“Polyvinylidene chloride”的意思、由来-开放百科全书

Ralph Wiley accidentally discovered polyvinylidene chloride in 1933.^[1] He, then, was a college student who worked part-time at Dow Chemical lab as a dishwasher.^[2] 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,^[3] first called "Eonite" and then "Saran".^[2]^[4]

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 alkalis and acids, is insoluble in oil and organic solvents, has a very low moisture regain and is impervious to mold, bacteria, and insects. But it is soluble in polar solvents.

Fiber types

Saran fiber comes in monofilament, multifilament-twist, and as a staple fiber. 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 other plastic films such as biaxially-oriented polypropylene (BOPP) and polyethylene terephthalate (PET). This coating increases the barrier properties of the film, reducing the permeability of the film to oxygen and flavours and thus extending the shelf life 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 to if applied over print.

Household

Industry

Screens, artificial turf, waste-water treatment materials, underground materials.

Miscellaneous

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.

Trademarks (producers)

See also

References

1. ^{{cite book|author=John W. Klooster|title=Icons of Invention: The Makers of the Modern World from Gutenberg to Gates|url=https://books.google.com/books?id=WKuG-VIwID8C&pg=PA466|accessdate=12 July 2012|date=30 July 2009|publisher=ABC-CLIO|isbn=978-0-313-34743-6|pages=466–}}
2. ^¹{{cite book|author1=David John Cole|author2=Eve Browning|author3=Fred E. H. Schroeder|title=Encyclopedia of Modern Everyday Inventions|url=https://books.google.com/books?id=rVQfBSlAZvAC&pg=PA129|accessdate=12 July 2012|date=30 April 2003|publisher=Greenwood Publishing Group|isbn=978-0-313-31345-5|page=129}}
3. ^{{cite book|author=Andrew F. Smith|title=The Oxford Companion to American Food and Drink|url=https://books.google.com/books?id=AoWlCmNDA3QC&pg=PT492|accessdate=12 July 2012|date=1 May 2007|publisher=Oxford University Press|isbn=978-0-19-530796-2|page=492}}
4. ^{{cite web | url=http://inventors.about.com/library/inventors/blsaranwrap.htm | title=Saran Wrap ® | work=inventors.about.com | accessdate=July 12, 2012 | author=Mary Bellis}}
5. ^{{cite book|author1=Otto G. Piringer|author2=A. L. Baner|title=Plastic Packaging: Interactions with Food and Pharmaceuticals|url=https://books.google.com/books?id=wxvTeGVK5o8C&pg=PA41|accessdate=12 July 2012|date=17 September 2008|publisher=John Wiley & Sons|isbn=978-3-527-62143-9|pages=41–}}

History