Investigating the effect of synthesis conditions on the formation of urea-formaldehyde microcapsules

In the current study, a set of urea-formaldehyde microcapsules (UFMs) were synthesized at different conditions via the in situ polymerization method. Encapsulation ability of the UFMs was studied by altering the synthesis parameters, such as formaldehyde to urea molar ratio (0.94, 1.88, 2.81), time (1, 4, 7 h), temperature (25, 55, 85 degrees C) and pH (3, 7, 11). The capsules were characterized by optical and electron microscopy (OM, SEM and TEM), particle size analysis (PSA), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric/differential thermal analysis (TG/DTA). According to the results, for successful formation of UFMs, the pH value of the synthesis solution must be below 7 and the F/U molar ratio value must exceed 0.94. Effects of temperature and the pH value of the prepared solution were interdependent. To conclude, the results led to determination of the optimum UFM synthesis condition which presented the most effective formation of UFMs. The higher F/U molar ratio as well as higher curing temperatures in UFM-9, increased the UFMs degradation temperature. In order to further investigate the results, the synthesis of the optimized UFM (UFM-Opt.) was conducted, presenting the most effective development of UFMs. (C) 2018 Published by Elsevier Editora Ltda. on behalf of Brazilian Metallurgical, Materials and Mining Association.