How to bond Ethylene-Vinyl Acetate Copolymer (EVA)

The properties of ethylene-vinyl acetate copolymer vary primarily depending on the level of vinyl acetate in the copolymer. At lower levels of vinyl acetate, the copolymer is a thermoplastic with properties similar to low-density polyethylene. As the vinyl acetate content increases, the copolymer exhibits characteristics of a thermoplastic elastomer until the crystallinity drops to a point where the copolymer becomes a soft rubber-like material with minimal physical strength. Copolymers with high vinyl acetate content are primarily used as components in adhesives and coatings, but they can be vulcanized to achieve useful physical properties. Increasing the vinyl acetate content enhances the polymer’s flexibility, toughness, solubility in organic solvents, and clarity. The reduced crystallinity caused by the addition of vinyl acetate contributes to good durability at lower temperatures and resistance to environmental effects such as cracking. Increased flexibility also leads to lower softening temperatures as the vinyl acetate content rises, which limits the upper application temperatures of these materials. EVA has good resistance to saltwater and bases. Some types are resistant to hydrocarbon grease, but EVA copolymers are generally soluble in a wide range of aliphatic, aromatic, and chlorinated solvents. There are also types with good resistance to UV degradation and ozone.

Ethylene-vinyl acetate copolymer (EVA) is widely used in several industries due to its versatile properties. It is used as foam for electronics protection, in industrial hoses and tubes, for shrink film in packaging, in disposable medical gloves, masks, and tubing, as well as in various applications such as adhesives, coatings, sealants, and solar cell encapsulation.

EVA copolymer is available under different trade names, including ELVAX, ESCORENE, EVAZOTE, and ULTRATHENE. These names represent various manufacturers' versions of EVA with different properties and applications.

The surface tension of EVA is generally estimated to be around 30 to 35 dyn/cm.

Bonding
Due to EVA's low surface tension and thermoplastic nature, it may be beneficial to pretreat the surface with a primer or consider corona or plasma treatment. These methods can help increase surface adhesion and improve bond strength, especially for demanding applications.

When working with EVA and preparing it for bonding or other uses, it is important to clean the surface thoroughly with a non-residue cleaner.

Choose an adhesive compatible with EVA’s thermoplastic nature:

• Cyanoacrylate adhesive can be used to bond EVA. It cures quickly and generally has strong bonding properties on various materials.
• Methyl methacrylate adhesive (also known as MMA adhesive) is a type of adhesive that can be used for bonding EVA. MMA adhesives are known for their strong and flexible bonds on various materials, including some plastics.
• Hot melt adhesives adhere very well to EVA. Many types of hot melt adhesives exist, and some are EVA-based. These provide good results, such as PO hot melt, which has good adhesion.

Allow the EVA adhesive to cure as per the manufacturer’s instructions.

After curing, it is important to test the bond to ensure it meets the strength and durability requirements for the specific application.

Manufacturers
These trade names represent various EVA producers, each with specific product ranges and industrial applications:

ELVAX: Produced by DuPont.
ESCORENE: Produced by ExxonMobil Chemical.
EVAZOTE: Produced by B.P. Chemicals.
ULTRATHENE: Produced by Quantum Chemicals.

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