| Currently, the phase change material applied to the study of the construction sector to achieve comfort and energy saving has become a hot spot. However, because of its own shortcomings, such as in conjunction with the base material, volume change of phase change, life time and other issues, these problems have constrained the application in wall materials. In order to overcome these problems, wrapping the phase change material to form microcapsules is a good solution.In this paper, microencapsulated phase change material with dodecanol as core material, melamine-formaldehyde resin and urea-formaldehyde resin as wall material was prepared using in situ polymerization approach and its performance was characterized. The particle size and stability of the obtained emulsion were detected by the particle size analyzer and the full functional stability analyzer; The structure, surface morphology, particle size and particle size distribution, thermal properties of the microcapsules were characterized by FT-IR, SEM, particle size analyzer, DSC and TGFirstly, microencapsulated phase change material with dodecanol as core material, melamine-formaldehyde resin as wall material was prepared using in situ polymerization approach, and was detected and characterized by different methods. The effects of different emulsifiers, crosslinking agent, the molar ratio of melamine to formaldehyde, the concentration of emulsifier, the concentration of resorcinol, the ratio of core to wall material (mass ratio) on the morphology and thermal properties of the microcapsules were evaluated by univariate method and we determined the parameters:the OP-100was the emulsifier, crosslinking agent was resorcinol, the molar ratio of melamine to formaldehyde was1:3, the concentration of emulsifier was0.40%, the concentration of resorcinol was2.5%and the ratio of core to wall material was1.5:1. FT-IR analysis showed that the dodecanol was coated by melamine-formaldehyde. In addition, we conducted the second series that is microencapsulated phase change material with dodecanol as core material, urea-formaldehyde resin as wall material was prepared using in situ polymerization approach. In this series, we studied prepolymer and emulsion phases in detail. At prepolymer phase, we took the SEM photographs and TG data as the evaluation criterion and determined parameters:the optimal pH was9, temperature of prepolymerization was70℃, time of prepolymerization was60min, speed of prepolymerization was300rpm; At emulsion phase, we studied the surface morphology, particle size distribution of the microcapsules and determined OP-100as the emulsifier, considering the average particle size of the emulsion, particle size distribution and stability, we determined the optimal concentration range of emulsifier was0.1-0.3%, and the optimum concentration range of resorcinol was1-2%, we took the average particle size of the microcapsules of the product as an evaluation criterion and determined parameters: time of emulsion was30min, speed of emulsion was1500rpm.We designed17groups’ three factors and three levels experiments with the ratio of core to wall material, the concentration of OP-100, the concentration of resorcinol as independent variables, mass content of dodecanol as the response using Box-Behnken center combination of response surface methodology. Analysis of variance showed better simulation, we got optimal conditions through optimization software:the ratio of core to wall material was1.5, the concentration of OP-100was0.24%and the concentration of resorcinol was2%. FT-IR analysis showed that dodecanol was wrapped into the urea-formaldehyde resin. SEM pictures showed, the diameter of the resulting microcapsule was about1μm, the surface morphology was smooth, and the particle size distribution was uniform. Through data of TG analysis, we knowed these samples had large mass loss in two stages. |
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