Phenol-formaldehyde solutions, color

Water-soluble phenol-formaldehyde solutions can also be impregnated into degraded wood and polymerized (14), Although this resin system greatly improves strength and integrity, the color of the treated wood is always reddish-brown. This color may not be a problem for darker wood, but it is a serious drawback for many potential applications. 

Phenol-formaldehyde is a thermosetting polymer and has a number of desirable properties for a polymer, it is very heat resistant and hard is less brittle than many of the ceramic materials is very stable and unreactive with most common solutions and solvents and doesn t easily chip, fade, or discolor. Furthermore, it is a relatively inexpensive material, and modem phenolics can be produced having a large variety of colors. The elastic characteristics of this polymer are very similar to those of ivory, and when phenolic bilhard baUs coDide, they make the same chcking sound as ivory baUs. Other uses of this important polymeric material are given in Table 15.3. 

Acidity (as acetic acid) Mix 38 mL of sample with an equal volume of carbon dioxide-free water, add 0.1 mL of phenol-phthalein TS, and titrate with 0.1 A sodium hydroxide. Not more than 0.1 mL is required to produce a pink color. Aldehydes (as formaldehyde) Prepare a Sample Solution by diluting 2.5 mL of sample with 7.5 mL of water. Prepare a Standard Solution containing 40 p,g of formaldehyde in 10 mL of water. Add 0.15 mL of a 5% solution of 5,5-dimethyl-1,3-cyclohexanedione in alcohol to each solution, and evaporate on a steam bath until the Acetone is volatilized. Dilute to 10 mL with water, and cool quickly in an ice bath while stirring vigorously. Any turbidity produced in the Sample Solution does not exceed that produced in the Standard Solution. 

The method of Fan and Dasgupta (1994) relics on tlie reaction of formaldehyde with 1,3-cyclohexane-dione in acidified ammonium acetate to form the fluorescent dihydropyridine derivative in a flow injection analysis system. Formaldehyde trapped in water can be reacted with pararosaniline and sodium sulfite under mild conditions (neutral pH, room temperature equilibration) to produce a colored product that is measured at 570 nm (Petreas et al. 1986). The presence of bisulfite is an interference in this reaction so the method cannot be used to sample atmospheres that contain sulfur dioxide. In addition, the method is reported to suffer from interferences resulting from the presence of other aldehydes and phenol (Hoogenboom et al. 1987). The indirect method of Hoogenboom et al. (1987) relies on the reaction of excess bisulfite in an aqueous solution of formaldehyde with 5,5 -dithiobis(2-nitrobenzoic acid) to form a colored product, the absorbance of which is measured at 412 nm. The method reported by Naruse et al. (1995) relies on the formation of a colored product obtained by reacting the aqueous formaldehyde with acetylacetone and ammonium acetate in acetic acid. Absorbance is measured at 414 nm. 

In sulfuric acid solution the nitric acid oxidizes the formaldehyde to formic acid while being reduced to nitrous acid. RDX dissolved in cold, concentrated sulfuric acid decomposes when the solution is allowed to stand. Reduction of RDX dissolved in hot phenol yields methylamine, nitrous acid, and hydrocyanic acid but if solid RDX is suspended in 80 percent ethanol and reduced, both hydrolysis and reduction take place and the products are methylamine, nitrous acid, ammonia, and formaldehyde. With diphenylamine and sulfuric acid, RDX gives a strong blue color. RDX dissolves, without decomposing, in concentrations of up to 70 per-... 

The characteristic reactions of formaldehyde with phenolic componnds and amines have also been adapted to the detection of the aldehyde in food-.stuffs. In such instances the material i generally steam-distilled and a qualitative analysis is then carried out on the distillate obtained. Cohn -shakes 2 ec of the distillate with an equal volume of 0.1 per cent resorcinol solution, then carefully adds 2 ce of concentrated sulfuric acid to produce a dense precipitate at the zone of contact between acid and solution with a dark violet-red zone immediate v below. Fomiic, ox alic, and tartaric acids are claimed not to interfere with this color reaction, which is sensitive to OjOO(K>5 mg foimaldehi de. Gallic acid reacts with like sensitivity to form an emerald green bandb The test devi.Sed by Pittarelli (page 247) is reported to be of value for the detection of formaldehyde in wine, milk. 

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