Introduction To EVA Plastic: Key Properties And Applications

1. Overview of EVA Properties

Ethylene Vinyl Acetate (EVA) is a thermoplastic resin formed by the copolymerization of non-polar ethylene and highly polar vinyl acetate (VAc). EVA is a highly branched, random copolymer. Its physical, chemical, and processing properties depend mainly on the VAc content and melt flow rate (MFR). As VAc content increases, the crystallinity of EVA decreases. With moderate VAc levels, some ethylene segments still crystallize, acting as the "hard phase" in a thermoplastic elastomer (TPE).

EVA exhibits TPE characteristics because the crystallized polyethylene segments within the polymer chain provide physical cross-linking points, while the amorphous VAc segments offer elasticity. When VAc content reaches 40–50%, the polymer becomes fully amorphous, enhancing its rubber-like flexibility.

2. How VAc Content Affects EVA Performance

Increasing the VAc content enhances the copolymer's polarity, leading to noticeable changes in properties:

• Decreased: Crystallinity, hardness, softening point, rigidity, tensile strength, chemical resistance, heat deformation resistance

• Increased: Stress crack resistance, permeability, coefficient of friction, compatibility with other polymers, and printability

Higher VAc content also leads to broader molecular weight distribution, affecting melt viscosity. Long-chain entanglements cause increased elastic response, influencing flow behavior and processing performance. Understanding this viscosity/shear relationship is essential when selecting EVA grades for extrusion, molding, or blending.

3. Applications of EVA Based on VAc Content

Different VAc levels result in distinct performance profiles and applications:

• 5–20% VAc: Ideal for injection molding, extrusion, and film blowing; used for PE modification or blending with non-polar rubbers like NR, SBR, BR, EPDM

• 10–25% VAc: Used in crosslinked foamed products such as shoe soles, faux leather, and transparent soles

• >30% VAc: EVA behaves more like rubber; suitable for crosslinking with peroxides (at 40–50% VAc)

• High VAc (40–50%) + High MFR: Commonly used in hot-melt adhesives, coatings, and foaming compounds

• 60–90% VAc: Suitable for PVC modification

4. Processing Methods and End Uses

EVA can be processed through injection molding, extrusion, and blow molding. It offers excellent tensile and impact strength, making it suitable for:

• Shoe soles

• Sheets and films

• Automotive parts

• Hoses and tubing

• Wire and cable insulation

• Food-grade packaging films

5. Additional Insights

• EVA is a type of TPO (thermoplastic polyolefin elastomer), where ethylene forms the hard segment and VAc the soft segment

• EVA hardness typically ranges from 75–95A, with a density of 0.94–0.98; hardness decreases and density increases with more VAc

• EVA improves the flexibility and toughness of PE and PP when blended

• EVA-based foams can be modified with rubber or SEBS to enhance abrasion and tear resistance

• Lower VAc EVA behaves more like PE, while higher VAc grades show TPE-like elasticity

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