Polyvinylidene chloride, or polyvinylidene dichloride (PVDC), is a homopolymer of

vinylidene chloride 1,1-Dichloroethylene, commonly called vinylidene chloride or 1,1-DCE, is an organochloride with the molecular formula . It is a colorless liquid with a sharp odor. Like most chlorocarbons, it is poorly soluble in water but soluble in organic solv ...

History

Ralph Wiley accidentally discovered polyvinylidene chloride polymer in 1933. At the time he was a college student who worked part-time at

Dow Chemical The Dow Chemical Company is an American multinational corporation headquartered in Midland, Michigan, United States. The company was among the three largest chemical producers in the world in 2021. It is the operating subsidiary of Dow Inc., ...

lab as a dishwasher. While cleaning laboratory glassware, he came across a vial he could not scrub clean. Dow researchers made this material into a greasy, dark green film, first called "Eonite" and then " Saran". Ralph Wiley went on to become one of Dow Chemical's research scientists and invent and develop many plastics, chemicals and production machines. The military sprayed Saran on fighter planes to guard against salty sea spray, and carmakers used it for upholstery. Dow later devised a formulation of polyvinylidene chloride free of unpleasant odour and green colour. The most well known use of polyvinylidene chloride came in 1953, when Saran Wrap, a plastic food wrap, was introduced. In 2004, however, the formula was changed to low-density polyethylene due to environmental concerns about its chlorine content and other disadvantages.

Properties

It is a remarkable barrier against water, oxygen, and aromas. It has a superior chemical resistance to

alkali In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The a ...

s and

acid An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...

s, is insoluble in oil and organic solvents, has a very low moisture regain and is impervious to mold, bacteria, and insects. It is soluble in

polar solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...

s. Above 125 °C, it decomposes to produce HCl.

Disadvantages

While extremely useful as a

food packaging Food packaging is a packaging system specifically designed for food and represents one of the most important aspects among the processes involved in the food industry, as it provides protection from chemical, biological and physical alterations ...

agent, the major disadvantage of polyvinylidene chloride is that it will undergo thermally induced dehydrochlorination at temperatures very near to processing temperatures. This degradation easily propagates, leaving

polyene In organic chemistry, polyenes are polyunsaturated organic compounds that contain multiple carbon–carbon double bonds (). Some sources consider dienes to be polyenes, whereas others require polyenes to contain at least three carbon–carbon d ...

sequences long enough to absorb visible light and change the color of the material from colorless to an undesirable transparent brown (unacceptable for one of polyvinylidene chloride's chief applications: food packaging). Therefore, there is a significant amount of product loss in the manufacturing process, which increases production and consumer costs.

Fiber types

Saran fiber is produced in monofilament, multifilament-twist, and

staple fiber A staple fiber is a textile fiber of discrete length. The opposite is a filament fiber, which comes in continuous lengths. Staple length is a characteristic fiber length of a sample of staple fibers. It is an essential criterion in yarn spinning ...

forms. It is also available in thermochromic (color changing) and

luminescent Luminescence is a spontaneous emission of radiation from an electronically or vibrationally excited species not in thermal equilibrium with its environment. A luminescent object emits ''cold light'' in contrast to incandescence, where an objec ...

(glow in the dark) fibers.

Uses

Packaging

Polyvinylidene chloride is applied as a water-based coating to films made of other plastics, such as biaxially-oriented

polypropylene Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer Propene, propylene. Polypropylene belongs to the group of polyolefin ...

(BOPP) and

polyethylene terephthalate Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P), is the most common thermoplastic polymer resin of the polyester family and is used in synthetic fibre, fibres for clothing, packaging, conta ...

(PET). This coating increases the barrier properties of the film, reducing the permeability of the film to

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

and flavours and thus extending the

shelf life Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or no longer on a s ...

of the food inside the package. It can also impart a high-gloss finish, which may be aesthetically pleasing and also provides a high degree of scuff resistance if applied over print.

Other

In household settings, PVDC is used in cleaning cloths, filters, screens, tape, shower curtains, and garden furniture. Industrially, it is used in screens, artificial turf, waste-water treatment materials, and underground materials. PVDC is also used in doll hair, stuffed animals, fabrics, fishnet, pyrotechnics, and shoe insoles. It was used in special photographic film.

Trademarks (producers)

*Saran TC and Saran LS (Asahi-Kasei) * (formerly) Saran Wrap and Saranex (Dow Chemical) *Ixan and Diofan (SolVin) *SK Saran

References

* B.A. Howell, J. Polym. Sci., Polym. Chem. (ed) 1987, 25, 1681–1695. * B.A. Howell, B.S. Warner, C.V. Rajaram, S.I. Ahemed and Z. Ahmed, Polym. Adv. Technol., 1994, 5, 485. * B.A. Howell and S. M. Jane, “Impact of Moisture on the Thermal Stability of Vinylidene Chloride Copolymers”, Proceedings, 34th Annual Meeting of the North American Thermal Analysis Society, 2006. * R.A. Wessling, D.S. Gibbs P.T. Delassus, B.E. Obi, B.A. Howell, Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley and Sons, New York, 4th Edition, 1997, Vol 24, pp. 883–923.

External links

Wiley mini-bio

{{Plastics Thermoplastics