Investigating the interfacial synthesis of polyurethane microcapsules and optimization of the process using response surface method

Polyurethane microcapsules containing polyurethane resin as the healing agent were successfully prepared via interfacial polymerization. To optimize the process of producing microcapsules, response surface method (RSM) was employed using central composite design (CCD). The rotation speed, homogenization duration time and amount of hardener were considered as affecting parameters on size and thickness of the microcapsules' wall. The percentage of healing agent and the encapsulation efficiency were considered as responses. Scanning Electron Microscope (SEM), Thermogravimetric analysis (TGA) and Fourier Transfer Infrared Spectroscopy (FTIR) were used to characterize the optimized microcapsules. The results of optimization showed the highest percentage of the healing agent (80%), microencapsulation efficiency (56%) and the smallest size (99 mu m) and wall thickness (11 mu m) of microcapsules were achieved at the condition of 2155 rpm with 2g hardener and the homogenization duration time of 24.9 min. The results of the thermogravimetric analysis showed that the produced microcapsules have favorable thermal stability up to 270 degrees C, so according to these characteristics, they can be applicable in self-healing coatings.