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Investigation of the Relationship between Microstructure and Mechanical Properties of High Density Polyethylene Film (HDPE) with Bimodal Weight Distribution

Darzi Bourkhani, Rasool | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53205 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pircheraghi, Gholamreza
  7. Abstract:
  8. Polymeric film for packaging applications are commonly made from a variety of polyethylenes using a blown film process. Nowadays high density polyethylene with bimodal molecular weight distributions are used to improve the performance and the final properties. In the present study samples with different bimodal molecular weight distribution in a similar film preparation are developed. The EX5 sample from the Jam Petrochemical showed microstructure with heavily oriented stack of lamellae in the machine direction. In contrast, the 7000F sample from the Mehr Petrochemical presented a microstructure with a lower degree of lamellae, containing lamella twist and more link between the crystalline columns. The degree of crystallinity and rate of crystallization of the 7000F sample were, respectively, higher and slower, in comparison with the other sample. The mechanical properties of these two samples were of different natures, due to the difference in the microstructure and the percentage of crystallinity. The dart impact of 7000F and EX5 samples were 116 and 88 g, respectively. The tear resistance in the machine and transverse direction for 7000F sample were 18 and 836 g, which the EX5 sample were reported to be 16 and 576 g. The mechanical results indicate that 7000F sample is significantly superior. The ratio of tear resistance in the transverse and machine direction represents the anisotropy, which recommends that the EXF sample is more anisotropic. A combination of EX5 with the 7000f and the LLDPE-22501 samples with different weight percent was suggested to be a possible solution to enhance properies of EX5 sample. Results recommended that the combination in physical form with 80/20 weight percent yields better final properties, compared to 80/10/10 and 50/50. A 20 percent incorporation of 7000F in the EX5 altered the tear resistance to 449 and 46, in the transverse and machine direction, respectively, and a 9.6 ratio, improving the anisotropy of the EX5 whilst maintaining the mechanical properties. Furthermore, the combination in the melt state using extruder was also investigated. The anisotropy of the EX5 sample could also be improved by combining in the melt state, since the structure order of the EX5 in the machine direction Is disrupted in the melt form. The addition of LLDPE and 7000F causes the polymers to react differently in the rheology test, indicating that the results meet the rule of mixtures
  9. Keywords:
  10. Relaxation Time ; Mechanical Properties ; Linear Low Density Poly Ethylene ; High Density Polyethylene ; Films Blowing ; Anisotropy ; Bimodal Molecular Weight Distribution

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