PVOH


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PVOH - short version

Polyvinyl alcohol.



PVOH - long version

Polyvinyl alcohol (PVOH, PVA, or PVAL) is a water-soluble synthetic polymer (not to be confused with polyvinyl acetate, a popular wood glue).

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, respectively. 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.

Some other uses of polyvinyl alcohol include:

Adhesive and thickener material in latex paints, paper coatings, release liner, hairsprays, shampoos and glues.
Textile sizing agent
Carbon dioxide barrier in polyethylene terephthalate (PET) bottles
Carotid phantoms for use as synthetic vessels in doppler flow testing
Movie practical effect and 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
Used in eye drops and hard contact lens solution as a lubricant
Used in protective chemical-resistant gloves
Used as a fixative for specimen collection, especially stool samples
When doped with iodine, PVA can be used to polarize light
As an embolization agent in medical procedures
As a film used in the water transfer printing process

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.

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.



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