Polyvinylidene chloride, or polyvinylidene dichloride (PVDC), is a
homopolymer
A polymer (; Greek '' poly-'', "many" + '' -mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and ...
of
vinylidene chloride
1,1-Dichloroethene, commonly called 1,1-dichloroethylene or vinylidene chloride or 1,1-DCE, is an organochloride with the molecular formula CHCl. It is a colorless liquid with a sharp odor. Like most chlorocarbons, it is poorly soluble in water, ...
.
History
Ralph Wiley accidentally discovered polyvinylidene chloride polymer in 1933.
He, then, was a college student who worked part-time at
Dow Chemical
The Dow Chemical Company, officially Dow Inc., is an American multinational chemical corporation headquartered in Midland, Michigan, United States. The company is among the three largest chemical producers in the world.
Dow manufactures plastics ...
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
Saran is a trade name used by S.C. Johnson & Son, Inc. for a polyethylene food wrap. The Saran trade name was first owned by Dow Chemical for polyvinylidene chloride (PVDC), along with other monomers. The formulation was changed to the less eff ...
, a plastic food wrap, was introduced. In 2004, however, the formula was changed to
low-density polyethylene
Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerization. Its ...
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 ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic 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 s ...
s and
acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a s ...
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 (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
s.
Above 125 °C, it decomposes to produce
HCl.
Disadvantages
While extremely useful as a food packaging 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 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 forms. It is also available in
thermochromic (color changing) and
luminescent (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 (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 fibres for clothing, containers for liquids and foods ...
(PET). This coating increases the barrier properties of the film, reducing the permeability of the film to
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
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 ...
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.
Trademarks (producers)
*Saran TC and Saran LS (Asahi-Kasei)
* (formerly) Saran Wrap and Saranex (Dow Chemical)
*Ixan and Diofan (SolVin)
*SK Saran
See also
*
Polyvinyl chloride (PVC)
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