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 (NaClO 2), 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.

Zhurkov’s Stress-Driven Fracture as a Driving Force of the Microcrystalline Cellulose Formation

“…Variations of the destruction activation energy of 10–15% can be caused by the structural reorganization (or stress) of the polymer matrix that was shown for nitrocellulose [ 31 ]. Besides that, the enthalpy of the MCC decomposition process ( –700 J/g) was two-to-three times greater than that of initial cellulose ( J/g), which qualitatively corresponds to the earlier results: the MCC thermal destruction always requires greater energy than initial raw [ 15 , 17 , 20 , 21 , 32 , 33 , 34 ]. Such a ratio confirms our hypothesis.…”

“…The critical step was probably using caustic soda for the acid neutralization after hydrolysis that we did not use. MCC is known to dissolve in alkalis, so even a short treatment with 1 N NaOH [ 15 , 17 , 20 , 21 ] could affect the cellulose structure and cause an increase in the decomposition temperature. Taking the rates of the cellulose and MCC thermal destruction to be approximately equal, the difference in the temperatures of decomposition allows rough accessing the difference in activation energies ( ) of this process: …”

“…The particles’ size does not depend significantly on the cellulose origin and the lignin removal technique [ 19 ]. However, the thermal stability and crystallinity of the MCC depend a bit on the delignification method [ 20 , 21 ]. In the course of acid hydrolysis, the degree of polymerization (DP) of the initial cellulose decreases by a factor of 5–10 [ 15 , 18 , 19 ].…”

“…On average, in raw cellulose, the second peak appears between 320 [ 15 , 17 ] and 350 °C [ 20 , 21 ], depending on the raw used. In MCC, the second peak can be found in a wide range of the temperatures (320–450 °C [ 33 ] either at greater temperatures [ 15 , 20 , 21 , 34 ] or lower temperatures [ 33 ] compared to the raw cellulose. However, the enthalpy of the thermal destruction of MCC was greater than raw cellulose [ 15 ].…”

Development of a microbial coating for cellulosic surface using aloe vera and silane

“…4 (a), peaks at 1458 cm −1 and 1656 cm −1 correspond to the C=C (aromatic ring) and C=O (flavonoids groups), respectively ( Mot, Dumitrescu and Sarbu, 2011 ). Commonly, the peaks at 3336 cm −1 and 2901 cm −1 in uncoated cloth are attribute to -OH stretching groups ( Beroual et al, 2020 , Beroual et al, 2020 ). The C-H bond is stretching vibration of CH 2 group.…”