Study of acid hydrolysis based synthesis of microcrystalline and nanocrystalline cellulose from local lignocellulosic materials

Abstract

Cellulose is one of the most important substances among natural and synthetic polymeric materials. Fibrous cellulosic materials are capillary porous disperse systems with high specific surface areas. The degraded (low molecular weight product) micro and nano cellulose is highly renewable. Because of their inherent renewability and sustainability and unsurpassed quintessential physical and chemical properties, microcrystallinecellulose (MCC) and nanocrystalline cellulse (NCC) have a great attention to the researcher. The highly crystalline cellulose can be prepared by selective methods based on the source of the cellulose. MCC and NCC can be derived from number of process like reactive extrusion process, enzyme mediated process, the steam explosion process and acid hydrolysis process etc. Out of this process acid hydrolysis process is most suitable to prepare the low cost degraded micro and nanocellulose. In this study, cotton based waster cloths and commercial wood pulp, which were collected from local shop, hosiery industry and paper industry, were used to prepare MCC and NCC by acid hydrolysis and ultrasound assisted acid hydrolysis process, respectively. Since the cellulose contains both amorphous and crystalline structures, MCC and NCC is derived by severe acid hydrolysis to remove the amorphous portions of cellulose, yielding low molecular weight micro and nano particles. In this study cellulosic materials were hydrolyzed in different concentration of HCl (2.5-10N) at different temperatures (80-110)0C to optimize the preparation condition for the preparation of MCC powder from local waste lignocellulosic materials. It was observed that the formation of MCC depends upon the source of cellulose and the reaction conditions of hydrolysis. On the other hand, the stable suspension of cellulose nanocrystals was prepared by sulfuric acid hydrolysis followed by ultrasound. For that purpose the optimum conditions for the formation of transparent gel of NCC were established for the local cotton cloths. Set of experiments were performed to examine the optimum condition viz. temperature, time and concentration of acid for the preparation of NCC. The optimum condition of hydrolysis was: concentration of acid 63-65 % (w/w), temperature 60oC and time 35 minutes. Surface morphology and particle size were investigated through Field Emission Scanning Electron Microscopy (FESEM). The analysis showed that the average diameter of prepared MCC was about 5-10 μm and length was about 50 μm and the average fiber diameter of NCC was less than 20 nm with a length of 100 nm to few micrometers. Comparison of commercial MCC and prepared MCC of FTIR confirmed the preparation of typical microcrystalline cellulose. The FTIR analysis of NCC was also observed. The results of chemical analysis, XRD confirmed the crystalinity of MCC and NCC. Thermogravimetric analysis results showed the stability of the prepared MCCs from different sources. Thermogravimetric analysis results showed that MCC have higher thermal stability than NCC.