EVOH in multilayer sheets for food packaging!
Basically 3 different types of EVOH are used in the multilayer films for food packaging. These types differ mainly in their ethylene content and thus in their barrier ability.
Low ethylene content in EVOH (approx. 32 mol% ethylene) offers good barrier properties against oxygen and carbon dioxide, but is less suitable for protection against water vapour. These types are often used in packaging for foods such as meat, cheese and snack foods.
Average ethylene content in EVOH approx. 38 mol% ethylene) offers improved barrier properties against water vapor and can therefore be used in packaging for products such as coffee or dried fruit.
High ethylene content EVOH (approx. 44 mol% ethylene) offers the highest barrier properties against water vapor and aromas.
The choice of EVOH type depends on the specific requirements of the packaging, such as the desired barrier ability to specific gases or moisture.
The processing temperature of EVOH is usually between 190 and 230 °C. EVOH is water soluble, so the presence of moisture during processing will result in a decrease in barrier properties.
EVOH has a low melting temperature, the melt spreads poorly within the matrix of the multilayer film, so it is advisable to measure the distribution with suitable thickness gauges (please see chapter: Multilayer)
melt-pumps- thickness gauges - automatic systems for extrusion-dies - extrusion dies