Polyvinyl alcohol

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Chemical structure of polyvinyl alcohol

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

1 Preparation
2 Properties
3 Uses
4 Fishing
5 Production
6 External links

[edit] Preparation

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

[edit] Properties

Polyvinyl alcohol has excellent film forming, emulsifying, and adhesive properties. It is also resistant to oil, grease and solvent. PVOH is an atactic material but exhibits crystallinity as the hydroxyl groups are small enough to fit into the lattice without disrupting it. It has high tensile strength, flexibility, as well as high oxygen and aroma barrier. 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. PVOH has a melting point of 230°C and 180-190°C for the fully hydrolysed and partially hydrolysed grades. PVOH also decomposes rapidly above 200°C.

[edit] Uses

Some uses of polyvinyl alcohol include:

Adhesive and thickener material in latex paints, paper coatings, hairsprays, shampoos and glues.
Carbon dioxide barrier in polyethylene terephthalate (PET) bottles.
Carotid phantoms for use as synthetic vessels in doppler flow testing.
Children's play putty or slime when combined with borax.
Feminine hygiene and adult incontinence products as a biodegradable plastic backing sheet.
As a mold release because materials such as epoxy do not stick to it.
As a water-soluble film useful for packaging.
As fiber reinforcement in concrete
As a surfactant for the formation of polymer encapsulated nanobeads
Used with polyvinyl acetate to make Elmer's glue

[edit] 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, though it does result in dissolved plastic in the water.

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

PVOH is odorless and nontoxic, but can undergo pyrolysis at high temperatures. There are varieties approved by the FDA for direct food contact.

[edit] Production

There are over 22 producers worldwide with ~ 1 million tons on the open market in 2002. Larger producers include Kuraray (Japan) and Celanese (USA) but mainland China has installed a number of very large production facilities in the past decade.