Permeability in Clay/Polyesters Nano-Biocomposites

In this chapter we focus on the barrier properties of nanocomposite of biodegradable polyesters with layered inorganic fillers. First of all, to better understand the influence of the lamellar inorganic fillers on the permeability, the theory of permeation and the barrier models so far developed for polymer nanocomposites are reviewed. Afterwards the barrier properties of the most important biodegradable polyesters filled with inorganic lamellar solids, such as Polylactic acid (PLA), Polycaprolactone (PCL), Polyhydroxbutyrate (PHB), and Polybutylenesuccinate (PBS) are reviewed and the outstanding results enlightened. As a general trend, the best improvement of barrier properties is related to the exfoliation of clay platelets into the polymeric matrix, and this in turn is dependent on the chemical structure of the clay, the organic modification, the filler concentration and the processing procedure to prepare the composite. Where possible, all these parameters were reported and correlated with the final properties. Also the contrasting effect of clays on the two parameters determining the water permeability, that is sorption and diffusion, is reported in many cases.