The Relationship between Microstructure, Properties and Processing in Bimodal Polyethylene with Medium Density Used in Drip Irrigation Tapes

Haghparast, Sina | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54132 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pircheraghi, Gholamreza
  7. Abstract:
  8. In recent years, Jam Petrochemical has produced and designed irrigation tape polyethylene grades but because these grades don’t have sufficient melt strength during high-speed processing, it hasn’t been welcomed by manufacturers. Therefore, in first step of this study we tried to characterize the specimens by using referenced grade and by taking advantages of thermal, rheological and mechanical analysis. We observed that main difference between jam petrochemical grades and referenced grade is related to type and content of comonomer and also long chain branches. Based on the obtained results, the ideal molecular structure of irrigation tape grade, include chains with bimodal distribution that some of them are chains with long chain branches which cause melt strength in these grades and some of them with low amounts of comonomer and high crystallizable length, lead to proper mechanical properties. Also, it was determined that crystallization kinetics in referenced grade is much faster due to broad molecular weight distribution and chains with high crystallizable length. Furthermore, microscopic images indicate micro-segregation in referenced grade with considerable amounts of long chain branches, which can cause decrease in mechanical properties. So that natural draw ratio starts at lower strain in JPC grade. In the next step of this study, the attempt was made to represent polyethene blend for processing irrigation tapes at high speed. So, we used two approaches include increasing molecular weigh and adding long chain branches. We observed blend of MD3510 with 30% LDPE, can create rheological properties similar to referenced grade, although this advantage is associated with a decrease in mechanical properties. Also, changing comonomer from 1-butene to 1-hexene has no considerable effect on melt strength. Moreover, adding component with high molecular weight improve mechanical properties but doesn’t have significant effect on melt strength. So, by using LDPE we can produce polyethylene blend with sufficient melt strength. Also, it was observed that blending with SCG resistant grades can increase mechanical properties by 20%
  9. Keywords:
  10. Melt Strength ; Mechanical Properties ; Rheological Properties ; Drip Irrigation Tape ; Long Chain Branches

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