Fabrication And Characterization Of Micro/Nano-encapsulated Phase Change Materials With Ultra Low Content Of Formaldehyde

Microencapsulated phase change materials (MicroPCMs) and nanoencapsulated phase change materials (NanoPCMs) are tiny particles composed of phase change materials (PCMs) as core and a protective matrix as shell. MicroPCMs and NanoPCMs can absorb, store and release large amount of latent heat over a defined temperature range while undergoing phase changes. Owing to their unique advantage, they. have been widely applied in many fields such as heat-storage and thermo-regulated textiles, architectural materials, solar energy utilization, mechanical manufacture, and electronic devices. MicroPCMs with melamine-formaldehyde (MF) as shell have been studied by many researchers because of its good seal tightness and endurance, water, acid and alkaline resistance, fire resistance, etc. Remnant formaldehyde inevitable exists in the formed shell; however, it limits the application of Micro/NanoPCMs to some extent. The present research has investigated the mechanism of encapsulation via in-situ polymerization with MF as shell in order to fabricate MicroPCMs and NanoPCMs with ultra low content of formaldehyde.MicroPCMs and NanoPCMs with ultra low content of formaldehyde were synthesized by in-situ polymerization, which were composed of n-octadecane as core and MF resin as shell. The employed MF prepolymer was prepared by putting in formaldehyde once and melamine for three times, besides ammonium chloride was used to reduce the residual formaldehyde content during the encapsulation process. Moreover, MicroPCMs and NanoPCMs were heat-treated at 160℃ for 30min. The effects of dropping rate of MF prepolymer and encapsulation time were also studied. The surface morphology, shell thickness, thermal properties and stability, free formaldehyde content, etc of MicroPCMs and NanoPCMs were investigated by Scanning Electronic Microscopy (SEM), Wide-angle X-ray Diffraction (WAXD), Differential Scanning Calorimetry (DSC), Thermogravimetry Analysis (TGA),Fourier Transform Infrared Spectroscopy (FTIR), Spectral Photometer and so on. The conclusions are presented as follows.1. The lowest free formaldehyde content of microcapsules synthesized via in-situ polymerization is 67.1 mg·kg^-1, and the employed MF prepolymer prepared by putting in formaldehyde once and melamine for three times.2. The best period of microencapsulation is no less than 120 min and the best dropping rate of MF prepolymer is no higher than 0.82 ml·min^-1, when the microcapsule properties, the microencapsulation efficiency and the micro-encapsulation time were taken considered comprehensively.3. Microcapsules with ultra low content of formaldehyde were prepared, and ammonium chloride was added in during the encapsulation process and the prepared microcapsules were then heat-treated. The residual content of formaldehyde is below 20 mg·kg^-1. The average diameter of microcapsules was 2.2 μm and its distribution was narrow, besides, the shell thickness was 30-70 nm.4. NanoPCMs with contents of formaldehyde below 20 mg·kg^-1 were synthesized. The average diameter of microcapsules was 840 nm and its distribution was narrow, moreover, the shell thickness was in the range of 70-150 nm.5. The thermal stability of both MicroPCMs and NanoPCMs heat-treated at 160 ℃ for 30 min enhanced.6. The encapsulation efficiency of capsulated PCMs prepared via ultrasonic apparatus was quite low and the distribution of diameters was wide.