Sunflower oil cake-derived cellulose nanocrystals: Extraction, physico-chemical characteristics and potential application

Abstract

In this work, sunflower oil cake (SOC) was identified as bio-sourced material for cellulose nanocrystals (CNC) production using chemical treatments followed by sulfuric acid hydrolysis. The hydrolysis was performed at 64% acid concentration, a temperature of 50 °C and at two different hydrolysis times, 15 min (CNC₁₅) and 30 min (CNC₃₀). It was found that CNC exhibited a diameter of 9 ± 3 nm and 5 ± 2 nm, a length of 354 ± 101 nm and 329 ± 98 nm, a crystallinity of 75% and 87%, a surface charge density of ~1.57 and ~1.88 sulfate groups per 100 anhydroglucose units and a zeta potential value of -25.6 and -30.7 mV, for CNC₁₅ and CNC₃₀, respectively. The thermal degradation under nitrogen atmosphere started at 225 °C (CNC₁₅), which is relatively higher than the temperature for sulfuric acid hydrolyzed CNC from other sources. Due to a high importance of CNC application in aqueous systems, the rheological behaviour of CNC suspensions at various concentrations was evaluated by the steady shear viscosity measurements and the oscillatory dynamic tests. The results showed that the CNC suspensions exhibited a gel-like behaviour at very low CNC concentrations (0.1-1%) wherein a strong CNC entangled network is formed. Polymer nanoreinforcing capability of the newly produced CNC was also investigated in this study. CNC filled PVA nanocomposite films were produced at various CNC contents (1, 3, 5 and 8 wt%) and their mechanical and transparency properties were investigated, resulting in transparent nanocomposite materials with strong mechanical properties. The study suggested other possibilities to utilize agricultural wastes from SOC for CNC production with potential application as reinforcement in polymer nanocomposites.

Keywords: Cellulose nanocrystals; Polymer nanocomposites; Sunflower oil cake.