In recent years, the use of polymer films has become widely widespread due to its desirable properties, good transparency and suitable cost for greenhouse coatings, as well as packaging of various products, including food, vegetables, etc.
One of the challenges in using polymer films is fog, or dew. The formation of fog is due to the condensation of water vapor on the surface. In greenhouse films or food packaging, this phenomenon is more likely due to the high humidity. In fact, due to the temperature fluctuations of water vapor, droplets form on the surface of the film which remain on the surface of the film because of the difference in surface tension of water with the non-polar polymer that forms the film.
Occurrence of fog and accumulation of water droplets on the film surface, by reducing light transmission and making lens effect causes interference in the process of plant growth in the greenhouse, destruction and damage to crops and also reduces the clarity of food packaging.
To solve this problem, manufacturers use an anti-fog additive in the formulation of polymer films. These additives have an incompatible nature with the polymer base, so migrate to the film surface, increase the surface tension of the film and water and reduce the contact angle of water droplets with the film surface; as a result, water droplets are placed on the film surface as a continuous layer. This phenomenon improves the transparency and clarity of the film surface and thus reduces the effect of the lens, which occurs due to the presence of water droplets.
Falling water layer from the surface, the light can transmit from layer and also prevent water droplets from falling on the product; this helps the product no to be destroyed.
Anti-fog additive is mainly used as a masterbatch in film formulation. The concentration of this additive decreases over time due to the migration of additives to the surface and its tendency to dissolve in water, thus weakening its performance. That’s why manufacturers of polymer films need to consider the optimal amount of this additive in their formulation.
For polymer films, especially polyethylene-base ones, there are various additives used as anti-fog agent which are incompatible with polyethylene and have the ability to migrate to the film surface. These additives have different migration rates depending on the type and amount of consumption.