Physicochemical Properties and Thermal Stability of Microcrystalline Cellulose Isolated from Esparto Grass Using Different Delignification Approaches

Abstract

Esparto grass, known as alfa, is a renewable biomass widely distributed in southern and western Mediterranean basin. The present work focused on the isolation of pure cellulose from alfa stems, via different approaches, i.e., acidified sodium chlorite (NaClO2), totally chlorine free (TCF) or their combination, followed by the preparation of microcrystalline cellulose (MCC) using acid hydrolysis method. The obtained samples were characterized using infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TGA) and differential scanning calorimeter (DSC). The FTIR spectroscopy exhibited the removal of lignin and hemicellulose after the delignification and alkaline treatments. The XRD data showed that all of the MCCs have higher crystallinity indexes (Alfa-MCC 73–82%) and belong to cellulose I type. From SEM images, it is clear that the different MCC particles presented rough surface and micro-sized particles. The DSC/TGA analyses revealed that MCC samples present better thermal stability than their respective cellulose ones, with higher temperature of decomposition (more than 350 °C). Moreover, the use of a combined process yields to MCC with higher crystallinity and better thermal stability. Consequently, based on these findings, the delignification with combined method can be considered as a promising approach to extract MCC from alfa fibers with outstanding features.