Uron resins

Uron Resins. In the textile industry, the term uron resin usually refers to the mixture of a minor amount of melamine resin and so-called uron, which in turn is predorninantly N,]S -bis(methoxymethyl)uron [7388-44-5] plus 15—25% methylated urea—formaldehyde resins, a by-product. 

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. 

There was a tendency to use these resins mixed with urea—formaldehyde or melamine-type resins. Preparation of pure tria2ones or uron resins is difficult and expensive (61,62). Furthermore, the basic nature of the amine nitrogen in tria2one permits the use of mixtures of tria2ones with other agents to yield finishes that retain strength in hypochlorite bleaching. 

In the literature, various other types of resin preparation procedures are described, e.g. yielding uron structures [20-22] or triazinone rings in the resins [23,24]. The last ones are formed by the reaction of urea and an excess of formaldehyde under basic conditions in the presence of ammonia or an amine, respectively. These resins are used to enhance the wet strength of paper. 

When polysaccharides contain uronic acids, it is often convenient to separate the acidic oxidation-products on ion-exchange resins and to generate the lactones, which are then reduced. Applied to... 

Humic acids are those humic substances that are precipitated at pH = 1. Fulvic acids stay in solution at pH = 1 they contain more —COOH and —OH groups than humic acids. Dissolved organic acids, which are not retained by a nonionic XAD resin, are hydrophilic acids, they are not very well defined They contain, in addition to single aliphatic acids, uronic and polyuronic acids. 

One must be cautious in interpreting data on carbohydrates, hydroxyl acids, and uronic acids in humic substances. As Thurman and Malcolm 11983) have pointed out, the amount of these materials in a fulvic acid is a function of the way that it was isolated. They have shown that nonassociated carbohydrates, uronic acids, and hydroxyl acids may be separated from fulvic acid by adsorption chromatography on XAD resins. For example, a prairie soil fulvic acid contained 20% carbohydrate before XAD adsorption chromatography and only 5% after chromatography. In the fulvic acid isolated by Sposito et al. (1978) adsorption chromatography was not used in the purification process and therefore some of the carbohydrate that they report may not be an integral part of the fulvic acid structure. 

There is no standardised procedure for the hydrolysis of dissolved polymeric uronic acids. Mopper (1977) su ests much milder procedures than are used for sugars since uronic acids are much more labile towards decarboxylation or transformation reactions. The hydrolysis procedure suggested by Burney and Sieburth (1977) may therefore prove to be adequate. The use of cation-exchange resin in the form may also be effective. 

Mopper, K., 1978b. Improved chromatographic separations on anion-exchange resins. II. Separation of uronic acids in acetate medium and detection with a noncorrosive reagent. Anal. Biochem., 86 597—601. 

The reaction between urea and formaldehyde is complex. The combination of these two chemical compounds results in both linear and branched polymers, as well as tridimensional networks, in the cured resin. This is due to a functionality of 4 in urea (due to the presence of four replaceable hydrogen atoms) (in reality urea is only trifunctional as tetramethylolurea has never been isolated, except in the formation of substituted urons [2]) and a functionality of 2 in formaldehyde. The most important factors determining the properties of the reaction products are (1) the relative molar proportion of urea and formaldehyde, (2) the reaction temperature, and (3) the various pH values at which... 

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