The Crosslinking Mechanism of Camellia Oleifera Protein Adhesive with Amine Resins by 13C-NMR and ESI-MS

A new protein wood adhesive was studied with Camellia oleifera protein. Formaldehyde and N-(2)-L-Ala-L-Gln (LAG) were used as the model compounds of amino resins and Camellia oleifera protein, aiming to provide scientific foundations for the improvement and applications of Camellia oleifera protein adhesive by the reaction of model compounds. The experimental results demonstrate that, under alkaline conditions, formaldehyde is easier to react with Camellia oleifera protein by quicker reaction and lower curing temperature. Under acid conditions, amino hydroxymethylated structure of aliphatic series from LAG is difficult to form stable reactive intermediates and further polycondensation. Hydroxymethylation of end acylamino and peptide bond amino from LAG is relatively weak. Under alkaline conditions, the free aliphatic amino and acylamino of LAG both can make hydroxymethylation reaction with formaldehyde. In the polycondensation, hydroxymethyl amide is the initial structure and the reactive intermediate is produced by E1cb reaction of hydroxymethyl amide. Methylene bridge bonds and methylene ether bonds are structures of the polycondensation products, which are competing reactions. The former is mainly formed by the reaction between alkaline reactive intermediate and amino of aliphatic series, and the latter is produced by the reaction of reactive intermediate and amino of hydroxymethyl aliphatic series with hydroxymethyl amide.