Urea/formaldehyde, reaction with cellulose

Reactions of urea-formaldehyde products with cellulose yield products with more stable crosslinks than reaction with formaldehyde. Examples of these reactions are... 

Phosphoric Acid-Based Systems for Cellulosics. Semidurable flame-retardant treatments for cotton (qv) or wood (qv) can be attained by phosphorylation of cellulose, preferably in the presence of a nitrogenous compound. Commercial leach-resistant flame-retardant treatments for wood have been developed based on a reaction product of phosphoric acid with urea—formaldehyde and dicyandiamide resins (59,60). 

Cellulosic fibers (cotton, rayon) are crosslinked by reaction of the hydroxyl groups of cellulose with formaldehyde, diepoxides, diisocyanates, and various methylol compounds such as urea-formaldehyde prepolymers, /V, /V -di tnethylol-A(A -dimethy lene urea, and trimethyl-olmelamine [Marsh, 1966]. Crosslinking imparts crease and wrinkle resistance and results in iron-free fabrics. 

Vinyl acetal polymers can be formulated with other thermoplastic polymers and with a variety of multifunctional cross-linkers. Examples of polymers that are at least partially compatible with PVF or PVB resins include some types of polyurethanes, some types of celluloses, epoxies, isocyanates, phenolics, silicones, unsaturated polyesters, and melamine- and urea-formaldehyde polymers (19-21). Although vinyl acetal polymers are thermoplastic, hydroxyl groups permit cross-linking reactions with a variety of thermosetting resins, for example. 

In 1906 Eschalier reported that cellulosic fibers had improved wet strengths after reaction with formaldehyde." Subsequently, countless publications and patents have reported investigations of the reactions of formaldehyde and of formaldehyde adducts of urea, melamine and carbamates with cellulose. Before the macromolecular structure of cellulose was generally accepted, the reaction of formaldehyde with cellulose was proposed (equation 8)" " ... 

Since the original Tootal patent there has been much research on alteration of the properties of cellulosic materials by the formation of polymers in situ. The original formaldehyde urea method for the crease-resistant finish is probably still -the most commonly used. Dimethylol-urea is now used as the monomer instead of a mixture of urea and formaldehyde. It is the product of the reaction of one molecule of lurea with two molecules of formaldehyde ... 

Further molecular mechanics investigations in the same direction but for UF resins also followed, with equally interesting results. In these the efficiency of resin adhesion to both amorphous and crystalline celluloses was computed by following the synthesis of the resin. This was achieved by calculating by molecular mechanics the adhesive/adherend interactions with the two types of cellulose for each isomeride produced through the reaction of urea with formaldehyde. This was done up to the level of trimer. The adhesive/adherend interactions were calculated for urea, monomethylene diureas. 

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