Self-healing EPDM rubbers with highly stable and mechanically-enhanced urea-formaldehyde (UF) microcapsules prepared by multi-step in situ polymerizationopen access
- Authors
- Jeoung, H.-J.; Kim, K.W.; Chang, Y.J.; Jung, Y.C.; Ku, H.; Oh, K.W.; Choi, H.-M.; Chung, J.W.
- Issue Date
- Sep-2020
- Publisher
- MDPI AG
- Keywords
- Dicyclopentadiene (DCPD); Ethylene-propylene-diene-monomer (EPDM) rubber; In situ polymerization; Microcapsules; Self-healing
- Citation
- Polymers, v.12, no.9
- Journal Title
- Polymers
- Volume
- 12
- Number
- 9
- URI
- https://scholarworks.bwise.kr/cau/handle/2019.sw.cau/53663
- DOI
- 10.3390/POLYM12091918
- ISSN
- 2073-4360
2073-4360
- Abstract
- The mechanically-enhanced urea-formaldehyde (UF) microcapsules are developed through a multi-step in situ polymerization method. Optical microscope (OM) and field emission scanning electron microscope (FE-SEM) prove that the microcapsules, 147.4 μm in diameter with a shell thickness of 600 nm, are well-formed. From 1H-nuclear magnetic resonance (1H-NMR) analysis, we found that dicyclopentadiene (DCPD), a self-healing agent encapsulated by the microcapsules, occupies ca. 40.3 %(v/v) of the internal volume of a single capsule. These microcapsules are mixed with EPDM (ethylene-propylene-diene-monomer) and Grubbs' catalyst via a solution mixing method, and universal testing machine (UTM) tests show that the composites with mechanically-enhanced microcapsules has ca. 47% higher toughness than the composites with conventionally prepared UF microcapsules, which is attributed to the improved mechanical stability of the microcapsule. When the EPDM/microcapsule rubber composites are notched, Fourier-transform infrared (FT-IR) spectroscopy shows that DCPD leaks from the broken microcapsule to the damaged site and flows to fill the notched valley, and self-heals as it is cured by Grubbs' catalyst. The self-healing efficiency depends on the capsule concentration in the EPDM matrix. However, the self-healed EPDM/microcapsule rubber composite with over 15 wt% microcapsule shows an almost full recovery of the mechanical strength and 100% healing efficiency. © 2020 by the authors.
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