A difficult name, Ethylene Vinyl Acetate, for a widely used plastic raw material

The EVA copolymer it is a raw material in continuous growth in the world, in fact it was used in 2020, despite the production stops due to the pandemic, about 640,000 tons, with an average increase in the last decade of 4.3% per year.

The Asian market is certainly the area in which EVA is used the most, with China in the lead, which has had a growth in consumption 2019-2020 by 2-3%, followed by the United States which holds about 17% of world consumption.

What are the characteristics of EVA?

EVA, as we said, is a copolymer obtained from the polymerization of Vinyl Acetate, the different proportions of the latter in the recipe change the final characteristics of the product, creating an affinity for LDPE.

The two determining values in EVA recipes are its fluidity (MFI) and the percentage of VA (vinyl acetate), in particular, as the content of the comonomer the crystallinity decreases, consequently influencing numerous properties of the EVA.

In fact, an increase in the VA content increases the density, transparency and flexibility of the material, while reducing its melting point and hardness.

What are the Physical-Mechanical properties of EVA?

EVA, composed of the vinyl acetate comonomer, is a semi-crystalline product and, compared to the characteristics of LDPE, it normally becomes more transparent and more flexible with increasing the percentage of vinyl acetate contained in the recipe.

As the strength of the material decreases, its melting range also reduces, so the melting temperature of EVA is therefore lower than that of LDPE.

During injection molding, for example, the melt temperature should be between 175 and 225 ° C and its processing is similar to that of the LDPE.

The VAC (vinyl acetate) content determines the following changes in the finished products:

• 1-10%: compared to an LDPE film they will be more transparent, flexible and plastic, easier to seal, less breakages, greater shrinkage at temperatures low.

• 15-30%: very flexible and soft, thermoplastic workable, similar to rubber,

• 30-40%: high elastic elongation, flexibility with charge absorption capacity, good strength and high adhesiveness.

• 40-50%: extreme elasticity, crosslinkable with peroxides.

• 70-95%: use in the form of latexes for dyes in emulsion, paper coating and adhesives.

The vinyl acetate in EVA is also responsible for the material's characteristic vinegar smell.

EVA, compared to PVC, has a better resistance to low temperatures, no migration of plasticizer characterizing a permanent elasticity, a greater resistance to bending and better resistance to chemicals.

It also has better electrical insulation properties, on the other hand the gas barrier properties are lower such as resistance to light and abrasion.

We can group the physico-chemical characteristics of EVA in this scheme:

 Good abrasion resistance

 Excellent resistance to light

 Expanded with closed cells

 Excellent resistance to ozone and oxygen

 Hardness 25/30 Shore A

 Good anti-slip characteristics

 Excellent elastic memory

 Water repellent

 Pleasant to the touch

 Colorable, with excellent aesthetic effects

 Good anti-vibration ability

 Good tear resistance

 Medium resistance to mineral oils

 Excellent resistance to hot air

What are the electrical properties of EVA?

Compared to LDPE the insulating properties, from an electrical point of view, remain lower but EVA is often required, for example in the cable industry, for its easy crosslinking and good flexibility.

Thanks to the high capacity of the EVA copolymers to incorporate fillers, such as carbon black, they are also used for the manufacture of semiconductor compounds.

• Volume resistivity Ohm / cm 2,5 × 1016

• Dielectric constant 2.6 - 3.2

• Dissipation factor 0.03 - 0.05

What are the chemical properties of EVA?

In the presence of UV radiation, the EVA copolymer has a decay of physical properties, such as toughness, elongation at break and color change.

Furthermore, some chemical agents (wetting agents, polar substances and various organic liquids), can crack the product internally.

With the increase of the vinyl acetate content, the resistance to mineral oils increases significantly, on the contrary the electrical insulation characteristics are seen to decrease.

What are the thermal properties of EVA?

• Operating temperature: 60 to + 80 ° C

• Brittleness point: - 30 ° C

• Maxima temperature in static use: + 80 ° C

• Low Temperature Range: - 30 to - 50 ° C

What are the applications of EVA?

The EVA copolymer finds great application in the packaging sector, such as stretch film, by virtue of the high coefficients of friction and adhesiveness that give the product a good sealing characteristic .

It is also used in co-extrusion processes for the production of multilayer films, especially in the food sector.

Finally, it finds wide application in the footwear sector, such as the soles or the inside of ski boots and in the telecommunications sector as a lining element for tubes and cables.

How is EVA recycled?

The EVA waste can have a post-industrial origin, this means that during the processing for the production of objects, trimmings or scraps can be generated. If the processing waste is not expanded, it can be recovered by grinding it, taking care to keep the waste coming from different recipes separate.

Once reduced in volume, it can be used as a secondary raw material in the production of new products.

If the non-cross-linked material, on the other hand, comes from separate collection, it is necessary to provide for recycling steps that can separate any materials combined in the product to be recycled by separating the EVA .

For example, if we have a shoe with an EVA sole and a fabric structure or composed of other materials, the various materials that compose it must be separated before the operations final recycling.

If, on the other hand, the waste materials are composed of cross-linked EVA, this can be used, after being ground or micronized, as an inert in mixtures of binders for various products.

Automatic translation. We apologize for any inaccuracies. Original article in Italian.