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Xing Liu,이종근,Michael R. Kessler 한국고분자학회 2011 Macromolecular Research Vol.19 No.10
Norbornene-based healing agent candidates, 5-ethylidene-2-norbornene (ENB) and ENB with a custom crosslinker, were prepared into uniform microspheres using a Shirasu porous glass (SPG) emulsification technique,and microencapsulated by in situ polymerization of melamine-urea-formaldehyde (MUF). The resulting microcapsules were observed by optical and scanning electron microscopy for their morphology, outer and inner surface and shell thickness. Particle size analysis revealed a more uniform size distribution with a mean diameter of 40 μm than a conventional method using a mechanical impeller. The thermal and mechanical properties of the microcapsules were also examined by considering fabrication of self-healing composites.
Liu, Xing,Sheng, Xia,Lee, Jong Keun,Kessler, Michael R. WILEY-VCH Verlag 2009 Macromolecular materials and engineering Vol.294 No.6
<P>Microcapsules for self-healing applications were produced with a melamine-urea-formaldehyde (MUF) polymer shell containing two different healing agent candidates, 5-ethylidene-2-norbornene (ENB) and ENB with 10 wt.-% of a norbornene-based crosslinking agent (CL), by in situ polymerization in an oil-in-water emulsion. Relatively neat outer surfaces with minor roughness were observed on the MUF microcapsules under optical and scanning electron microscopy. Shell thickness of the capsules ranged from 700 to 900 nm. Particle size analysis of the microcapsules showed narrow size distributions with a mean diameter of 113 µm for ENB-filled and 122 µm for ENB + CL-filled microcapsules at an agitation rate of 500 rpm. The microcapsules were found to be thermally stable up to 300 °C and exhibited a 10 to 15% weight loss when isothermally held at 150 °C for 2 h from thermogravimetric analysis. Overall, these MUF microcapsules exhibited superior properties compared to the urea-formaldehyde (UF) microcapsules used extensively for self-healing composites to date. In addition, the manufacturing process of MUF microcapsules is much simpler than those made from UF. Additional advantages of MUF microcapsules for self-healing composites are discussed.</P><P> <img src='wiley_img/14387492-2009-294-6-7-MAME200900015-gra001.gif' alt='wiley_img/14387492-2009-294-6-7-MAME200900015-gra001'> </P> <B>Graphic Abstract</B> <P>Microencapsulation of two self-healing agent candidates with a new shell material is reported. The two healing agents include 5-ethylidene-2-norbornene (ENB) and ENB with a norbornene-based crosslinker. Melamine-urea-formaldehyde (MUF) was used for microencapsulating the two healing agents. These MUF microcapsules exhibited superior properties compared to the UF microcapsules for further development of composites with self-healing functionality. <img src='wiley_img/14387492-2009-294-6-7-MAME200900015-content.gif' alt='wiley_img/14387492-2009-294-6-7-MAME200900015-content'> </P>