Extraction and Characterization of Cellulose Nanofibers From Yellow Thatching Grass (Hyparrhenia filipendula) Straws via Acid Hydrolysis

Abstract

A variety of lignocellulosic raw materials have been previously reported for the production of cellulose and cellulose derivatives, but little research effort has been dedicated to producing cellulose from Hyparrhenia filipendula. In this study, cellulose nanofibers (CNFs) were extracted from Hyparrhenia filipendula waste straws via sulphuric acid hydrolysis. The straws were pretreated with a combination of physiochemical processes and hydrolyzed using sulphuric acid at three different concentrations (1 M, 3 M and 5.6 M) for 2 h at 80 °C. The properties of the CNFs was checked by Fourier Transform Infrared spectroscopy (FTIR) for surface chemistry, X-ray diffraction (XRD) for crystallinity, Scanning Electron microscopy and Transmission electron microscopy (TEM) for morphology. A high-performance liquid chromatograph (HPLC) was used to quantify the amount of biopolymers in the CNFs. The results show that CNFs, denoted as CNF 1, CNF 3, and CNF 5.6 for 1 M, 3 M, and 5.6 M sulphuric acid, respectively, were successfully extracted at the various concentrations of sulphuric acid. The cellulose content of CNF1, CNF3, and CNF5.6 determined by HPLC analysis were 85%, 77% and 78% respectively. Also, the hemicellulose content in CNF 1, CNF 3, and CNF 5.6 was 10%, 15%, and 12% respectively, showing a high carbohydrate content of the CNFs. The FTIR spectra confirm the absence of characteristic peaks for lignin in the CNFs. The XRD analysis reveals presence of characteristic cellulose Iβ peaks at 2θ of 18°, 26°, and 40° with the crystallinity of 78%, 74% and 73% for CNF1, CNF3 and CNF5.6, respectively. Moreover, SEM analysis shows the deposition of lignin polycondensate on the surface of CNF 1, CNF 3, and CNF 5.6 while the bleached sample has a smooth and glossy appearance. The TEM analysis shows long unbranched nano-sized fibers for CNF 1 and shorter fibrous network of fibers for CNF 3, and CNF 5.6. The average diameter of the fibers, measured with ImageJ software is 40 nm for CNF 1, 57 nm for CNF 3, and 92 nm for CNF 5.6. CNFs were successfully produced from Hyparrhenia filipendula and reported for the first time in open literature. In view of the structure and properties of the produced CNFs, they are a potential material for value-added applications such as polymer matrices, films, and membranes, thus enabling efficient utilization of agricultural waste.