Thermal properties of ZnO and bimetallic Ag–Cu alloy reinforced poly(lactic acid) nanocomposite films

Abstract

Poly(lactic acid) (PLA)-based nanocomposite films were prepared by incorporating zinc oxide (ZnO) (<50 and <100 nm) and bimetallic Ag–Cu alloy (<100 nm) nanoparticles (NP), and polyethylene glycol as a plasticizer via a solvent casting method. Thermal properties of the nanocomposites films were investigated using differential scanning calorimeter and thermogravimetric analyzer. The addition of 20 % PEG to the neat-PLA decreased the glass transition temperature (Tg) significantly from about 60 to 17 °C, whereas the melting temperature (Tm) did not drop significantly. Metallic nanoparticles increased the Tg; however, Ag–Cu alloy exhibited a greater increase than ZnO nanocomposite films. Particle size of ZnO NP did not show significant difference in the Tg values of the films. The Tm value of the nanocomposite films was not influenced by the NP. The addition of plasticizer initiated the crystallization (cold and melt) of the PLA/PEG blend, which was substantially improved by the incorporation of NP in the composite films, in particular, 1 mass% loading. Non-isothermal crystallization was significantly affected by the cooling and heating rates. Thermogravimetric analysis data indicated that only Ag–Cu alloy could improve the thermal stability of nanocomposite films. Furthermore, nanoparticles significantly influenced the UV barrier and the transmittance of plasticized films.