Influence of process parameters on microcapsules loaded with n-hexadecane prepared by in situ polymerization

A series of melamine–formaldehyde microcapsules containing n-hexadecane were synthesized by in situ polymerization from partial etherified melamine–formaldehyde resins. This research was conducted to clarify the influence of different parameters on the encapsulation process, i.e. during the emulsion formation step and during the shell formation using surface tension measurement, Fourier-transform infrared spectroscopy and differential scanning calorimetry. By carefully analyzing the influencing factors including phase volume ratio, types of surfactants and content, stirring rate and time, pH, reaction time, feeding weight ratio of core/shell pre-polymer, the optimum synthetic conditions were found out. The results indicated that a binary mixture of Tween-20 and Brij-35 was found suitable emulsifier at low pH. Furthermore, formaldehyde/melamine (F/M) mole ratio influenced not only the shell formation mechanism but also the particle size distribution, microcapsule morphology and resin conversion rate.