Degradation of polypropylene–poly-L-lactide blend by bacteria isolated from compost

Polypropylene (PP) degrading bacteria (P1 to P16) were isolated from compost using enrichment technique. Five isolates (P3, P6, P8, P10, and P13) were selected based on their degradation abilities. These isolates were identified as Bacillus spp. through biochemical characteristics and 16S rDNA sequence analysis. The isolates were tested for their ability to degrade blends of PP and poly-L-lactide (PLLA) (PP80 and PP80C6) in minimal media as well as in soil. In minimal media, the growth of bacteria increased with time, showing utilization of blend as carbon source. The protein content was estimated at the end of 15 days and maximum amount was secreted by isolate P8 indicating maximum potential to degrade polymers compared to other isolates. Scanning electron microscopy (SEM) results revealed the formation of biofilm on the polymer surface. Fourier-transform infrared spectroscopy (FTIR) analysis showed the formation of new bond at 2123 cm−1 and breakage of old C=O ester bond at 1757 cm−1 in case of polymer PP80C6. Thermogravimetric analysis (TGA) showed decrease in thermal stability of polymers after degradation. The carbon dioxide evolved from sample was measured and biodegradation degree was also calculated. The degree of biodegradation shown by the isolate P8 was 12% and the P6 was 10%. The results demonstrated that Bacillus species isolated from composted samples in this study provided promising evidence for the biodegradation of polypropylene and poly-L-lactide (PP-PLLA) blends in the environment.