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| Effect of Catalysts on the Performance of Vitrimers Based on Dynamic Ester Exchange |
| Liu Hechen1,2, Wei Liwei1, Sun Zhanglin1, Liu Chang1, Liu Yunpeng1,2 |
1. Hebei Key Laboratory of Green and Efficient New Electrical Materials and Equipment North China Electric Power University Baoding 071003 China;
2. State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University Beijing 102206 China |
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Abstract Epoxy resins are widely used in electrotechnical equipment because of their dimensional stability, resistance to cracking, and excellent electrical insulation and mechanical properties after curing. However, the irreversible crosslinking network of traditional thermosetting epoxy resins makes it difficult to degrade and recycle. As the operating life of epoxy resin-based electrotechnical equipment increases, the management of large quantities of thermoset waste faces great difficulties. Current recycling methods of resin waste are environmentally polluting, energy intensive, and do not meet the eye of sustainable development. In order to elimate thermosetting epoxy resin waste from the source, this paper investigates the effect of catalyst type on the performance of glass-like epoxy resins (Vitrimers) and explores the degradation rate of different resin systems in alcohol solutions.
Firstly, different Vitrimers systems, named V-TBD, V-TEOA, V-Sn, V-Zn, were prepared using 1,5,7-triazabicyclo(4.4.0)dec-5-ene (TBD), triethanolamine (TEOA), stannous isooctanoate (Sn(Oct)2), and zinc acetylacetonate (Zn(acac)2) as catalysts in this paper. Comparatively, we analyzed the conventional resins (T-DMP) and different Vitrimers for their mechanical, electrical and thermal properties. The results showed that compared with the conventional epoxy resin, the tensile strength, flexural strength and electrical properties of Vitrimers were reduced, but its elongation at break was higher and showed good toughness. Among them, the comprehensive mechanical properties of V-TEOA was second only to T-DMP. Its tensile strength, bending strength and elongation at break were 77.33 MPa, 23.08 MPa and 10.98%, respectively. V-TBD had high retention rate of electrical insulation properties. It had only 5.2% decrease in breakdown strength, and the leakage current and dielectric loss factor were slightly higher than those of T-DMP. Catalysts containing metal ions led to a serious degradation of the electrical properties of Vitrimers. In addition, the thermal stability of all Vitrimers systems was lower than that of conventional resin, which was caused by the weak bonding of the dynamic bonds. However, V-TBD and V-Zn had higher glass transition temperatures than the conventional resin, which were 163.89℃ and 158.65℃. Then, the stress relaxation of the conventional resin and Vitrimers was investigated. Unlike the conventional resin, Vitrimers showed good stress relaxation at high temperatures due to the activation of exchange reactions between the dynamic ester bonds contained in the crosslinked network. Among them, V-TBD had the shortest stress relaxation time at the same temperature, indicating the fastest rate of ester exchange reaction. Finally, the degradation characteristics of conventional resins and Vitrimers were studied in a solution of ethylene glycol (EG). The conventional epoxy resin could not be dissolved, while Vitrimers can be able to achieve dissolution. Among them, V-TBD showed the best dissolution effect.
In conclusion, the introduction of dynamic bonds in the cross-linking network after the curing of epoxy resins makes the degradation and recycling of resins possible, which provides a base material for new green electrotechnical equipment. Vitrimers using TBD as a catalyst has good mechanical, electrical, and thermal properties, can be fast dissolved in ethylene glycol solution, and is expected to be used as a matrix resin in the field of electrical equipment.
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Received: 13 June 2023
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2024, Vol. 39 
