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Study of the Evolution of Three-dimensional Pore Structure during Sintering of High Density Polyethylene Powders with Different Particle Size and Melt Flow Index

Salehi, Amir Mehdi | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52158 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pircheraghi, Gholamreza
  7. Abstract:
  8. Recently, macroporous polymers have gained wide acceptance for applications such as filters, membranes, biodegradable scaffolds, retention media, sound mufflers and etc. In this research, by keeping in mind the importance of the pore structure in the functionality of the porous part, three dimensional images of the pore structure during sintering was obtained using an optimized manual serial sectioning technique. Then, using the Euler number as a property of the topology of the pore surface, evolution of the three dimensional pore structure was scrutinized for two types of powders, powder A with a mean particle size of 200 micron and melt flow index of 0.2 (g/10 min) and powder B with a mean particle size of 400 micron and melt flow index of 0.8 (g/10 min). Specifically, pore structure evolution was proposed to be comprised of three different stages, the first stage characterized by the surface relaxation of the particles, the second stage featured by the long range diffusion of polymer chains and a more speedy evolution of structure and the final stage marked by the most rapid changes in the structure brought about by the realaxation of the more of the polymeric chains. It was observed that despite the first stage being longer for powder A (with lower melt flow and smaller particle size), pore structure evolved towards elimination quicker for particle A (after 12 hours of sintering) as opposed to particle B (after 18 hours of sintering). This indicates the stronger influence of particle size on the overall rate of the sintering process
  9. Keywords:
  10. Sintering ; Porous Polymers ; Pore Structure ; Modeling ; High Density Polyethylene

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