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

Abstract

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.

Recent innovations in analytical methods for the qualitative and quantitative assessment of lignin

“…At the United States Department of Agriculture Forest Products Laboratory, Umesh Agarwal and co-authors have been a leading team in developing Fourier-transform (FT) Raman spectroscopy for lignin analysis [32,33,[84][85][86]. The assignment of the characteristic vibrational modes of hard-and softwood lignins have been extensively reported, and are tabulated in Table 3.…”

“…Acetylation and methylation produced significant changes in the aliphatic C-H region of the Raman spectra, and gave rise to new vibrational modes not present in unmodified lignin, while measured spectra following alkaline peroxide and hydrogenation reactions were not significantly altered compared to untreated samples. Ethylenic residues in spruce and thermomechanical pulp were measured using the band intensities at 1133 and 1654 cm À 1 , representative of coniferaldehyde and coniferyl alcohol, respectively [86]. Quantitation based on these vibrational modes provided good correlation with NMR.…”

Raman Imaging of Lignocellulosic Feedstock

“…The differences in lignin structure in the cell corner of spruce and poplar are reflected by the different intensity and band shape in the region at about 1600 cm -1 as well as in the other bands ( Figure 4A). Contribution from coniferaldehyde units is expected at 1623 and 1660 cm -1 , whereas coniferyl alcohol contributes at 1654 cm -1 as well as other chromophores [169]. Using these bands the amount of coniferyl alcohol and aldehyde groups compared to the total amount of lignin was imaged in pine and spruce wood samples [170].…”

Comparison of Anatomy and Composition Distribution between Normal and Compression Wood of Pinus Bungeana Zucc. Revealed by Microscopic Imaging Techniques

“…layer. , 1987;Agarwal & Ralph, 1997, 2008Edwards et al, 1997;Agarwal, 1999!. The bands at 380, 1,097, and 1,121 cm Ϫ1 are assigned to cellulose, while those at 1,273, 1,600, 1,654, and 3,068 cm Ϫ1 stem from lignin.…”