Green films from grafting of modified pla onto starch nanocrystals

N. L. GARCÍA; M. LAMANNA; NORMA DACCORSO; ALAIN DUFRESNE; MIRTA ARANGUREN; SILVIA GOYANES

Conferencia; 6th International ECNP Conference on NANOSTRUCTURED POLYMERS AND NANOCOMPOSITES; 2010

The lack and the high costs of fossil resources, have generated numerous initiatives aimed at replacing these sources with renewable ones. As polylactic acid is a biodegradable, thermoplastic polymer derived from renewable resources, it is an ideal candidate to replace oil derivatives. On the other hand, starch is a cheap, abundant, renewable and biodegradable biopolymer, and then it is also a viable alternative. (David G.; Song, J.H. Ind. Crops Prod, 2006) In previous works, the production and characterization of starch nanoparticles was reported; together with its applications as reinforcement in nanocomposites by virtue of their rigidity. (Angellier et al., 2006) Starch-PLA composites seems to be the most promising combination for starch -based packaging (Wang et al., 2008; Jang et al., 2007), but PLA and starch are thermodynamically immiscible. To solve this problem, we propose the modification of PLA with different functional groups, followed by the grafting of PLA onto the surface of modified starch nanocrystals. In this work, polylactic acid was grafted to the surface of starch nanocrystals, previously obtained by acidic hydrolysis of waxy maize starch. The PLA was subjected to a two-steep reaction. The first one was performed to protect the hydroxyl groups of PLA and the second one to replace the OH group of the terminal carboxylic acid by chlorine, to form its more reactive acid chloride, and ensure the reaction with the hydroxyl groups of the starch nanoparticles. The evolution of the reactions was studied by infrared spectroscopy, which confirmed the success of each steep. The grafting efficiency was investigated by TGA and FTIR. Films were successfully prepared from the nanoparticles grafted with modified PLA and from PLA without nanoparticles. The morphology of the films was investigated by means of scanning electron microscopy of fracture surfaces; and compared with the morphology of films prepared with pure PLA. Since this material has important applications in packaging, it turned out to be fundamental to characterize its thermal behaviour and mechanical properties through differential mechanic analysis and tensile testing. Contact angle measurements were performed on the films obtained, in order to study the change in the polarity of the modified surface.