Effect of Choline Chloride/Citric Acid Ratios on Physical and Mechanical Properties of Citrus Maxima Rind Pectin-Based Bioplastic

Pectin-based bioplastic without a plasticiser is characterised as brittle and glassy. The incorporation of a common plasticiser, such as glycerol is not sufficient in increasing the mechanical strength of the bioplastic. As a result, in the present study, bioplastics were synthesised utilising pectin extracted from Citrus maxima rind and a deep eutectic solvent (DES) as a sustainable alternative plasticiser. Four types of bioplastics consisting of 5% Citrus maxima pectin and 1% DES with different ratios of choline chloride (ChCl) and citric acid (CA) (0:1, 1:1, 1:2, 2:1, and 3:1) were formulated and prepared using the casting method. Pectin-derived bioplastics with and without CA were used as controls. The physical properties of bioplastics were characterised by FTIR-ATR and mechanical properties of the bioplastics, including thickness, tensile strength, elongation at break, and Young’s modulus, were investigated to observe the effect of adding different ratios of ChCl and CA as plasticisers. The study found that bioplastics with ChCl:CA worked better than those with only CA. A higher proportion of CA in DES promotes better extensibility at the expense of a lower tensile strength and Young’s Modulus. Meanwhile, a higher ChCl content resulted in a higher tensile strength and Young’s modulus with poorer extensibility. In addition, DES increased the moisture absorption and biodegradability of bioplastics by up to 13.23% and 50.49%, respectively, compared to those without DES. In conclusion, DES significantly improved the physical properties and biodegradability of bioplastics.