Development of amorphous PLA-montmorillonite nanocomposites

The large amounts of plastics that are produced mainly from fossil fuels, once they are consumed and discarded into the environment, finally end up as undegradable wastes, and therefore contribute greatly to global pollution. For this reason, there is an urgent need to produce renewable source-based environmentally benign plastic materials, specially in short term packaging and disposable applications that could allow the composting of naturally occurring degradation products. One of the most promising candidates in this direction is poly(lactic acid) (PLA), produced from renewable resources and readily biodegradable. PLA is a linear thermoplastic polyester produced by the ringopening polymerization of lactide. Lactide is a cyclic dimmer prepared by the controlled depolymerization of lactic acid, which is obtained from the fermentation of sugar feedstocks, corn, etc. [1, 2]. In general commercial PLA grades are copolymers of poly(L-lactic acid) and poly(D,L-lactic acid), which are produced from L-lactides and D,L-lactides respectively. The ratio of L-enantiomers to D,L-enantiomers is known to affect the properties of PLA [3], i.e. if the materials are semicrystalline or amorphous; until now all the efforts reported in order to improve the properties of PLA are focused on the semicrystalline material [3], e.g. D-content less than 6%. There is increasing interest in using PLA for disposable degradable plastic articles; however, there are properties such as flexural properties, gas permeability, impact strength, processability, etc. that are often not good enough for some end use applications [4]. On the other hand confinement of polymer in a two-dimensional silicate gallery, so-called polymer nanocomposite, is one of the effective ways to improve material performance [5]. The most widely utilized clay is the montmorillonite (MMT) for its large cation exchange capacity [5]. Ogata et al. [4] first prepared