Ethylene-vinyl acetate, commonly known as EVA, is a versatile plastic used across many industries. It is a copolymer, formed from two different basic units, or monomers, through polymerization. Valued for its unique properties, EVA is prevalent in numerous products, from consumer goods to specialized industrial components.
Chemical Composition
EVA is a copolymer of ethylene and vinyl acetate. Its characteristics are heavily influenced by the proportion of vinyl acetate (VA) incorporated, which typically ranges from 10% to 50%. This variable ratio allows for different types of EVA copolymers, each tailored for specific uses.
A higher percentage of VA generally results in a softer, more flexible, and more elastic material, similar to rubber. Conversely, a lower VA content makes the material behave more like low-density polyethylene, with increased stiffness. Adjusting the VA content impacts its adhesion, clarity, and overall performance. For example, EVA with about 11% VA content is often used for hot-melt adhesives.
Key Characteristics
EVA possesses a set of physical and chemical attributes. It is flexible and soft, providing a rubber-like feel, and maintains this flexibility even at low temperatures. It also demonstrates good elasticity, allowing it to be molded and shaped without losing its form. EVA is durable, resistant to impact, and resists stress-cracking.
The material exhibits excellent water resistance, making it suitable for applications exposed to moisture. Depending on its formulation, EVA can also have good clarity and gloss. Many EVA formulations offer resistance to UV radiation, which contributes to its suitability for outdoor use and enhances its longevity. Its lightweight nature is an important characteristic, contributing to its popularity in products where reduced mass is beneficial.
Common Applications
EVA’s properties make it suitable for a diverse array of common applications. In footwear, EVA foam is extensively used for midsoles in athletic and casual shoes due to its lightweight nature, flexibility, and excellent shock-absorbing capabilities. This cushioning helps reduce impact on joints and provides comfort for prolonged wear, making it a preferred choice for running shoes and other high-impact footwear.
Hot-melt adhesives are another significant application. These are solid at room temperature and melt when heated to bond materials. EVA-based hot melts are widely utilized in packaging, woodworking, and automotive industries because of their fast setting time and strong adhesion to various substrates like paper, cardboard, and certain plastics. These adhesives are valued for their versatility and ability to formulate for specific bonding needs.
EVA also serves as an encapsulant film in solar panel manufacturing. This film protects solar cells from environmental factors such as moisture and UV light, ensuring the panel’s long-term performance and efficiency. Its transparency allows maximum sunlight to reach the cells, while its adhesive properties securely bond the panel components.
EVA foam is also used for sports equipment padding, including yoga mats, gym mats, and protective gear like helmets and gloves, offering cushioning, high rebound, and impact absorption. In the medical field, EVA is used in orthotics, prosthetics, and cases for sensitive medical instruments, benefiting from its flexibility, durability, and protective qualities.