Rice starch-assisted reduction of silver nanoparticles on cellulose paper for active food packaging applications

In this study, hanadmade paper (HP) was fabricated on a laboratory scale, replicating the methods used in HP-making industries. The paper was then in situ coated with silver nanoparticles (AgNPs) following an ecofriendly method that involved the use of rice-grain starch (ST) and irradiation in middle-day sunlight of an average intensity around 640.7 ± 90.5 W/m². The various properties of the uncoated and coated papers (HP-ST/Ag) were systematically compared. For HP, the recorded values of thickness, grammage, density, opacity, and brightness were 0.27 ± 0.03 mm, 82.52 ± 6.19 g/m², 0.30 ± 0.01 g/cm³, 74.8 ± 2.1%, and 33.37 ± 1.95%, respectively. Compared to uncoated paper, a remarkable increase in thickness (0.30± 0.05 mm), grammage (124.83 ± 12.40 g/m²), density (0.43 ± 0.12 g/cm³), and opacity (95.9 ± 2.9%) was observed in the HP-ST/Ag, whereas brightness (4.78 ± 0.28%) decreased significantly. A substantial positive correlation (r = +0.93) between the grammage and thickness was noticed. The coated paper demonstrated a reduced water vapor transmission rate (193.78 ± 1.42 gm^-2 h^-1), enhanced mechanical strength (TS = 9.13 ± 0.06 MPa), and significant antimicrobial properties against E. coli, S. aureus, and C. albicans compared to HP. The SEM analysis of HP-ST/Ag revealed the formation of AgNPs consisting of an average particle size of 110.03 ± 3.17 nm, which was further confirmed via XPS analysis. The calculated overall migration values of HP-ST/Ag in various simulants were lower than the permissible limit, caused by essential immobilization of AgNPs in the HP-ST matrix. The shelf life of a white bread slice packaged with the antimicrobial paper at ambient conditions was significantly increased, thereby offering a sustainable approach to transform HP into an active packaging material.