Phenol formaldehyde toxicity

Most processors of fiber-reinforced composites choose a phenol formaldehyde (phenoHc) resin because these resins are inherently fire retardant, are highly heat resistant, and are very low in cost. When exposed to flames they give off very Htde smoke and that smoke is of low immediate toxicity. PhenoHc resins (qv) are often not chosen, however, because the resole types have limited shelf stabiHty, both resole and novolac types release volatiles during their condensation cure, formaldehyde [50-00-0] emissions are possible during both handling and cure, and the polymers formed are brittle compared with other thermosetting resins. 

Phenol-formaldehyde resins using prepolymers such as novolaks and resols are widely used in industrial fields. These resins show excellent toughness and thermal-resistant properties, but the general concern over the toxicity of formaldehyde has resulted in limitations on their preparation and use. Therefore, an alternative process for the synthesis of phenolic polymers avoiding the use of formaldehyde is strongly desired. 

Tisler, T. and Zagorc-Koncan, J. Comparative assessment of toxicity of phenol, formaldehyde, and industrial wastewater to aquatic organisms. Water, Air, SolIPoIIut., 97(3/4) 315-322, 1997. 

Debate is continuing on the safety and toxicity of formaldehyde and its products, especially urea-formaldehyde foam used as insulation in construction and phenol-formaldehyde as a plywood adhesive. Presently the TLV-STEL of formaldehyde is 0.3 ppm. Formaldehyde is on the Reasonably Anticipated to Be Human Carcinogens list. 

Urea-formaldehyde resins are used for applications in which the panel is not in contact with water. For applications with high level of humidity, the phenol-formaldehyde resins are required. In all cases, free formaldehyde constitutes a dangerous pollutant that is slowly released and can be particularly toxic in confined rooms. Recent research has been done to substitute this type of resin by natural binders, such as cross-linkable proteins (Silvestre et al., 2000 Yang et al., 2006). 

Some nonconventional bonding methods are based on the use of agricultural by-products, i.e., on nonpetroleum-based materials this use constitutes another advantage. Some nonconventionally bonded materials produce reduced amounts of toxic gaseous materials, such as formaldehyde, that make them preferable to phenol-formaldehyde products and urea-formaldehyde resins. Economically, the nonconventional methods do not offer any particular advantages, although they appear to be competitive with the conventional methods. 

PF is made by the condensation polymerisation of phenol and formaldehyde. Due to the volatile and toxic/irritant nature of formaldehyde, this is usually fixed with ammonia giving hexamine. Polymerisation of hexamine and phenol not only produces phenol formaldehyde but may release residues of phenol, formaldehyde or ammonia. In certain cases some residues may remain in the moulding and be released into the product. As with UF, PF is mainly used for closures but due to the fact that the material is naturally dark, it is used for dark or deep colours. PF is generally more resistant to heat and moisture than UF. Both UF and PF are used with a range of fillers, e.g. wood flour, synthetic fibre. Density 1.25-1.45. General pharmaceutical applications have now reduced. 

BGVV Empfehlung XL for Germany. Depending on the raw material, most as-sup-plied resols contain relatively large amounts of toxic substances (phenols, formaldehyde, etc.). They must therefore be properly labelled, stored, and handled. As a result of improvements in production methods and the choice of suitable raw materials, useable resols with greatly reduced levels of toxic substance have been developed and made available to the paint industry. 

Phenolic polymers and phenol-formaldehyde resins are of great commercial interest for a number of electronic and industrial applications (7). However, there have been serious concerns regarding their use due to various toxic effects of formaldehyde and harsh synthesis environments (2). Peroxidase-catalyzed oxidative polymerization of phenol and substituted phenols provides an alternate route for the synthesis of phenolic polymers (3,4), The increased interest in this type of enzyme-based polymerization is mostly due to its environmental compatibility and potential for producing industrial polymers in high yield (5). 

Phenol-formaldehyde (PF) resins have been successfully used in FRP materials as inherently fire retardant resins, because they have low flame spread indexes and produce very Utde smoke or toxic fumes without the assistance of other fire retardant fillers. Applications include many fire-sensitive areas such as rocket... 

The natural resins present in native guayule have been extensively studied and include mono-, sesqui-, di-, and triterpene groups, as well as other secondary metabolites (108). Unfractionated guayule resin has shown considerable promise in the areas of wood preservation (in marine and terrestrial environments) (129) and insect antifeedents (termite resistance) (130-132). These resins also show promise as a biobased renewable replacement for petroleum-based monomers and oligomers in adhesives and coatings. Additional profitable uses for the resins include a natural, low toxicity replacement for creosote in wood treatment and for prevention of termite attack. Resin/lignin products, such as additives for phenol formaldehyde resins, may also prove possible. 

Phenol-formaldehyde polymers, including novolaks and resoles, have a number of applications in coatings, finishes, adhesives, composites, laminates and related areas. Concerns have been raised regarding the continued use of phenol-formaldehyde resins due to the various toxic effects of formaldehyde. Consequently, there has been active investigation for alternative sources of these types of oligomers and polymers with a consideration for environmental compatibility. 

CAUTION Toxicity) Phenols, formaldehyde, and other aldehydes are toxic and should be handled with adequate ventilation and skin protection [17]. Where possible the use of hydrogen chloride in the presence of formaldehyde or formaldehyde sources (hexamethylenetetramine and the like) should be avoided. Recent reports have indicated that formaldehyde and hydrogen chloride spontaneously react to give the known carcinogen 6w(chloromethyl) ether. 

Resin types are determined by the end-use of the laminate. Such types as melamine formaldehyde, urea formaldehyde, polyester, polystyrene, epoxies etc., are all common-place, either alone or in mixtures. Some laminates, notably decorative HPL, employ two t)q)es in the same construction. The decorative surface is obtained with melamine formaldehyde, which is desirable for its colourless, tasteless, non-toxic characteristics, but cheaper and stronger (although brittle) phenol formaldehydes are used in the core of the laminate. 

During the last ten years, many research results have shown that oxidative polymerization catalyzed by peroxidases is a convenient, resource-saving, and environmentally friendly method for synthesizing phenol polymers. In contrast to the conventional synthesis of phenol-formaldehyde resins, the peroxidase-catalyzed polymerization of phenol proceeds under mild reaction conditions (room temperature, neutral pH). The polymerization of toxic phenols has promising potential for the cleaning of wastewaters. Moreover, the polymerization of phenols from renewable resources is expected to attract much attention in times of worldwide demand for the replacement of petroleum-derived raw materials. Besides the environment-protecting aspects of this innovative type of polymerization, the enzyme-catalyzed polymerization represents a convenient method to reahze new types of functional polyaromatic polymers. Phenol polymers made by peroxidase catalysis should have much potential for electronic and optical apphcations. The synthesis of functional phenol polymers is facihtated by the fact that poly-... 

Various polymers and latexes ai e used in manufacturing different articles for medical use. Safety measures in using such articles require strict control measures which provide for detecting toxic substances on hygienic standard levels or on the permissible migration level (PML) (mg/dm ). Chromatographic reaction methods ai e used to reveal formaldehyde, phenol, and epichlorhydrin. 

Benzoxazines are heterocyclic compounds obtained from reaction of phenols, primary amines, and formaldehyde.98,99 As described previously, they are key reaction intermediates in the HMTA-novolac cure reaction.40,43 Crosslinking benzoxazine monomers at high temperatures gives rise to void-free networks with high Tgs, excellent heat resistance, good flame retardance, and low smoke toxicity.100 As in HMTA-cured novolac networks, further structural rearrangement may occur at higher temperatures. 

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