Preparation Of Microencapsulated Phase Change Materials With Low Formaldehyde Content

With global energy crisis becoming serious,the development of new energy and energy storage technology became the key work of researchers from worldwide.Latent thermal energy storage technology with phase change materials has become a hotspot because of its incomparable advantages compared to sensible thermal energy storage.Microencapsulated phase change materials(MicroPCMs)is an important branch of phase change materials,which has been utilized in military,architectural,medical and other fields.At present,more than 54% of MicrosroPCMs are made of melamine resin,urea-formaldehyde resin,urea-modified melamine resin.The MicroPCMs have high embedding rate,good storage performance and outstanding physicochemical properties with good application prospects in packaging.It was shown that content of free formaldehyde residues is high in the wall of microcapsules,and the toxicity and teratogenicity of formaldehyde have been confirmed.Therefore,it is necessary to develop low formaldehyde or formaldehyde-free MicroPCMs.If this problem is solved,the safety of melamine resin phase change microcapsules can be greatly improved,and it will be widely applied in more fields.Based on the requirement of temperature-controlled packaging,this project aims to prepare phase change microcapsules with good comprehensive properties which meet the needs of storage at medium and low temperatures,and to solve the problem of high free formaldehyde of phase change microcapsules,optimize the preparation process,find new materials to prepare environment friendly phase change microcapsules.Low formaldehyde residual phase change microcapsules were modified to improve their comprehensive properties and make them more suitable for packaging,storage and transportation.The main research contents are as follows:(1)Preparation microcapsules by batch addition of melamineIt was shown that the addition of melamine in batches can reduce the residual formaldehyde content of resin.Based on the forming mechanism of melamine resin and phase change microcapsules,the process of preparing melamine resin microcapsules by batch addition of melamine was discussed.Effects of pH of reaction medium and the proportion of melamine addition by three times on the residual formaldehyde content of microPCMs Thermal storage,mechanical strength and stability of microPCMs were studied in order to prepare low toxicity microcapsules with excellent comprehensive properties.(2)Analysis of coupling effect between formaldehyde capture agent and phase change microcapsulesFormaldehyde trapping agent was added during making process to react with residual formaldehyde and free formaldehyde in wall.Several kinds of formaldehyde trapping agents with high safety were selected to compare the aldehyde removal activity.Effects of the concentration and adding methods of the trapping agents on the morphology,phase transformation performance and residual formaldehyde content were investigated.Reaction characteristics of the trapping agents and their coupling effects with microcapsules were also studied,so as to select the best microencapsulation aldehyde removal process.(3)Performance optimization of phase change microcapsulesBecause of the large amount of triazine ring structure in the melamine resin,the resin has high brittleness and insufficient toughness.The thin shell of the microsphere is easily broken when it is impacted by external force,which leads to the leakage of the core material and is not conducive to the long-term storage and usage.Therefore,it is necessary to improve the flexibility of microcapsule wall materials,improve their impact strength,and enhance the stability of phase change microcapsules in cold storage.