Supramolecular Approach for Efficient Processing of Polylactide/Starch Nanocomposites

All-biobased and biodegradable nanocomposites consisting of poly(L-lactide) (PLLA) and starch nanoplatelets (SNPs) were prepared via a new strategy involving supramolecular chemistry, i.e., stereocomplexation and hydrogen-bonding interactions. For this purpose, a poly(D-lactide)-b-poly(glycidyl methacrylate) block copolymer (PDLA-b-PGMA) was first synthesized via the combination of ring-opening polymerization and atom-transfer radical polymerization. NMR spectroscopy and size-exclusion chromatography analysis confirmed a complete control over the copolymer synthesis. The SNPs were then mixed up with the copolymer for producing a PDLA-b-PGMA/SNPs masterbatch. The masterbatch was processed by solvent casting for which a particular attention was given to the solvent selection to preserve SNPs morphology as evidenced by transmission electron microscopy. Near-infrared spectroscopy was used to highlight the copolymer-SNPs supramolecular interactions mostly via hydrogen bonding. The prepared masterbatch was melt-blended with virgin PLLA and then thin films of PLLA/PDLA-b-PGMA/SNPs nanocomposites (ca. 600 mu m) were melt-processed by compression molding. The resulting nanocomposite films were deeply characterized by thermogravimetric analysis and differential scanning calorimetry. Our findings suggest that supramolecular interactions based on stereocomplexation between the PLLA matrix and the PDLA block of the copolymer had a synergetic effect allowing the preservation of SNPs nanoplatelets and their morphology during melt processing. Quartz crystal microbalance and dynamic mechanical thermal analysis suggested a promising potential of the stereocomplex supramolecular approach in tuning PLLA/SNPs water vapor uptake and mechanical properties together with avoiding PLLA/SNPs degradation during melt processing.