(640f) Water Vapor Permeability, Solubility and Diffusivity through Polylactic Acid Nanocomposites

Polylactic acid (PLA), a bio-derived and biodegradable polymer, is considered to be a good substitute for conventional non-biodegradable polymers for many applications, including food packaging. However, PLA’s poor water vapor barrier properties limit its use in this application. However, the water vapor permeability can be reduced by incorporating nanoplatelets of high aspect ratio in the polymer. These form impermeable barriers to the mass transfer and cause the diffusing molecules to travel along a tortuous path resulting in reduced permeability.

In this work, we show the effect of adding Cloisite 30B, an organically modified nanoclay, on the water vapor permeability, solubility and diffusivity for PLA-matrix nanocomposites. Optimized melt mixing conditions in an internal mixer were determined to obtain the best dispersion of Cloisite 30B in the PLA matrix. Measurements with MOCON WVTR equipment showed that as the content of Cloisite 30B increased, the permeability decreased, and, at 10 wt% (5.3 vol%) loading, the water vapor permeability was reduced by 69% when compared to neat PLA. In addition, sorption experiments were performed to determine the water vapor solubility which showed that the solubility increased with increasing nanoclay content with a corresponding reduction in the diffusivity. We also present the combined effect of crystallinity and nanoclay on the water vapor permeability properties, and these show that the presence of crystallinity results in a further decrease in permeability. Finally, predictions from finite element modeling of the diffusion process are presented and compared with the experimental results.