Raman Spectroscopy and the Raman Microprobe: Valuable new tools for Characterizing Wood and Wood Pulp Fibers

Abstract

Abstract A brief overview of Raman spectroscopy and the photon scattering phenomena which underly it is presented, together with the rationale for applying the methodology to the study of lignocellulosics. The sequence of studies undertaken at The Institute of Paper Chemistry to apply the methods to investigation of celluloses, chemical pulps, wood and high yield fibers are then reviewed. The program began with studies on cellulose and related model compounds. These early efforts provided a basis for interpretation of the spectra of celluloses and for investigating the effects of various process variables on the aggregation of cellulose in pulp fibers. Among the effects touched upon are the differences between kraft and sulfite pulps, the effects of refining, and the influence of press drying on pulp crystallinity. More recently studies using the Raman microprobe made possible progress in the assignment of the vibrational spectra of cellulose and established the basis for using the microprobe to investigate variability of fibril orientation in native woody tissue. In addition our extension of the studies to include lignin are noted. These included studies of fiber sections in native wood which show the orientation of lignin in the cell wall and observations of the variability of the ratio of lignin to cellulose. Finally, the opportunities arising from new instrumental developments are reviewed. The new multichannel detectors will greatly enhance the efficiency of acquisition of spectra and allow more comprehensive explorations of the architecture of fibers. In addition, gated detectors coupled with pulsed laser excitation will allow studies of woody tissue and of high yield pulps that would not be feasible with single channel detection and continuous laser excitation.