Technical Overview of EVOH (Ethylene Vinyl Alcohol Copolymer)

1. Basic Overview

EVOH (Ethylene Vinyl Alcohol Copolymer) is a crystalline polymer formed by the copolymerization of ethylene and vinyl alcohol. It is recognized as one of the world's three major high-barrier resins (alongside PVDC and Polyamide). It is produced through the saponification or partial saponification of ethylene-vinyl acetate copolymer (EVA) and can be considered a modified form of polyvinyl alcohol. Its ethylene content typically ranges from 20% to 45% molar content, with vinyl alcohol content between 60% and 80%.

Key Molecular Characteristic

EVOH molecular chains contain hydroxyl groups (-OH) that form a dense structure through hydrogen bonding.

● Ethylene content typically ranges from 20% to 45% mol%.

● As ethylene content increases, gas barrier performance decreases, but moisture resistance and processability improve.

2. Key Technical Properties & Advantages

Property Category	Technical Description	Specific Advantages
Excellent Gas Barrier	Gas barrier is >10x that of PVDC, ~100x higher than PA, and ~10,000x higher than PP/PE	Effectively prevents oxygen ingress, maintains food flavor and quality; effectively retains CO₂ or N₂ in gas-flushed packaging
Oil/Solvent Resistance	Extremely high resistance to most organic solvents and oils	Zero weight gain after 1-year immersion in cyclohexane, xylene, petroleum ether, benzene, and acetone at 68°F
Mechanical Properties	High mechanical strength, elasticity, and surface hardness	Typical tensile strength at break: approx. 44-49 MPa
Optical Properties	High gloss, low haze, high transparency	Films exhibit excellent optical clarity
Thermal Stability	Highest thermal stability among all commercial high-barrier resins	Processing waste is recyclable; regrind can contain >20% EVOH
Environmental Friendliness	No plasticizers; combustion produces no dioxins	Complies with FDA and EU food contact standards; safe for direct food/ pharmaceutical contact

3. Typical Property Ranges

Property	Typical Value Range	Notes
Density	1.13 – 1.21 g/cm³	Typically 1.15-1.19 g/cm³
Melt Index	0.7 – 20 g/10min	At 190°C/2.16kg
Ethylene Content	20 – 45 mol%	Common range: 38-44%; 32% is typical balance point
Melting Point	158 – 190°C	Typically 160-168°C
Tensile Strength	44 – 49 MPa	Film grade
Elongation at Break	320 – 340%	Film grade
Oxygen Transmission Rate	0.6 cm³/(m²·24h·0.1MPa)	Measured in multilayer structures
Water Vapor Transmission Rate	2.0 g/(m²·24h)	Measured in multilayer structures

4. Processing Guidelines

4.1 Basic Processing Methods

There are three primary methods for incorporating EVOH as a barrier layer in multilayer structures:

Coextrusion: Combining EVOH with polyolefins or polyamide to form multilayer structures

Film Lamination: Laminating EVOH film to other substrates or coating with other materials

Direct Coating: Using EVOH resin as a coating for various substrates or single-layer containers

4.2 EVOH-Specific Extrusion Screw Design Considerations

EVOH is a semi-crystalline thermoplastic with high melt viscosity and a narrow melting range. Special attention is required during processing:

Design Parameter	Recommended Range	Notes
Screw Diameter	Smaller diameter preferred for given output	Reduces heat exposure time, increases material flow rate, enhances self-cleaning
L/D Ratio	24-30:1, commonly 24-26:1	Too short risks poor plasticization and air entrapment
Compression Ratio	3-4:1, commonly 3:1
Feed Section Length	8-9D	Adjust based on ethylene content
Compression Section Length	6-10D
Metering Section Length	8-13D

4.3 Processing Precautions

● To prevent "gels" and carbonization, screws should feature full-flight designs and be chrome-plated

● EVOH is shear-sensitive; appropriately increasing screw speed helps reduce viscosity for better matching with other resins

● Processing temperatures should be strictly controlled to avoid melt stagnation

5. Detailed Applications by Industry

Industry Sector	Primary Applications	Key Properties Utilized
Food Packaging	• Aseptic Packaging: Liquid food packaging board • Hot-fill & Retort Pouches: High-temperature sterilization resistance • Freshness Packaging: Meat, seafood, dairy, juice • Condiment Packaging: Spicy seasonings, cooking oil • Coffee/Tea Packaging: Aroma retention	Oxygen barrier, aroma retention, extended shelf life, high-temperature resistance
Non-Food Packaging	• Household Chemicals: Cosmetics, toothpaste • Fine Chemicals: Pesticides, coatings, organic toners • Pharmaceutical Packaging: Medicines, health products • Hazardous Goods Packaging: Xylene, benzene	Organic solvent resistance, leak prevention, safety, non-toxicity
Automotive Industry	• Multilayer Plastic Fuel Tanks: 6-layer structures, EVOH ~3% • Fuel Lines: Coextruded with Nylon 12	Fuel permeation resistance, lightweighting, design flexibility
Barrier Pipes/Tubing	• Underfloor Heating Oxygen Barrier Layers: Prevents metal corrosion • Heating System Pipes: Inhibits algae/bacteria growth	Oxygen barrier, weather resistance
Other Sectors	• Agriculture: Soil fumigation films • Medical Materials: Embolism, selective permeable membranes • Textiles: Functional apparel • Polymer Modification: Resin modifier	Versatility, high performance

6. Recent Technological Developments & Trends

6.1 Humidity Resistance Improvements

Mitsubishi Chemical developed Soarnol™ RB7205B; Kuraray developed KURARISTER™ series targeting retort film applications. These effectively address delamination and whitening during retorting, with barrier properties recovering within 3-7 days.

6.2 Bio-based EVOH

Mitsubishi Chemical introduced Soarnol™ PB7104B, containing >25% bio-based content.

6.3 Recyclability Solutions

Mitsubishi Chemical developed Soaresin™ recycling aid, improving compatibility between polyolefins and EVOH to facilitate packaging material recycling.

Kuraray developed EVAL™ XEP series, designed for recyclability.

6.4 Specialized Grades

Development of grades with ethylene contents of 27%, 29%, 44% etc., tailored for specific applications.

Kuraray offers 7 EVAL™ series (M, L, F, etc.) covering automotive, thermoforming, pipe, and film applications.

7. Important Considerations

7.1 Humidity Sensitivity

EVOH is hydrophilic and hygroscopic. When it absorbs moisture, its gas barrier performance is affected. Therefore, EVOH is typically combined with high-moisture-barrier resins like polyolefins (PE/PP), sandwiching the EVOH layer in the middle of the multilayer structure.

7.2 Processing Thermal Stability

Although EVOH has high thermal stability, melt stagnation during processing must be avoided. Stagnation can lead to molecular dehydration, double bond formation, crosslinking, resulting in "gels" or even carbonization.

7.3 Compatibility with Other Resins

Incompatible with polyolefins (PE, PP): Requires a tie layer (adhesive resin) for bonding.

Good compatibility with PA6: Can be used to create blends.

Limited compatibility with PBAT: Mechanical properties may degrade at high EVOH loading.

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