Chitosan-stabilized polylactic acid emulsions: A green coating strategy to improve barrier properties of packaging materials

Mixing polymers in solution by emulsification can combine the best characteristics of each polymer and obtain coatings with specific oxygen and water vapor barrier properties. In this work, innovative water-based coatings based on polymeric emulsions of chitosan (CS) and polylactic acid (PL) were successfully developed through the emulsification-evaporation method. Modifying the CS concentration in the aqueous phase of the emulsions resulted in coatings with different PL/CS ratios, which in turn led to variations in the barrier properties of the resulting coated substrates against oxygen and water vapor. The effect of these ratios on the morphological and rheological properties of the obtained dispersions and the barrier properties of resulting bilayers systems were studied. CS played a key role in stabilizing the emulsions and their corresponding dispersions. Morphological analysis indicated that developed coatings were composed by homogeneous dispersions of PL particles whose distribution of particle size depended on PL/CS ratio. All dispersions exhibited a shear-thinning behavior and suitable viscosity values for coating applications. Bilayer systems composed by commercial PLA sheets coated with developed water-based coatings showed an improvement in oxygen barrier, one of them standing out with reduction of oxygen permeability of approx. 78% with respect to the neat PLA film at 50% RH.