Improvement of the Gas Barrier Properties of PLA/OMMT Films by Regulating the Interlayer Spacing of OMMT and the Crystallinity of PLA.

A high gas barrier performance should be ensured in case of biodegradable packing applications. However, the gas barrier properties of the biodegradable poly(lactic acid) (PLA) are not much effective. Nanocomposites can provide innovative solutions to enhance the barrier performance. In this study, different weight percentages of organically modified montmorillonite (OMMT) (0, 2, 4, 6, 8, and 10 wt %)-incorporated PLA/OMMT nanocomposites were prepared by melt mixing. Ethylene glycol diglycidyl ether (EGDE) was used to regulate the interlayer spacing of OMMT and increase the PLA crystallinity to further improve the gas barrier performance of the PLA/OMMT films. The crystallinity of PLA was significantly improved because EGDE-modified OMMT served as an efficient nucleating agent. The PLA/EGDE/OMMT films demonstrated a unique structure such that the adjacent OMMT layers were linked through the PLA crystals that serve as a bridge with respect to the spaces between the OMMT layers. The O permeability of the PLA/EGDE4/OMMT-6 film decreased by approximately 79% when compared with that of the neat PLA film. X-ray diffraction and differential scanning calorimetry analyses denoted that the reduced oxygen permeability of the PLA/EGDE4/OMMT-6 film can be primarily attributed to the high crystallinity of the PLA matrix and the bridging effect of the PLA crystals between two adjacent layers. Based on the experimental results, the relation between the relative permeability and vol % OMMT is in good agreement with that of the predicted values obtained using the Bharadwaj model when = 0. The added EGDE weakened the thermal stability and tensile strength, mainly because of degradation of the hydroxyl groups of EGDE formed by epoxy ring opening, and these hydroxyl groups can promote PLA matrix degradation. However, the practical application temperature of the packaging film is considerably lower than the thermal decomposition temperature; therefore, the reduction of the thermal decomposition temperature does not affect the use of the packaging film.