Development of a process raman probe of wood pulp as a continuous gauge of the physical and mechanical properties of end-use product: spectroscopy and chemometrics

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Canadian northern bleached softwood kraft (NBSK) market pulps represent the worldwide benchmark for fibre strength, length, fineness, and uniformity. To maintain this premier position in the world marketplace, the Canadian pulp industry must continuously develop and deploy process technologies that sharpen the quality control of pulp composition, particularly with reference to those intrinsic fibre characteristics that govern process parameters and key product properties, such as tensile strength, softness and absorbency. For example, the degree of cellulose crystallinity and distribution of chemical constituents, such as lignin, hemicullose, and hexenuronic acid (HexA), determine pulp digestibility and bleachability, while the degree of fibre deformation incurred during pulping process affects how the fibre delivers strength and softness in a network during sheet formation. These and other parameters have been shown to be important determinants of manufacturing efficiency, energy utilization, environmental performance and product value, however, aside from lignin, none can be easily measured in a timely manner for process control. The present proposal calls for the development of a novel Raman system, and systematic chemometric approach that will allow for rapid spectral data acquisition and definitive spectrochemical analysis of wet pulp under harsh manufacturing conditions. The instrument system will combine a novel backscattering Raman probe with a sophisticated chemometrics data-processing strategy, employing wavelet transform and template-guided genetic-algorithm (TOGA) feature selection with multivariate classification to extract maximum analytical information from raw Raman spectra. A program of research correlating spectrochemical observations with conventional characterization of fibre parameters, such as, curl, coarseness, area, perimeter and CSF, and end-use sheet properties, including burst, stretch, tear, smoothness, compression, stiffness, TEA and tensile indices, will give rise to a comprehensive Raman gauge for the instantaneous determination of pulp quality and the online prediction of paper appearance, strength, softness and absorbency.