Cellulose I crystallinity determination using FT–Raman spectroscopy: univariate and multivariate methods

Abstract

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 R 2 = 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 univariateRaman and WAXS determined crystallinities were used as references. The calibration models had strong relationships between determined and predicted crystallinity values (R 2 = 0.998 and 0.984, for univariateRaman 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.

Processing and structure–property relationships of natural rubber/wheat bran biocomposites

“…Therefore, more detailed characteristics of crystallinity in cellulosic fillers could be achieved using X-ray diffraction (French 2014;French and Santiago Cintrón 2013), Raman spectroscopy (Agarwal et al 2010), nuclear magnetic resonance (Bernardinelli et al 2015), differential scanning calorimetry (Bertran and Dale 1986) or combination of these methods. Amongst them, X-ray diffraction (XRD) gives the most direct results and quantitative information.…”

Raman Imaging of Lignocellulosic Feedstock

“…Noteworthy, changes in fibre orientation often correspond to alterations in cellulose crystallinity. The effect of changes in crystallinity on the shape of the cellulose Raman bands was also investigated in detail: amorphous cellulose results in a significant decline in band heights accompanied by band broadening [143]. …”

FT-Raman Analysis of Cellulose based Museum Textiles: Comparison of Objects Infected and Non-infected by Fungi

“…Th e fi rst ratio has proved to be stable and reliable in several articles (as confi rmed by Jähn and co-workers [25]). For the second ratio Agarwal and co-workers [23] have proved that the bands at 380 cm -1 and 1096 cm -1 are signifi cantly aff ected by cellulose crystallinity modifi cation and that this ratio generated excellent regression (R2 = 0.992) and showed good sensitivity to crystallinity change. Heights of the bands were measured using OPUS soft ware.…”

“…Some bands in the spectrum c decreased relative to other when compared to the reference spectrum. Th e decrease of the band at 380 cm -1 , typical of vibrations of glycoside ring [24], is a sign of decreased crystallinity of the cellulose [23]. Th e decrease of the band at 437 cm -1 , typical of glucose rings vibrations [24,26], is a sign of cellulose degradation [26].…”