Solution-state NMR analysis of hydroxymethylated resorcinol cured in the presence of crude milled-wood lignin from Acer saccharum

Abstract

Resorcinol-formaldehyde adhesives can reinforce stress fractures that appear from wood surface preparation. Researchers have found that applying the resorcinol-formaldehyde prepolymer, hydroxymethylated resorcinol is thought to plasticize lignin components and stabilize stress fractures through reactions with lignin subunits and hemicelluloses in wood. In this study, a dilute solution of hydroxymethylated resorcinol (HMR) is cured in the presence of a crude milled-wood lignin (cMWL) from Acer saccharum and subsequently dissolved in dimethylsulfoxide-d₆ to delineate reactivity with lignin and O-acetyl-(4-O-methylglucurono) xylan using solution-state NMR spectroscopy. ¹H—¹³C single-bond correlation NMR experiments revealed that the HMR only formed 4,4’-diarylmethane structures with itself in the presence of the cMWL; the 2-methylols that formed remained free and did not crosslink with resorcinol. Cured HMR resin formed both 4,4ʹ - and 2,4-diarylmethane structures, confirming that the presence of lignin and O-acetyl-(4-O-methylglucurono) xylan hinders crosslinking at the C-2 position. No evidence of reactivity between HMR and lignin subunits was found. New peaks consistent with ester linkages were observed in ¹³C-NMR spectra of the cMWL sample treated with HMR moieties condensing with glucuronic acid substituents.

Citation

Yelle, Daniel J. 2017. Solution-state NMR analysis of hydroxymethylated resorcinol cured in the presence of crude milled-wood lignin from Acer saccharum . Journal of Applied Polymer Science. 134(41): 1-9.