Microcapsules For Composite Repair Synthesis

Microcapsule technology and its development are introduced in this paper. The main function, raw material, synthetic method and characterization of microcapsules are concerned. According to the application of microcapsules in recent years, the developement on self-healing composites with microcapsule embedded in polymeric matix is emphasized. The backround, meaning and way of our study are also pointed out.In this paper, two kinds of microcapsules were synthesized by in-situ polymerization in an oil-in-water emulsion with urea and formaldehyde as the raw shell material, and epoxy resin (E-51) or dicyclopentadiene (DCPD) as the core material, separately. The optimum conditions of microencapsulation were studied in detail to ensure that the microcapsules possess excellent maneuverability. The physical and chemical properties were investigated by optical microscopy (OM), scanning electron microscopy (SEM), Fourier-transform infrared spectrometer (FTIR), differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The poly(urea-formaldehyde) microcapsules synthesized in experiments were compared.The results showed that two kinds of poly(urea-formaldehyde) microcapsules containing DCPD or E-51 had been successfully synthesized. The optimum conditions are as follows: mass ratio of the core material to the shell material, 0.8:1;final pH value, 2.0-4.0;acidification time, 2.0³.0h;heating rate, 0.17⁰.25℃·min^-1;surfactant, sodium dodecylbenzene sulfonate (DBS), 0.8wt%;reaction temperature, 55⁶0℃, reaction time, 2³h. The processing parameters, such as mass ratio of the core material to the shell material, final pH value, acidification time, heating rate, agitation rate, and surfactant, greatly influence the properties of microcapsules during in-situ polymerization. The state of microencapsulation is dramatically dependent on mass ratio of the core material to the shell material, final pH value and surfactant. The microcapsule surface morphologies are better when acidification time and heating rate are properly increased. The microcapsule size decreases and its distribution narrows with the increasing of agitation rate.Both poly(urea-formaldehyde) microcapsules containing DCPD or E-51 synthesized in this experiments possessed excellent physical properties, such as surface morphology, microcapsule size and its distribution. However, the latter microcapsules showed betterchemical properties than those of the former. It could be thermally stable to keep intact up to 200°C, superior to the former (50°C), and its low penetrability indicated its using lifetime was longer.