Polyvinyl alcohol
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Polyvinyl alcohol (PVOH, PVA, or PVAL) is a water-soluble synthetic polymer.
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.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°CUses
Some uses of polyvinyl alcohol include:- Adhesive and thickener material in latex paints, 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.
Safety
PVOH is odorless and nontoxic, but can undergo pyrolysis at high temperatures.
External links
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