Surface modification of lignocellulosic fibers using high-frequency ultrasound

Abstract

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 A 1736 /A 1511 in the FTIR-transmission spectra and by A 1728 /A 1509 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.

Thermally initiated solvent-free radical modification of beech (Fagus sylvatica) wood

“…There are also reports on free radicals generation using high-frequency ultrasound (Petrier et al 1994;Gadhe et al 2006), UV laser energy (Dodson et al 2009), or cirradiation (Supe et al 1993) which, in fact, are a combination of physical and chemical modification. Moreover, many successful radical graftings were efficiently applied to a range of lignocellulosic materials-like high-yield pulp (Hornof et al 1976), wheat straw (Fanta et al 1987), or jute fiber (Huque et al 1980;Abou-Zeid et al 1984;Sikdar et al 1995).…”

Ultrasound irradiation in the production of ethanol from biomass

“…The ultrasound waves can cause the surface erosion of cellulosic materials, which is due to cavitation collapse in the surrounding liquid. Low frequency of ultrasound around 20 kHz can affect even more surface disruption because low frequency ultrasound waves can produce more violent cavitation [35,36].…”

Wood production, wood technology, and biotechnological impacts

“…Enzymatic activation of the surface lignin, treatment of the fibres with Fenton´s reagent (H 2 0 2 /FeSO 4 ; see Chapter 17 of this book) without or in presence of chelators such as 2,3-dihydroxybenzoic acid (DHBA), and irradiation with γ-radiation are further methods shown to increase auto-adhesion , Kharazipour et al 1991, Supe et al 1993,b, 1998,b,c, 2003a, Yelle et al 2004; see Chapter 18 of this book). High-frequency ultrasound was recently also positively tested for increasing reactive groups of wood fibres (Gadhe et al 2006). As the lignins on fibre surfaces, technical lignins are not as reactive and are therefore normally not applied as pure binder but as extenders for improving board properties, particularly the swelling properties.…”