Polyvinyl alcohol
 | This article needs additional citations for verification. (August 2007) |
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| Names | |
|---|---|
| Other names
PVOH; Poly(Ethenol), Ethenol, homopolymer; PVA; Polyviol; Vinol; Alvyl; Alkotex; Covol; Gelvatol; Lemol; Mowiol
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| Identifiers | |
| ECHA InfoCard | 100.121.648 |
| E number | E1203 (additional chemicals) |
| KEGG | |
| RTECS number |
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CompTox Dashboard (EPA)
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| Properties | |
| (C2H4O)x | |
| Density | 1.19-1.31 g/cm³ |
| Melting point | 230°C |
| Boiling point | 228°C |
| Hazards | |
| NFPA 704 (fire diamond) | |
| Flash point | 79.44°C |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose)
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14,700 mg/kg (Mouse) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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(356-374 degrees Fahrenheit) 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.
PVA is close to incompressible. The Poisson's ratio has been measured to between 0.42 and 0.48.[1]
Uses
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Polyvinyl alcohol is the raw material to make other polymers like:
- Polyvinyl nitrate (PVN): It is an ester of nitric acid and polyvinyl alcohol.
- Polyvinyl acetals: Polyvinyl acetals are prepared by reacting aldehydes with polyvinyl alcohol. Polyvinyl butyral (PVB) and polyvinyl formal (PVF) are examples of this family of polymers. They are prepared from polyvinyl alcohol by reaction with butyraldehyde and formaldehyde, respectively. Preparation of polyvinyl butyral is the largest use for polyvinyl alcohol in the U.S. and Western Europe.
Polyvinyl alcohol is used as a emulsion polymerization aid, as protective colloid, to make polyvinyl acetate dispersions. This is the largest market application in China.
In Japan its major use is vinylon fiber production.[2]
Some other uses of polyvinyl alcohol include:
- Paper adhesive with boric acid in spiral tube winding and solid board production
- Thickener, modifier, in polyvinyl acetate glues
- Textile sizing agent
- paper coatings, release liner,
- As a water-soluble film useful for packaging. An example is the envelope containing laundry detergent in "liqui-tabs".
- Feminine hygiene and adult incontinence products as a biodegradable plastic backing sheet.
- Carbon dioxide barrier in polyethylene terephthalate (PET) bottles
- As a film used in the water transfer printing process
- As a mold release because materials such as epoxy do not stick to it
- Movie practical effect and children's play putty or slime when combined with borax
- Used in eye drops and hard contact lens solution as a lubricant
- PVA fiber, as reinforcement in concrete
- As a surfactant for the formation of polymer encapsulated nanobeads
- 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
- Carotid phantoms for use as synthetic vessels in Doppler flow testing
- As agent in artificial Tears for treatment of dry eye.
- See more specific polyvinyl alcohol uses
The North Korean-manufacture fiber Vinalon is produced from polyvinyl alcohol. Despite its inferior properties as a clothing fiber, it is produced for self-sufficiency reasons, because no oil is required to produce it.
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.[2] Larger producers include Kuraray (Japan and Europe) and Sekisui Specialty Chemicals (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 many 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 (sometimes referred to in this case as saponification) of polyvinyl acetate to remove acetate groups.
See also
References
- ^ Characterization of PVA cryogel for intravascular ultrasound elasticity imaging, Fromageau, J.; Brusseau, E.; Vray, D.; Gimenez, G.; Delachartre, P.; IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Volume: 50, Issue: 10. 2003, Page(s): 1318 - 1324.
- ^ a b SRI Consulting CEH Report Polyvinyl Alcohol, published March 2007, abstract retrieved July 30, 2008.