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EVOH): a Review Polymer Reviews ISSN: 1558-3724 (Print) 1558-3716 (Online) Journal homepage: https://www.tandfonline.com/loi/lmsc20 Recent Updates on the Barrier Properties of Ethylene Vinyl Alcohol Copolymer (EVOH): A Review Caroline Maes, Wout Luyten, Geert Herremans, Roos Peeters, Robert Carleer & Mieke Buntinx To cite this article: Caroline Maes, Wout Luyten, Geert Herremans, Roos Peeters, Robert Carleer & Mieke Buntinx (2018) Recent Updates on the Barrier Properties of Ethylene Vinyl Alcohol Copolymer (EVOH): A Review, Polymer Reviews, 58:2, 209-246, DOI: 10.1080/15583724.2017.1394323 To link to this article: https://doi.org/10.1080/15583724.2017.1394323 © 2018 The Author(s). Published by Taylor & Accepted author version posted online: 24 Francis Group, LLC Oct 2017. Published online: 18 Jan 2018. Submit your article to this journal Article views: 3240 View related articles View Crossmark data Citing articles: 14 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=lmsc20 POLYMER REVIEWS 2018, VOL. 58, NO. 2, 209–246 https://doi.org/10.1080/15583724.2017.1394323 REVIEW Recent Updates on the Barrier Properties of Ethylene Vinyl Alcohol Copolymer (EVOH): A Review Caroline Maes a,b, Wout Luytena, Geert Herremansa, Roos Peetersb, Robert Carleerc, and Mieke Buntinxb aKuraray–Eval Europe NV, Haven 1053 Nieuwe Weg 1, Bus 10, Zwijndrecht, Belgium; bHasselt University, Packaging Technology Center IMO-IMOMEC, Wetenschapspark 27, Diepenbeek, Belgium; cHasselt University, Applied and Analytical Chemistry IMO-IMOMEC, Agoralaan Building D, Diepenbeek, Belgium ABSTRACT ARTICLE HISTORY The gas barrier properties of ethylene vinyl alcohol copolymer (EVOH) Received 26 June 2017 against oxygen, carbon dioxide and water vapor have been Accepted 15 October 2017 widely investigated in relation to different material characteristics, KEYWORDS environmental conditions and new processing technologies. Recently, Ethylene vinyl alcohol EVOH is gaining more attention as a barrier material against other gases copolymer; EVOH; and organic substances such as aromas, flavors,fuels,chemicals(e.g., permeability; barrier BTEX), and as a functional barrier, e.g., to avoid mineral oil migration. properties; functional barrier; This review contains an update on permeability data of EVOH mineral oils; (volatile) organic emphasizing its potential as a barrier material for new and versatile compounds applications in food and pharmaceutical packaging, agriculture, construction, automotive, etc. 1. Introduction Ethylene vinyl alcohol copolymer (EVOH) was first commercialized by Kuraray under the trade- mark EVALTM in 1972. The barrier properties of EVOH against oxygen had been investigated for fifteen years and were found to be valuable. After Kuraray obtained the patent in 1971, they started producing EVOH commercially. Later, NipponGohseiandChangChunalsostartedtheir – commercial production of EVOH.[1 4] Kuraray is the largest producer of EVOH. Since 2001 they have more than doubled their global production capacity from 45,000 tons to 92,000 tons in 2016 – and a further expansion of 11,000 is planned in 2018, due a continued market growth.[5 7] EVOH is a random copolymer with a semi-crystalline structure, consisting of ethylene and vinyl alcohol monomer units. The synthesis of EVOH occurs in a two-step process as shown in Fig. 1.[8,9] Vinyl alcohol is unstable and it cannot be isolated, therefore the first step is a copoly- merization reaction between ethylene and vinyl acetate, which results into the random copoly- mer ethylene vinyl acetate. In the second step polyethylene vinyl acetate is converted into EVOH through a transesterificiation with methanol and as a side product methyl acetate is produced. Nowadays, EVOH has gained worldwide recognition for its barrier properties against per- manent gases such as oxygen (O2), carbon dioxide (CO2) and nitrogen (N2). Especially its CONTACT Mieke Buntinx [email protected] Hasselt University, Packaging Technology Center IMO- IMOMEC, Martelarenlaan 42, 3500 Hasselt, Belgium. � 2018 The Author(s). Published by Taylor & Francis Group, LLC This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way. 210 C. MAES ET AL. Figure 1. Synthesis of EVOH is a two-step process: copolymerization of ethylene and vinyl acetate result- ing in polyethylene vinyl acetate (a) followed by a transesterification with methanol, which results into EVOH and methyl acetate as a side product (b). outstanding oxygen barrier has made EVOH one of the most commonly used gas barrier – materials in multilayer food packages.[9 14] EVOH can also be used in clinical and pharma- ceutical applications such as in parenteral nutrition bags and ampoules to increase shelf- life.[15] However, the applications for EVOH as an oxygen gas barrier material reach further than only food and pharma. Pipes for floor heating in the building industry, for example, contain an EVOH layer to keep oxygen out and thus preventing the oxygen from travelling to the boiler and causing corrosion.[16] In addition the radon barrier of EVOH is another application in the construction sector, where it is used to decrease radon exposure and improve the indoor air quality.[17] The excellent barrier properties of EVOH are attributed to the strong inter- and intra- molecular bonding caused by the polar hydroxyl groups present in the vinyl alcohol unit.[9,10,14] These hydroxyl groups are also responsible for the moisture sensitivity because water is easily absorbed due to the hydrophilic character of the polymer. Gradually, when more water is absorbed, EVOH will be plasticized and the inter- and intra-molecular bonds will weaken, causing a decrease in the barrier properties.[10] This plasticizing effect is the rea- son why EVOH is mainly applied in multilayer structures. This same effect is also known to occur with alcohols such as methanol and ethanol.[18] Nevertheless, even with its sensitivity to humidity, EVOH remains one of the best gas barrier materials amongst polymers.[9] More recently, there has been an increasing interest in EVOH as a barrier material against organic substances such as chemicals, hydrocarbons (e.g., mineral oils and fuel), aromas, and flavors. EVOH proved to be successful in fuel tanks to prevent fuel emission to the environ- ment, in agricultural films to improve herbicide retention and in geomembrane films to – keep the methane release from landfills in check.[19 21] EVOH can also pose as a functional barrier in food packaging as it offers good chemical resistance and prevents the migration from chemical substances out of other materials into the packaging’s content.[22] In this paper the recent findings on the barrier properties of EVOH copolymer towards different molecules are summarized and reviewed. 2. Oxygen permeability of EVOH EVOH has one of the lowest oxygen permeability coefficients amongst polymers, as shown fi in Table 1. In this review, the oxygen permeability or oxygen permeability coef cient (PO2 ) POLYMER REVIEWS 211 Table 1. Oxygen permeability (PO2 ) of commonly used polymers. Based on data from Kuraray co. Ltd. (2017)[7], McKeen (2012),[21] Lange and Wyser (2003),[54] and Lagaron et al. (2004).[24] 3 m 2 Polymer PO2 [cm . m/(m .day.atm)] PVOH 1.5 a EVOH32 6 b EVOH44 38 b PVDC 10–300 c PA 6 400–2,000 a PET 1,000–5,000 c PP 50,000–100,000 c PS 100,000–150,000 c LDPE 100,000–200,000 c HDPE 40,000–100,000 c aPermeability at 23C and 0% RH. bPermeability at 20C and 65% RH. cPermeability at 23C and 50% RH. is the thickness and pressure normalized rate at which O2 passes through a material and will 3 m 2 be expressed in cm . m/(m .day.atm), and the oxygen gas transmission rate (O2GTR) is the fi 3 2 actual amount of transmitted O2 measured for a certain package or lm in cm /(m .day. [21,23] atm) with no thickness normalization under a pressure difference of 1 atm. The PO2 of EVOH containing 32 mol% ethylene (EVOH32) and EVOH containing 44 mol% ethylene (EVOH44) measured at 20C and 65% relative humidity (RH) according to the ISO 14663-2 standard is respectively 6 and 38 cm3.mm/(m2.day.atm).[7] Poly(vinyl alcohol) (PVOH) has a lower oxygen permeability coefficient, i.e. 1.5 cm3.mm/ (m2.day.atm) at 23C and 0% RH,[24] however, this polymer is difficult to process because of its low thermal degradation point, which is about 150C, while its melting temperature is around 180–190C. Apart from this, PVOH is also soluble in water, explaining its limited use in packaging applications.[25] However, PVOH can be used as a coating on other plastics to increase the barrier properties. Other barrier polymers are poly(vinylidene dichloride) (PVDC), the polyamide nylon 6 (PA 6) and poly(ethylene terephthalate) (PET). These poly- mers have a PO2 that is 1 to 3 orders of magnitude higher than EVOH. When compared to the non-polar polymers such as low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS) the PO2 is over 3 orders of magnitude higher than EVOH.[9,26] In the following sections several factors that influence the oxygen permeability of EVOH will be discussed. These can be attributed to intrinsic factors of the material itself as well as extrinsic factors such as environmental conditions and permeant properties.[27] 2.1. Influence of material characteristics First, the intrinsic material characteristics of EVOH, including chemical structure, crystallinity, thickness, glass transition temperature and free volume that are related to the O2 barrier properties are discussed. 2.1.1. Ethylene content The structure of EVOH copolymer is key for understanding its outstanding barrier properties.
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