Surface modification of lignocellulosic fibers using high-frequency ultrasound
Enzymatic and chemical oxidation of fiber surfaces has been reported in the literature as a method for producing medium density fiberboards without using synthetic adhesives. This work focuses on modifying the surface properties of wood fibers by the generation of free radicals using high-frequency ultrasound. A sonochemical reactor operating at 610 kHz is used to sonicate the aqueous suspensions of thermomechanical pulp fibers (TMP). TMP is analyzed using FTIR-transmission, FTIR-ATR spectroscopy and inverse gas chromatography (IGC). The non-conjugated carbonyl groups in TMP are represented by the peak area ratio A1736/A1511 in the FTIR-transmission spectra and by A1728/A1509 in the FTIR-ATR spectra. The increase in these ratios suggests that there is an increase in the number of non-conjugated carbonyl groups in TMP after sonication. To further investigate, sonication of the hydrolytic lignin was also carried out and analyzed using UV, UV-ionization and FTIR-transmission spectroscopy. The changes in the surface properties of the fibers are analyzed using IGC which showed an increase in the surface free energy of fibers. The effect of operating parameters such as power of ultrasound and sonication time is also studied.