Two distinct enzymatic approaches for coupling fatty acids onto lignocellulosic materials

Two enzyme based strategies for hydrophobic functionalization of lignocellulose materials were developed and mechanistically compared using sinapic acid and the dimer syringylglycerol β-guaiacyl ether as models respresenting (hardwood) lignin substructures for coupling fatty acid esters. Coupling of lipase/hydrogen peroxide treated methyl linoleate to sinapic acid indeed resulted in a 1:1 coupling product with an m/z peak at 575.5 measured with HPLC–MS. Using laccase for coupling, oligo/polymerization of sinapic acid seems to prevent a coupling-reaction to methyl linoleate. However, methyl linoleate was successfully coupled by laccase 1:1 onto syringylglycerol β-guaiacyl ether through the ether bond at position four. The efficient enzyme mediated incorporation of fatty acid esters as hydrophobic molecules were further confirmed when triglycerides were used to treat veneers resulting in a water contact angle increase from 58.3° to 93.5°. Thus, this study demonstrates for the first time that both (laccase mediator and lipase-hydrogen peroxide) systems can act as promising strategies for introducing fatty acid esters in wood leading to increased hydrophobization.