Interfaces in biopolymer nanocomposites: Their role in the gas barrier properties and kinetics of residual solvent desorption

Poly(lactic acid) nanocomposite films were prepared by solvent casting method dispersing lauryl-functionalized cellulose nanocrystals in the biopolymer matrix. The gas transport properties of nanocomposites with different filler content were studied by gas phase permeation technique while the release of residual solvent molecules (CHCl3) was analyzed by Thermal Desorption Spectroscopy. The aim of this work is to study the correlations between the two processes that so far were studied separately. The analysis reveals that both the gas barrier properties of the nanocomposite and the kinetics of the residual solvent desorption are controlled by interface LNC-PLA layers. The improved gas barrier properties observed up to a critical filler content of 6.5 wt. % are attributed to the formation of a gas-impermeable PLA regions with thickness in the 10 nm order surrounding the functionalized filler particles. In the pure PLA matrix residual solvent molecules form small aggregates which desorb through a thermally activated process showing a peak at T = 393 K and following a zero-order kinetic process. In the nanocomposites, interface regions trap a fraction of residual solvent molecules that increases with the LNC content: solvent release occurs at higher temperatures and follows a first-order desorption kinetics.