Preparation and mechanical properties of poly (urea-formaldehyde) microcapsules containing liquid polysulfide

In this paper, we first report the preparation of poly (urea-formaldehyde) (UF) microcapsules filled with liquid polysulfide by one-step in situ polymerization. For obtaining the optimal preparation condition, the influences of various process factors including emulsifier type and its usage, initial pH value of the solution, reaction temperature and time on the dispersion, and encapsulation effects of liquid polysulfide were experimentally investigated. The structure and morphology of the prepared microcapsules were characterized by Fourier-transform infrared spectroscopy, optical microscopy, and scanning electron microscopy, respectively. The relative content of liquid polysulfide in microcapsules was determined using ultraviolet spectrum method. Furthermore, the mechanical properties of cured liquid polysulfide films before and after encapsulation were measured according to the relative standards. Results indicated that the liquid polysulfide was successfully encapsulated in UF microcapsules, which had a well-defined spherical shape, a continuous inner shell wall, a rough exterior surface, and an average diameter of about 200 mu m. The breakaway, disassembly torques, tensile strength, and hardness of microcapsule sealant were greatly improved in comparison with those of unencapsulated one. The study provides a valuable support for the automatic pre-coating technology of polysulfide sealants in the future.