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Influence of Beta Nucleation Method with the Use of Calcium Pimelate on Low-Temperature Toughness of Polypropylene Block Copolymer

Afshari, Niloofar | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57097 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Bagheri, Reza
  7. Abstract:
  8. One drawback of polypropylene (PP) as a widely-used semicrystalline thermoplastic is its low toughness at sub-zero temperatures. Along with adding elastomers to PP as impact modifiers, modification of PP’s crystalline structure by means of beta-phase nucleating agents —beta being the toughest polymorph of PP —is a standard method of improving PP’s toughness. Nucleation efficiency is highly dependent on the optimum dispersion of the nucleating agent. Therefore, improving the dispersion of the nucleating agents assumes an essential role. The objective of this study is to determine the influence of the incorporation method of calcium pimelate (CaPi), a highly-selective beta nucleating agent, on increasing the low-temperature toughness of an injection-grade block copolymer of PP. One method consisted of the dilution of the masterbatch of ex-situ synthesized CaPi, while in the other, CaPi was synthesized in situ during the extrusion of PP. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) were utilized to analyze the structure of the ex-situ synthesized CaPi. Characteristic peaks of CaPi in the XRD pattern demonstrated the formation of crystalline CaPi. Further evidence of this was found in the absence of characteristic bands of carboxyl functional groups in the FTIR spectrum of the CaPi and the appearance of carboxylate characteristic peaks which are absent in the spectrum of pimelic acid, a precursor of CaPi. Differential scanning calorimetry (DSC) was used to determine the crystallinity and the polymorphic composition in polymeric samples. Consequently, a minimum amount of 0.2 wt% of the nucleating agent and compression molding were determined to be the requirements for obtaining high beta contents of up to 80%. The incorporation of 0.2 wt% of the in-situ synthesized CaPi increased the low-temperature toughness of PP by 37% and its room-temperature toughness by 53%. The corresponding values for samples containing the masterbatch of ex-situ synthesized CaPi were 10% and 21%, respectively. The sample with 0.2 wt% in-situ synthesized CaPi showed the lowest decrease in elastic modulus (-7%) and the highest increase in non-isothermal crystallization temperature (+7.8 °C). The superior mechanical properties of this sample were thus attributed to its high beta content of nearly 80% and its high crystallization temperature
  9. Keywords:
  10. Toughness ; Grain Refining ; Polypropylene Block Copolymer ; Beta Modification

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