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Degradation of Polypropylene Random Copolymer in Aqueous Solution of Chlorine Dioxide: Effect of Crystalline Structure and Morphology

Rohollah Shamizadeh | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56491 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pircheraghi, Gholamreza
  7. Abstract:
  8. Polypropylene is a semi-crystalline thermoplastic used in various industries and the second most used polymer globally. Polypropylene is sensitive to degradation by o agents due to having tertiary carbon in its chain. Chlorine-based disinfectants, used to disinfect drinking water, cause the degradation of hot water pipes made of polypropylene random copolymer. The stability of polypropylene against oxidizing chemical agents depends on the type of crystalline phase and polymer morphology. This research investigated the effect of alpha, beta, and gamma crystalline phases and spherulite size on random polypropylene copolymer's chemical stability in chlorine dioxide. Three samples were prepared, sample P without nucleating agent, sample A containing alpha nucleating agent (NA-11), and sample B containing beta nucleating agent (NAB-82). Tensile tests, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were used to investigate the effects of degradation on the samples in the solid state. A frequency sweep test was also used to study the structure of degraded chains and their behavior in the molten state. Finally, the recrystallization and melting behavior of the samples were studied using an optical microscope in polarized and transmission mode and differential scanning calorimetry test (DSC) in non-isothermal and isothermal modes. The XRD results for the initial samples showed that the P sample consists of a combination of alpha, beta, and gamma crystalline phases. Also, sample A comprises alpha and gamma phases and sample B is composed of a combination of alpha and beta phases. The study of the initial morphology of the samples showed that sample P has the largest and sample A has the smallest spherulite size among the samples. The results of tensile and FTIR tests showed that sample A has the least stability and sample P has the most stability against degradation. The rheology test results showed that the polymer chain scission process occurs during the degradation, and the DSC studies showed that the crystallization behavior of all three samples changes with the passage of degradation time due to the creation of a different chain structure. Finally, summarizing the test data concluded that the spherulite size controls the chemical stability of polypropylene random copolymer in water containing chlorine dioxide
  9. Keywords:
  10. Crystalline Structure ; Morphology ; Oxidative Degradation ; Random-Copdypropylene ; Spheralite ; Spherulite Size ; Chlorine Dioxide

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