Morphology and Mechanical Properties of Poly(vinyl alcohol)/Poly(lactic acid) Blend Films Prepared from Aqueous Dispersions

In this study, the preparation of poly(vinyl alcohol) (PVA)/poly(lactic acid) (PLA) blends of different compositions, 100/0, 75/25, 50/50, 25/75, and 0/100, by mixing water solutions of the former and water dispersions of the latter polymer, is reported. Two distinct dispersions of PLA are prepared using a commercial-grade polyester and two different surfactants, an anionic one and a neutral one. Films of PLA and of the corresponding blends are obtained by simply drying at 60 °C the water dispersions without or with the PVA. The films are characterized by infrared spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscope (SEM) analysis. This evidences an island-like morphology, with the continuous phase consisting of a PVA rich phase at all compositions except 25/75, for which an inverted phase composition, with a continuous phase made mostly of PLA, is instead found. Voids caused by air bubbles trapped in the initial mixture are observed in particular in the formulations with the anionic surfactant. The trapped bubbles result in premature thermal degradation by thermogravimetric analysis (TGA) and mechanical failure during clamping. Films with the neutral stabilizer are tougher than the bare commercial PLA, with Young modulus and elongation at break depending on the combination of the composition and arrangement of blend phases.