Synthesis of calcium oxide and antimicrobial activity enhancement of chitosan bio-composite films: An active...

The incorporation of antimicrobial agents into renewable polymers has significant potential to develop sustainable materials for active packaging, addressing perishable food waste and environmental issues. Calcium oxide (CaO) particles were synthesized as an alternative antimicrobial agent using a co-precipitation technique and calcination at 650 °C for 1 h. The effect of synthesis stirring times (60, 90, and 120 min) on antimicrobial activity was analyzed. A simple solution casting technique was used to fabricate chitosan bio-composite (CS-CaO) films with different CaO contents. All CaO particles were cubic. The crystallite and particle sizes of the synthesized CaO depended on the synthesis stirring time. The average crystallite sizes were 30.9, 28.4, and 27.4 nm for CaO-60, CaO-90, and CaO-120, respectively. All CaO particles showed excellent antibacterial activity against S. aureus and E. coli (>99.99 % reduction). Remarkably, CaO-120 exhibited outstanding antimicrobial activity, achieving a 99.9999 % reduction in S. aureus and E. coli, primarily due to its smallest crystallite and particle sizes, which were influenced by the optimal synthesis stirring time. The incorporation of 3 % CaO content into CS enhanced thermal stability (T_d10% = 186.3 °C) and tensile strength (85.3 MPa), and reduced water vapor permeability (0.14 g·m/m²·d·mmHg) of the films due to optimal CaO content, good CaO dispersion, and strong interaction between CaO and CS. Moreover, CS-CaO 3 % film exhibited a bactericidal effect against S. aureus and E. coli, achieving a 6-7 log reduction (99.999-99.9999 % reduction), demonstrating its potential as an active packaging material for food products.