The morphologies of samples were characterized by optical microscopy (OM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). OM was performed using an Olympus SZX9 stereomicroscope system. FESEM was conducted on a Carl Zeiss (Germany) Supra 35 VP using an extra high tension (EHT) of 8—10 kV. The samples were sputter-coated with gold prior to observation. The microstructure of PLA nanocomposites and the filler dispersion in the matrix were investigated using TEM (JEOL JEM-2010, USA). Samples for TEM analysis were sectioned with an ultramicrotome (RMC, model MTXL) to obtain 70 nm thick slices.
Biodegradation of the neat PLA, P/MT5 nanocomposite, and hybrid nanocomposites were carried out by soil burial method to stimulate natural composites biodegradation as previously reported by Chuayjuljit et al. (2009a). Rectangular samples with 25 X 25 X 0.1 mm dimensions were dried in a desiccator until their weights became constant (Wj). The samples were then buried in the compost soil at a depth of 20—25 cm from the surface for 8 weeks. One group of samples were carefully taken out for testing every 14 days, and then washed with distilled water to remove the sand from the surface of samples and dried at 55°C until their weights became constant (W2). Five samples were analyzed from each formulation and the average value was reported. The percentage of weight loss (%WL) was calculated using the following equation (7.1):