Preparation And Characterization Of Modified Melamine - Formaldehyde Resin Microcapsules

Energy problem is increasing with the continuous development of global industry. And phase change materials as an energy-storing vector, can effectively improve the energy utilization and relieve the problem of energy shortage. Microcapsules containing dodecanol with melamine-formaldehyde shell were fabricated by in situ polymerization. The surface morphology, chemical structure and thermal properties of microcapsules were investigated using fourier-transform infrared spectroscope (FT-IR), scanning electron microscope (SEM), thermogravimetry analysis (TG) and differential scanning calorimetry (DSC), respectively. Based on the existing problems of microcapsules in the practical application such as poor stability and bad performance of energy-storing, the relationship between reaction conditions and the process of microencapsulated phase change materials were studied, in order to find the key factors to control the energy-storing and stability of microcapsules.The key factors to control the emulsification process were analysised and found that the optimal reaction conditions were OP-10 as emulsifier, sodium salt of styrene-maleic anhydride copolymer (SMA) as dispersant, the weight ratios of core/shell materials 3:1 and and the stirring rate 4000 rpm. And the microcapsules prepared with such conditions had smooth outer surface, good disparity and complete morphology.The relationships between the pre-polymerization conditions of melamine-formaldehyde prepolymer were investigated by using the response surface methodology. The pre-polymerization time and temperature were positively correlated with the viscosity of prepolymer, while pH inversely correlated. When the viscosity of prepolymer was excessively big, this resulted the sticking of microcapsules, deposition of M-F prepolymer and stability-decreasing of shell. And when the viscosity was too small, the incomplete pre-polymerization resulted in the high residual formaldehyde content. The optimal reaction conditions were reaction temperature 72.5℃, reaction time 75 min and pH 8.5. And the microcapsules prepared with such conditions had smooth outer surface, high stability and low remnant formaldehyde content.The FT-IR spectra and DSC analysis confirmed that the melamine-formaldehyde shell was successfully fabricated on the surface of the core materials dodecanol and the content of core materials in the microcapsules was about 70.47%. And the TG analysis showed the thermal stability of phase change material dodecanol rised gently as microencapsulated.Based on the poor toughness and high brittle characteristics of melamine-formaldehyde resin owing to its unique structure of triazine ring, the resin was modified respectively with polyethyl eneglyco, polyvinyl alcohol and m-dihydroxybenzene. The damage temperature of the microcapsule shell can be obtained by thermogravimetry analysis (TG). The strength of the shell was evaluated through observing the surface change under pressure by mean of scanning electron microscopy (SEM). As a result, the stability of the modified-resin microcapsules were improved greatly.