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Improving the Properties and Increasing the Recyclability of Polypropylene Using Vitrimerization Reactions

Khodabandelou, Omid | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57339 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pircheraghi, Gholamreza
  7. Abstract:
  8. Among the plastics produced around the world, polyolefins are the most used in human daily life and make up about two-thirds of the plastics produced in the world. Also, the most plastic waste is related to polyolefins, which are non-biodegradable plastics. One of the things that have challenged the recycling of polyolefins by traditional methods such as mechanical recycling is the loss of mechanical and rheological properties as well as their degradation. One of the methods of improving properties and postponing degradation is the use of vitrimerization reactions, as a result of which, in thermoplastics, a compatible covalent network is created, which gives the plastic the ability to behave like thermosets at low temperatures and have the properties of thermoplastics at high temperatures. In this research it has been tried to use the transesterification reaction, which is based on the exchange of bonds between hydroxyl and ester groups, to improve the properties and increase the recyclability of polypropylene. Due to the specific problems in the degradation of polypropylene (such as chain scission), not much research has been done in the field of its vitrimerization. The main approach in this research is to use diglycidyl ether bisphenol A (DGEBA) and butanediol (BDO) separately in separate reactions to create dynamic crosslinks on polypropylene functionalized with maleic anhydride (MA) and compare them with the reference sample (which is non-cross-linked polypropylene). It should be noted that zinc acetylacetonate (Zn(acac)2) was used as a catalyst. The melt flow index test showed that one of the vitrimer samples had only a 7% increase after 5 thermal cycles compared to the first cycle, while this number for the control sample is 43%; that is, the vitrimerization reaction causes a decrease in the melt flow index and a decrease in the trend. It is destroyed. Transmission optical microscopy images showed that vitrimerization reduces the size of the cells, so that the cell size of the control sample was 220 microns, while the cell size of one of the vitrimer samples was measured as 11 microns. The tensile test showed that the reticulation of the system increases the tensile strength by 9–14% in different Vitrimer samples compared to the control sample. The tensile test at a temperature of 60 degrees Celsius also showed that the tensile strength of vitrimers is 6–17% higher than the control sample. Then, due to the loss of mechanical properties after each recycling cycle in the industry, all the samples were processed two more times. The results obtained from the tensile test after the third processing showed that the amount of tensile strength loss of the manufactured vitrimers is far less than the control sample, and sometimes they have increased, so that one of the selected vitrimer samples had a 5% increase in tensile strength compared to the first processing. while the control sample has decreased by 10%. Also, the impact test after the third processing showed that the amount of fracture energy of different Vitrimer samples is between 27 and 122% higher than the control sample. In order to compare the rheological properties of vitrimers with the control sample, the rheology test was used in two modes of temperature sweep and frequency sweep, the results of which showed an increase in the storage modulus, loss modulus, and viscosity of the vitrimers compared to the control sample. Also, through the rheology test, the TV temperature was determined, which helps to better study the behavior of vitrimers. The results of the stress-relaxation test also showed that due to the existence of the network, vitrimers maintain more tension for a longer time than the control sample, and the stress-relaxation rate is lower in them. Finally, among the reactions performed and vitrimers produced, 5 samples were introduced as selected samples in terms of improving the said properties. It should be noted that the results of this research can lead to an increase in recyclability and an improvement in the loss of mechanical and rheological properties of polypropylene in the recycling industry
  9. Keywords:
  10. Polypropylene ; Vitrimerization ; Rheology ; Mechanical Properties ; Recyclability ; Mechanical Properties Improvement

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