by What is Ethylene Vinyl Acetate?
Ethylene vinyl acetate (EVA) is a thermoplastic polymer produced by the copolymerization of ethylene and vinyl acetate monomers. Vinyl acetate is grafted onto the polyethylene backbone, introducing polar groups into what would otherwise be a nonpolar molecule. The result is a copolymer with properties that can be widely varied depending on the proportions of monomers used. EVA can contain anywhere from 10-40% vinyl acetate by weight.
Uses and Properties of EVA
Due to its flexibility and impact strength across a wide range of temperatures, EVA finds use in many applications including hot melt adhesives, footwear, medical devices, wires and cables. Some key properties and uses of EVA include:
Hot Melt Adhesives
EVA is widely used as a hot melt adhesive due to its excellent bonding strength, flexibility and resistance to water. Hot melt ethylene vinyl acetate adhesives are used to bond a variety of substrates like wood, foil, fabric and plastics. They are used in the assembly of shoes, apparel, disposable hygiene products and more.
Footwear and Soles
The soft yet durable properties of EVA make it ideally suited for use in footwear. Over 60% of athletic shoes contain EVA midsoles which provide cushioning and support. EVA content in midsoles can range from 30-100% depending on the cushioning needs. EVA is also used in footwear heels and outsoles for its resilience.
Medical Devices
In the medical field, ethylene vinyl acetate finds use in devices like ostomy bags, wound and burn dressings, medical tubing and prosthetics. Its flexibility, low toxicity and chemical resistance make it suitable for applications that involve contact with skin or wounds. EVA can be fabricated into films, foams or other forms.
Wires and Cables
EVA plays a major role as an insulating material in power cables and wires. As an insulation layer, EVA provides arc resistance, flexibility even at low temperatures, and resistance to hydrocarbons like oils. It is usually applied as a sheath over metal conductors in cable construction.
Impact Modification of Plastics
With its flexible, rubbery qualities, EVA functions well as an impact modifier when blended with more brittle polymers. Common examples include EVA modification of PVC used in piping, siding and window frames to improve toughness and flexibility at low temperatures.
Factors Affecting Ethylene Vinyl Acetate Properties
The proportion and placement of the vinyl acetate monomer in the polymer chain determines the properties of EVA. In general:
– Higher vinyl acetate (VA) content increases flexibility, adhesion and polarity while decreasing water vapor and gas barrier properties as well as mechanical strength.
– Lower VA makes EVA closer to polyethylene in behavior – more crystalline with better strength but less flexibility and adhesion.
– VA content as low as 10% enhances properties like hot melt adhesion and as high as 40% delivers rubbery, flexible qualities.
– Not only the amount but also the distribution of VA along the chain impacts performance – a more uniform pattern yields better properties.
– Adding plasticizers further enhances flexibility and softness but reduces strength and glass transition temperature (Tg).
– Fillers can reinforce EVA cost-effectively for properties like higher tensile strength and stiffer backings. Common fillers include calcium carbonate, clay and fibers.
Processing Ethylene Vinyl Acetate
EVA has a melt index in the range of 500-5000 g/10 min, showing its good melt flowability. It can be easily processed by:
– Extrusion: Used to make EVA pipes, cables, sheets, films and more. Both single-screw and twin-screw extruders are employed.
– Injection molding: Popular for manufacturing toys, small medical devices, automotive parts and more.
– Blow molding: Used to manufacture EVA bottles and containers that require transparency.
– Calendering: For production of thick EVA sheets that are further fabricated.
– Foam extrusion: To create EVA foam sheets used for footwear, mats, gaskets and more.
– Rotational molding: An economical process for making hollow EVA shapes.
EVA’s widespread use comes from the ease with which its composition and molecular structure can be tailored to achieve the exact requirements through adjustment of vinyl acetate content and processing methods.
As a versatile copolymer with compatibility across many substrate types, Ethylene Vinyl Acetate fulfills a diverse range of needs from footwear to cables to medical devices. With properties that range from soft and rubbery to stiff yet flexible, EVA continues to displace other materials in many applications due to its cost-effectiveness, design flexibility and ease of processing. Its popularity endures because it is a remarkably adaptable material.
*Note:
1. Source: Coherent Market Insights, Public Source, Desk Research
2. We have leveraged AI tools to mine information and compile it
About Author - Priya Pandey
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