Preparation of modified-TiO2/PLA nanocomposite films: Micromorphology, photo-degradability and antibacterial studies

Abstract

Today bio-nanocomposites of biopolymers are from great interest from the point of view of environmentally friendly concerns (1). Among all types of PLA nanocomposites, the ones including oxides of semi-conductive materials such as TiO2 have attracted the attention of many research centers and industries due to their photocatalytic and antibacterial properties (2). Although there seems to be a great interest about producting the nanocomposite of PLA and TiO2 nanoparticles, but aggregation of TiO2 nanoparticles in an organic matrix like PLA, makes it difficult to reach a homogenous film with good properties (3). Therefore, using a method in order to modify TiO2 nanoparticles surface before introducing into the PLA matrix, seems to be necessary. In this study first, PLA chains were grafted onto TiO2 nanoparticles surface via reactive melt mixing using a novel approach in presence of SnCl2 as catalyst. In this step, PLA grafted chains were characterized on the TiO2 nanoparticles using FTIR analysis. Then, PLA-grafted-TiO2/PLA nanocomposite films with different amounts of modified TiO2 nanoparticles, were produced using a twin screw extruder. The microstructure of nanocomposite films was characterized using SEM technique, and this way, it was observed that the dispersion state of TiO2 nanoparticles has been greatly improved after modifying TiO2 surface. Finally, the PLA-grafted-TiO2/PLA nanocomposite films were put under UV irradiation, in the range of 360-420 nm, for 2 months and the weight loss of the films was followed during this period. The nanocomposite films containing modified TiO2 nanoparticles, showed higher amount of weight loss in comparison with the film containing bare TiO2 nanoparticles. The PLA-grafted-TiO2/PLA nanocomposite films were also used to investigate the antibacterial properties against both gram negative and gram positive bacteria, under UV irradiation for 2 hours, using a combined method of JIS Z2801:2000 and ASTM E2180-07. The nanocomposite films showed high antibacterial properties against E-coli gram negative bacteria, although this amount was lower in case of St.aureous gram positive bacteria, due to the natural structural differences between gram negative and gram positive bacteria’s cellular membrane.