Abstract
Microcrystalline cellulose (MCC) is a semi-crystalline material with inherent variable crystallinity due to raw material source and variable manufacturing conditions. MCC crystallinity variability can result in downstream process variability. The aim of this study was to develop models to determine MCC crystallinity index (%CI) from Raman spectra of 30 commercial batches using Raman probes with spot sizes of 100 µm (MR probe) and 6 mm (PhAT probe). A principal component analysis model separated Raman spectra of the same samples captured using the different probes. The %CI was determined using a previously reported univariate model based on the ratio of the peaks at 380 and 1096 cm−1. The univariate model was adjusted for each probe. The %CI was also predicted from spectral data from each probe using partial least squares regression models (where Raman spectra and univariate %CI were the dependent and independent variables, respectively). Both models showed adequate predictive power. For these models a general reference amorphous spectrum was proposed for each instrument. The development of the PLS model substantially reduced the analysis time as it eliminates the need for spectral deconvolution. A web application containing all the models was developed.Graphic abstract
Highlights
Microcrystalline cellulose is widely used and has diverse applications across different industry sectors
The baseline subtraction method developed (‘‘Raman spectroscopy’’ section) eliminated the fluorescence background and standard normal variate (SNV) eliminated intensity differences observed between the spectra
Crystallinity index was determined for 30 commercial batches of microcrystalline cellulose using two different models, i.e. 380-method and PLS regression
Summary
Microcrystalline cellulose is widely used and has diverse applications across different industry sectors. Cellulose chains are present in wood pulp in the form of packed layers that are held together by lignin, and strong hydrogen bonds (Thoorens et al 2014). MCC is obtained by purification of wood using mineral acid solution, i.e. acid hydrolysis, followed by rinsing and drying. The presence of hydroxyl groups in the product of this purification process and the relatively large surface to volume ratio of micro fibrils give rise to MCC’s hygroscopic character (Sun 2008)
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