Polyvinyl alcohol is a water-soluble synthetic polymer. It has the idealized formula [CH2CH(OH)]n.
It is used in papermaking, textiles, and a variety of coatings. It is white and odorless.
It is sometimes supplied as beads or as solutions in water.
Uses Polyvinyl acetals: Polyvinyl acetals are prepared
by reacting aldehydes with polyvinyl alcohol. Polyvinyl butyral and polyvinyl formal 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 an 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. 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
bottles As a film used in the water transfer printing
process As a form 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
Raw material to polyvinyl nitrate. an ester of nitric acid and polyvinyl alcohol.
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
Used in 3D printing as support structure that can then be dissolved away.
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, is unstable with respect to acetaldehyde. PVA instead is prepared
by first polymerizing vinyl acetate, and the resulting polyvinylacetate is converted to
the PVA. Other precursor polymers are sometimes used, with formate, chloroacetate groups instead
of acetate. The conversion of the polyesters is usually conducted by base-catalysed transesterification
with ethanol: [CH2CH(OAc)]n + C2H5OH → [CH2CH(OH)]n +
C2H5OAc The properties of the polymer depend on the
amount of residual ester groups. Worldwide consumption of polyvinyl alcohol
was over one million metric tons in 2006. Larger producers include Kuraray and Sekisui
Specialty Chemicals but mainland China has installed a number of very large production
facilities in the past decade and currently accounts for 45% of world capacity. 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. Structure and properties
PVA is an atactic material that exhibits crystallinity. In terms of microstructure, it is composed
mainly of 1,3-diol linkages [-CH2-CH(OH)-CH2-CH(OH)-] but a few percent of 1,2-diols [-CH2-CH(OH)-CH(OH)-CH2-]
occur, depending on the conditions for the polymerization of the vinyl ester precursor.
Polyvinyl alcohol has excellent film forming, emulsifying and adhesive properties. It is
also resistant to oil, grease and solvents. 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 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 close to incompressible. The Poisson's ratio is between 0.42 and 0.48.
Safety PVA is nontoxic. It biodegrades slowly, but
solutions containing up to 5% PVA are nontoxic to fish.
See also Polyvinyl acetate
Vinyl acetate Polymerization
Polyvinyl nitrate References
^ a b c d Manfred L. Hallensleben "Polyvinyl Compounds, Others" in Ullmann's Encyclopedia
of Industrial Chemistry, 2000, Wiley-VCH, Weinheim. doi:10.1002/14356007.a21_743
^ a b SRI Consulting CEH Report Polyvinyl Alcohol, published March 2007, abstract retrieved
July 30, 2008. ^ 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. External links
MSDS Listed as a plastic by the Society of the
Plastics Industry "Slime" recipe
Forming PVA layers in PET bottles An Introduction to PVA for Carp Fishing
PVA Mowiol applications PVA Mowiol specifications
polyvinyl alcohol uses