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Investigating the Biodegradability of Bioplastics Based on Polypropylene and Starch

Ganji, Alireza | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58224 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Yaghmaei, Soheila; Ghobadi Nejad, Zahra; Borghei, Mehdi
  7. Abstract:
  8. Due to the environmental crisis caused by the accumulation of plastics and disposable containers in nature, along with the significant challenges associated with their waste management, finding effective solutions to reduce plastic-related pollution was considered essential. One potential approach to address this issue is the use of indigenous microorganisms capable of plastic biodegradation, as well as the replacement of conventional plastics with biodegradable bioplastics that, owing to their degradable structures, reduced the environmental pollution load. In this study, the biodegradability of bio-based disposable containers was investigated through the isolation and purification of native microorganisms and a bacterial consortium capable of degrading polyethylene. Three types of polymers were examined: a petrochemical polymer (pure polypropylene) and two bio-based products (composites of polypropylene and starch with different weight ratios). Samples were collected from plastic-contaminated sites and industrial waste, and the microorganisms present in these samples were isolated and purified. The biodegradation capability of these microorganisms was evaluated over different incubation periods using various methods, including macroscopic observation, gravimetric analysis, microbial enumeration, FE-SEM, EDS, XRD, FTIR, and TGA. The results showed that the indigenous Bacillus sp. strain achieved weight reductions of 4.73%, 7.1%, and 4.9%, while the bacterial consortium resulted in 5.1%, 7.25%, and 5.3% reductions in the petrochemical polymer, bio-based product 1, and bio-based product 2, respectively, after five months of incubation. The analysis of bacterial counts in the biofilm and culture medium provided insight into the degradation process. FE-SEM images revealed significant structural degradation on the sample surfaces, while changes in FTIR spectra indicated the onset of starch and polypropylene degradation. Additionally, variations in crystallinity observed through XRD analysis confirmed the structural breakdown and changes in the amorphous-to-crystalline ratio of the samples
  9. Keywords:
  10. Polypropylene ; Biodegradability ; Starches ; Bacillus Sp ; Bioplastic ; Bacteria

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