Formaldehyde release concentration

N,]S7-bis(methoxymethyl)uron was first isolated and described in 1936 (41), but was commercialized only in 1960. It is manufactured (42) by the reaction of 4 mol of formaldehyde with 1 mol of urea at 60°C under highly alkaline conditions to form tetramethylolurea [2787-01-1]. After concentration under reduced pressure to remove water, excess methanol is charged and the reaction continued under acidic conditions at ambient temperatures to close the ring and methylate the hydroxymethyl groups. After filtration to remove the precipitated salts, the methanolic solution is concentrated to recover excess methanol. The product (75—85% pure) is then mixed with a methylated melamine—formaldehyde resin to reduce fabric strength losses in the presence of chlorine, and diluted with water to 50—75% soHds. Uron resins do not find significant use today due to the greater amounts of formaldehyde released from fabric treated with these resins. 

It does have a number of draw backs. It has poor thermal stability (a property common to most formaldehyde release biocides) and, in some instances, may cause blackening of metalworking fluid concentrates if heated above 50°C for a period of time. Recently, this active ingredient was placed on Annex 1 of the Dangerous Substances Directive having been identified as a potential skin sensitiser. This means that formulations containing efficacious levels of this class of triazine in them would have to be labelled with R43 - may cause sensitisation by skin contact. This is unacceptable to many UK customers. As this material is only bactericidal, it needs to be co-formulated with a fungicide to provide complete protection for a product. 

The pH of a metalworking fluid must be kept above neutrality in order to prevent acid corrosion of the metal In vitro, acid catalyzed nitrosation is optimized at pH 3.5 (4 0) however, it has been shown that In the presence of other catalysts, aqueous solutions of amines and nitrite leads to significant yields of nitrosamines at room temperature over the pH range of 6.4 to 11.0 (41). Furthermore, C-nitro-containing, formaldehyde-releasing biocides, such as bronopol or tris nitro, exert their potential catalytic effect in alkaline solution. It would thus be desirable to determine the optimum pH for a metalworking fluid that would lead to the lowest concentration of nitrosamine possible. 

There are a number of other variations of the Friedel-Crafts reaction which are useful in synthesis. The introduction of chloromethyl substituents is brought about by reaction with formaldehyde in concentrated hydrochloric acid and a Lewis acid, especially zinc chloride.56 The reaction proceeds with benzene and derivatives with electron-releasing groups. The reactive electrophile is probably the chloromethylium ion. 

Formaldehyde-releasing preservatives, such as quater-nium-15, diazolidinyl urea, and imidazolidinyl urea, are widely used in cosmetics and topical medications and are well-known contact sensitizers. In spite of positive patch test reactions to these preservatives in a number of patients, only some of these patients will react when they use the corresponding commercial formulations. This is because the concentrations of preservatives in the commercial products are often below the threshold necessary to produce a clinical reaction. This finding confirms the importance of using commercial formulations of topical agents in estimating the clinical relevance of patch test results (10). 

Formaldehyde release from pressed wood products is due to latent formaldehyde. During the pressing process, hot steam from moist wood particles transfers heat, formaldehyde, and other volatiles from the surface of the mat to the core of the board where un reacted urea-formaldehyde resin components accumulate. The resulting formaldehyde concentration in the core is approximately twice that of the surface. Release of formaldehyde is diffusion-controlled and gradually decreases over time (Meyer and Hermanns 1985). Formaldehyde can also be produced by hydrolytic cleavage of unreacted hydroxymethyl groups in the formaldehyde resins. Melamine formaldehyde resins generally are more stable, and the amounts of formaldehyde emitted from them are much lower (WHO 1989). 

Reduced sample loadings in the dynamic chamber led to decreased formaldehyde concentrations in the chamber as noted or predicted previously by others (17, 20-22). This resulted in increased release rate coefficients (yg m 2 day"b. Samples analyzed at 1.4 and 1.6 m2 of product surface area/m of chamber volume chamber loadings had formaldehyde chamber concentrations of 28-32% of the calculated equilibrium air concentrations of formaldehyde (17), suggesting better relative ventilation than that at higher chamber loadings. 

This is sufficient for partial conversion to cellulose-hemiacetal, with a residual formaldehyde concentration of less than 0.1 wt% In the cell water. This formaldehyde concentration is enough to produce an equilibrium vapor pressure of 20 Torr of formaldehyde (34) in the wood cell. The kinetics of the formaldehyde release from water are also pH dependent (35). 

Due to its affinity for water, formaldehyde will concentrate in wood products in their water reservoirs. Since wood collects water in Its S-2 secondary wall on the surface of wood cellulose, formaldehyde will come into contact with wood cellulose. This work shows that formaldehyde can be expected to react with wood cellulose forming hemiacetals. Since this reaction is reversible, these hemiacetaIs constitute a temporary reservoir for formaldehyde within wood. This fact may explain the complex formaldehyde release and absorption properties of UF-bonded wood products. 

Two sensitive fluorometric enzymatic methods for the determination of formaldehyde release from wood products were described. These methods were developed using the enzyme formaldehyde dehydrogenase to catalyze the oxidation of formaldehyde to form formic acid and NADH in the presenc of oxidized nicotinamide adenine dinucleotide (NAD ). The increase in NADH, which is directly proportional to the concentration of formaldehyde, is measured fluorometrically at em ... 

In cooperation with DSM, MCN developed a method of measurement for the determination of the formaldehyde release from particle board, based on a theorie for mass transfer, implying that under steady state conditions the emission of formaldehyde of a given particle board can and should be defined by two parameters of the particular board. These two parameters are (1) Ce defined as the equilibrium formaldehyde concentration (with ventilation rate 0") and (2) kgg defined as the overall mass transfer coefficient of the board. In (ideal mixed) climate rooms the stationary formaldehyde... 

Out of the results of the intersection should follow an equilibrium concentration of 0.35 mg/m, which is not in accordance with the determined equilibrium value. So this experimental set up is a case of a situation which is not well defined and therefore not suitable for measurement of the relevant formaldehyde release parameters of the particleboard. 

The purpose of this study was to evaluate laboratory formaldehyde release test methods for predicting real-life formaldehyde air concentrations human exposure levels, and health risk. Three test methods were investigated the European perforator test, the gas analysis method at 60 C and 3% RH, and the gas analysis method at 23 C and 55% RH. Different types of particleboard bonded with urea-formaldehyde and urea-melamine-formaldehyde resins were tested. The results were used to rank boards as a function of test method, conditioning, short-term humidity, and temperature variations during storage. Additional experiments were conducted in small experimental houses at a Dutch research institute. Our conclusions are that relative ranking of products is influenced by the test method and by change in relative humidity. The relationship between test method and release in real-life situations is not clear. In fact, it seems impossible to use laboratory measurements to predict real-life product performance of board if the board is not fully in equilibrium with the atmosphere. 

Thus, as we currently try to reduce formaldehyde release into air through regulations, it would seem that actions taken for the sake of "health are currently going beyond scientifically established facts. Thus, by way of example, in the Federal Republic of Germany the following approach was proposed some time ago The total formaldehyde air concentration from all sources should not reach air concentrations higher than 0.1 ppm, on and after the 1st of July 1985, and, from the 1st of July 1990, the total concentration in the air should not exceed 0.05 ppm. Fortunately, the latest official... 

A similar analytical scheme for following the transformation of 3,4,6-tri-O-methyl-D-fructose gave somewhat better results. In these experiments, the disappearance of 3,4,6-tri-O-methyl-n-fructose was determined by measuring the formaldehyde released on periodate oxidation. The periodate consumption by these mixtures served as a check on the formation of products other than 3,4,6-tri-0-methyl-n-glucose and 3,4,6-tri-O-methyl-D-mannose, since each of the 3,4,6-tri-O-methylhexoses consumes 1 mole of periodate per mole. Actually, the periodate titers increased approximately 20% during the time-period that the apparent concentration of 3,4,6-tri-O-methyl-D-fructose diminished to about 60% of the initial concentration (when the reaction was carried out in sodium hydroxide solution). The change in periodate consumed was attributed to occurrence of demethylation. When the transformation was carried out in either calcium hydroxide or barium hydroxide solutions, the periodate consumption increased markedly. Hence, calcium and barium ions appear to catalyze this side reaction. ... 

Formaldehyde is generally the aldehyde used in the preparation, setting, and curing of tannin adhesives. It is normally added to the tannin extract solution at the required pH, preferably in its polymeric form of paraformaldehyde, which is capable of fairly rapid depolymerization under alkaline conditions, and as urea-formalin concentrates. Hexamethylenetetramine (hexamine) may also be added to resins due to its potential formaldehyde releasing action under heat. Hexamine is, however, unstable in acid media [24] but becomes more stable with increased pH values. Hence under alkaline conditions the liberation of formaldehyde might not be as rapid and as efficient as wanted. Also, it has been fairly widely reported, with a few notable exceptions [25], that bonds formed with hexamine as hardener are not as boil resistant [26] as those formed by paraformaldehyde. The reaction of formaldehyde with tannins may be controlled by the... 

Certain other reactions of aromatic molecules are closely related to the Friedel-Crafts reaction. The introduction of chloromethyl groups is brought about by formaldehyde in concentrated hydrochloric acid in the presence of halide salts, especially zinc chloride. The reaction is restricted in scope to benzene and derivatives with electron-releasing substituents. Several mechanistic pathways could be operative in the chloromethylation reaction, but the active electrophile is probably protonated chloromethyl alcohol. 

Dimethylol-dimethyl hydantoine (DMDM hydan-toin, Glydant). This is a cosmetic preservative and formaldehyde releaser. The patch-test concentration 1% aqua (Perrenoud et al. 1994). 

Dowicil 100, Dowicil 75, Dowicide Q, CAS no. 4080-31-3). This is a quaternary ammonium compound and a formaldehyde releaser. It is used mainly in water-based cosmetics, as a preservative (Jacobs et al. 1995 Boffa and Beck 1996 Prue et al. 1998). The patch-test concentration is 2% pet. 

Benzyl alcohol is listed in the EC positive list of preservatives for cosmetic products (maximum concentration for application 10 000 mg/litre). The activity of benzyl alcohol is not very much affected by the pH and the composition of the medium to be protected. As an auxiliary solvent with antimicrobial efficacy benzyl alcohol is used in preservative compositions for industrial fluids (Paulus et al., 1970 z). A well-known preservative for cosmetics and industrial fluids is benzyl alcohol mono(poly)hemiformal (Paulus, 1976) which is a formaldehyde releasing compound and therefore listed in Section 3.1.1. 

It could be demonstrated that in emulsion paints the addition of formaldehyde releasers, in limited concentration of providing not more than lOOmg/kg of free formaldehyde in the can, did not split off formaldehyde into the indoor air above the recommended limits of the German BfR for living rooms (Bagda, 1997). A special advantage of formaldehyde is the high volatility. The formaldehyde evaporates within the first days after application and poses no risk for the end user of the room, while the emissions while painted are below worker s exposure thresholds set up by international standards. (Colon, 1998). In the USA the 100 ppb OSHA limit. 

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