Amino resins formaldehyde release

Amino and Phenolic Resins. The largest use of formaldehyde is in the manufacture of urea—formaldehyde, phenol—formaldehyde, and melamine—formaldehyde resins, accounting for over one-half (51%) of the total demand (115). These resins find use as adhesives for binding wood products that comprise particle board, fiber board, and plywood. Plywood is the largest market for phenol—formaldehyde resins particle board is the largest for urea—formaldehyde resins. Under certain conditions, urea—formaldehyde resins may release formaldehyde that has been alleged to create health or environmental problems (see Amino RESINS AND PLASTICS). 

Paraformaldehyde [30525-89-4] is a mixture of polyoxymethylene glycols, H0(CH20) H, with n from 8 to as much as 100. It is commercially available as a powder (95%) and as flake (91%). The remainder is a mixture of water and methanol. Paraformaldehyde is an unstable polymer that easily regenerates formaldehyde in solution. Under alkaline conditions, the chains depolymerize from the ends, whereas in acid solution the chains are randomly cleaved (17). Paraformaldehyde is often used when the presence of a large amount of water should be avoided as in the preparation of alkylated amino resins for coatings. Formaldehyde may also exist in the form of the cycHc trimer trioxane [110-88-3]. This is a fairly stable compound that does not easily release formaldehyde, hence it is not used as a source of formaldehyde for making amino resins. 

It is important that the amino resins used in the postcure process should ( /) not react with the fabric before it has been fashioned into a garment, and (2) release a minimum amount of formaldehyde into the atmosphere, especially while the goods are in storage or during the cutting and sewing operations. These requirements are met, at present, with the diethylene glycol modified DMDHEU resin. 

Urea—Formaldehyde Reaction Products. Urea—formaldehyde (UF) reaction products represent one of the older controlled release nitrogen technologies. An early disclosure of the reaction products of urea [57-13-6] and formaldehyde [50-00-0] was made in 1936 (1) (Amino resins and plastics). In 1948, the USDA reported that urea (qv) and formaldehyde (qv) could react to produce a controlled release fertilizer at urea to formaldehyde mole ratios (UF ratio) greater than one (2). 

Formaldehyde emission from particleboard has been studied at our laboratory for over 15 years. We search for an answer to the following question Given the fact that amino-resin bonded wood products have the ability to release formaldehyde into indoor air when they are in use, what simple and rapid analysis method can be used at the time of manufacture to predict formaldehyde release under use conditions as quantitatively as possible Obviously, the chosen method needs to be applicable for all types of boards that are available on the market. 

Environmental Protection. The potential release of formaldehyde during application and cure is a serious problem in the handling of amino resins. Depending on the structure and the conditions of manufacture a resin can contain 0.25-3% free... 

Fully alkylated MF resins may contain <0.25% free formaldehyde. Partially alkylated resins usually have a higher content (< 3%). The free formaldehyde content of an amino resin is largely responsible for the formaldehyde released during the application process. This is only a small fraction of the total formaldehyde released. Hydrolysis of the amino resin and subsequent dehydroxymethylation during curing account for > 80% of the total formaldehyde release (see also p. 84). 

Although resins with a high amino content have a higher content of free formaldehyde than fully alkylated resins, they release lower amounts of formaldehyde during cure. The lowest amount of formaldehyde during application and cure is released by alkylated glycoluril-formaldehyde resins [2.155]. 

Urea-Formaldehyde and Related Adhesives. Urea-formaldehydes (UF) are the most significant members of the class of materials known as the Amino Resins or aminopolymers. These are the polymeric condensation products of the reaction of aldehydes with amines or amides. A molar excess of formaldehyde is used, and this along with the temperature and the pH dictate the properties of the final product. The initial reactions of urea and formaldehyde to form mono- and dimethylolureas can be catalyzed by either acids or bases, but the final condensation reactions will proceed only under acid conditions. These adhesives are widely used to make plywood and particleboard in processes utilizing heated hydraulic presses with multiple outlets for water vapor release. Temperatures up to 200°C... 

Phenolic and amino resins Usually as dry prepreg Free Phenol, also released on cure. Formaldehyde is strong eye, skin and respiratory irritant... 

Paraformaldehyde is available as a solid in the form of flakes or powder. It is an unstable polymer and can easily release formaldehyde when dissolved in water. Formaldehyde also exists in the form of a cyclic trimer, trioxane. It is a fairly stable compound and is not used in the manufacture of amino resin adhesives. 

General Properties. Amino resins are generally aqueous solutions of acid-catalyzed urea-formaldehyde (UF) polymers. A typical resin would be about 60% solids containing urea and formaldehyde in molar ratios of about 1 1.2. UFs are cured with heat under pressure and usually with an acid catalyst if the wood species is not acidic. The resultant bond is not water resistant, especially at elevated temperature. Formaldehyde is slowly released from UFs as they decompose. Even at low concentrations, the released formaldehyde may be a nuisance in poorly ventilated living quarters. 

Formaldehyde is used as a chemical intermediate in the manufacture of a large variety of organic compounds, ranging from amino and phenolic resins to slow release fertilizers (Gerberich et al. 1980). Table 4-3 shows the distribution of formaldehyde use for select periods between 1963 and 1977. The demand for formaldehyde in North America was 11.6 billion pounds in 1995, a slight increase from the... 

The irritancy of amino plastic is mainly due to formaldehyde, which can be released from plastics. Nowadays, resins used in textiles release lower levels of free formaldehyde than previously (Belsito 1993). Occupational irritant contact dermatitis from fiber board containing urea-formaldehyde resin has been reported (Vale and Rycroft 1988). Dust from urea-formaldehyde insulating foam has caused airborne irritancy (Dooms-Goossens et al. 1986). 

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