Urea-formaldehyde (UF), also known as urea-methanal, so named for its common synthesis pathway and overall structure, is a
nontransparent thermosetting
resin
In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on n ...
or
polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
. It is produced from
urea
Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid.
Urea serves an important ...
and
formaldehyde
Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section ...
. These resins are used in
adhesives
Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation.
The use of adhesives offers certain advant ...
,
plywood,
particle board
Particle board, also known as chipboard or low-density fiberboard, is an engineered wood product manufactured from wood chips and a synthetic resin or other suitable binder, which is pressed and extruded. Particle board is often confused with ...
,
medium-density fibreboard
Medium-density fibreboard (MDF) is an engineered wood product made by breaking down hardwood or softwood residuals into wood fibres, often in a defibrator, combining it with wax and a resin binder, and forming it into panels by applying high t ...
(MDF), and molded objects.
UF and relate amino resins are a class of
thermosetting resins of which urea-formaldehyde resins make up 80% produced worldwide. Examples of amino resins use include in automobile tires to improve the bonding of rubber to in paper for improving tear strength, in molding electrical devices, jar caps, etc.
History
UF was first synthesized in 1884 by Dr Hölzer, who was working with
Bernhard Tollens, neither of whom realized that the urea and formaldehyde were polymerizing.
In the following years a large number of authors worked on the structure of these resins.
In 1896, Carl Goldschmidt investigated the reaction further. He also obtained an amorphous, almost insoluble precipitate, but he did not realize that polymerization was occurring; he thought that two molecules of urea were combining with three molecules of formaldehyde. In 1897 Carl Goldschmidt patented the use of UF-resins as a disinfectant. General commercialisation followed this and in the following decades, more and more applications were described in the literature.
In 1919, Hanns John (1891–1942) of Prague, Czechoslovakia, obtained the first patent for UF resin in Austria.
Urea-formaldehyde was object matter of judgment via the
European Court of Justice (now CJEU) of 5 February 1963, Case 26–62 ''Van Gend & Loos v Netherlands Inland Revenue Administration''.
Properties
Urea-formaldehyde resin's attributes include high
tensile strength
Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials t ...
,
flexural modulus In mechanics, the flexural modulus or bending modulus is an intensive property that is computed as the ratio of stress to strain in flexural deformation, or the tendency for a material to resist bending. It is determined from the slope of a stres ...
, high heat-distortion temperature, low water absorption, mould shrinkage, high surface hardness, elongation at break, and volume resistance. It has a
refractive index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, or ...
of 1.55.
Chemical structure
The chemical structure of UF polymer consists of
2NH">O)CNHCH2NHsub>n repeat units. In contrast, melamine-formaldehyde resins feature NCH
2OCH
2N repeat units. Depending on the polymerization conditions, some branching can occur. Early stages in the reaction of formaldehyde and urea produce
bis(hydroxymethyl)urea.
Production
About 20 million metric tons of UF are produced annually. Over 70% of this production is then put into use by the forest-products industry for bonding particleboard, MDF, hardwood plywood, and laminating adhesive.
General uses
![A selection of urea formaldehyde objects at the science museum](https://upload.wikimedia.org/wikipedia/commons/b/ba/A_selection_of_urea_formaldehyde_objects_at_the_science_museum.JPG)
Urea-formaldehyde is pervasive. Examples include decorative laminates, textiles, paper, foundry sand molds,
wrinkle-resistant fabric
Wrinkle-resistant or permanent press or durable press is a finishing method for textiles that avoids creases and wrinkles and provides a better appearance for the articles. Most cellulosic fabrics and blends of cellulosic rich fabrics tend to ...
s, cotton blends,
rayon,
corduroy
Corduroy is a textile with a distinctively raised "cord" or wale texture. Modern corduroy is most commonly composed of tufted cords, sometimes exhibiting a channel (bare to the base fabric) between them. Both velvet and corduroy derive from fu ...
, etc. It is also used as wood glue. UF was commonly used when producing electrical appliances casing (e.g. desk lamps). Foams have been used as artificial snow in movies.
Agricultural use
UF is also used in agriculture as a
slow-release source of nitrogen. Its rate of decomposition into and is determined by the action of microbes found naturally in most soils. The activity of these microbes, and the rate of ammonia release, is temperature-dependent. The optimum temperature for microbe activity is around .
Foam insulation
![Urea-formaldehyde insulation](https://upload.wikimedia.org/wikipedia/commons/c/c5/Urea-formaldehyde_insulation.jpg)
Urea-formaldehyde
foam insulation
Building insulation materials are the building materials which form the thermal envelope of a building or otherwise reduce heat transfer.
Insulation may be categorized by its composition (natural or synthetic materials), form (batts, blankets, lo ...
(UFFI) commercialisation dates to the 1930s as a synthetic insulation with
R-values up to 5.0 °F⋅ft2⋅h/BTU (0.8 K⋅m2/W). UFFI is a foam with similar consistency to shaving cream, that is easily injected or pumped into voids. It is normally made on site using a pump set and hose with a mixing gun to mix the foaming agent, resin, and compressed air. The fully expanded foam is pumped into areas in need of insulation. It becomes firm within minutes, but cures within a week. UFFI is generally found in homes built or retrofitted from the 1930s to the 1970s, often in basements, wall cavities, crawl spaces and attics. Visually, it looks like oozing liquid that has been hardened. Over time, it tends to vary in shades of butterscotch, but new UFFI is a light yellow colour. Early forms of UFFI tended to shrink significantly. Modern UF insulation with updated catalysts and foaming technology have reduced shrinkage to minimal levels (between 2 and 4%). The foam dries with a dull matte colour with no shine. When cured, it often has a dry and crumbly texture.
Health concerns
Health effects occur when UF-based materials and products release formaldehyde into the air. Generally, no health effects from formaldehyde are seen when air concentrations are below 1.0 ppm. The onset of respiratory irritation and other health effects, and even increased
cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
risk, begin when air concentrations exceed 3.0–5.0 ppm. This triggers watery eyes, nose irritations, wheezing and coughing, fatigue, skin rash, severe allergic reactions, burning sensations in the eyes and throat, nausea, and difficulty in breathing in some humans (usually > 1.0 ppm).
Occupants of UFFI-insulated homes with elevated formaldehyde levels experienced systemic symptoms such as headache, malaise, insomnia, anorexia, and loss of libido. Irritation of the
mucous membrane
A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It i ...
s (specifically the eyes, nose, and throat) was a common upper respiratory tract symptom related to formaldehyde exposure. However, when compared to control groups, the frequency of symptoms did not exceed the controls except for wheezing, difficult breathing, and a burning skin sensation. Controlled studies have suggested that tolerance to formaldehyde's odor and irritating effects can occur over a prolonged exposure.
See also
*
*
Phenol formaldehyde resin
Phenol formaldehyde resins (PF) or phenolic resins (also infrequently called phenoplasts) are synthetic polymers obtained by the reaction of phenol or substituted phenol with formaldehyde. Used as the basis for Bakelite, PFs were the first commerc ...
References
External links
Urea formaldehyde (Plastics Historical Society)* History of urea-formaldehyde: Chapter 1 of: Carl Meyer, ''Urea-Formaldehyde Resins'' (Reading, Massachusetts: Addison-Wesley, 1979)
Urea-Formaldehyde Foam InsulationCanada Mortgage and Housing Corporation
Canada Mortgage and Housing Corporation (CMHC) (french: Société canadienne d'hypothèques et de logement) (SCHL) is Canada's national housing agency, and state-owned mortgage insurer. It was originally established after World War II, to help re ...
)
Indoor Air Quality: FormaldehydeUS
Environmental Protection Agency)
Formaldehyde.... its safe use in foundries(UK
Health and Safety Executive)
(United States Environmental Protection Agency)(Environmental and Occupational Health Assessment Program, Connecticut Department of Public Health)*
ttp://www.fpl.fs.fed.us/documnts/pdf1996/conne96a.pdf (Forest Products Laboratory: USDA Forest Service)*
unky, M., "Urea-formaldehyde (UF) adhesive resins for wood," International Journal of Adhesion and Adhesives, 1998. (18:2).(Encyclopædia Britannica)(U.S. Dept. of Labor, Occupational Safety and Health Administration (OSHA))
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Polyamides
Synthetic resins
Plastics
Thermosetting plastics