Fabrication and characterization of novel starch-grafted poly l-lactic acid/montmorillonite organoclay nanocomposites

• Poly(l-lactic acid)-g-starch layered silicate nanocomposites were fabricated.
• Preintercalated LA-MMT organoclay exhibit dual functions as catalyst and compatibilizer.
• LA-MMT organoclay accelerated in situ graft copolymerization via esterification of LA.
• The obtained results confirmed the intercalation/exfoliation of silicate galleries.
• Highly exfoliation of clay and graft copolymerization led to high thermal stability of NCPs.

In this work, poly(l-lactic acid)-g-starch layered silicate nanocomposites (NCs) (PLLA-g-starch/MMT) were fabricated by intercalative bulk graft copolymerization of LA with starch, in the presence of either stannous octoate acting as a catalyst or LA-MMT organoclay acting as a cocatalyst-nanofiller. This procedure was performed inside a custom vacuum micro-reactor. To better understand the graft copolymerization mechanism, in situ processing types, interfacial interactions and nanostructure formation of PLLA-g-starch/MMT NCs, methods such as FT-IR, XRD, 1H NMR, 13C CP/MAS-NMR, DSC/TGA, TEM and SEM were utilized. The morphology and thermal behaviors of nanocomposites were found to be strongly dependent on the loading mass fraction of LA-MMT within the nanocomposite structure and the type of in situ processing such as interfacial, physical and chemical interactions. Preintercalated LA-MMT organoclay exhibited dual functions. It demonstrated the ability to act as a catalyst, essentially accelerating in situ graft copolymerization via esterification of LA carboxyl groups with hydroxyl groups of starch macromolecules, whilst also acting as a nananofiller-compatibilizer.