Poly(lactic acid) (PLA) was synthesized using condensation polymerization of L-lactic acid using a controlled ultrasonic cavitation technique. Polystyrene (PS) was used to prepare the PS:PLA and PS:PLA:organically modified montmorillonite (OMMT) composites. PS was dissolved in benzene (10:90) and kept overnight for dissolution. Meanwhile, surface modification of montmorillonite was done using a column chromatography technique and referred to as OMMT. The d-spacing was found to be 22 Å after modification due to sufficient column length and diameter with good retention time during ion exchange. PLA and OMMT were kept in hot air oven at 100 ℃ for 30 min to remove the moisture. The mixtures of 10%, 15%, 20%, 25%, and 30% of PS:PLA:OMMT were subjected to ultrasonic irradiation (50 Hz) for homogenization and to form a biodegradable polymer nanocomposite sheet (5 × 5 cm2). The amount of OMMT loading was from 0.5-5 mass%. These composites were subjected to degradation in minimal medium using Pseudomonas aeruginosa bacteria at controlled conditions, and the polymer is a major source of carbon. The degradation was confirmed using scanning electron microscopy, extracellular protein content change, biomass production, and % degradation with respect to time (up to 28 days) after incubation.