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Anhui Liwei Chemical Co., Limited.

EVOH para embalagens flexíveis de alimentos em geral

    • Nome do produto: EVOH para embalagens flexíveis de alimentos em geral
    • Site da Factroy: Lingwu, Yinchuan, Ningxia, China
    • Consulta de preço: sales2@liwei-chem.com
    • Fabricante: Anhui Liwei Chemical Co., Limited.
    • Contacte Agora
    Especificações
    Código SH 686205
    Densidade 1,13 g /cm3 dependendo do teor de etileno
    Ponto De Fusão Aprox. 160 190 ° C dependendo do grau
    Barreira De Oxigênio Excelente; taxa de transmissão de oxigénio muito baixa, normalmente <1 cm3 · mm /m2 · dia · atm em condições secas
    Barreira De Aroma Excelente retenção de sabores alimentares e prevenção da permeação do aroma
    Transparência Alta clareza e brilho para visibilidade do produto
    Resistência à Tracção Alta resistência à tração adequada para filmes de embalagem
    Alongamento Na Ruptura Bom alongamento, proporcionando flexibilidade e absorção de impacto
    Resistência à Punção Boa resistência a furos e rachaduras flexíveis
    Resistência A óleo E Graxa Excelente resistência a óleos, gorduras e graxas
    Resistência Química Resistente à maioria dos solventes, ácidos e álcalis
    Termoformabilidade Adequado para termoformagem e embalagem de desenho profundo
    Resistência Ao Calor Estável sob condições de processamento de enchimento a quente e retorta
    Processabilidade Compatível com processos de coextrusão, revestimento por extrusão e laminação
    Sensibilidade à Umidade O desempenho da barreira de oxigênio reduz com o aumento da umidade; requer camadas externas protetoras de umidade

    Como fábrica acreditada EVOH para embalagens flexíveis de alimentos em geral, aplicamos protocolos de qualidade rigorosos – cada lote passa por testes rigorosos para garantir padrões de eficácia e segurança consistentes.

    Embalagem e armazenamento
    Embalagem Resina de copolímero de etileno-álcool vinílico (EVOH) em sacos selados de 25 kg para aplicações gerais de embalagens flexíveis de alimentos.
    Carga de contêiner (20' FCL) Resina EVOH embalada em sacos de 25 kg, paletizada e carregada em recipiente FCL de 20 para transporte seguro.
    Envio EVOH para navios de embalagem de alimentos como pelotas de resina sensíveis à umidade em recipientes selados de qualidade alimentar ou sacos forrados. Proteja da umidade e contaminação; armazene seco à temperatura ambiente. Use recipientes ou caminhões limpos e secos, evite a exposição direta aos raios UV e siga os protocolos padrão de manuseio de produtos químicos para preservar o desempenho da barreira.
    Armazenamento Armazene o EVOH em uma área fria, seca e bem ventilada, longe da luz solar direta e fontes de calor. Mantenha a embalagem original selada para evitar a absorção de umidade, pois o EVOH é higroscópico. Evite alta umidade e mudanças drásticas de temperatura. Use dentro da vida útil recomendada e siga as práticas de manuseio de materiais em contato com alimentos para manter a qualidade e a segurança.
    Prazo de validade Armazene na embalagem original selada em local fresco e seco. A vida útil típica é de 12 meses a partir da data de fabricação.
    Aplicação de EVOH para embalagens flexíveis de alimentos em geral
    Five-layer cast coextrusion dominates barrier web production for vacuum skin packaging of case-ready red meat and sliced cured meats. A 90 mm skin extruder, two 35 mm tie extruders, and a 45 mm EVOH extruder feed a five-layer feedblock with the barrier layer positioned as the third layer. For this application the EVOH is typically a 32 mol% ethylene copolymer with a melt flow rate of 1.6–3.2 g/10 min at 210 °C, 2.16 kg, per ISO 1133-1:2022. The EVOH core is kept at 3–5 µm in a total web of 90–150 µm, with tie-resin layers at 2–3 µm per side. Melt temperature at the barrier extruder is limited to 210–225 °C, while the feedblock and die are held at 220–225 °C. Barrel settings above 230 °C initiate thermal degradation that appears as cross-linked gel particles and layer instability at the die lip. Oxygen transmission rate for the finished structure is specified at or below 2.0 cm³/(m²·day·atm) at 23 °C and 65 % RH, measured according to ASTM D3985-17; at 0 % RH the same EVOH layer typically drops below 0.2 cm³/(m²·day·atm). Water vapour transmission rate is controlled mainly by the polyolefin skins and is commonly verified at 38 °C, 90 % RH under ASTM F1249-20. The sealant skin is often an ethylene-vinyl acetate copolymer or an ionomer to allow skin adhesion to the tray flange without destroying the barrier core. In EU food-contact terms the multilayer is assessed under Commission Regulation EU 10/2011/EC Annex I with an overall migration limit of 10 mg/dm²; in the United States the EVOH layer is generally supplied under 21 CFR 177.1350 coverage, with the surface and adhesive layers cleared separately. On production lines the main interdependency is viscosimetric: if the tie resin MFR deviates from the EVOH grade by more than about 2 g/10 min at the same test conditions, the resulting interfacial shear produces wavy layer distribution rather than a continuous core. Because vacuum skin package forming occurs at 120–160 °C film surface temperature, the EVOH core must remain solid while the sealant skin softens, placing an upper practical limit on total film thickness.
    ParameterStandardRelevant condition for EVOH multilayer
    Oxygen transmission rateASTM D3985-17 /ISO 15105-2:200323 °C, 0 % RH and 65 % RH
    Water vapour transmission rateASTM F1249-2038 °C, 90 % RH
    Melt flow rate of EVOHISO 1133-1:2022210 °C, 2.16 kg or 5.0 kg
    Tensile properties of filmASTM D882-18Machine and transverse direction, 500 mm/min
    Heat seal strengthASTM F2029-16Sealing dwell 0.5 s, variable pressure

    What Limits Barrier Recovery After Steam Retort Processing?

    Transparent retort pouches in which an EVOH layer replaces aluminum foil are built as PA/EVOH/CPP or PET/EVOH/CPP adhesive laminates, and the controlling process parameter is not the extrusion condition but the moisture history. A retort cycle at 121 °C for 30 min in a steam/air overpressure vessel at 1.8–2.5 bar forces water into the polyamide or polyester outer layers and ultimately into the EVOH interlayer. Dry EVOH at 0 % RH can provide oxygen transmission below 0.1 cm³/(m²·day·atm); at 90 % RH the same film commonly loses more than one order of magnitude in oxygen barrier. Because retorted food is sealed with headspace saturated at high relative humidity, the EVOH cannot dry back during storage. Post-retort oxygen transmission is therefore specified at 23 °C, 90 % RH under ASTM D3985-17, and the barrier layer is thickened to 8–12 µm or the formulation is shifted to a higher ethylene content to limit plasticization. Where adhesion must survive the same thermal excursion, a maleic anhydride-grafted polypropylene tie layer is selected instead of an EVA-based tie. Delamination resistance is usually checked as seal or bond strength under ASTM F88/F88M-21 before and after retort. Regulatory assessment under EU 10/2011/EC for this application requires migration testing on the retorted article, not on the pre-retort film, because thermal history can change surface concentration. The limitation in production is that EVOH barrier recovery cannot be specified on dry film alone; an incoming QC value at 65 % RH will underpredict the actual oxygen ingress in a high-moisture retort pouch if the pouch is not conditioned and tested under the intended storage humidity.For high-speed tray lidding lines running 80–120 packs/min, the barrier web is typically a printed PET outer layer adhesive-laminated to a three-layer or five-layer EVOH coextruded film carrying an EVA peelable sealant. The EVOH layer in the coextruded core is held at 4–6 µm, while the sealant film is 20–30 µm and the outer PET is 12–23 µm. A solventless or solvent-based polyurethane laminating adhesive at 1.8–2.5 g/m² is used, and the laminate requires 3–7 days of curing at 35–45 °C before slitting. The lidding web is designed for modified atmosphere trays with residual oxygen below 1.0 %; oxygen transmission rate of the laminate is specified below 1.0 cm³/(m²·day·atm) at 23 °C, 50 % RH, per ASTM D3985-17, though the value must be verified after laminate curing because residual adhesive can depress barrier values. Seal initiation temperature is set at 85–105 °C to allow peelable opening without tearing the EVOH core. The terminal use is a lidding film for fresh pasta, processed meat trays, or ready-meal bowls under gas flush. Compliance is established under EU 10/2011/EC with migration tested in contact simulants for the sealant side and, where reverse-printed outer surfaces are not direct food contact, the functional barrier concept may apply. In the United States the EVOH layer is supplied under 21 CFR 177.1350, while the EVA sealant and PET outer layer have separate clearances. A known process fault is tunnel formation after lamination when the EVA sealant film contains slip or antiblock migration to the surface; corona treatment is therefore kept above 42 dyn/cm before lamination to ensure adhesive wet-out.

    Stand-Up Pouch Core Layer and Tie-Resin Interlocking Morphology

    Seven-layer coextruded films for stand-up pouches place the EVOH core between two polyamide layers to suppress flex-crack propagation. A common arrangement is PE/tie/PA/EVOH/PA/tie/PE. Blown film coextrusion is run at a blow-up ratio of 2.0–2.5, a die gap of 1.0–1.6 mm, and a frost line height of 0.8–1.2 m, with the EVOH melt at 210–225 °C. The EVOH layer is maintained at 5–8 µm in a total structure of 70–120 µm, while each PA layer is 8–12 µm and each tie layer is 2–3 µm. The tie-resin choice directly controls interlayer adhesion and pouch drop resistance; a maleic anhydride-grafted polyethylene tie with a melt index of 1.0–2.0 g/10 min at 190 °C, 2.16 kg, is typical. If the tie layer is reduced below 2 µm, adhesion after orientation and pouch forming can fall below 4 N/15 mm in a 90° peel test under ASTM F88/F88M-21. Oxygen transmission of the intact film is commonly below 1.0 cm³/(m²·day·atm) at 23 °C, 65 % RH, per ASTM D3985-17, but flex-crack testing under ASTM F392-20 is required to verify that oxygen barrier remains above target after 50–100 flex cycles. The terminal package is a retort- or hot-fill stand-up pouch for sauces, liquid condiments, and high-water-activity ready meals. Compliance relies on EU 10/2011/EC overall migration testing in aqueous and fatty simulants and on 21 CFR 177.1350 for the EVOH layer. Because the inner PE skin is the food-contact surface, EVOH does not require direct food-contact clearance in this configuration; however, the tie and polyamide layers must be assessed for non-intentionally added substances through the laminate's migration profile.

    If EVOH Replaces PVDC in Bag-in-Box Wine Liners

    Where a bag-in-box liner is converted from PVDC to EVOH, the design must account for the increase in oxygen permeability at high relative humidity and the absence of chlorinated-material disposal constraints. A typical blown film structure places the EVOH core between two metallocene LLDPE skins: mLLDPE/tie/EVOH/tie/mLLDPE at 60–90 µm total thickness, with EVOH at 4–8 µm and tie layers at 2–3 µm. The film is produced on a three-layer or five-layer blown line at a melt temperature of 210–225 °C for EVOH and a blow-up ratio of 1.8–2.4 to preserve machine-direction and transverse-direction impact strength. The oxygen transmission target for wine liners is commonly set between 0.5–1.0 cm³/(m²·day·atm) at 23 °C, 65 % RH, measured under ASTM D3985-17, but this single point is insufficient: the inner surface sees liquid or saturated vapour, so a qualification test at 90 % RH and 23 °C is also required. Compared with a PVDC-coated polyester or PVDC latex layer, EVOH loses more barrier in the plasticized state, and the compensation is usually a thicker EVOH layer or the use of a 44 mol% ethylene grade rather than a lower-ethylene grade. The terminal product is a 1.5–20 L bag-in-box liner for still wine, where collapse fatigue and flex-crack resistance are verified under ASTM F392-20 before oxygen barrier qualification. In production, bubble stability at 1.8–2.4 BUR is the main processing bottleneck because the EVOH layer solidifies at a higher temperature than the mLLDPE skins, causing frost-line oscillation if cooling-air temperature varies by more than 2–3 °C. EU compliance is under EU 10/2011/EC Annex I overall migration; U.S. clearance for EVOH is 21 CFR 177.1350, while the mLLDPE skin is covered separately. For wine contact, organoleptic testing is typically required because EVOH can sorb aroma compounds if the barrier layer is breached or if tie-layer coverage is incomplete.

    Shredded Cheese FFS Webs Demand Transverse Seal Integrity

    Shredded cheese packaging uses a five-layer blown film with mLLDPE skin layers and an EVOH core to maintain residual oxygen below 0.5–1.0 % in the nitrogen-flushed headspace. The EVOH layer is kept at 3–5 µm; the sealant skin is 20–30 µm mLLDPE with a seal initiation temperature of 85–100 °C; the outer skin is 20–30 µm LLDPE or mLLDPE. The film is produced on a five-layer blown line with the EVOH extruder at 210–225 °C, die gap 1.2–1.8 mm, and blow-up ratio 2.2–2.8. The oxygen transmission rate of the finished film is specified below 1.0 cm³/(m²·day·atm) at 23 °C, 65 % RH, per ASTM D3985-17; at freezer temperatures the oxygen ingress is lower, but the package must maintain barrier during refrigerated distribution at 4–7 °C. Horizontal form-fill-seal lines run at 60–120 bags/min, and the sealant must achieve 3–5 N/15 mm hot tack strength while the film is still under draw. Sealant failure occurs if the mLLDPE skin is downgauged below 15 µm or if the EVOH layer is placed too close to the seal, causing stiffening and incomplete caulking at the transverse seal. The terminal pack is a pillow bag for retail shredded mozzarella, cheddar, and blended cheese. EU food-contact assessment is performed under EU 10/2011/EC with the mLLDPE food-contact layer tested for overall migration; EVOH is supplied under 21 CFR 177.1350. Process control is critical at the transverse seal intersections where four film layers are sealed through the EVOH-containing web; seal pressure above 3.5 bar can induce microcracks in the barrier layer, which are detected as a sharp increase in oxygen transmission after drop testing.
    Cotação Grátis

    Competitive EVOH para embalagens flexíveis de alimentos em geral preços que se encaixam no seu orçamento — termos flexíveis e orçamentos personalizados para cada encomenda.

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    Telefone: +8615380400285

    E-mail: sales2@liwei-chem.com

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    Certificação e Conformidade
    Mais Introdução

    EVOH for general food flexible packaging is a semi-crystalline melt-processable barrier resin with ethylene contents between 27 mol% and 44 mol% in most commercial extrusion grades. The balance is vinyl alcohol, which forms a dense hydrogen-bonded network responsible for oxygen permeability values below 1.0 cm³·20 μm/m²·day·atm at 23 °C and 0% RH when measured under ASTM D3985. Commercial grades are produced by saponification of ethylene-vinyl acetate copolymers and are supplied as pellets with density from 1.12 g/cm³ to 1.21 g/cm³ under ISO 1183. Melt flow rate ranges from 1.6 g/10 min to 14 g/10 min at 190 °C, 2.16 kg under ISO 1133-1:2022. In a flexible package, EVOH is not used as a skin layer; it is buried between polyolefin skins or between polyamide and sealant layers because direct exposure to liquid water or high humidity reduces barrier performance.

    Barrier performance in desiccated conditions is governed by ethylene content. Lower ethylene grades provide the lowest oxygen transmission rate, while higher ethylene grades offer broader thermoforming windows, greater flex-crack resistance, and lower moisture sensitivity at the expense of a higher oxygen transmission rate. The resin is commercially available under trade designations such as EVAL and Soarnol, with extrusion-grade families including F, H, E, J, DT, DC, and A. Grade selection for a specific film structure is made by matching the ethylene content and melt flow rate to the coextrusion line configuration and the shelf-life target of the food category.

    Why does relative humidity govern the oxygen barrier of EVOH?

    In desiccated conditions, the hydroxyl groups in EVOH form interchain hydrogen bonds that reduce free volume and restrict oxygen diffusion. Water molecules absorbed from the package interior or from the outside environment act as plasticisers and disrupt that network. For a 32 mol% ethylene grade, the oxygen transmission rate at 85% RH is commonly reported to be 10–20 times the 0% RH value. Water vapour transmission rate measured under ASTM F1249 at 38 °C, 90% RH may exceed 20 g·20 μm/m²·day, so EVOH alone is not a moisture barrier.

    Moisture uptake is not uniform across the layer thickness. In a lidding film, the EVOH layer is placed at the centre of the structure, with 20–30 μm of polyethylene or polypropylene on each side. These outer layers delay water ingress, but they do not eliminate it. Tie layers of anhydride-modified polyolefin, typically 2–3 μm thick, are required between EVOH and nonpolar skins because interfacial adhesion between EVOH and polyethylene is insufficient for flexing, retort, and thermoforming stresses. The tie layer must be selected for low moisture carry-over and for chemical compatibility with EVOH; maleic-anhydride-functionalised LLDPE or PP is used depending on the skin resin.

    High-barrier flexible packaging that must function above 85% RH may use higher-ethylene EVOH grades, thicker EVOH layers, or a secondary barrier layer such as polyvinylidene chloride or MXD6. When the application requires long shelf life in high-humidity distribution, oxygen transmission testing should be conducted at 90% RH using ASTM F1927 rather than at 0% RH because the desiccated value can understate package oxygen ingress. Specimens are conditioned at 23 °C and 90% RH for at least 48 h before testing because oxygen transmission changes with moisture uptake.

    When EVOH passes through a three-layer blown-film die, processing limits apply

    On coextrusion lines with a 45 mm barrier-layer extruder and 24:1 L/D single screw, EVOH should enter the die at 220–240 °C. Barrel set points above 250 °C have been associated with acetic acid generation, amber gel formation, and die-lip deposits that require purging with low-density polyethylene. Pre-drying at 80 °C for 4–8 h is applied when ambient relative humidity exceeds 60%; target moisture content below 0.01% is verified before processing. The polymer should not be exposed to equipment previously used for polyvinyl chloride or polyvinylidene chloride without thorough purging because decomposition products catalyse EVOH degradation.

    Batch-to-batch variation in melt flow rate of approximately ±0.5 g/10 min around a nominal 3.2 g/10 min grade affects thickness uniformity in a 5 μm layer when the barrier extruder is operated near its lower output limit. Production-scale cast coextrusion experience shows that melt pressure fluctuations above ±5 bar can produce visible layer thickness variation in the EVOH layer, and the resulting thin spots control oxygen transmission. For this reason, barrier-layer thickness is specified as a minimum, not an average. Multilayer dies with dedicated barrier-layer flow channels and independently controlled barrier extruders are used to maintain layer distribution across web widths up to 1,600 mm.

    EVOH should not be compounded with amine-based additives or certain amine-rich polyamide regrinds unless bounded by tie layers, because amine terminal groups can promote yellowing and gel formation at processing temperatures. Direct contact with high-acidity sealants can also accelerate degradation; the packaging structure should isolate EVOH from acidic components with intact tie layers. During line stoppages, EVOH left in an idle heated barrel above 200 °C for more than 30 min may crosslink, so purging with low-density polyethylene or a dedicated purging compound is required.

    The specification table below reports values obtained under desiccated conditions

    The following commercial grades are representative of flexible packaging extrusion. Values are drawn from public supplier literature and should be confirmed against current datasheets because grade specifications are revised. OTR values refer to a 20 μm film at 20 °C, 0% RH and are not package values.

    Representative commercial EVOH grades and typical technical data from supplier literature
    Commercial gradeEthylene content (mol%)Melt flow rate at 190 °C, 2.16 kg (g/10 min, ISO 1133-1:2022)Density (g/cm³, ISO 1183)Melting point (°C, ISO 11357-3)OTR at 20 °C, 0% RH, 20 μm (cm³/m²·day·atm, ASTM D3985)
    EVAL F101B321.61.191830.4
    EVAL H171B381.71.171750.8
    EVAL E105B445.51.141651.5
    Soarnol DC3203323.21.191830.4
    Soarnol A441244121.141651.5

    Grade selection follows the processing method. Low-melt-flow grades such as F101B are used in cast film and blown film where high melt strength is required. Medium-melt-flow grades such as DC3203 are chosen for thin layers where extrusion pressure must be controlled. High-ethylene grades such as E105B and A4412 are used in thermoforming, retort pouches, and high-moisture packaging because they retain more of their barrier after steam exposure and flexing. The trade-off is that oxygen transmission rate for 44 mol% ethylene can be more than 3 times the 32 mol% value at 0% RH; therefore, higher-ethylene grades may require a thicker barrier layer to deliver the same shelf life.

    Form-fill-seal lidding films for processed meat, cheese, and ready meals often employ a structure of 20–30 μm LLDPE sealant, 2–3 μm anhydride-modified tie resin, 3–5 μm EVOH, 2–3 μm tie resin, and 12–20 μm biaxially oriented polyester or cast polypropylene print web. The EVOH layer is positioned near the centre of the structure so that polyolefin skins delay moisture ingress. Oxygen transmission rates below 2.0 cm³/m²·day·atm at 23 °C, 50% RH are typical for the complete laminate when the EVOH layer is 5 μm thick. For modified-atmosphere packaging, the same barrier layer maintains headspace gas composition against ingress from ambient air; carbon dioxide transmission rate data are required for package shelf-life calculations and can be measured using ASTM F2476. Published data for carbon dioxide transmission rate in high-humidity EVOH structures are more limited than oxygen data, so package-specific testing is required.

    For hot-filled and retort applications, grades with ethylene content of 38–44 mol% are preferred because they retain more barrier after exposure to steam at 121 °C for 30 min. Even then, oxygen transmission rate can increase by a factor of 2–5 after retorting, so post-retort barrier testing according to ASTM D3985 at 90% RH is used to define the minimum EVOH layer thickness. In pouches, the typical EVOH layer is 5–7 μm; below 3 μm, defects from die lines and layer encapsulation variability dominate oxygen transmission. For dry snacks and cereals, a 3 μm EVOH layer may be sufficient because the package interior remains below 50% RH.

    Regulatory status for food contact is grade-specific. In the European Union, EVOH is evaluated under Regulation (EU) No 10/2011 through the substances used in its manufacture; converters must verify migration of ethylene, vinyl alcohol, and residual saponification by-products against the applicable migration limits. In the United States, individual EVOH grades may be covered by Food Contact Notifications, and compliance statements in supplier documentation should identify the grade, the authorised food types, and the maximum use temperature. Supplier statements should also identify registration obligations under REACH for the monomer substances used in manufacture.

    When EVOH is compared with polyvinylidene chloride, the selection criterion is not simply desiccated oxygen transmission rate but the ratio of oxygen barrier retention to moisture sensitivity. The table below summarises oxygen transmission rate and water vapour transmission rate ranges from public supplier literature and standard test methods.

    Comparative barrier properties of flexible packaging materials
    MaterialOTR at 23 °C, 0% RH, 20 μm (cm³/m²·day·atm)WVTR at 38 °C, 90% RH, 20 μm (g/m²·day)Moisture sensitivity
    EVOH, 32 mol% ethylene0.3–0.620–50High
    EVOH, 44 mol% ethylene1.2–2.015–40Moderate
    PVDC copolymer0.5–2.01–3Low
    PA615–3080–150Moderate
    MXD62–510–30Moderate
    Aluminium foil 9 μm<0.01<0.01Negligible

    Polyvinylidene chloride retains its oxygen barrier at high relative humidity and provides a lower water vapour transmission rate, typically 1–3 g·20 μm/m²·day at 38 °C, 90% RH under ASTM F1249, but it is thermally less stable during extrusion and may release hydrogen chloride if overheated. Polyamide 6 has oxygen transmission rate roughly 15–30 cm³·20 μm/m²·day·atm at 23 °C, 0% RH; its toughness and thermoforming performance are superior, but its oxygen barrier is insufficient as a single high-barrier layer in long-shelf-life processed meat packaging. MXD6, a poly(m-xylylene adipamide), offers oxygen transmission rate between 2 cm³·20 μm/m²·day·atm and 5 cm³·20 μm/m²·day·atm under desiccated conditions and better retention during retorting, but it is more expensive than EVOH for equivalent oxygen barrier in dry conditions. Aluminium foil below 0.01 cm³/m²·day·atm remains the only practical absolute barrier, but it is opaque, cannot be microwaved, and introduces pinholing risk after flexing; EVOH is selected when transparency, microwaveability, and chlorine-free incineration are required.

    Unplasticised polyvinyl alcohol has lower oxygen transmission in completely desiccated conditions, but it is water-soluble and cannot be melt-processed into a flexible packaging layer without severe plasticisation. EVOH is distinguished by the insertion of ethylene units into the vinyl alcohol chain, which restores melt processability at the cost of a higher oxygen transmission rate. The ethylene content is therefore a direct specification variable that sets the boundary between processability and barrier performance. For packages requiring oxygen transmission below 0.01 cm³/m²·day·atm, aluminium foil or metal oxide barrier coatings remain necessary.

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