Preparation And Characterization Of Reticular Structure Shell Microencapsulated Phase Change Materials By Interfacial Polymerization

Polyurea shell,due to the formaldehyde-free structure and properties in preparation and application,is widely used as microcapsules shell in researches of preparation of microcapsules phase change material.Traditional polyurea shell is normally prepared by the reaction between aromatic diisocyanate with aliphatic diamines or diatomic alcohol.Due to the fast reaction rate and linearity Structure in the above reaction,leading to poor thermal stability and compactness in microcapsules,limiting its'application.In this paper,network crosslinking structure shell were prepared by interfacial polymerization.The object of this investigation is to obtain microcapsules with satisfactory stability and compactness to meet the special high functional requirements.Two main aspects of the content were involved as follows,first one,network structure polyurea shell MicroPCMs were prepared after the reacting of hexamethylene diisocyanate trimer?HDI trimer?and diethylene triamine?DETA?was accomplished.And secondly,the prepared polyurea shell was modified by polyols triethanolamine or pentaerythritol,and polyurea/polyurethane composite shell MicroPCMs with more compact network structure were prepared simultaneously.The surface morphology,phase change behavior,chemical structure,thermal stability and compactness of the prepared MicroPCMs were characterized by optical microscopy,scanning electron microscopy?SEM?,differential scanning calorimetry?DSC?,infrared spectrometer?FTIR?and thermo-gravimetric analyzer?TGA?,respectively.In this paper,butyl stearate was used as the core material,acetone as solvent,styrene maleic anhydride copolymer sodium salt?SMAS?as emulsifier,electing HDI trimer and DETA to react to prepare MicroPCMs of reticular structure shell.The influence of reaction monomer dosage,emulsifier dosage,amount of solvent,emulsifying temperature,emulsifying time and stirring speed to emulsifying were researched and discussed.The results showed that the emulsifying effect was good when emulsifier dosage was 1.5g,emulsifying speed was 9000rpm and emulsifying time was 10min.The particle size distribution of the prepared emulsion was narrow and there was no agglomeration and adhesion between particles and prepared MicroPCMs were spherical in shape and the surface of the shells had different degrees of wrinkles and concavity,The amount of solvent,the dosage of monomer and the preparation process had a great influence on the surface morphology of the microcapsules.When the amount of solvent and monomer was insufficient,coating is inadequate and have serious adhesion between the particles.Prepared MicroPCMs have better thermal stability and compactness and with the increase of HDI trimer and DETA dosage,the thermal stability and compactness gradually improved.When Additional 1g of DETA was added during the preparation,prepared microcapsules has greatest thermal stability and compactness.heat resistant temperature above 200?,after 120?drying 2h the mass loss rate of not more than 4%.The amount of monomer and the preparation conditions have a great impact on the degree of reaction,the isocyanate reaction is not complete when the HDI trimer amount of 8.3g and DATA dosage of 1.7g,but As the amount of DETA increased to 2.5 g the isocyanate reacted completely.DSC results showed that the melting and crystallization temperature of the prepared microcapsules were about21?and 15?,the enthalpy of phase change was between 70⁸0J.g^-1.The microcapsule of polyurea/polyurethane composite shell was prepared by adding polyfunctional triethanolamine or pentaerythritol to the modified polyurea shell and investigate the influence of adding multifunctional triethanolamine or pentaerythritol monomer dosage to MicroPCMs,property.Investigation results showed that the surface morphology of composite shell have not significant distinction comparing to polyurea shell.However,the surface concavity become evident with the increase of the amount of polyol and this change does not affect the polyol species.FTIR results showed that the microcapsules were prepared with butyl stearate as the core material and the shell material as the polyurea/polyurethane composite structure.Heat stability and compactness of polyurea/polyurethane composite shell MicroPCMs have improved obviously and The thermal stability and compactness property of the modified-microcapsules by pentaerythritol are better than that of triethanolamine,mass loss rate of not more than 2%after 120?drying2h when adding DETA dosage was 1g.