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Correlation between Microstructure and Properties of black PE100 Compounds

Sarafpour, Amir Hossein | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50843 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pircheraghi, Gholamreza
  7. Abstract:
  8. Polyethylene, due to its low production and maintenance costs, light weight and excellent chemical resistance, is the most widely used material for production of water and gas transfer pipes. Pipe grade polyethylene (PE100) with bimodal molecular weight distribution has excellent mechanical properties, especially long-term creep performance. In order to prevent UV degradation, carbon black is added as masterbatch to PE100 to produce black compounds, which acts as most effective industrial UV stabilizer of polyethylene. Five PE100 black compounds and one white PE100 as reference sample were produced using a twin-screw extruder. Rheological, melt flow DSC, TGA, FE-SEM and tensile tests were used to analyze the effect of different masterbatch grades on PE100 black compounds and compare them with white PE100 sample. Results indicated that a small presence of lubricants, as a processability agent in masterbatch samples not only can be detected by MFI, rheological and TGA tests, but can also significantly affect the microstructure of the compounds. The two compounds whose respective masterbatches had highest amount of lubricants in their structure didn’t show any strain hardening behavior, which is a direct indicator of resistance to creep and slow crack growth. This might be due to a decrease in density of tie molecules in crystalline structure. To reiterate, a small amount of lubricants can directly and negatively affect excellent creep performance of PE100. Isothermal DSC and avrami equation revealed that rheological and melt flow have a direct correlation with geometry and dimension of growing crystals. The sample with highest values of shear and complex viscosities, as also confirmed by FE-SEM images, tend to establish two dimensional crystals in form of lamellae, while the sample with highest MFI and lowest shear and complex viscosities has three dimensional spherulite. Also, role of carbon black particles as nucleating agent of crystals was confirmed and a decrease in total crystallinity of PE100 due to carbon black addition was observed. XRD results revealed that except for one sample, no change in the lattice parameter of the PE100 due to masterbatch carrier addition occurs. Given the potential of masterbatch to highly influence properties of PE100, it is essential to study masterbatch properties to be able to choose most suitable masterbatch
  9. Keywords:
  10. Polyethylene ; Carbon Black ; Mechanical Properties ; Rheology ; Crystallization ; Microstructure

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