“Polyvinyl alcohol”的意思、由来-开放百科全书

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.^[3]

Fishing

PVA is widely used in freshwater sport fishing. PVA moulded capsules and 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 dissolves in water, leaving the hook bait surrounded by ground bait, pellets etc.

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.^[4] 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:

Worldwide consumption of polyvinyl alcohol was over one million metric tons in 2006.^[3] Larger producers include Kuraray (Japan, Europe, and USA) 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 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.^[4]

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 (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 close to incompressible. The Poisson's ratio is between 0.42 and 0.48.^[5]

Tradenames of polyvinyl alcohol

Safety

PVA is nontoxic. It biodegrades slowly, and solutions containing up to 5% PVA are nontoxic to fish.^[4]

See also

References

1. ^{{cite journal|last1=Schnepf|first1=M.J.|last2=Mayer|first2=M.|last3=Kuttner|first3=C.|last4=Tebbe|first4=M.|last5=Wolf|first5=D.|last6=Dulle|first6=M.|last7=Altantzis|first7=T.|last8=Formanek|first8=P.|last9=Förster|first9=S.|last10=Bals|first10=S.|last11=König|first11=T.A.F.|last12=Fery|first12=A.|title=Nanorattles with tailored electric field enhancement|journal=Nanoscale|volume=9|issue=27|year=2017|pages=9376–9385|doi=10.1039/C7NR02952G}}
2. ^{{Cite web|url=https://www.chemsrc.com/en/cas/9002-89-5_342468.html|title=Poly(vinyl alcohol)_msds}}
3. ^¹SRI Consulting CEH Report Polyvinyl Alcohol, published March 2007, abstract retrieved July 30, 2008.
4. ^¹²³Manfred L. Hallensleben "Polyvinyl Compounds, Others" in Ullmann's Encyclopedia of Industrial Chemistry, 2000, Wiley-VCH, Weinheim. {{DOI|10.1002/14356007.a21_743}}
5. ^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.

Uses