The term “fog” refers to the collection of water in the form of dense small droplets on the surface of a polymer film. Fog occurs when the temperature of the air around the polymer film is cold to the dew point, and as a result, there is a temperature difference between the inner and outer layers of the polymer film. The extent of this phenomenon depends on the relative humidity of the surrounding air mass and the temperature of the polymer film.
The occurrence of fog in the food packaging industry is often observed with fresh foods that are stored in refrigerators and freezers at low temperatures and high relative humidity. The water droplets formed in the inner layer of food packaging, in addition to losing the transparency of the packaging and reducing the visibility of its contents, also have destructive effects on the quality of food.
In the films used in the agricultural and greenhouse industries, fog prevents the transmission of sufficient light to plants, which reduces plant growth and productivity. Also, due to the existence of a lens-like property in water droplets, it causes plant tissue to burn.
Anti-fog compounds increase the surface energy of the film until it balances with the surface energy of the water droplets. The increase in surface energy in the polymer film leads to a decrease in the contact angle between the liquid and the solid surface, the ease of merging water droplets adjacent to each other, and finally the formation of a continuous and thin layer of water on the film. The presence of this layer prevents large drops from dripping down. Also, reducing the internal reflection of incident light inside the water droplets in this layer increases the transparency of the plastic film.
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This post is written by MZ140005