mechanical properties proved to be the relative humidity (RH) during storage. Plasticized starch‐EVOH blends stored at 0 and 50% RH changed significantly over time, with, for example, the tensile strength (TS) of the glycerol‐plasticized blend increasing from 4.7 to 26.3 MPa over 8 weeks when maintained at 0% RH. In contrast, the TS of this same sample stored at 75% RH remained unchanged for 8 weeks. Amino acids provided relatively minor, but significant changes in mechanical properties with time. Based on TS, elongation‐to‐break, and modulus, it may be concluded that β‐alanine, sarcosine, and L ‐proline were more effective than glycerol at maintaining strong flexible blends. Increases in crystallinity and changes in morphology with time, as described by modulated DSC were correlated to these changes in mechanical properties. Published in 2007 by John Wiley & Sons, Ltd.     

Improved oxygen barrier performance of poly(vinyl alcohol) films through hydrogen bond complex with poly(methyl vinyl ether-co-maleic acid)

Hydrogen bonding between poly(methyl vinyl ether-co-maleic acid) (PMVE-MA) and poly(vinyl alcohol) (PVOH) has resulted in films with lower oxygen transmission rates (OTR) than pure PVOH. In the range 20-30% (w/w) PMVE-MA, complexation between the two polymers in the blend was maximized, as shown by viscometry, Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) analysis. OTR measurements have shown that the maximum interpolymer complexation ratio also correlates with the lowest OTR values of the resulting film. The improved oxygen barrier properties are believed to be a combination of the relatively intact PVOH crystalline regions as shown with X-ray diffraction (XRD) and a higher degree of hydrogen bonding in the amorphous regions of the PVOH and PMVE-MA films as indicated by glass transition temperature (T_g) shifts. This leads to denser amorphous regions that reduces the rate of gases diffusing through the polymer film, hence the reduced OTR.     

Raman spectral study of solid and dissolved poly(vinyl alcohol) and ethylene-vinyl alcohol copolymer

We have measured the Raman spectra of ethylene-vinyl alcohol copolymer (EVOH) and poly(vinyl alcohol) (PVOH). Spectra of 88% hydrolyzed PVOH were examined from the partially crystalline solid, from PVOH dissolved in both H₂O and D₂O, and from films precipitated from these solutions. The spectrum in H₂O differs from that of the starting material by disappearance of sharp bands having Raman shift values of 1146 and 1093 cm^?1, strengthening of a band near 915 cm^?1, decrease in frequency of bands at 480, 1356, and 1441 cm^?1, and increase in frequency of bands at 369, 413, 1023, 1371, and 2910 cm^?1. The spectrum of the film shows partial reversal of these trends. With D₂O as the solvent, the band shifts are slightly different from those listed above and new bands appear. These changes are indicative of loss of crystallinity, change in stereochemistry, and partial deuteration of hydroxyl during dissolution of this PVOH sample at room temperature. © 1994 John Wiley & Sons, Inc.     

Effect of different blend compositions on properties of low-density polyethylene/ethylene vinyl alcohol/clay toward high oxygen barrier nanocomposite films

In this study, high oxygen barrier nanocomposite films were prepared by melt blending of low-density polyethylene/ethylene vinyl alcohol/nanoclay/polyethylene-grafted-maleic anhydride (LDPE/EVOH/nanoclay/LDPE-g-MA). Effect of each component presence was determined by using Box-Behnken experiment design methodology. For all the responses obtained, R ² was between 0.956 and 0.981 indicating a very good fitting of the experimental data with the response surface method (RSM) in the models. Oxygen transfer rate (OTR) results shown that the addition of EVOH, compatibilizer, and nanoclay in formulations significantly decreases oxygen permeability. The experimental results showed that addition of 30 wt % EVOH, 4 wt % nanoclay, and 5 wt % LDPE-g-MA to the LDPE matrix gave the best oxygen barrier properties. The crystallization behaviors of the samples and thermal analysis have been characterized by using differential scanning calorimetry (DSC). The addition of nanoclay to the blends has resulted in increased crystallinity of LDPE phase. The state of nanoclay dispersion in the samples was examined by the X-ray diffraction (XRD) tests. The reduction of EVOH and nanoclay content, as well as the increase of LDPE-g-MA, has resulted in the better dispersion of nanoclay in the polymer matrix. The morphology of specimens was observed by using energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM).     

Characterization of extruded ethylene-vinyl alcohol copolymer based barrier blends with interest in food packaging applications

Based on previous work a number of optimum extruded blends with high contents of a high barrier ethylene-vinyl alcohol copolymer were selected and characterized in terms of phase morphology, water sorption and barrier properties. Blend components were an ethylene vinyl-alcohol copolymer (EVOH with 32 mol% ethylene), an amorphous polyamide (aPA) and a nylon-containing ionomer. A fine two phase structure was found for these blends in all cases. However, Raman spectroscopy results indicated a poor interface interaction between the blend components in the case of the EVOH/aPA blends. Higher interface interaction had been previously found in the dry EVOH/ionomer blends. Equilibrium moisture solubility and diffusion were found to be higher than expected from simple additivity. However, the oxygen transmission rate was found to be clearly lower than expected from the rule of mixtures, particularly under dry conditions, fitting closely a simple Maxwell model.     

Nanofibrillated cellulose (NFC) reinforced polyvinyl alcohol (PVOH) nanocomposites: properties, solubility of carbon dioxide, and foaming

Polyvinyl alcohol (PVOH) and its nanofibrillated cellulose (NFC) reinforced nanocomposites were produced and foamed and its properties—such as the dynamic mechanical properties, crystallization behavior, and solubility of carbon dioxide (CO₂)—were evaluated. PVOH was mixed with an NFC fiber suspension in water followed by casting. Transmission electron microscopy (TEM) images, as well as the optical transparency of the films, revealed that the NFC fibers dispersed well in the resulting PVOH/NFC nanocomposites. Adding NFC increased the tensile modulus of the PVOH/NFC nanocomposites nearly threefold. Differential scanning calorimetry (DSC) analysis showed that the NFC served as a nucleating agent, promoting the early onset of crystallization. However, high NFC content also led to greater thermal degradation of the PVOH matrix. PVOH/NFC nanocomposites were sensitive to moisture content and dynamic mechanical analysis (DMA) tests showed that, at room temperature, the storage modulus increased with decreasing moisture content. The solubility of CO₂ in the PVOH/NFC nanocomposites depended on their moisture content and decreased with the addition of NFC. Moreover, the desorption diffusivity increased as more NFC was added. Finally, the foaming behavior of the PVOH/NFC nanocomposites was studied using CO₂ and/or water as the physical foaming agent(s) in a batch foaming process. Only samples with a high moisture content were able to foam with CO₂. Furthermore, the PVOH/NFC nanocomposites exhibited finer and more anisotropic cell morphologies than the neat PVOH films. In the absence of moisture, no foaming was observed in the CO₂-saturated neat PVOH or PVOH/NFC nanocomposite samples.     

Preparation and Characterization of Blend Films of Poly(Vinyl Alcohol) and Sodium Alginate

Blend films of poly(vinyl alcohol) (PVA) and sodium alginate (NaAlg) were prepared by casting from aqueous solutions. This blend films were characterized by tensile strength test, Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The miscibility in the blends of PVA and NaAlg was established on the basis of the thermal analysis results. DSC showed that the blends possessed single, composition‐dependent glass transition temperatures (T_gs), indicating that the blends are miscible. FT‐IR studies indicate that there is the intermolecular hydrogen bonding interactions, i.e. –OH…^?OOC– in PVA/NaAlg blends. The blend films also exhibited the higher thermal stability and their mechanical properties improved compared to those of homopolymers.     

Miscibility-structure-property correlation in blends of ethylene vinyl alcohol copolymer and polyamide 6/66

Blends of ethylene vinyl alcohol (EVOH; 44 mol% ethylene) and polyamide 6/66 (PA; 75 mol% PA 6) random copolymers were studied in the entire composition range. Specific interaction between the components was analyzed by IR spectroscopy; furthermore, coefficients related to the Flory-Huggins interaction parameter were derived from equilibrium water uptake and tensile strength. Morphology of the blends was investigated by thermal analysis (DSC), density measurements, and SEM micrographs. The two polymers form heterogeneous blends in each composition. Although the components crystallize in separate phases, the morphology and the mechanical properties are greatly affected by the association of OH and NH groups. Crystallization is restricted in the blends, and the increase of the amorphous fraction, as well as specific interaction between the components, results in essential improvement in the mechanical properties.     

Poly(ethylene-co-vinyl alcohol) and poly(methyl methacrylate) blends: Phase behavior and morphology

In this work blends of poly(ethylene-co-vinyl alcohol) (EVOH) with different ethylene contents (27, 32, 38 and 44 mol%) and poly(methyl methacrylate) (PMMA) were prepared by mechanical mixing in the melted state. The miscibility and melting behavior as a function of blend composition and the ethylene content in EVOH copolymers were investigated by means of differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The morphology of the cryofractured surfaces was examined by scanning electron microscopy (SEM). DSC and DMTA data show that EVOH/PMMA blends are immiscible, independent of EVOH and blend composition. The SEM analysis in agreement with DMTA analysis indicates that the morphology of phases depends on the blend composition, with phase inversion occurring as the concentration of one or other polymer component increases. However, the copolymer composition apparently does not affect the domain size distribution for blends containing 20 wt% of EVOH or 20 wt% of PMMA. A better phase adhesion is observed mainly for blends with 50 wt% of each polymer component.     

Interfacial interaction and morphology of EVOH and ionomer blends by scanning thermal microscopy and its correlation with barrier characteristics

In a blend, the interfacial interaction between the component phases can be effectively utilized to bring about homogeneous mixing and unique performances. While in conventional blends, preserving the morphology of the melt mixed state is unfeasible because of the strong thermodynamic tendency of the components to phase separate, herein, we report the intermolecular interaction of two hydrogen bonded polymers such as a barrier polymer poly(ethylene-co-vinyl alcohol) (EVOH) with an ionic polymer in their blends, which work symbiotically to achieve the desirable characteristics. We demonstrate the creation of a unique ellipsoid microfibrilliar morphology and melt exfoliation of one polymer in the blends through intermolecular interaction and achieve high oxygen barrier characteristics. Scanning thermal microscopy and scanning electron microscopy investigations confirm the presence of such unique morphology. The interfacial interaction and formation of interphase was evident from the local thermal analysis results combined with photoacoustic Fourier transform infrared spectroscopy (PA-FTIR). PA-FTIR confirms the chemical nature of the interaction, while the differential scanning calorimetry results indicate modification of the EVOH phase by the ionomer. The shift of Tg and broadening of the tan delta curve is evident from dynamic mechanical analysis confirming the interaction of the blend components. The blend B(60) with microfibrillar morphology shows fourfold drop in oxygen permeability indicating the role of interfacial interaction and desired morphology.     

Recent Updates on the Barrier Properties of Ethylene Vinyl Alcohol Copolymer (EVOH): A Review

The gas barrier properties of ethylene vinyl alcohol copolymer (EVOH) against oxygen, carbon dioxide and water vapor have been widely investigated in relation to different material characteristics, environmental conditions and new processing technologies. Recently, EVOH is gaining more attention as a barrier material against other gases and organic substances such as aromas, flavors, fuels, chemicals (e.g., BTEX), and as a functional barrier, e.g., to avoid mineral oil migration. This review contains an update on permeability data of EVOH emphasizing its potential as a barrier material for new and versatile applications in food and pharmaceutical packaging, agriculture, construction, automotive, etc.     

Structural interaction and gas barrier properties of ethylene‐vinyl alcohol/tin phosphate glass composites

The strength of interaction between tin phosphate glass (PGlass) filler droplets and an ethylene‐vinyl alcohol (EVOH) matrix were investigated by image, thermal, and rheological analysis. 10% PGlass droplets in EVOH were smaller than those previously observed in maleated polypropylene. Analysis using the Fox equation showed that EVOH/97 °C T_g PGlass composites are not miscible systems. Dynamic shear and extensional rheology data of those composites exhibited a weak physical network, with relaxation times longer than that of pure EVOH at all strain rates. The tensile properties of the EVOH/10 vol % PGlass composite showed it to be more ductile and flexible than a typical polymer/inorganic filler system, supporting interaction between PGlass and EVOH sufficient to interrupt polymer–polymer hydrogen bonding. While undrawn EVOH/PGlass composite films showed increased oxygen gas permeability when compared to undrawn neat EVOH film, the drawn composite films exhibited oxygen permeability 6–7 times lower than that of neat EVOH, attributed to the presence of high aspect ratio PGlass particles after orientation. The concept of hydrogen bonding between polymer and PGlass can likely be applied to other polymers such as polyamides which possess numerous hydrogen bonding sites. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 989–998     

Melt blending of ethylene‐vinyl alcohol copolymer/clay nanocomposites: Effect of the clay type and processing conditions

Ethylene‐vinyl alcohol copolymer (EVOH)/clay nanocomposites were prepared via dynamic melt blending. The effect of the processing parameters on blends containing two clay types in different amounts was examined. The blends were characterized with a Brabender plastograph and capillary rheometer, differential scanning calorimetry, dynamic mechanical thermal analysis (DMTA), X‐ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). XRD showed advanced EVOH intercalation within the galleries, whereas TEM images indicated exfoliation, thereby complementing the XRD data. A dilution process with EVOH and clay treatment in an ultrasonic bath before melt blending did not add to the intercalation level. Different trends were observed for the EVOHs containing two different clay treatments, one claimed to be treated for EVOH and the other for amine‐cured epoxy. They reflected the differences in the amounts of the strongly interacting polymer for the two nanocomposites. Thermal analysis showed that the melting temperature, crystallization temperature, and heat of fusion of the EVOH matrix sharply decreased with both increasing clay content and processing times. Significantly higher viscosity levels were obtained for the blends in comparison with those of the neat polymer. The DMTA spectra showed higher glass‐transition temperatures for the nanocomposites in comparison with those of the neat EVOH. However, at high clay loadings, the glass‐transition temperature remained constant, presumably because of an adverse plasticizing effect of the low moleculared mass onium ions treating the clays. The storage modulus improved when clay treated for EVOH was used, and it deteriorated when amine‐cured epoxy clay was incorporated, except for the sonicated clay. TGA results showed significant improvements in the blends' thermal stability in comparison with that of the neat EVOH, which, according to TEM, was greater for the intercalated structures rather than for exfoliated ones. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1741–1753, 2002     

微层共挤出(PP+EVOH)/PP阻隔材料的结构与性能研究

利用微层共挤出技术制备了具有交替层状结构的(PP+EVOH)/PP复合材料,其中PP为聚丙烯,EVOH为乙烯-乙烯醇其聚物.通过扫描电子显微镜观察、气体渗透实验、差示扫描量热仪分析以及力学性能测试研究了微层共挤出复合材料的形态结构及其对复合材料气体阻隔性能、力学性能以及结晶性能的影响.研究结果表明,通过微层共挤出技术,PP层和(PP+EVOH)层沿挤出方向交替排列,EVOH在PP基体中的的分散形态由零维球形变为一维纤维状,进而演变为二维片状.这些形态导致微层共挤出材料的氮气渗透系数和断裂伸长率较普通共混物分别下降了两个数量级和提高了27倍,并且显著影响其结晶行为.当层数超过64层后,由于PP层减薄,界面增多,EVOH不仅对(PP+EVOH)层中PP相存在结晶成核作用,而且对PP层也有结晶成核作用.     

Does nanoclay addition always lead to amelioration? Dual effects of the nanoclay on the PA‐6/EVOH/SEBS ternary blends

This work presents the investigation of properties of polyamide‐6 (PA‐6)/ethylene vinyl alcohol (EVOH)/styrene‐ethylene‐butylene‐styrene (SEBS) ternary blends and related nanocomposites with nanoclays. In this way, the effect of the mixing protocol and nanoclay type on the morphology, mechanical, and rheological properties of the blends was comprehensively studied. Scanning electron microscopy (SEM) observation revealed that, for the neat ternary blends, core‐shell droplets were formed in which SEBS droplets were encapsulated by EVOH phase in the PA‐6 matrix. In this regard, experimental observations were compared and discussed with the predictions of phenomenological models. According to the X‐ray diffraction analysis, the distribution and degree of dispersion of the nanoclays were significantly influenced by mixing protocol. It was demonstrated that competition between the intrinsic effect of the nanoclay on the physical properties and its inhibiting effect on the interactions between PA‐6 and EVOH phases led to some interesting observations for the rheological and mechanical properties of the ternary blends. The results revealed that optimum properties could be obtained by selecting appropriate nanoclay and mixing protocol.     

Grafting of polycaprolactone onto poly(ethylene‐co‐vinyl alcohol) and application to polyethylene‐based bioerodable blends

Poly(ethylene‐co‐vinyl acetate) (EVA) powders containing 10 and 20 wt % of vinyl acetate (VAc) units was saponified in ethanol/KOH solution in a heterogeneous manner. Intermolecular interaction between vinyl alcohol(VOH) units in the produced poly(ethylene‐co‐vinyl alcohol) (EVOH) promoted the crystallization of intervening segments composed of ethylene units. Ring opening polymerization of caprolactone (CL) in the presence of EVOH gave EVOH‐g‐PCL graft copolymers with relatively short chain branches. Even though the graft copolymerization was carried out in a homogeneous solution, all the VOH units were not equally reactive for the PCL grafting. And the unreacted VOH units decreased very slowly with the graft copolymerization time. EVOH‐g‐PCL decreased the domain size of the dispersed phase in low density polyethylene (PE)/biodegradable master batch (MB) blends, and thus increased their tensile properties significantly. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2561–2569, 2002     

Preparation and Properties of Poly（vinyl alcohol）/Chitosan Blend Bio-nanocomposites Reinforced by Cellulose Nanocrystals

The aim of this paper is to report the effect of the addition of cellulose nanocrystals（CNCs） on the mechanical, thermal and barrier properties of poly（vinyl alcohol）/chitosan（PVA/Cs） bio-nanocomposites films prepared through the solvent casting process. The characterizations of PVA/Cs/CNCs films were carried out in terms of X-ray diffraction（XRD）, transmission electron microscopy（TEM）, scanning electron microscopy（SEM）, thermogravimetric analysis（TGA and DTG）, oxygen transmission rate（OTR）, and tensile tests. TEM and SEM results showed that at low loading levels, CNCs were dispersed homogenously in the PVA/Cs matrix. The tensile strength and modulus in films increased from 55.1 MPa to 98.4 MPa and from 395 MPa to 690 MPa respectively, when CNCs content went from 0 wt% to 1.0 wt%. The thermal stability and oxygen barrier properties of PVA/Cs matrix were best enhanced at 1.0 wt% of CNCs loading. The enhanced properties attained by incorporating CNCs can be beneficial in various applications.