Formaldehyde releasers

In this case, the components are mixed, the pH adjusted to about 6.0 with sodium hydroxide, and the solution appHed to the textile via a pad-dry-cure treatment. The combination of urea and formaldehyde given off from the THPC further strengthens the polymer and causes a limited amount of cross-linking to the fabric. The Na2HP04 not only acts as a catalyst, but also as an additional buffer for the system. Other weak bases also have been found to be effective. The presence of urea in any flame-retardant finish tends to reduce the amount of formaldehyde released during finishing. 

Their performance falls short of most present finishes, particularly in durabiUty, resistance to chlorine-containing bleaches, and formaldehyde release, and they are not used much today. Both urea and formaldehyde are relatively inexpensive, and manufacture is simple ie, 1 —2 mol of formaldehyde as an aqueous solution reacts with 1 mol of urea under mildly alkaline conditions at slightly elevated temperatures. 

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. 

Early Gross-Linking Agents. Eormaldehyde, urea—formaldehyde, and melamine—formaldehyde were among the eadiest agents utilized for resin finishes. Concerns about the safety of formaldehyde, the need for lower formaldehyde release values, and the safety of exposure to melamine have reduced the use of these early cross-linking agents by industry substantially. 

Curing Catalysts for A Methylol Agents. Many acid-type catalysts have been used in finishing formulations to produce a durable press finish. Catalyst selection must take into consideration not only achievement of the desked chemical reaction, but also such secondary effects as influence on dyes, effluent standards, formaldehyde release, discoloration of fabric, chlorine retention, and formation of odors. In much of the industry, the chemical suppher specifies a catalyst for the agent so the exact content of the catalyst may not be known by the finisher. 

Extraction tests are used primarily in Japan and Europe, a release test is used in the United States, and standard tests have been compared based on the sources of formaldehyde present in a finished fabric (76,78—80). Finished fabric may contain free formaldehyde, or formaldehyde released from unreacted /V-methy1o1 moieties. 

Researchers had noted the release of formaldehyde by chemically treated fabric under prolonged hot, humid conditions (85,86). The American Association of Textile Chemists and Colorists (AATCC) Test Method 112 (87), or the sealed-jar test, developed in the United States and used extensively for 25 years, measures the formaldehyde release as a vapor from fabric stored over water in a sealed jar for 20 hours at 49°C. The method can also be carried out for 4 hours at 65°C. Results from this test have been used to eliminate less stable finishes. 

Control of Formaldehyde Release. Once the sealed-jar test became a factor in measuring the formaldehyde release of fabrics suppHed to garment cutters, limitations were placed on the allowable limits acceptable to the garment producers. These limits brought to the fore two classes of reagents those based on DMDHEU, and those based on the /V, /V- dim ethyl o1 ca rh am a tes (4) (88). 

Prior to 1965, it was not unusual for unwashed finished fabrics to release 3—5000 ppm of formaldehyde when tested by an AATCC test method. Formaldehyde release was reduced to the level of 2000 or less by appHcation of DMDHEU or dimethyl olcarhama tes. This level was reduced to approximately 1000 in the mid-1970s. Modification of the DMDHEU system and use of additives demonstrated that release values below 100 ppm were achievable. As of this writing (1997), good commercial finishing ranges between 100 and 200 ppm of formaldehyde release. 

Several factors were utilized in bringing formaldehyde release down. In particular, resin manufacturer executed more careful control of variables such as pH, formaldehyde content, and control of methylolation. There has also been a progressive decrease in the resin content of pad baths. The common practice of applying the same level of resin to a 50% cotton—50% polyester fabric as to a 100% cotton fabric was demonstrated to be unnecessary and counter productive (89). Smooth-dry performance can be enhanced by using additives such as polyacrylates, polyurethanes, or siUcones without affecting formaldehyde release. 

One technique that has been employed to lower formaldehyde release has been the alkylation of the /V-methy1o1 agent (90—93) with an alcohol (eq. 

Nonformaldehyde Finishing. The concern for formaldehyde release prompted interest in the development of cross-linking systems that did not contain formaldehyde. A number of systems were investigated but generally these systems seemed to fall short in performance (106,107). For example, l,3-dimethyl-4,5-dihydroxyethyleneurea (DMeDHEU) (5) has been used in Japan since 1974. This same agent has been marketed in the United States and elsewhere, but generally the level of smooth-dry performance is substantially lower than the level achievable with DMDHEU. The cost of dimethylurea also raises the overall cost of DMeDHEU above that of DMDHEU. 

As of this writing (1997), researchers are exploring combinations of acids, additives, and catalysts to achieve a suitable economic finish. However, commercial appHcation of these finishes would require costs akin to that of DMDHEU as well as compliance with formaldehyde release levels by consumers, regulators, and the textile industry. Another possible impetus could be marketing considerations. Nevertheless, this work has sparked intense effort in the use of cross-linkers containing ester cross-links and has broadened the scope of cross-linker research. 

Products that are allowed to remain on the skin are differentiated from those that are meant to be rinsed off. Components of products left on the skin can be expected to penetrate the viable epidermis and to be systematically absorbed. Products that are rinsed off shordy after skin contact, such as shampoos, can, if propedy labeled, contain preservatives that might eUcit adverse reactions if left on the skin. Typical examples of such preservatives are formaldehyde, formaldehyde releasers such as Quatemium 15 or MDM hydantoin, and the blend of methylchloroisothia2olinone and methylisothia olinone. 

Another formaldehyde-releasing preservative is imidazolidinyl urea (see page 36). 

Various formaldehyde condensates have been developed to reduce the irritancy associated with formaldehyde while maintaining activity and these are described as formaldehyde-releasing agents or masked-formaldehyde compounds. 

Formaldehyde release biocides are perhaps the most commonly used biocides in metalworking fluids. One of die best know examples of this chemistry is hexahedron -l,3,5-tris(2-hydroxyethyl)-s-triazine, (see Figure 2). 

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. 

Another class of formaldehyde release biocide are the oxizolidines. 

Secondly, customers are applying ever greater pressures on formulators to make less use of some chemistries, for example formaldehyde release biocides. Customers would prefer preservatives that are good for die environment and possess no adverse mammalian toxicity characteristics. This would require that new actives are developed. This is unlikely considering the new regulatory frameworks. 

Formaldehyde, released from certain antimicrobials in metalworking fluids, activates amines toward nitrosation by nitrite (21). This reaction enhances nitrosation in neutral and basic medium. Since metalworking fluids are typically of pH 9-11, formaldehyde released from... 

Biocides that function as formaldehyde-releasers comprise about 60 % of total sales of antimicrobials (29). Thus, such antimicrobials are expected to be common additions to metalworking fluids. Examples of formaldehyde-releasing antimicrobials are tris(hydroxy methyl) nitromethane, trivially called tris nitro, 4,4 -(2-ethyl-2-... 

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. 

The toxic potential of metabolic intermediates, of the carrier moiety, or of a fragment thereof, should never be neglected. For example, some problems may be associated with formaldehyde-releasing prodrugs such as N- and 0-[(acyloxy)methy 1] derivatives or Mannich bases. Similarly, arylacetylenes assayed as potential bioprecursors of anti-inflammatory arylacetic acids proved many years ago to be highly toxic due to the formation of an intermediate ketene. 

Hydrolysis may be faster when R" = H rather than Me in the general structure RR,N-C0-0-CHR"-0-C0-R ". However, the toxicity of the formaldehyde released in this case may be a cause for concern. 

Chapman studied the nitrolysis of symmetrical methylenediamines. The nitrolysis of N, N, N, M-tetramethylmethylenediamine with nitric acid-acetic anhydride-ammonium nitrate mixtures gives both dimethylnitramine and RDX the latter probably arises from the nitroT ysis of hexamine formed from the reaction of ammonium nitrate and formaldehyde released from the hydrolysis of the methylenediamine. The same reaction with some morpholine-based methylenediamines (105) allows the synthesis of l,3,5-trinitro-l,3,5-triazacycloalkanes (106). 

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