For the preparation of M–F prepolymer, weighted amount of
37% formaldehyde and melamine (formaldehyde/melamine molar
ratio: 3.7) was put in a 3 neck rounded flask containing 100 mL
of distilled water. The mixture was adjusted to 8.8 to 9.0 using
0.5 M NaOH solution and it was stirred for 10 min at 70 ◦C. For
the preparation of o/w emulsion, 7 g of thyme oil as a corematerial
was added to 100 mL of SLS, T80, and P127 solution and then the
solution was emulsified by high speed homogenizer (Ultra-Turrax
T-25, IKA, Staufen, Germany) at a rotational speed of 11000 rpm
for 3 min. The prepared o/w emulsion was poured into the M–F
prepolymer solution and the pH of mixture was adjusted at 5.0 to
5.2 using 0.5 M citric acid. Note that 0.15% PVA solution was
gradually added to the mixture while the mixture was stirred at
70 ◦C for 2 h. After completing the microencapsulation process
the resultant solution was filtered and washed with 30% ethanol
to remove thyme oil on the surface of microcapsules and then was
freeze-dried for 24 h.