| Urea-formaldehyde Microcapsules are widely used in many fields due to their excellent mechanical property, thermal stability and sealing property, etc. In recent years, with the application of microcapsules into self-healing materials, it makes the preparation of microcapsules that applied to polymeric matrix composites more prominent. In this work, the mechanism of urea-formaldehyde microcapsules prepared by one-step process was studied. Microcapsules with good strength and barrier property were prepared and then used to epoxy (EP) and polyurethane (PU) system. The addition of microcapsules on the damping properties of EP and PU were discussed. The main contents are listed as follows:A series of microcapsules were prepared by in-situ polymerization with poly (urea-formaldehyde) as the shell material and glass beads as the core material. Glass beads were chosen as the core material because their size distribution was narrow and their surface was easily changed to be hydrophobic. OM and SEM were used to investigate the respective effects of process parameters, such as initial pH value, concentration of wall material and surfactant, stirring rate etc, on the surface morphology of microcapsules. The results showed that the surface morphology of the microcapsules depends mainly on the final pH value and a high final pH value corresponded to a smooth-surface microcapsule. Controlled surface morphology of UF microcapsules can be prepared by adjusting the concentration of the emulsifier and wall material and the stirring rate. Addition of ammonium chloride was found to be very important in the process preparation of PUF microcapsules. The involvement of ammonium chloride can cause a drop in the pH value substantially during the course of reaction and enhance the deposition of the UF nanoparticles onto the surface of microcapsule.The effects of emulsifier on the physical properties of poly (urea-formaldehyde) (PUF) encapsulated tetrachroloethylene (TCE) microcapsules were investigated by anionic, synthetic and natural macromolecular emulsifier. The properties of microcapsules were investigated by optical-photographic microscope (OM) and scanning electron microscope (SEM). Experimental results showed that: GA is a favorable emulsifier for preparing smooth-surface and good-strength microcapsule. The orthogonal test indicated that the concentration of the shell material has a great effect on the microcapsules'mechanical strength. A Slow heating rate and high initial pH value can help to prepare microcapsules with high degree of sphericity, small size and narrow distribution. The addition of Sodium chloride during the reaction is favor to increase the sealing property of the capsules. The optimizing conditions are initial PH value 3.5, concentration of the shell material 3.6×10-2g/ml, heating rate 0.5℃/min and concentration of Sodium chloride 2.5×10-2 g/m.To improve the microcapsules' barrier properties, layered silicates were dispersed in the wall of microcapsule. TEM, SEM, XRD and FTIR were used to investigate the physical property of microcapsules. The tests showed that, MMT is successively introduced to the wall of microcapsule and exfoliate completely. Compared with conventional microcapsules (CMs), nano-composite microcapsules (NCMs) have better barrier property. This can be attributed to nano-composite structure of the microcapsules, in which nano-sized montmorillonite dispersed in UF to decrease core material cross-over.A series of epoxy composites filled with microcapsule of different core materials were prepared in this work. Microstructure analysis as well as damping properties of microcapsule/ EP composites was made by SEM and DMTA. The results showed that the content and diameter as well as viscosity of the core material of the filled microcapsules have a significant effect on the damping properties of microcapsule/EP composite. The loss factor (tan8) of composite at Tg temperature reached to the maximum value under 10vol% content of microcapsule. The larger diameter and higher viscosity of the core material are, the damping property of the EP/microcapsule composite is better. The tan8-f cure showed that the composite has excellent low-frequency damping property. However, the involvement of the capsules decreases the compressive strength of EP and changes the damager forms of EP.PUF microcapsules with viscous liquid core were prepared and applied to PU system. The synthetic process and involvement of capsules on the dynamic mechanical property of PU were studied. The studies showed that choosing the theory content of-NCO in the PU pre-polymer as 6%, and controlling the reaction temperature as 75-80℃and time as 1h can synthesis the PU polymers with good mechanical and dumping properties. The addition of capsules improves the peak value of tanδof PU at Tg temperature by about 28%—54%, and widened the range of temperatures of tanδabove 0.7. The dynamic mechanical parameters of the composites in broadband were achieved through time-temperature superposition principle.The results indicated that the addition of capsules improves the tanδof PU over the low-frequency ranged from 0-1000Hz. Compression test showed that the microcapsules embedded in the PU can maintain intact structure and not rupture at a high pressure, which meet the material requirement of being used in underwater pressure environment.
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