Rheological Properties of Poly(lactic acid) Solutions Added with Metal Oxide Nanoparticles for Electrospinning

Abstract

Nanocomposites based on poly(lactic acid) (PLA) with antibacterial properties are of great potential interest as food packaging biomaterials. The investigations carried out in this study include the rheological properties of PLA/ZnO nanoparticles solutions used in the electrospinning of nanofibrous mats and the morphological evaluation of the mats. A detailed rheological analysis of the solutions used for electrospinning was carried out to understand the achieved morphology and structure of nanofibers (NFs). The effect of ZnO nanoparticles (ZnO-NPs) was investigated for various PLA solutions and solvents. The polymer solutions were prepared at various loading levels of ZnO: 0.4, 0.8, 1, 3 and 5 wt% relative to the polymer. Two solvent systems were used: 2,2,2-trifluoroethanol (TFE) and a mixture of dichloromethane/trifluoroethanol (DCM/TFE) (50:50 v/v). PLA with a low loading level of ZnO-NPs showed higher viscosity than neat PLA solutions. They also showed a maximum value of viscosity at 3 wt% content. Solutions containing more than 3 wt% ZnO exhibited a notable decrease in viscosity, which was attributed to PLA degradation. Other nanoparticles (NPs) such as SiO2 and TiO2 showed no decrease in the solution viscosity for all concentrations. The morphological characterization of the electrospun nanofibers was performed using scanning electron microscopy (SEM). The SEM images showed a network of smooth, randomly oriented, PLA nanofibers (PLA-NFs) and ZnO agglomeration was observed on the surface of the NFs. In the case of the PLA mats produced from PLA/TFE/ZnO suspensions with decreased viscosity, the SEM results confirmed the generation of beaded-fibers.