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Investigating the Chemical Degradation of Pipe Grade Polyethylene in the Chlorinated Water

Rezai Gharabaghlar, Ali | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55843 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pircheraghi, Gholamreza
  7. Abstract:
  8. Polyethylene is one of the most widely used polymers for the production of drinking water pipes. The presence of chlorine-based disinfectants in drinking water leads to long-term chemical destruction of pipes and sometimes reduces the life of pipes by half. Therefore, it is very important to investigate various factors affecting the chemical resistance of polyethylene pipes. The crystalline microstructure of the substance is affected by the average molecular weight, type and distribution comonomer on the chain, is one of the important and influential factors on the chemical resistance of these species against chlorine dioxide as a disinfectant. In this research, the chemical resistance of two types of PE80 (AK-80 and AS-80) and one type of PE100 (J-100) with different distribution and type of comonomer under the aging process with optimal conditions (10 ppm of chlorine dioxide) was investigated. By observing the FTIR results, the 1-butene comonomer was determined for AK-80 and J-100 and the 1-hexene comonomer was determined for AS 80, and the distribution of short comonomer in the samples was obtained by SSA analysis.The highest and lowest amount of crystallinity was 59.9% and 51% respectively for AS-80 and J-100, which after aging reached 63.2% and 68% respectively, which shows the high degradation of J-100 in the layer is destroyed. The rate of loss of elongation at break in J-100, AK-80 and AS-80 in the third week of aging was 25%, 65% and 5%, respectively, and it shows the stability of AS-80 compared to other samples and the greatest loss in AK-80 have been. On the other hand, the comparison of rheology properties test results before and after aging shows the most extreme drop in molecular weight in J-100 compared to other two samples. The reason for the inconsistency of the mechanical results with the rheology properties test and the thermal test for AK-80 and J-100 is due to the low depth of the destruction layer and on the other hand, the difference in the crystal microstructure of these two samples which is affected by the different distribution of comonomer. The low amount of comonomer in AS-80 leads to the reduction of points prone to destruction and the long length of the comonomer increases the conflict between the chains, and as a result, it causes the suitable chemical resistance of this sample. In the end, it can be concluded that the type and distribution of short chain branches have a great effect on the crystal microstructure and ultimately the chemical resistance of the polyethylene pipe. The best behavior is related to AS -80 sample with short comonomer of type 1-hexene and uniform distribution and low amount
  9. Keywords:
  10. Polyethylene ; Polyethylene Pipe ; Oxidation ; Short Chain Branches Distribution ; Comonomer ; Disinfectant

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