Poly is a water-soluble synthetic polymer. It has the idealized formula n. It is used in papermaking, textile warp sizing, as a thickener and emulsion stabilizer in pvac adhesives formulatons and a variety of coatings. It is colourless and odorless. It is sometimes supplied as beads or as solutions in water.
Uses
PVA is used in a variety of medical applications because of its biocompatibility, low tendency for protein adhesion, and low toxicity. Specific uses include cartilage replacements, contact lenses, and eye drops. Polyvinyl alcohol is used as an aid in suspension polymerizations. Its largest application in China is its use as a protective colloid to make polyvinyl acetate dispersions. In Japan its major use is the production of vinylon fiber. Another application is photographic film. Medically, it may also used as the embolic agent in a Uterine Fibroid Embolectomy
PVA is prepared by hydrolysis of polyvinyl acetate. Other vinyl ester-derived 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: The properties of the polymer are affected by the degree of transesterification. 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 but a few percent of 1,2-diols 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.
Safety and environmental considerations
PVA is widely used, thus its toxicity and biodegradation are of interest. Solutions containing up to 5% PVA are nontoxic to fish. It biodegrades slowly.
