Preparation and characterization of oak tree acorn starch-based bioplastic starch/halloysite nanotube/clove essential oil and bioplastic starch/halloysite nanotube/silver nanoparticle composite materials with antibacterial property

In this study; oak tree acorn starch-based new bioplastic films were prepared by using starch obtained from oak tree acorns, which are widely grown in our country. Halloysite nanotube (HNT) was doped into the starch film matrix to improve the mechanical and thermal properties of the bioplastic films. In addition, Starch-HNT-CEO and Starch-HNT-AgNP bioplastic composite films were prepared by adding the different amounts of clove essential oil (CEO) and silver nanoparticle (AgNP) to give the bioplastic film antibacterial property. Bioplastic film samples were characterized by using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), opacity, color, water contact angle, mechanical strength, thermal gravimetric analysis (TGA) and water vapor permeability analysis. With the morphological analysis performed, it was observed that there was an increase in the smoothness of the bioplastic film surface with the effect of the increase in the concentrations of CEO and AgNP in the film matrix. Opacity measurement results showed that Starch-HNT-CEO composite films have higher opacity values than Starch-HNT-AgNP composite films. It was determined that the brightness decreased as the CEO concentration increased in Starch-HNT-CEO films, while the brightness increased when AgNP concentration increased in Starch-HNT-AgNP films. In the Starch-HNT-CEO and Starch-HNT-AgNP bioplastic composite films, it was observed that there was an increase in the water contact angle value of the film material as the concentration of CEO and AgNP doped into the film matrix increased. Among the studied film materials, it was determined that the highest water contact angle of 71° belonged to the Starch-HNT-AgNP3 film. The mechanical property measurement results of the bioplastic films showed that the addition of HNT into the starch film matrix caused a significant increase in the maximum tensile stress and Young's modulus values and a decrease in the maximum tensile strain values of the composite films. With the increase in AgNP concentration, the maximum tensile stress and Young's modulus values of the composite films increased while a significant decrease was observed in these values with the increase in CEO concentration. Among the films prepared, the highest maximum tensile stress (18.71 MPa) and Young's modulus (1527 MPa) values were measured in the Starch-HNT-AgNP3 film. Among the prepared films, the highest maximum tensile strain was recorded as 31.09% for Starch-HNT-10% CEO film. The use of HNT during the preparation of starch-based film materials caused an increase in the termal stability of films. The presence of HNT, CEO and AgNP in the starch film matrix caused a decrease in the water vapor permeability rate (WVTR), permeance and water vapor permeability (WVP) values of the film materials. Bioplastic films containing CEO and AgNP showed antibacterial property against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The experimental results revealed that low-cost and eco-friendly Starch-HNT-CEO and Starch-HNT-AgNP films have great potential to be used as food packaging material.