Polyvinyl acetate

Essigsäureethenylesterhomopolymer (Chemical Abstracts )

Thermoplastic

Amorphous, transparent, odorless, tasteless plastic

Fixed

1170-1200 kg/m3 (depending on the degree of polymerization )

70-210 ° C (depending on the degree of polymerization )

18-45 ° C (depending on the degree of polymerization )

Polyvinyl acetate ( PVAc abbreviation sometimes just PVA ) is a thermoplastic. The synthesis of the polymer from the group of polyvinyl occurs by means of radical polymerization. Besides the pure homopolymers, many co-and terpolymers of vinyl acetate have great industrial importance.

History

The bases for the production of polyvinyl acetate were discovered by Fritz Klatte in Germany in 1912. He recognized the polymerization ability of vinyl compounds in the sunlight. In the years 1912 and 1913 there followed the first targeted production of polyvinyl acetate and Polyvinylchloracetat by Klatte. Since the 1930s a number of different products in the form of granules, powders, solutions, and emulsions for various applications is manufactured by several companies.

Production and recovery

The production of vinyl acetate from polyvinyl acetate is carried out by radical polymerization. Often, however, copolymerized with acrylic acid, acrylates, crotonic acid, vinyl laurate, vinyl chloride or ethylene. Care must be taken to a high purity of the monomers, since the impurities slow down the polymerization process greatly (eg crotonaldehyde, vinyl acetylene ) or undesirable chain transfer (eg acetic acid, acetaldehyde, acetone, benzene, toluene) lead. Also undesirable impurities with two copolymerizable double bonds (eg: Crotonsäurevinylester ) as these contribute by spatial crosslinking to form insoluble polymers. The polymerization is ( organic, inorganic hydroperoxides and azo compounds ) started mostly with free-radical initiators. Photopolymerization or radiation-induced polymerization have not yet reached technological importance.

As a polymerization process for the production of polyvinyl acetate homopolymers both bulk, solution, suspension or emulsion polymerization and Perl are possible.

Polyvinyl acetate is a necessary intermediate in the production of polyvinyl alcohol, and polyvinyl acetals.

Structure and Properties

Chemistry

In homopolymer outweighs the head -to-tail arrangement of monomer units. By decreasing the polymerization temperature, the proportion of monomers in head -to-head further reduced. The degree of polymerization of polyvinyl acetate typically is 100 to 5000.

Physical Properties

Polyvinyl acetate is an amorphous, odorless and tasteless plastic with high light and weather resistance. It is combustible, but not flammable. The glass transition temperature of the homopolymer varies depending on the degree of polymerization between 18 and 45 ° C. Electrical, mechanical and thermal properties are also dependent to a large extent by the degree of polymerization.

The minimum film forming temperature of homopolymer dispersions is about 15 to 18 ° C.

Chemical Properties

The ester groups in polyvinyl acetate are relatively slightly alkaline to saponify, causing the polymer to slowly converted into polyvinyl alcohol and thereby becomes hydrophilic and water sensitive. This problem is the reason for the frequent copolymerization with other monomers.

Polyvinyl acetate is insoluble in water, butanol, diethyl ether, petroleum ether, and aliphatic hydrocarbons but insoluble in lower alcohols, various ketones, esters, cyclic ethers, aromatic and chlorinated hydrocarbons.

In case of thermal decomposition of polyvinyl acetate, acetic acid is free.

Use, processing

Polyvinyl acetate are processed in the form of solutions in organic solvents or as a dispersion.

It is used as a binder in paints and varnishes. Another use of the plastic as white glue ( wood glue ) or adhesive. As UHU ® is a 40% solution of polyvinyl acetate in acetone / ethyl acetate. Other application areas include papermaking and coating, textile impregnation, carpet back coating or modification of plaster and concrete. In addition, there is often a component of chewing gum compositions and is used for the coating of cheese or sausage.

Trade names of polyvinyl acetate, for example, Emultex ® F, Mowilith.RTM ®, Rhodopas ®, Vinamul ® or Vinnapas ®.

Environmental aspects & Toxicology

• Toxicology: studies on skin and mucous membrane tolerance in animals (LD50, feeding on rats, dermal application ) showed no adverse effects.

• Wastewater: polyvinyl acetate can easily get in the form of dispersions into the wastewater. Although they are non-toxic according to current knowledge, but they are in an aqueous environment very badly degraded. The preparation dispersionshaltiger wastewater in sewage treatment plants is usually not a problem, they are easy to precipitate, and then accumulate in the sludge, which they can then be disposed of.

Proof

• Cleaving of acetic acid during the thermal decomposition can be used as an indication of the presence of vinyl acetate -containing polymers and copolymers. However, acetic acid cellulose split off during the thermal decomposition.
• The acetic acid can be demonstrated as follows: A few milligrams of the substance to be pyrolyzed. The vapors are captured with some moistened cotton wool. This is washed with water and the solution is then charged with 3 to 4 drops of a 5% aqueous lanthanum nitrate solution, 1 drop of 0.1 N iodine solution and 1 to 2 drops of concentrated ammonia was added. In the presence of acetic acid, the solution turns deep blue to almost black.
• Wets one polyvinyl acetate with 0.01 N iodine Iodkaliumlösung, produces a purple-brown color, which is reinforced by the washing with water.
• As a further indication of the presence of polyvinyl acetate and the reaction according to Liebermann - Storch - Morawski is used.