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Investigation the Effect of Antioxidant on Amount of Crosslink and Mechanical Behavior of Peroxide Crossliked Polyethylene (PEX-A)

Berarzadeh Grivdehy, Meisam | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54315 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pircheraghi, Gholamreza
  7. Abstract:
  8. Polyethylene is the most widely used plastic material in the world for reasons such as lightweight, good strength, good processability, low cost, and low maintenance cost, and very good chemical resistance. One of the applications of polyethylene that has received much attention in recent decades is its use in the manufacture of hot water pipes. To maintain the properties of polyethylene at high temperatures, it must be crosslinked at a proper level. Appropriate antioxidants should be used to prevent the degradation and oxidation of polyethylene during the process as well as long-term operation. Concomitant use of phenolic antioxidants for long-term stability during service and phosphorus antioxidants for stability during the production process leads to synergistic properties. On the other hand, the use of antioxidants prevents the increase of crosslinking density (network). Therefore, samples with different ratios of Irganox1010 to Irgafos168 and 0.5 wt.% constant concentration of 2,5-Dimethyl-2,5-di(tert-butylperoxy) hexyne-3 as a crosslinking agent were produced in both laboratory and industrial conditions. There is a strong correlation between gel content and crosslink density amount so the gel percent and crystallinity data fit in a line and the equation of the percentage of gel in terms of percentage of crystallinity follow the equation of y=-0.99x+115.23, but in industrial condition sample with the maximum antioxidant amount (sample with the code of P-22) is responsible for non-linear fitting. Comparison of rheological data also indicates that the process of crosslinking in laboratory conditions is much better than in industrial conditions and cross-links are made completely; Because the storage modulus is higher than the loss modulus at all frequencies, but in the industrial mode this happens from a determined frequency onwards. FTIR graphs also indicate that a small degradation happening in PEX-A in ambient conditions and also the existence of some peaks in 950 cm-1, 1267 cm-1, 1551 cm-1 indicates poor dispersion and not fully solution of antioxidants in some samples, especially in P-12. For the production of industrial samples, due to the presence of peroxide and considerations such as inactivation of peroxide in the extruder, there is a temperature limit in the production process, which leads to incomplete melting and improper distribution of the antioxidant Irgafos168. This consideration does not increase the oxidation induction time (OIT) by increasing the amount of antioxidants and sometimes reduces this parameter. In the manufacturing of PEX-A gel content percent and OIT are the most important parameters in quality control point of view, P-12 is the best industrial samples produced because it is highly crosslinked (80%) and has the maximum OIT (26 minutes)
  9. Keywords:
  10. Polyethylene ; Peroxides ; Antioxidant ; Gel Content ; Crosslink Density ; Oxidation Induction Time (OIT) ; PEX-A Pipes

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