Photoyellowing of Thermomechanical Pulps: Looking Beyond α-Carbonyl and Ethylenic Groups as the Initiating Structures

Agarwal, Umesh P.; McSweeny, James D.

doi:10.1080/02773819708003115

Cited by 31 publications

(18 citation statements)

References 18 publications

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“…Except for the band position at 1136 cm -1 , where the contribution is entirely due to the coniferaldehyde units, the other posi tions (1623 and 1662 cm -1 ) have contributions from not only coniferyl alcohol and coniferaldehyde (Table 1) but also from other chromophore structures in lignin (Agarwal and McSweeny 1997;Agarwal and Landucci 2004). For example, when spectra of unbleached and bleached TMPs were compared in this region, it was observed that bleaching resulted in the removal of contributions in addi tion to that of coniferaldehyde.…”

Section: Coniferaldehydementioning

confidence: 99%

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Determination of ethylenic residues in wood and TMP of spruce by FT-Raman spectroscopy

Agarwal

Ralph

2008

HFSG

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A method based on FT-Raman spectroscopy is proposed for determining in situ concentrations of ethylenic resi dues in softwood lignin. Raman contributions at 1133 and 1654 cm -1 , representing coniferaldehyde and coni feryl alcohol structures, respectively, were used in quan tifying these units in spruce wood with subsequent conversion to concentrations in lignin. For coniferalde hyde units, the intensity of the 1133 cm -1 peak was measured in the difference spectrum obtained by sub tracting the bleached-wood spectrum from that of the unbleached. In the case of coniferyl alcohol residues, the intensity of the 1654 cm -1 band was calculated from the spectrum of extensively bleached wood. The concentra tions of coniferaldehyde and coniferyl alcohol units in spruce lignin were found to be 3.8% and 3.4%, respec tively, and were in good agreement with values deter mined by conventional techniques. This quantification of the ethylenic residues was based on the Raman inten sities of 1% coniferaldehyde and 1% coniferyl alcohol in bleached softwood kraft pulp. Initially, as background for this work, a number of suitable lignin model compounds and a softwood lignin model polymer (G-DHP) were used to calibrate the Raman method and demonstrate that the Raman technique was well suited for quantification of ethylenic structures. Experimental results demonstrated that thermomechanical pulping reduced the concentra tions of coniferaldehyde and coniferyl alcohol residues in comparison to wood by 28% and 24%, respectively.

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Section: Coniferaldehydementioning

confidence: 99%

“…Lignin retaining bleaching is a good possibility. It is known that such bleaching does not remove coniferyl alcohol units (Agarwal and Atalla 1993;Agarwal and McSweeny 1997). The bleaching sequences are listed in Table 2 for sample numbers 5 to 11.…”

Section: Coniferyl Alcoholmentioning

confidence: 99%

Determination of ethylenic residues in wood and TMP of spruce by FT-Raman spectroscopy

Agarwal

Ralph

2008

HFSG

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“…Considering that the Raman spectra of lignins (syringyl, guaiacyl, and coumaryl) are complex, significant advances have been made to interpret them. This has come about as a result of studying, with a number of approaches, not only lignins (native [18], milled wood [18,42,43], and residual lignins [37,[44][45][46][47]) and their models (deuterated and normal dehydrogenation polymer [DHP] lignins [48] and a large number of lignin model compounds [38,49]) but also chemic ally modified (e.g., bleaching, hydrogenation, and acetylation) lignins and lignocellulosics [10,39,43,50,51]. An additional tool in the aid to interpretation has been the theoretical cal culations on lignin models wherein some degree of preliminary work has been done [52,53], but a lot more remains.…”

Section: Wood Componentsmentioning

confidence: 99%

Raman Spectroscopic Characterization of Wood and Pulp Fibers

Agarwal

2008

Characterization of Lignocellulosic Materials

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This chapter reviews applications of Raman spectroscopy in the field of wood and pulp fibers. Most of the literature examined was published between 1998 and 2006. In addi tion to introduction, this chapter contains sections on wood and components, mechanical pulp, chemical pulp, modified/treated wood, cellulose I crystallinity of wood fibers, and the "self-absorption" phenomenon in near-infrared (IR) Fourier-transform (FT)-Raman spectroscopy. When needed, the sections are further categorized into various subsections. For example, the section on wood and components contains a variety of topics ranging from Raman band assignments to molecular changes during tensile deformation. From this review it will become clear that Raman spectroscopy has become an essential analytical technique in the field of wood and pulp fibers. IntroductionTechniques that can provide information on the chemical constitution of wood and pulp fibers and on processing-related changes of these materials are of great interest. Raman spectroscopy [1] is one such technique that provides fundamental knowledge on a molecu lar level and does not require chemical treatment of the sample (contrary to the case, for example, in fluorescence and electron microscopy). It has become an important analyt ical technique for nondestructive, qualitative, and quantitative analysis of materials. The technique is useful in a number of areas, including analytical measurements, mechan istic studies, and structural determinations. Studying a sample is very simple and usually involves sampling an area of interest by directing a laser excitation beam and analyzing the collected molecularly specific scattered light [2]. Although initially, obtaining good-quality Raman data required operator skill and training, this has started to change as a result of the commercial availability of compact, easy-to-use, integrated instruments at reasonable cost.Nevertheless, although the specificity of Raman spectroscopy is very high, its sensitivity is somewhat poor. Considering that only a small number of the incident laser photons are inelastically scattered, the detection of analytes present in very low concentrations is limited. To overcome this problem, special Raman signal-enhancing techniques can be applied. The two most prominent approaches are the resonance Raman effect [3] and the

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“…In the cellulose and in the other substances many double bonds are moreover present to which atmospheric oxygen can be added, possibly with radical formation, with reactions that determine a discoloration of the paper. Meanwhile new different bonds, formed by oxygen, cause a polymerisation, which produces the yellowing of paper 5,7,8 . • biodegradation 5, 9 : it is due to fungi and bacteria species that use the paper like cultivation medium; their vital cycle is carried out in the paper and the alterations depend on their metabolism; in a generalized manner these organisms produce enzymes which break fibres, eat the glucose and can also produce coloured pigments with aesthetic damage; • photodegradation: it is caused from remarkable energy of light that determines formation of free reactive radicals oxidising alcoholic groups 6,8,10 .…”

Section: Introductionmentioning

confidence: 99%

Studies on Simulated Ageing of Paper by Photochemical Degradation

2005

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The study of the ageing of two paper types was performed on monitoring it during a simulated process by means of the measure of the photocatalytic degradation of the paper cellulose. Such evaluation was possible due to the combined responses of a photosensor based on titanium dioxide in suspension, of an enzymatic biosensor based on superoxide dismutase (SOD), of a specific conductivity sensor and of an enzymatic biosensor based on glucose oxidase.

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Photoyellowing of Thermomechanical Pulps: Looking Beyond α-Carbonyl and Ethylenic Groups as the Initiating Structures

Cited by 31 publications

References 18 publications

Determination of ethylenic residues in wood and TMP of spruce by FT-Raman spectroscopy

Determination of ethylenic residues in wood and TMP of spruce by FT-Raman spectroscopy

Raman Spectroscopic Characterization of Wood and Pulp Fibers

Studies on Simulated Ageing of Paper by Photochemical Degradation

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