Transport properties of water vapor in polylactide/montmorillonite nanocomposites

摘要

Both intercalated and exfoliated poly(L-lactide) (PLA) layered aluminosilicate nanocomposites were synthesized and characterized in terms of barrier properties. Intercalated polylactide/montmorillonite nanocomposites were obtained by melt blending PLA and a montmorillonite modified with bis-(2-hydroxyethyl)methyl (tallow-alkyl) ammonium cations (MMT) (1, 3, 5, and 10 wt/wt%). A sample containing 3 wt% of MMT was prepared with 20 wt% of PEG1000 as plasticizer. Exfoliated nanocomposite containing 3 wt% of MMT was synthesized by in situ coordination-insertion ring-opening polymerization of L,L-lactide, after adequate activation of the primary hydroxyl groups functionalizing the organo-modifier. The barrier properties were studied for water vapor at 30degreesC. The sorption (S) and the zero-concentration diffusion coefficient (D-0) were evaluated. The sorption curves of water vapor in all the samples follow the dual-sorption behavior. The amount of solvent absorbed derived from the linear part of the curve appears lower in the intercalated nanocomposites for all studied MMT content than for the exfoliated sample. The thermodynamic diffusion parameters, D-0, decreased by one order of magnitude with increasing MMT content from 0 to 10 wt% in the intercalated samples. In comparison with the value of D-0 for the parent unfilled PLA, the intercalated samples containing 3 wt% of MMT (with or without PEG 1000) were found to be slightly lower. On the other hand, the exfoliated nanocomposite showed strong deviation in the D-0 value, being lower by about two orders of magnitude with respect to the results obtained for all the other samples (unfilled and intercalated). The exfoliation of the inorganic component in the continuous polymeric phase seems to be the most important factor to improve the barrier properties of the material to water vapor.