Use of Cellulose and Oxidized Cellulose Nanocrystals from Olive Stones in Chitosan Bionanocomposites

Cellulose nanocrystals (CNC) and 2,2,6,6-tetramethyl-1-piperidinyloxyl- (TEMPO-) oxidized cellulose nanocrystals (CNC-TEMPO) were prepared from olive stones. The prepared nanocrystals were characterized using transmission electron microscopy (TEM), Fourier transforminfrared spectroscopy (FTIR), and carboxylic groups content determination. The prepared nanocrystals were used as reinforcing elements in chitosan nanocomposites, which were characterized using X-ray diffraction (XRD) and tensile strength properties. In addition, the bioactivity of the prepared chitosan nanocomposites was studied in vitro in simulated body fluid (SBF) using scanning electron microscopy (SEM) and electron diffraction X-ray spectroscopy (EDX). The results showed positive effect of the nanocrystals on tensile strength properties of chitosan and noticeable reduction in its rate of dissolution in SBF due to presence of cellulose nanocrystals. Chitosan nanocomposites containing CNC-TEMPO showed higher tensile strength properties and higher rate of dissolution in SBF than those containing cellulose nanocrystals. Nanocomposites containing CNC or CNC-TEMPO could not form significant amounts of hydroxyapatite (HAp) upon immersion in SBF for up to 4 weeks. Upon addition of nanohydroxyapatite to chitosan/cellulose nanocrystals films, formation of new hydroxyapatite depositions was observed. Presence of cellulose nanocrystals in chitosan/HAp resulted in formation and deposition of higher amounts of new HAp than in case of using chitosan/HAp without cellulose nanocrystals.