FT-IR Study of the Effect of Irradiation Wavelength on the Colour Reversion of Thermomechanical Pulps

Abstract

The effect of irradiation by light of wavelengths 270, 320, 390 and 500nm on the colour reversion of unbleached and bleached thermomechanical pulp was monitored by FT-IR transmission spectroscopy. The aromatic ring structure in lignin and the C-O and C-H bonds in the wood carbohydrates decreased much more rapidly at shorter irradiation wavelengths for bolh unbleached and bleached pulp samples. The rate of decrease of aromatic ring and guaiacyl structures is the same at all wavelengths for the unbleached pulp, whereas for the bleached pulp, the rate of decrease of the guaiacyl structure is much larger than that of the total aromatic ring structure for irradiation at 270 and 320 nm. New bands at 1719 and 1684 cm' 1 were generated by all wavelengths but the increase in the 1684 cm" 1 band caused by 390nm radiation is especially large, compared with the 1719cm"" 1 band. The increase in non-conjugated carbonyl group content is strongly related to the disappearance of aromatic rings for 270 and 320nm radiation, but not for 390 nm radiation, indicating that colour reversion reactions at 270 and 320 nm are different from those at 390 nm. A band at 1584cm" 1 also increases with irradiation at 390 nm. The increasing bands at 1684 and 1584cm" 1 may be due to the formation of quinone structures.

Structural analysis of photodegraded lime wood by means of FT-IR and 2D IR correlation spectroscopy

“…3-5. Lignin decay and carbohydrate loss as a consequence of UV irradiation of wood pulp were shown by Kimura et al [33,34]. Furthermore, they demonstrated that, the decay of the lignin functionality is combined with the formation of aliphatic carbonyl groups.…”

Review: Light-Induced Yellowing of Lignocellulosic Pulps – Mechanisms and Preventive Methods

“…The difference in photostability between oxidatively (hydrogen peroxide) bleached and reductively (dithionite, bisulfite) bleached pulps is not fully understood, and different opinions regarding the effect of reductive and oxidative bleaching exist (Jansen and Lorås 1968;Abou-State 1976;Janson and Forskåhl 1991;Janson 1993;Kuys and Abbot 1996;Forsskåhl 2000). The discrepancy in reported observations could be due to differences in exposure conditions, light sources, exposure times, grammage of the exposed samples, and procedures chosen for quantifying the color reversion (Schmidt and Heitner 1993a;Kimura et al 1994;Paulsson and Ragauskas 1998b).…”

Photo-induced Yellowing of Mg(OH)2-based Peroxide Bleached Deinked Pulp

“…7, and the assignment of bands in the ATR-FTIR spectra is listed in Table 1 (Kimura et al 1994;Kimura et al 1995;Pandey 1999;Tshabalala et al 2005;Rosu et al 2010). As shown in Fig.…”

“…Lignin is known to be responsible for yellowing. Over the last several decades, the color reversion of mechanical pulps has been studied by many researchers (Kimura et al 1994;Leary 1994;Müller et al 2003;Zou 2004;Pandey 2005;Rosu et al 2010), but the underlying mechanism of photo yellowing has yet to be discovered. Moreover, the studies on the yellowing of deinked pulp, especially on the comparison of Mg(OH)2-based with NaOH-based hydrogen peroxide bleached pulp, were much fewer (Savoye et al 2011).…”