Polyvinyl Acetate

In the United States, polyvinyl acetate (PVA, PVAc, poly(ethenyl ethanoate)), often known as wood glue, white glue, carpenter's glue, school glue, or Elmer's glue, is a widely used adhesive for porous materials such as wood, paper, and cloth. It's a rubbery aliphatic synthetic polymer with the formula (C₄H₆O₂)nthat belongs to the polyvinyl ester family, with the general formula-[RCOOCHCH₂]-. It's a thermoplastic material.    

Vinyl Acetate Structure

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In the above-shown vinyl acetate structure, you can see that the acetate group is attached to the vinyl carbon group. The carbon of the vinyl group is sp2 hybridised.

Properties of Poly vinyl acetate

• Polyvinyl acetate polymerizes to a degree of 100 to 5000, but its ester groups are vulnerable to base hydrolysis, converting PVAc to polyvinyl alcohol and acetic acid slowly.

• Polyvinyl acetate has a glass transition temperature of 30 to 45 °C, depending on the molecular weight.

• Elmer's Glue-All, for example, contains polyvinyl alcohol as a protective colloid. Boron chemicals like boric acid or borax cause the polyvinyl alcohol to cross-link in alkaline conditions, resulting in tackifying precipitates or toys like Slime and Flubber.

• Polyvinyl acetate can be degraded by a variety of bacteria. Filamentous fungus is the most prevalent cause of degradation, though algae, yeasts, lichens, and bacteria can all degrade polyvinyl acetate.

Preparation of Polyvinyl Acetate

PVA stands for polyvinyl alcohol. Polymerization of vinyl acetate monomer yields polyvinyl acetate (free radical vinyl polymerization of the monomer vinyl acetate). Ethylene is converted to vinyl acetate (CH₂=CHO₂CCH₃)using a palladium catalyst in a reaction with oxygen and acetic acid. Vinyl acetate monomers (single-unit molecules) can be linked into long, branched polymers (big, multiple-unit molecules) using free-radical initiators, with the vinyl acetate repeating units having the following structure:

A milky-white emulsion can be formed by polymerizing the monomer while it is spread in water. The PVAc in this fluid can be used to make latex paints, which forms a strong, flexible, and adhering layer. It can also be turned into white glue or Elmer's glue, a typical household adhesive.

Polyvinyl Acetate Uses

• PVAc formulations are used as adhesives for porous materials, particularly wood, paper, and cloth, and as a consolidant for porous building stone, notably sandstone, as a dispersion in water.

• PVAc is known as "white glue" for wood glue and "carpenter's glue" for yellow glue. Due to its flexible strong bond and non-acidic nature, it is used as a paper adhesive during paper packaging conversion in bookbinding and book arts (unlike many other polymers).

• The use of PVAc on the Archimedes Palimpsest throughout the twentieth century made dismantling the book and conserving and imaging the pages in the early twenty-first century extremely difficult, in part because the adhesive was stronger than the parchment it held together.

• In preparing handicrafts

• As an envelope adhesive

• As a wallpaper adhesive

• As drywall and other substrate primers

• In chewing gum as a gum base

• For use as a cigarette paper adhesive

• The stiff homopolymer PVAc, but mostly the more soft copolymer vinyl acetate ethylene (VAE), a mixture of vinyl acetate and ethylene, is used in paper coatings, paint and other industrial coatings, as a binder in nonwovens, sanitary napkins, filter paper, and textile finishing.

Polyvinyl Acetate is also Used to Create Various Polymers, Such as:

Polyvinyl alcohol (HOCHCH₂): To make polyvinyl alcohol, polyvinyl acetate is partially or totally hydrolyzed. This reversible saponification and esterification reaction provided Hermann Staudinger with a powerful suggestion in the construction of his macromolecule theory.

Pvap (Polyvinyl Acetate Phthalate): PVAP is made by partially hydrolyzed polyvinyl acetate and then esterifying it with phthalic acid.

Cross-Linking in Poly Vinyl Acetate

There are free hydroxyl groups on the polymer because PVAc is polymerized with tiny amounts of vinyl alcohol. Hydrolysis of the acetate groups can also result in the formation of free hydroxyl groups. These hydroxyl groups provide cross-linking sites. Strongly chelating metal salts, such as chromium complexes, are used as cross-linking agents. Other adhesive resins, such as UF, MF, and isocyanates, have also been utilised as chemical cross-linkers with success. Cross-linked PVAcs have a higher initial tack, are stiffer, and have better moisture and heat resistance.

Source and Exposure of Poly Vinyl Acetate

Individuals may be occupationally exposed to vinyl acetate by inhalation or skin contact during its manufacture or usage, which is most likely to occur in the workplace.

Inhalation of ambient air in the vicinity of facilities that make or use this substance can also cause exposure.

Health Effect of Poly Vinyl Acetate

Acute Effects:

• Workers' eyes and upper respiratory tracts have been irritated as a result of acute inhalation exposure to vinyl acetate.

• In rodents exposed to high quantities of vinyl acetate via inhalation, nasal discomfort, laborious breathing, lung damage, and convulsions have been recorded.

•  Vinyl acetate has been shown to have moderate acute toxicity in rats, mice, and rabbits after inhalation, oral, or cutaneous exposure. 

Chronic Effects (Noncancer):

• Workers did not experience any major harmful effects as a result of chronic workplace exposure. There have been reports of upper respiratory tract discomfort, cough, and/or hoarseness.

• Chronic inhalation exposure resulted in nasal epithelial lesions, as well as irritation and inflammation of the respiratory tract in mice and rats. 

• Based on nasal epithelial lesions in rats and mice, the Reference Concentration (RfC) for vinyl acetate is 0.2 milligrammes per cubic metre (mg/m3). The RfC is an estimate of a continuous inhalation dose to the human population (including sensitive subgroups) that is unlikely to cause harmful noncancer consequences throughout a lifetime (with uncertainty spanning maybe an order of magnitude). It is a reference point to measure the potential impacts rather than a direct risk estimator. The risk of unfavourable health effects increases as exposures exceed the RfC. A lifetime of exposure above the RfC does not always suggest that a negative health consequence will occur. 

Because it established both a no observed-adverse-effect level and a no observed-adverse-effect level, EPA has high confidence in the study on which the RfC was based. (NOAEL) and a LOAEL for histopathology of the nasal olfactory epithelia in rats and mice in chronic 2-year research that employed an adequate number of animals and was meticulous in documenting experimental and exposure information; high confidence in the database because it provides sufficient supporting evidence for the RfC; and, as a result, high confidence in the RfC.

Based on the altered body and kidney weights in rats, the EPA has determined a provisional Reference Dose (RfD) for vinyl acetate of 1.0 milligrammes per kilogramme body weight per day (mg/kg/day). The tentative RfD is a value that has been reviewed by the Agency, but it is not included on IRIS.

Reproductive/Developmental Effects:

There is no information on the effects of vinyl acetate on human reproduction or development.

In one study, rats exposed to high doses of vinyl acetate via inhalation had lower body weight gain.

At the highest exposure level, foetal growth retardation was observed, but this was likely due to a significant reduction in maternal body weight gain rather than a direct developmental effect of vinyl acetate on the foetus. At the highest exposure level, minor skeletal foetal defects/variants were also observed, but these effects may have been secondary to maternal toxicity. 

In a study of rats exposed to vinyl acetate in their drinking water, body weight gain was reduced, but there were no impacts on reproductive performance. 

Cancer Risk:

• In humans, no evidence of the carcinogenic consequences of vinyl acetate is available.

• Inhalation exposure caused a rise in the incidence of nasal cavity cancers in rats, but not in mice. 

• An elevated tumour incidence (including neoplastic nodules of the liver, adenocarcinomas of the uterus [in females], and C-cell adenomas or carcinomas of the thyroid) was observed in rats exposed to vinyl acetate in drinking water. This study, however, has several flaws. 

• No treatment-related malignancies were seen in rats in another drinking water investigation.

Did You Know?

• Vinyl acetate has not been categorised by the EPA as a potential human carcinogen.

• PVAc is frequently partially hydrolyzed to a water-soluble polymer known as polyvinyl alcohol when used in coatings or adhesives.

• In 2006, about one million metric tonnes of polyvinyl alcohol were consumed globally. Kuraray (Japan, Europe, and the United States) and Sekisui Specialty Chemicals (US) are large producers, while mainland China has built several very large production facilities in the last decade and now accounts for 45 percent of global capacity.

• Polyvinyl acetate resin is a colourless, water-soluble synthetic resin that is mostly used in the treatment of textiles and paper.