Spectra and crystallographic analysis of combined ultrasonic and mild acid hydrolysis structural effects on lignin-containing cellulose nanofibrils (LCNFs) and cellulose nanofibrils (CNFs)

Abstract

Cellulose nanofibrils (CNFs) and lignin-containing cellulose nanofibrils (LCNFs) have been isolated from sunflower stalks through varying mechano-chemical process. The processing conditions were used to evaluate the structural differences between CNFs and LCNFs. This study has been able to establish that outside the strong lignin aromatic bands found in the FT-IR finger-print region of the LCNF, the CNF, LCNF, and the acid hydrolyzed samples (aCNF and aLCNF) possess same chemical structures. They however exhibited varying crystal systems with LCNF and aLCNF showing monoclinic and orthorhombic structures respectively, while CNF and aCNF were tetragonal and orthorhombic. The average crystallite size calculated from the XRD analysis shows that the lignin containing samples are larger in size (4.08 nm to 5.36 nm) than other samples (2.03 nm to 2.52 nm) while the average AFM heights of all samples ranged from 12 nm to 35 nm. The ultrasonic treatment was observed to have adversely affected the XRD crystallinity index of the cellulose nanofibril samples while improving that of lignin-containing samples. This underscores the importance of understanding the compromise to be established between structure and size in the fabrication of cellulose nanomaterials. This work has shown that despite the varying processing conditions and fiber components of the nanocellulose, they maintained similar FT-IR crystallinity ratios and crystalline structure meaning that LCNF can complement CNF where its properties supersedes and vice versa.