Preparation And Properties Of Encapsulated PCMs And Its Composites Based On Temperature Regulating Package Technology

In recent years,insulating package technology of passive cold-chain has an increasingly significance as the enhanced requirement of shipping quality of temperature sensitive production in passive cold chain.Phase change materials(PCMs)and insulating materials play an important role in passive cold chain.And problems of PCMs in practical application can be solved by microencapsulated PCMs(microPCMs),which makes the micro PCMs become hot points for researchers.However,traditional microPCMs are not suitable for insulating package area in view of its problems and the particularity of insulating package area.Therefore,the main work of this paper is to design and prepare microPCMs that are suitable for temperature control package field.Poly(methyl methacrylate)(PMMA)and urea-formaldehyde(UF),the most popular shell materials,as the basis of this article,several newly functional phase change microcapsules and thermal energy storage composite were prepared through a series of chemical modification and physical blending,and their properties were also characterized and discussed.The research contents are as follows:(1)Two kinds of microcapsules were prepared with n-tetradecane as core material,PMMA and UF as the shell materials,respectively.Morphologies,chemical structure,and thermal properties of the microcapsules were characterized.The results were discussed and reasons of the differences were talked,which provides theoretical foundations for the following stage.Different types of emulsifiers were attempted in the preparation of microcapsules and the perfect emulsifier was determined on the basis of different performences of the microcapsules.(2)Millimeter-scale macrocapsules were prepared using calcium alginate gels as the matrix material,PMMA and UF shell microcapsules as core materials.The properties were also discussed.Most of the calcium alginate gels distributed on the surface of the macrocapsules,and the existence of calcium alginate gels do not obviously change the morphology of microcapsules inside the macrocapsule.The phase change enthalpy of macrocapsule can be promoted with the rise of phase change enthalpy of microcapsules.And the phase change enthalpy of the prepared macrocapsule was reached up to 163.2 J/g which is equal to microcapsules in other literatures.As matrix material,one part of calcium alginate gels can be a second shell of the PCMs,the other part can be a bond between microcapsules inside the macrcapsule.Therefore,the macrocapsule samples revealed much stronger thermal durability of core material than microcapsules.In view of that macrocapsules need to contact other products,there may be extrusion situations.The mechanical property need to be investigated.No PCM leaked out when deformation over half the size of 1.8 mm and the compressive resistance was 7 N on average,which was sufficient for practical applications on textile,building and cold chain transportation fields.(3)PMMA/NMA/UF hybrid shell microPCMs were prepared using bifunctional Nmethylol acrylamide(NMA)as crosslinking agent,MMA and UF prepolymer as raw materials.The properties were also characterized.Reaction mechanism between MMA and UF prepolymer with crosslinker was analyzed and molecule structure of PMMA/NMA/UF was also speculated.The morphology of hybrid shell microcapsule has both advantages of the two single shell microcapsule,and agglomeration phenomenon was related to ratio of PMMA/UF and additive amount of NMA.Latent heat of hybrid shell microcapsule was 175.5 J/g,which is higher than the two single shell microcapsule.Crosslinked macromolecule PMMA/NMA/UF effectively promoted water resistence and thermal endurance of the hybrid shell microcapsule.(4)Polyurethane(PU)foam composite with phase change energy storage property was fabricated by combining phase change capsules.Collapse of foam bulk of PU may be caused by the combination of capsules,while can be improved by supplement of polyisocyanate or DBTL.PU foam composite may keep normal bulk structure and performance when the dopant content of microcapsule was below 20wt%,while the dopant content of macrocapsule can reach more than 50wt% under similar circumstances.PU foam composite revealed phase change storage performance after doping with capsules.Duration of phase transformation platform of macrocapsules/PU composite last 7 times longer than microcapsules/PU composite.The thermal stability of microcapsules/PU composite is much better than PCM due to the combination of microcapsules and PU foam.The cell structure of PU foam is damaged by microcapsules,which reduced the mechanical strength of PU foam composite.Macrocapsules can act as joints in PU foam,which inhenced the mechanical strength of PU foam composite.Macrocapsules/PU composite remedied the drawbacks of microcapsules/PU composite about low phase change efficiency and mechanical strength,which can be marketing promotion in insulating package area.