A molecular mechanics approach to the adhesion of urea-formaldehyde resins to cellulose. Part 1. Crystalline Cellulose I

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Abstract
The energies of interaction of urea, methylol ureas, and urea-formaldehyde (UF) condensates, methylolated and non-methylolated, linear and branched, up to trimers, with the surfaces of an elementary model of the crystal of Cellulose I were obtained by molecular mechanics techniques. The results indicated, firstly, that methylolation enhances adhesion, especially at low molecular weights, while branching tends to decrease it; secondly, that adhesion of UF resins to the cellulose surface can be enhanced by shifting the resin preparation conditions to increase the proportion of species having higher specific adhesion. The theoretical results obtained are in agreement with published experimental evidence. While urea resins show stronger average affinity for cellulose than the average affinity of water, this trend is less marked than in phenol-formaldehyde (PF) resins. The results obtained also appear to infer that the lack of water resistance of UF resins is mainly due to the instability in water of the internal, covalent, aminoplastic bond rather than to UF adhesion to cellulosic substrates. Resin-substrate H-bonding was shown to be of lesser importance in UF than in PF resins.

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