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Influence of Microstructure on Mechanical Properties and Fracture Behavior of Hybrid PP/GF/CaCO3 Composites

Tabatabaei Ardakani, Ramin | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40114 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ekrami, Ali Akbar; Bagheri, Reza
  7. Abstract:
  8. Homo-polymer of Polypropylene is a commodity thermoplastic with good physical and mechanical properties along with fair recyclability and cost. However, its application is limited in some cases, especially in automotive industry, due to a lack of toughness. One of the approaches for PP toughening is the copolymerization of PP with some ethylene co-monomers. However, existence of elastomers in this kind of polymers causes a decrease in tensile properties. Besides, glass fibers improve tensile properties of homo-and co-PP and decrease toughness of co-polymers but result in an increase for homo-polymers. A rise in expenditure of energy due to increasing the processing temperature and destruction of processing equipments are of disadvantages of using glass fibers. Destruction of PP molecular chains due to increasing the temperature also deteriorates PP recyclability. Studies performed in the Polymeric Materials Research Group (PMRG) of this department reveal that small amount of CaCO3 nano-particles cause an increase in the Homo and co-polymer toughness. In this study, efforts have been made to restrict decline of PP co-polymer toughness as a result of adding glass fibers by replacing a fraction of glass fibers with CaCO3 nano-particles and fabrication of PP/GF/CaCO3 nano-composite in PP co-polymer matrix. In addition it has been tried to replace glass fibers with CaCO3 nano-particles in PP homo-polymer matrix to reduce adverse effects of glass fibers. In this regard the crystallinity of samples has been studied by DSC. Additionally, the mechanical behavior of composites has been studied via different approaches including tensile and impact tests. Furthermore, the deformation and fracture micro-mechanisms have been analyzed by transmission optical microscopy (TOM) and scanning electron microscopy (SEM). DSC results show no change in crystallinity and creation of Phase as a result of replacing of glass fibers with CaCO3 nano-particles in both matrix. In addition, by replacing of glass fibers with nono-particles in PP co-polymer matrix elastic modulus, yield stress and impact strength decrease, on average 14, 17 and 20 percent, respectively and a decrease of about 15 percent is observed in the homopolymer-based composites. An increase in debonding of glass fibers, decrease in interfacial strength between fibers and matrix and change of fracture micro-mechanisms proved by TOM and SEM images is believed to be the source of deterioration in those properties
  9. Keywords:
  10. Polypropylene ; Nanometric Calcium Carbonate ; Glass Fibers ; Hybrid Nanocomposite

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