| Composite materials have wide application due to their favorable properties such as strength and stiffness combined with lighness as compared to metals. They have been used in transportation vehicles, for defense and automobile industry, space exploration and other commercial applications. No matter how carefully structure materials are designed and manufactures, all are susceptible to damage in the form of microcracks due to various reasons such as by a catastrophic event or though nature degradation, which will result in the mechanical performance of material descend and then shorten the span-time of life.The development of a self-healing polymer-marix composite material that possesses the ability to heal cracks autonomically is described. The system used a monomer repair agent, dicyclopentadiene (DCPD), which is stored in an epoxy matrix by dispersing microcapsules containing the liquid repair agent throughout the matrix. When the material is damaged, cracks propagate through the material and break open the microcapsules, releasing the repair agent into the crack plane. Finally, the DCPD repair agent solidifies by ring-openning matathesis polymerization (ROMP) after coming in contact with a WCl6 catalyst dispersed in the matrix.DCPD-filled microcapsules are prepared by in-situ polymerization technology with poly (urea-formaldehyde) (PUF) as a shell material and dicyclopentadiene (DCPD) as core materials. The effects of surfactant on the physical properties of poly (urea-formaldehyde) microcapsules were researched by using Styrene/maleic anhydride copolymer (SMA), Polyvinyl alcohol (PVA) and sodium dodecylbenzene sulfonate (DBS) solutions of different concentration. The DBS was favorable to microcapsulation and the microcapsules had compact outer surface when the concentration of DBS was close to critical micelle concentration (CMC). The effect of system pH on the microcapsules performance was studied at the same time. The properties of microcapsules, including the surface morphology, chemical structure, and thermal properties of microcapsules are characterized by using Optics microscope (OM), Scan electronic microscope (SEM), Fourier transfer infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC) and Thermal gravity analysis (TGA). The content of core material was calculated. The results indicated that PUF microcapsules can be synthesized successfully with mean diameter 210μm and 2~5μm wall thickness. The PUF microcapsules filled with DCPD had the content of DCPD was 80% and exhibit a good chemical stability below 215℃.The surface of PUF microcapsules were modified by using 3-aminopropyltriethoxy silane coupling agent (KH550), and the interfacial interactions between PUF microcapsules and KH-550 was also studied. Fourier transform infrared spec-tra (FT-IR) and X-ray photoelectron spectra (XPS) analyses showed that the silane coupling agent molecular binds strongly to PUF microcapsules surface. Chemical bond (Si–O–C) was formed by the reaction between Si–OH and the hydroxyl group of PUF microcapsules, Scanning electronic microscopy (SEM) observation showed that a thin layer was formed on the surface of modified PUF microcapsules. Additionally, fractured surface were observed under SEM to investigate the interfacial adhesion effect between PUF microcapsules and epoxy matrix. The result indicted that the silane coupling agent play an important role in improving the interfacial performance between microcapsules and resin matrix.Microcapsules were prepared by in situ polymerization technology with poly (urea- formaldehyde) (PUF) graftedγ-glycidoxypropyltrimethoxy silane (KH560) copolymer as a shell material and dicyclopentadiene (DCPD) as core materials. The aim was to improve the interfacial bond between microcapsules and epoxy matrix in composites through the epoxy functional group in KH560. The microcapsulating mechanism was discussed and the process was explained. The morphology and shell wall thickness of microcapsules were observed using SEM. The chemical structure and thermal properties of microcapsules were characterized by FTIR and TG. Results indicted that the PUF graft KH560 microcapsules containing DCPD can be synthesized successfully, the epoxy functional group was grafted on the wall material. The microcapsules are chemically stable before the heating temperature is up to approximately 215℃.A fracture-based protocol is established for characterizing healing efficiency of the self-healing epoxy. The fracture load of this composite is measured using a tapered double-cantilever beam (TDCB) specimen. The performance and concentration of catalyst and the healing temperature affect the healing efficiency. Catalyst concentration is shown to have a large effect on the healing efficiency of self-activite specimens. Maximal healing efficiencies of 64.9% were obtained for 15wt% catalysts. Fracture load decrease with the increasing catalyst concentration. Healing efficiencies of 59.7% were obtained for optimal 10wt% catalysts. Microcapsules concentration is shown to have an effect on the self-healing efficiency. Experiments on fracture specimens for self-healing samples with 10 wt% microcapsules and 10wt% catalysts have yielded as much as 38.0% recovery of virgin fracture load and 28.3% mean self-healing efficiency. Scanning electron microscopy is used to analyzed the fracture surface and provide physical evidence of repair.
|
PDF Full Text Request