| As a new type of thermal storage composite material for thermal storage,micro-encapsulated phase change materials can effectively improve the phase separation,leakage,corrosion and other issues that may be encountered during the direct use.In this paper,we reported an innovation microencapsulated preparation through in-suit polymerization that n-dodecanol as core,and the oil-soluble methanol etherified melamine-formaldehyde(MMF)copolymer as the shell,which replaced water-soluble MF prepolymer.Compared with the traditional microcapsule preparetion by dissolving the MF prepolymer in water,this paper dissolved the shell material in the core to form a homogeneous oil phase,and then they were fully emulsified and dispersed at the same time to get a stable O/W emulsion.By regulating pH,temperature and other conditions,the microcapsules with good morphology and excellent properties were successfully prepared through in-situ polymerization.The microcapsules have a uniform size and narrow distribution,and their average diameter is about 1.92 ?m,and the shell thickness is about 60nm.Through the FTIR and XRD analysis,no reaction occurred between the core and shell,and the n-dodecanol was coated inside the microcapsule.What's more,DSC and TG analysis showed that microcapsules had good heat storage and thermal stability:the microcapsule inner core content reached 49.9%,the encapsulation efficiency as high as 93.6%,and the enthalpy loss rate was only 1.92%after 50 cycles of cooling-heating.In order to optimize the preparation process and improve the product quality,the main influencing factors in the process of encapsulation were also investigated,including the composition of the shell material,the mass ratio of core to wall,the concentration of emulsifier and the dropping rate of acid.The results showed that the addition of a small amount of n-butanol etherified melamine-formaldehyde prepolymer to the methanol etherified melamine-formaldehyde prepolymer as raw material for the shell material not only made the surface of the microcapsule smooth and neat,but also improved the utilization of the shell material to enhance the encapsulation effect,but also improve the flexibility of the microcapsule and reduce the rigidity,so as to improve the mechanical properties of the microcapsule.In addition,the results also showed that the optimum mass ratio of core and shell of this experiment is 2:1,the suitable emulsifier concentration is 1.5?2.0%,and the appropriate acid dropping rate is 2 mL/h.Due to the poor toughness and high brittleness of melamine-formaldehyde resin which because of its unique triazine ring structure,the microcapsules were prepared by melamine-formaldehyde prepolymer with long chain alkane etherification as the shell material.The effects on the morphology and properties of microcapsules of etherification for shell monomer and the main influence factors in etherification process were explored as well.Through characterization and analysis,the alkyl chain of the n-dodecanol can be grafted into the methylolated melamine-formaldehyde prepolymer by etherification and the alkyl chain in the prepolymer can enhance the adsorption of the core,enhancing the encapsulation effect of the microcapsules.Results of analysis showed the optimal conditions in etherification reaction:melamine,formaldehyde and n-dodecanol molar ratio should choose 1:5:2 during the etherification,and one-step method should be used to prepare the n-dodecanol etherified melamine-formaldehyde prepolymer,which as the shell of microcapsules to encapsulate n-dodecanol.Finally,the microcapsules with complete structure,uniform particle size and good dispersion performance can be obtained with an enthalpy of 170.4 J/g and an effective loading of 74.1%. |
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