Antibacterial chitosan electrostatic/covalent coating onto biodegradable poly (l-lactic acid)

Abstract

Biodegradable, non-toxic and transparent poly (l-lactic acid) (PLLA) biopolymer is modified in order to obtain an improved material with antibacterial properties for its use as active packaging of food. For this, PLLA films were endowed with the bactericidal effect of ZnO nanoparticles by internal blending and the bacteria contact-killing properties of the biopolymer chitosan (CHI) by superficial modification. Surface functionalization with CHI was carried out by covalent or electrostatic functionalization which were comparatively analyzed in terms of yield and stability. Additionally, the effect of employed CHI concentration and molecular weight was also studied for both modification methods. Modified films were characterized by confocal fluorescence microscopy, contact angle measurements, UV–Vis spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and electrostatic force microscopy. The antibacterial properties of each modification on PLLA were studied against Escherichia coli, showing the greater microbial death after covalent functionalization with CHI. Moreover, stability of modified films was studied in enzymatic and non-enzymatic medium and it was improved by chemical crosslinking with the natural molecule genipin. The valuable properties of PLLA, as well as the derived antibacterial properties of the incorporation of ZnO nanoparticles and CHI, make prepared films highly attractive candidates for the innovative packaging industry.