Development of polylactide-clay nanocomposites for food packaging applications

Poly (lactic acid), abbreviated PLA, is a biodegradable polymer, made from renewable sources, with either a semi-crystalline or amorphous structure. Although these features make PLA an appropriate candidate for food packaging there are, however, some important issues that should be overcome such as poor thermal stability, low mechanical resistance, and limited gas barrier properties. Based on results reported in the literature, the addition of nano-sized fillers (clays) can efficiently improve the mechanical and barrier properties provided that they are well dispersed in the matrix and form an exfoliated structure. On the other hand, this work shows that the incorporation of organically modified clay into PLA enhances the rate of degradation and hence markedly decreases the thermal stability of the resulting nanocomposites. Therefore, control of PLA thermal degradation is another challenge in developing PLA-clay nanocomposites.;In the second part of this project, Joncryl-based nanocomposites were prepared using different strategies. The effect of chain extender and processing conditions on the degree of clay dispersion, mechanical, and barrier properties of the resulting nanocomposites were investigated. The Joncryl-based nanocomposites were prepared using five different strategies, and compared to a benchmark nanocomposite. Incorporating 2 wt. % CloisiteRTM30B (nanoclay) and 1 wt. % Joncryl into the PLA matrix led to a significant reduction in oxygen permeability and improvement of the mechanical properties such as tensile modulus, strain at break and toughness of PLA nanocomposites prepared by the second strategy based on the master batch of PLA/clay.;In the first step of this Master's project, PLA-clay nanocomposites containing different chain extenders were prepared. Polycarbodiimide (PCDI), tris (nonylphenyl) phosphite (TNPP), and Joncryl RTMADR 4368 were used as chain extenders in this work. The effect of incorporating chain extenders on controlling the thermal degradation, the rheological and thermo-physical properties and the molecular structure has been investigated. The results revealed that the incorporation of PCDI (2 wt. %), TNPP (1 wt. %), or Joncryl (1 wt. %) had a profound effect on controlling the degradation. Such concentrations not only stabilized the viscosity and modulus with time but also increased their magnitudes in some cases. The mechanism of stabilization is most likely chain extension. The chain extension led to the formation of longer linear chains in the PCDI and TNPP based nanocomposites, and to a long chain branched (LCB) structure in Joncryl-based nanocomposites. Thermal gravimetric analysis (TGA) revealed that the addition of clay into PLA decreased its thermal stability, whereas an increase in the temperature for the onset of degradation was observed after the incorporation of the chain extenders. Joncryl was found as the most efficient chain extender under processing conditions among the ones used in this study.