Structure And Properties Of Microcapsuled Self-healing Polysiloxane Elastomer

Polymer elastomers tend to be broken in the form of micro cracks under continuing stress of tensile, compression, shear and torsion in application. These micro cracks will be enlarged as time goes by, which will result in serious failure. In general, the materials must be replaced in time before their failure. However, for those elastomer components which are difficult to disassemble and in need of long service lifespan, self-healing of the damage inside elastomers seems to be very important. This self-healing performance can make the elastomers serve safely in practice, prevent the early damage and prolong the service life effectively. Self-healing elastomer can be applied in the field of aerospace, space station, special mechanical seal, etc. Besides, research on self-healing of elastomers has important theoretical value on enriching the existing types of self-healing materials and improving the self-healing mechanism.Microcapsuled self-healing system is one of the effective ways to achieve self-healing of elastomers. Self-healing microcapsules were synthesized by in-situ polymerization with poly(urea-formaldehyde) as shell material and hydroxyl silicone oil/trimethoxy siloxane as core material, respectively. The effects of different emulsifiers, emulsifier concentrations, core materials viscosity, ratios of core and shell materials, rotation speeds on the structure and properties of microcapsules were researched by using SDBS, OP-10, PVA and Arabic gum as emulsifiers. The structure and properties of microcapsules were characterized by optical microscope, fourier transform infrared(FT-IR) and thermogravimetric analysis(TGA). The research results showed that the microcapsules are of more uniform size, smooth surface and regular shape in the conditions of SDBS of 0.5wt.%, rotation speed of 550 rpm, the ratio of core to shell of 3:1, core materials viscosity of 803 m Pa·s, achieved a core material content of 77.4%. FT-IR analysis indicated that the poly(urea-formaldehyde) containing hydroxyl silicone oil/trimethoxy siloxane have been synthesized successfully. The microcapsules have stable property before the heating temperature reach to a temperature approximate to 210℃.Further study of self-healing properties of liquid silicone rubber with microcapsules was carried out. A protocol which used to evaluate the healing efficiency by tension mode is established by characterizing and calculating healing efficiency of the elastomers,which is used to evaluate the self-healing properties of the elastomers qualitatively. The effects of microcapsules size, microcapsules contents, catalyst contents, healing time, and core materials viscosity on the healing efficiency were investigated. The self-healing liquid silicone rubber is characterized by SEM, ATR and TGA. The results showed that the healing efficiency can reach to 41.4% in conditions of microcapsules size of 250μm, microcapsules content of 12 wt.%, catalyst(DBTL) content of 8wt.%, core materials viscosity of 803 m Pa·s, healing time of 10 h at room temperature. SEM analysis results showed that the fracture surface of liquid silicone rubber with microcapsules is rougher. After the microcapsules are divorced from the matrix, they leave visible holes on the matrix fracture surface. TGA analysis results showed that the initial decomposition temperature of liquid silicone rubber with microcapsules is 382.0℃,and the temperature of maximum weight loss rate is 473.4℃, they are lower by 33℃and 59℃ than neat liquid silicone rubber respectively, this is because that the decomposition temperature of shell materials is lower than liquid silicone rubber matrix.