Polyvinyl alcohol
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| Surname | Polyvinyl alcohol | ||||||
| CAS number | 9002-89-5 | ||||||
| Monomer | Vinyl alcohol | ||||||
| Molecular formula of the repeating unit | C 2 H 4 O | ||||||
| Molar mass of the repeating unit | 44.05 g mol −1 | ||||||
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| Physical state |
firmly |
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | |||||||
Polyvinyl alcohol ( abbreviated PVOH or PVOH) is a thermoplastic plastic , which as a white to yellowish powder mostly by saponification ( hydrolysis ) of polyvinyl acetate is produced (PVAC). The direct synthetic route is not possible. PVAL is resistant to almost all anhydrous organic solvents. Partially saponified types of PVAL with approx. 13% PVAC content are readily soluble in water. The water solubility decreases with increasing degree of saponification.
history
Polyvinyl alcohol was first introduced in 1924 by Willi Herrmann and tungsten Haehnel by hydrolysis of polyvinyl esters with stoichiometric amounts of sodium hydroxide produced. Another advance in the production of polyvinyl alcohols was made by Herrmann, Haehnel and Herbert Berg in 1932. They discovered that polyvinyl alcohol can also be produced by transesterifying polyvinyl acetate with absolute alcohols in the presence of catalytic amounts of alkalis . This process is also called a polymer-analog reaction .
Manufacture and extraction
Unlike most vinyl polymers , polyvinyl alcohol cannot be made by simply polymerizing the appropriate monomer . The monomer ethenol required for this only exists in its tautomeric form as acetaldehyde . The synthesis by polyaldol condensation from acetaldehyde has not yet been successful, since only low molecular weight polymers have been produced so far. Polyvinyl alcohols are obtained by transesterification or by alkaline saponification of polyvinyl acetate . The hydrolysis can be easily controlled. In addition, some polyvinyl alcohol copolymers are also important; they are obtained from polyvinyl acetate copolymers.
Structure and properties
Chemical structure
Similar to polyvinyl acetate, the head-to-tail arrangement of the monomers predominates in polyvinyl alcohol. The content of building blocks in a head-to-head arrangement is below 1% to 2%. The proportion of these proportions has a major influence on the physical properties of the polymer, such as its solubility in water. Polyvinyl alcohol is usually slightly branched due to chain transfers during the synthesis of polyvinyl acetate. The degree of polymerization is about 500 to 2500.
The degree of hydrolysis of the technically relevant types varies between 70 and 100 mol% depending on the intended use. If only partially saponified, the acetyl groups can be distributed randomly or in blocks in the polymer, depending on the process. The distribution of these acetyl groups influences important properties such as the melting point , the surface tension of aqueous solutions or protective colloid properties .
Polyvinyl alcohol, obtained from polyvinyl acetate, is an atactic plastic. However, it still has crystalline areas via the hydroxyl groups . The structure and history, i.e. branching, degree of hydrolysis, distribution of the acetyl groups, influence this crystallinity of the polymer. The higher the degree of hydrolysis, the better the crystallizability. By heat treatment of fully saponified products, the crystallinity can be increased, which in turn reduces the water solubility. The higher the proportion of acetyl groups, the weaker the formation of crystalline zones.
Physical Properties
Polyvinyl alcohol is excellent layer-forming, emulsifying and adhesive . It has high tensile strength and flexibility. These properties depend on the humidity , as the plastic absorbs water . Water acts as a plasticizer , PVAL (PVOH) loses its tensile strength at high humidity, but gains elasticity . The melting point is 230 ° C, the glass transition temperature 85 ° C for completely hydrolyzed forms. The ceiling temperature is 200 ° C. The temperature data vary with the molecular weight .
Chemical properties
It is resistant to oils, fats and organic solvents.
Use, processing
- Adhesion and thickening agent in latex lacquers, hair sprays , shampoos and adhesives .
- Part of the film of water-soluble individual packaging of machine dishwashing tablets
- Barrier layer for carbon dioxide in PET bottles.
- Part of play dough and so-called slime .
- Part of Aquabeads , a handicraft material for children
- Component for sealing hygiene products such as feminine hygiene or incontinence products.
- Mold release agent in the manufacture of fiber-plastic composites .
- Sizing agents in paper manufacture .
- As a water-soluble film for the production of packaging bags.
- As a water-soluble carrier material for a water transfer printing film.
- Carrier spray for handicrafts.
- Selective embolization of tumor vessels , for example as part of the preoperative treatment of juvenile nasopharyngeal fibroma
- Wetting and adhesive agents in artificial tear fluid
- One-day hydrogel - contact lenses with low oxygen permeability
- Inclusion immobilization of cells and enzymes in microbiology
- Artificial casings for sausage products.
- Sizing agents in the textile industry
- Textile fiber Vinalon , Vinylal or Vinylon fiber
- optionally cross-linked to paint the interior of petrol tanks
- as a water-soluble material for support structures in 3D printing
Environmental aspects & toxicology
toxicology
Investigations on skin and mucous membrane compatibility in animal experiments ( LD50 , oral and dermal application) showed no negative effects. No health hazards are expected either when ingested with food or through the skin.
- breathe in
Dust can form under certain conditions . When heated to over 200 ° C, smoke gases are generated , which can irritate the eyes, nose and throat. You may also experience tearing, chemical burns, red eyes or a burning sensation in the nose and throat.
There is no data on other health impairments for humans. Animal experiments showed a decrease in the number of hemoglobin and erythrocytes with occasional complete anticoagulation . Some animal experiments also suggest the possibility of carcinogenicity .
sewage
Polyvinyl acetate as a preliminary product can easily find its way into wastewater in the form of dispersions, but it is not toxic. However, it is poorly degraded in an aqueous medium.
The treatment of wastewater containing dispersion in sewage treatment plants is usually not a problem, it is easy to precipitate and is deposited in the sewage sludge with which it is then disposed of.
Trade names
Mowiol, Kuraray Poval, Celvol, Exceval, Polyviol, Elvanol, MonoSol
See also
literature
- Ernst Bartholomé, Ernst Biekert (ed.): Ullmanns Enzyklopädie der Technischen Chemie . Volume 19, 4th edition. Verlag Chemie, Weinheim 1980, ISBN 3-527-20019-3 .
Web links
- Entry on polyvinyl alcohol in the ChemIDplus database of the United States National Library of Medicine (NLM)
- Technical data sheet PVA at Kuraray Europe GmbH.
Individual evidence
- ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
- ↑ Bodo Carlowitz: plastic tables. Carl Hanser Verlag, Munich / Vienna 1995, ISBN 3-446-17603-9 , p. 93.
- ^ Karl Oberbach (Ed.): Saechtling plastic pocket book. Carl Hanser Verlag, Munich / Vienna 2004, ISBN 3-446-22670-2 , p. 458.
- ↑ European Pharmacopoeia , Deutscher Apotheker Verlag Stuttgart, 6th edition, 2008, pp. 3726–3727, ISBN 978-3-7692-3962-1 .
- ^ Polyvinyl alcohol drugs with the same active ingredients .
- ↑ Tech-Info Specialized Information Dailies ( Memento of the original from July 2, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 3.2 MB).
