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Studying Processability, Mechanical and Rheological Properties of Cross-Linked EVA Through Vitrimerization Reaction

Sedaghati, Amin | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57176 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pircheraghi, Gholamreza
  7. Abstract:
  8. Polymers are divided into two categories: thermoset and thermoplastic. Thermoset polymers cannot be reprocessed and deformed due to their network structure and permanent and rigid crosslinking connections. Vitrimer materials that have been proposed in recent years; In addition to maintaining their network properties at low temperatures, they have the ability to change shape and reprocess at high temperatures. Therefore, the production of Vitrimer materials can be a suitable solution to reduce the amount of plastic waste produced. These materials consist of a dynamic covalent network in which vitrimerization reactions are performed between different functional groups. The basic polymer used is ethylene vinyl acetate (EVA), which is subjected to cross-linking operations according to various applications. One of the applications of cross-linked EVA is shoe soles, which cannot be recycled and reused due to its conversion into a thermoset polymer and the formation of a permanent and rigid covalent network. In this research, an attempt has been made to make EVA vitrimer. EVA vitrimer is like a thermoset polymer at low temperatures and maintains its network properties and can be reshaped and reprocessed at high temperatures without the need for additional treatment or the addition of special substances. To make a network in EVA, dicumyl peroxide was used to supply the free electrons needed to form cross-links. Also, to carry out the transesterification reaction, a hydroxyl group is needed because the transesterification reaction occurs between two functional groups, ester and hydroxyl. Butane Diol alcohol was used to provide the hydroxyl group. Also, the presence of a catalyst is needed to carry out the transesterification reaction at a suitable temperature. For this purpose, tin (II) 2-ethyl hexanoate catalyst was used. According to the results of the rheology, stress relaxation and mechanical properties tests, the presence of alcohol and catalyst is required for the make of Vitrimer, and there is an optimal amount for both alcohol and peroxide. Based on the results of the rheology, immersion and melt flow index tests, a covalent network was formed in the vitrimer sample, but the degree of the network in the vitrimer sample was less than that of the classical thermoset. These tests, along with the tensile test results, confirm the formation of the network in the sample. Meanwhile, the stress relaxation test and processability studies confirm its ability to be reprocessed and changed in certain conditions. After the second reprocessing, the tensile properties of Vitrimer sample are improved compared to the classical thermoset sample. In fact, at ambient temperature, at strains of 100% and 300%, its stress has increased by 51% and 62%, respectively, compared to the classical thermoset sample. Also, in the tensile test at high temperature, Vitrimer sample showed superior properties compared to the pure EVA. The stress in the 100% and 300% strains of Vitrimer sample compared to the pure sample has been improved by 46 and 97% at 40°C and 68 and 118% at 60°C, respectively. As a result, Vitrimer's processability is similar to pure EVA and its properties are similar to classic thermosetting
  9. Keywords:
  10. Transesterification Reaction ; Ethylene Vinyl Acetate (EVA) ; Rheological Properties ; Mechanical Properties ; Dynamic Covalent ; Vitrimerization ; Reprocess

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