Deep Eutectic Solvent Pre-treated Sweet Sorghum Stalk (Sorghum Bicolor (L.) Moench) Nanocellulose and Its Application to Agar-Based Bioplastics

Nanocellulose is already established as a reinforcing agent in bioplastics. Sorghum stalk, an underutilized source of cellulose despite its high cellulose content and abundance, is put to use in this study. An alternative, more environmentally friendly isolation method using a deep eutectic solvent (DES) consisting of an oxalic acid/choline chloride (ChCl) mixture is similarly put to test. This study thus aims to investigate the effect of the addition of nanocellulose from this alternative source and isolation method on the characteristics of agar-based bioplastics. Using a previously established optimal oxalic acid:ChCl ratio of 1:1 resulted in cellulose nanofibrils (CNF) with a yield of 61.50%, zeta potential of − 21.7 mV, average diameter of 55.53 ± 2.89 nm, transparency of 0.035% and the highest degradation temperature compared to other tested ratios. When this nanocellulose was incorporated into agar-based bioplastics, the resulting bioplastic showed a significant (at p < 0.05) improvement in its physical (thickness, transparency, water vapor transmission rate (WVTR)) and mechanical (tensile strength, modulus of elasticity) properties. In addition, the addition of nanocellulose also improved the thermal properties of the bioplastics as well, showing an increase of 0.96% in melting point, 72.71% in T_onset, 19.10% and in T_max. These improvements open up the opportunity for the application of nanocellulose-reinforced agar-based bioplastics as food packaging material.