Isolation of cellulose nanocrystals from onion skin and their utilization for the preparation of agar-based bio-nanocomposites films

Cellulose nanocrystals (CNC) were isolated from onion skin using different concentrations of acid (45, 55, and 65 % H₂SO₄) and agar/CNC composite films were prepared to test their performance properties. The major component of onion skin was α-Cellulose (41.1 %). The yield, crystallinity index (CI), crystallite size, and thermal stability of the CNC varied depending on the acid concentration. The CNC isolated with 45 % of H₂SO₄ (CNC45) had the highest yield (48.6 %), CI (0.26), crystallite size (2.49 nm), and thermal stability among the tested CNCs. Performance test results of agar/CNCs composite films also indicated that the CNC45 reinforced composite film had the highest tensile strength (TS: 50 MPa) and Young’s modulus (YM: 1.98 GPa) with the lowest water vapor permeability (WVP: 1.78 × 10⁻⁹ g m/m² s Pa). The properties of agar/CNC45 composite films were also greatly influenced by the content of nanofiller. The composite film exhibited the maximum strength and water vapor barrier properties with 3 wt% inclusion of CNC45. The present study revealed that the onion skin is an interesting new source of cellulose material for the preparation of bio-nanocomposite materials.