- Saran (plastic)
Saran is the trade name for a number of polymers made from vinylidene chloride (especially polyvinylidene chloride or PVDC), along with other monomers. The main advantage of Saran film is its very low permeability to water vapor, flavor and aroma molecules, and oxygen compared with other plastics. The barrier to oxygen prevents food spoilage, and the barrier to flavor and aroma molecules helps food retain its flavor and aroma.
Saran is best known for having been used in Saran Wrap — a thin, clingy plastic wrap that was sold in rolls and used primarily for wrapping food. Saran Wrap is now a brand of S. C. Johnson & Son. The Saran Wrap product is no longer composed of PVDC due to purported "environmental concerns with halogenated materials". It is now composed of polyethylene. With this change, Saran Wrap no longer provides the excellent oxygen barrier and therefore the food spoilage prevention benefit of the original product formulation. For example, at 23°C and 95% relative humidity polyvinylidene chloride has an oxygen permeability of 0.6 cm3 μm m-2 d-1 kPa-1 while low-density polyethylene under the same conditions has an oxygen permeability of 2000 cm3 μm m-2 d-1 kPa-1.
In 1942, fused layers of original-specification Saran or PVDC were used to make ventilating insoles for boots, later adopted by the U.S. Army for use in their Jungle boot. PVDC is also used for high-quality doll hair that is valued by collectors for its shine, softness, and its ability to retain its style and curl.
In some jurisdictions, the name Saran is a registered trademark of the Dow Chemical Company, while in others, it has lost trademark status and become a generic term for these polymers. In Japan, Saran wrap is a trademark of Asahi Kasei.
Saran was first inadvertently discovered at Dow Chemical (Michigan, USA) in 1933 when a lab worker, Ralph Wiley was having trouble washing beakers used in his process of developing a dry-cleaning product. It was initially developed into a spray that was used on US fighter planes, and later automobile upholstery to protect them from the elements. Dow Chemical later refined Saran, eliminating its green hue and ridding it of its offensive odor. In 1949, Saran Wrap was invented and quickly became a common way to store food and keep it fresh.
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