Preparation and characterization of hollow phenolic microspheres via "in situ" polymerization

A new method was developed for preparation of phenolic hollow microspheres via in situ polymerization. Tetraethyl orthosilicate being the core and poly(acrylic acid) being the anionic surfactant were placed into flask, the mixture was stirred, and its pH value was adjusted to be acidic, then a stable oil-in-water emulsion was formed. Tetraethyl orthosilicate was emulsified uniformly in the aqueous solution and dispersed into a large quantity of droplets with very small size covered by anionic surfactant of poly (acrylic acid). The pre-prepared resoles, being the shell, were dribbled into the flask slowly. The mixture was stirred at 60 oC and hold for 3 h, and at 90 oC hold for 2 h, respectively. A large number of yellow microspheres were formed. The "core-shell phenolic microspheres were then filtered and dried. Hollow phenolic microspheres were produced after the yellow solids dried at 17 oC for 4 h to eliminate tetraethyl orthosilicate from the microspheres in an oven. The hollow phenolic microspheres were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TG). FTIR indicates that a significant number of the hydroxymethyl groups remain in the microspheres, which provide adherence force with the matrix resin during application. TG analysis demonstrates that the resultant hollow phenolic microspheres have good thermal stability. SEM results show that the average of diameter of the microspheres is about 600 ?m. The hollow microspheres have good close cell and smaller pores formed in the wall when water vaporized, It is also observed that the morphology of microspheres is very tough, which can provide good bonding between microspheres and resin matrix.