Title: Cellulose I crystallinity determination using FT-Raman spectroscopy : univariate and multivariate methods
Author: Agarwal, Umesh P.; Reiner, Richard S.; Ralph, Sally A.
Source: Cellulose. Vol. 17 (2010): p. 721-733.
Description: Two new methods based on FT–Raman spectroscopy, one simple, based on band intensity ratio, and the other using a partial least squares (PLS) regression model, are proposed to determine cellulose I crystallinity. In the simple method, crystallinity in cellulose I samples was determined based on univariate regression that was first developed using the Raman band intensity ratio of the 380 and 1,096 cm-1 bands. For calibration purposes, 80.5% crystalline and 120-min milled (0% crystalline) Whatman CC31 and six cellulose mixtures produced with crystallinities in the range 10.9–64% were used. When intensity ratios were plotted against crystallinities of the calibration set samples, the plot showed a linear correlation (coefficient of determination R2 = 0.992). Average standard error calculated from replicate Raman acquisitions indicated that the cellulose Raman crystallinity model was reliable. Crystallinities of the cellulose mixtures samples were also calculated from X-ray diffractograms using the amorphous contribution subtraction (Segal) method and it was found that the Raman model was better. Additionally, using both Raman and X-ray techniques, sample crystallinities were determined from partially crystalline cellulose samples that were generated by grinding Whatman CC31 in a vibratory mill. The two techniques showed significant differences. In the second approach, successful Raman PLS regression models for crystallinity, covering the 0–80.5% range, were generated from the ten calibration set Raman spectra. Both univariate-Raman and WAXS determined crystallinities were used as references. The calibration models had strong relationships between determined and predicted crystallinity values (R2 = 0.998 and 0.984, for univariate-Raman and WAXS referenced models, respectively). Compared to WAXS, univariate-Raman referenced model was found to be better (root mean square error of calibration (RMSEC) and root mean square error of prediction (RMSEP) values of 6.1 and 7.9% vs. 1.8 and 3.3%, respectively). It was concluded that either of the two Raman methods could be used for cellulose I crystallinity determination in cellulose samples.
Keywords: Cellulose, crystallinity, Raman spectroscopy, FT–Raman, univariate analysis, multivariate analysis, PLS, X-ray, analytic chemistry, chemistry, wood chemistry, Fourier transform spectroscopy, spectrum analysis, correlation, cellulose I, partial least squares, band intensity ratio, standard error
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Agarwal, Umesh P.; Reiner, Richard S.; Ralph, Sally A. 2010. Cellulose I crystallinity determination using FT-Raman spectroscopy : univariate and multivariate methods. Cellullose. 17: 721-733.
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