Jump to content

Polyvinyl alcohol

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by 66.104.46.178 (talk) at 15:37, 22 January 2009 (Grammar). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Template:Chembox new Polyvinyl alcohol (PVOH, PVA, or PVAL) is a water-soluble synthetic polymer.

Properties

Polyvinyl alcohol has excellent film forming, emulsifying, and adhesive properties. It is also resistant to oil, grease and solvent. It is odorless and nontoxic. It has high tensile strength and flexibility, as well as high oxygen and aroma barrier properties. However these properties are dependent on humidity, in other words, with higher humidity more water is absorbed. The water, which acts as a plasticiser, will then reduce its tensile strength, but increase its elongation and tear strength. PVA is fully degradable and is a quick dissolver. PVA has a melting point of 230°C and 180–190°C for the fully hydrolysed and partially hydrolysed grades. It decomposes rapidly above 200°C as it can undergo pyrolysis at high temperatures.

PVA is an atactic material but exhibits crystallinity as the hydroxyl groups are small enough to fit into the lattice without disrupting it.

Uses

Preparation of polyvinyl butyral is the largest use for polyvinyl alcohol in the U.S. and western Europe. Its use as a polymerization aid is the largest market in China. In Japan the major use is vinylon fiber production.[1]

Some other uses of polyvinyl alcohol include:

  1. Adhesive and thickener material in latex paints, paper coatings, hairsprays, shampoos and glues.
  2. Textile sizing agent
  3. Carbon dioxide barrier in polyethylene terephthalate (PET) bottles.
  4. Carotid phantoms for use as synthetic vessels in doppler flow testing.
  5. Movie practical effect and children's play putty or slime when combined with borax.
  6. Feminine hygiene and adult incontinence products as a biodegradable plastic backing sheet.
  7. As a mold release because materials such as epoxy do not stick to it.
  8. As a water-soluble film useful for packaging.
  9. As fiber reinforcement in concrete
  10. As a surfactant for the formation of polymer encapsulated nanobeads
  11. Used with polyvinyl acetate to make Elmer's glue
  12. Used in eye drops and hard contact lens solution as a lubricant.
  13. Used in protective chemical-resistant gloves
  14. Used as a fixative for specimen collection, especially stool samples
  15. When doped with iodine, PVA can be used to polarize light.
  16. As an embolization agent in medical procedures

Fishing

PVA is widely used in freshwater sport fishing. Small bags made from PVA are filled with dry- or oil-based bait and attached to the hook, or the baited hook is placed inside the bag and cast into the water. When the bag lands on the lake or river bottom it breaks down, leaving the hook bait surrounded by ground bait, pellets etc. This method helps attract fish to the hook bait.

Anglers also use string made of PVA for the purpose of making temporary attachments. For example, holding a length of line in a coil, that might otherwise tangle while the cast is made.

Production

Consumption of polyvinyl alcohol was over one million metric tons in 2006.[1] Larger producers include Kuraray (Japan) and Celanese (USA) but mainland China has installed a number of very large production facilities in the past decade and currently accounts for 45% of world capactity.

Preparation

Unlike most vinyl polymers, PVA is not prepared by polymerization of the corresponding monomer. The monomer, vinyl alcohol, almost exclusively exists as the tautomeric form, acetaldehyde. PVA instead is prepared by partial or complete hydrolysis of polyvinyl acetate to remove acetate groups.

References

  1. ^ a b SRI Consulting CEH Report Polyvinyl Alcohol, published March 2007, abstract retrieved July 30, 2008.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Polyvinyl_alcohol&oldid=265718466"