Biografting of ferulic acid onto lignocellulosic fibers by the use of laccases

Laccases can functionalize paper pulps with phenolic compounds but little is known about the formed linkages. Treatment of a high-kappa sisal pulp with Trametes villosa laccase and ferulic acid resulted in strong increases of kappa-number and acid-group content. This suggested extensive incorporation of ferulic acid, as confirmed by pyrolysis in the presence of tetramethylammonium hydroxide. The coupling linkages were investigated by 2DNMR of the lignin isolated from pulps. The aromatic region of the spectra showed incorporation of the cinnamic molecule, representing ~4% of the lignin content. Interestingly, the spectra revealed that ferulic acid is C4- etherified. The aliphatic region of the spectra showed that ferulic acid also incorporates as the corresponding _-_' dilactone (another ~4% of the total lignin) with characteristic 13C_-1H_ and 13C_-1H_ correlations. The lignin composition and interunit linkages in the treated pulps were only slightly modified revealing that the main effect of the treatment was ferulic acid biograftin