Effects of ammonium chloride and heat treatment on residual formaldehyde contents of melamine-formaldehyde microcapsules

Microencapsulated n-octadecane with melamine–formaldehyde resin (MF) shell was synthesized by in situ polymerization. Ammonium chloride was used to reduce the residual formaldehyde content of microencapsulated phase change materials (microPCMs) caused by the inherent characteristics of MF. Moreover, microPCMs were heat-treated at 160 °C for 30 min. The surface morphology of the microPCMs fabricated at various microencapsulation periods was examined, and the shell thickness was measured. The effects of heat treatment on the surface morphology, residual formaldehyde content, phase change properties, and thermal stability of the microcapsules were systematically investigated. The globular surface of microcapsules fabricated at microencapsulation period of 120 min was smooth and compact with an average diameter about 2.2 μm, and the shell thickness was ranged from 30 to 70 nm. The thermal stability of heat-treated microcapsules enhanced significantly as microencapsulation period increased; in addition, the residual formaldehyde content of microcapsules decreased from 125 ± 1 mg/kg to 19 ± 1 mg/kg.