Preparation Of Cross-linked Shell Microencapsulated Phase Change Materials With Low-yellowing And Flexibility Performance

The preparation of traditional polyurea microcapsule phase change materials is mostly based on the reaction of aromatic diisocyanate and diamine,which has some problems,such as high content of hard segment,high reaction activity,easy hydrolysis and difficult control of reaction process.These problems lead to the prepared microcapsules has high brittleness,poor thermal stability and compactness.Moreover,the microcapsule will also have serious yellowing when it is affected by light and heat,which has a great impact on its application performance.In view of the above problems,this paper adopts two new ways to solve them.on the one hand,aliphatic isophorone diisocyanate(IPDI)with low yellowing and low reactivity and polyether amine(PEA)with flexible polyether segments were selected as monomers to prepare the polymer shell of microcapsules.It not only effectively controlled the reaction rate of the polymerization system,but also introduced flexible segments into the structure of polyurea microcapsules,which solved the problems of severe yellowing,brittleness,poor thermal stability and compactness of microcapsules.On the other hand,in order to overcome the defects of linear structure of traditional polyurea shell,polyols containing three or more hydroxyl groups were used to modifying the shell to prepare microcapsule with cross-linked structure shell,which further improved the thermal stability and compactness of the microcapsules.Firstly,microencapsulated phase change materials with low-yellowing and flexibility performance were prepared by using butyl stearate as core and IPDI and PEA as monomers.The effects of monomer types,monomer mole ratio,capsule core,maximum reaction temperature and PEA addition mode on the surface morphology,chemical structure,compactness and thermal stability of microcapsules were investigated.The preparation conditions were improved and optimized.The yellowing properties of the products and their application properties in fabrics were also investigated.The results showed that the flexible segments greatly improved the thermal stability and compactness of microcapsules.The surface of microcapsules prepared with PEA as monomer was smoother and denser than that prepared with DETA.The molar ratio of IPDI to PEA and the reaction temperature have great influence on the properties of microcapsules.When the molar ratio of IPDI to PEA is 1:1.2 and the maximum reaction temperature is 60 ?,the microcapsule shell is smooth and dense and IPDI monomer reacts sufficiently.The prepared microcapsules have the best compactness and heat-resistant stability.The heat-resistant temperature is as high as 193.7 ?,and the mass loss was only 13.04% after drying at 120 ? for 6 hours.After microencapsulation,the crystallization behavior of phase change materials changed,double exothermic peaks appeared in DSC crystallization curve and supercooling phenomenon appeared.It was also found that adding a small amount of octadecanol could effectively improve the supercooling.With the increase of core material dosage,the protective ability of shell to core material decreases,and the density decreases.When the core material dosage is 40 g,the enthalpy value of microcapsule is the largest.By adding PEA in batches,the initial reaction rate can be further reduced,the compactness and thermal stability can be improved,and the mass loss rate can be reduced to 10.71%.The microcapsules prepared with IPDI as monomer also exhibited excellent low yellowing properties.After continuous drying at 150 ? for 1 h,no obvious yellowing occurred.However,the molecular chains in the polyurea structure were oxidized at 180 ?,and the yellowing was aggravated.Then,the polyurea shell was modified by adding polyols,and the cross-linked microcapsules were prepared.The effects of polyol type,reaction temperature and emulsifying speed on the surface morphology,chemical structure,compactness and thermal stability of microcapsules were investigated.Temperature-regulating textiles were prepared by coating finish,studying the finishing process,wearability,washability and temperatureregulating properties.At the same time,the differences in product and application were compared and analyzed between linear microcapsules and cross-linked microcapsules.The results showed that the surface morphology of the microcapsules was slightly different,but the thermal stability and compactness of the microcapsules were greatly improved.Under the same conditions,the mass loss rates of the microcapsules prepared by glycerol,triethanolamine and pentaerythritol respectively were 8.77%,6.09% and 8.19%.The microcapsules prepared by triethanolamine modification have the best thermal stability and compactness.The increase of emulsifying speed is helpful to improve the densification and decrease the average particle size of microcapsules,but when the emulsifying speed exceeds 18 000 rpm,the surface depression of microcapsules increases and the strength decreases.At the same time,emulsifying speed had a great influence on the crystallization behavior of microcapsules.When the emulsifying speed exceeded 8000 rpm,the microcapsules began to undergo supercooling.With the increase of microcapsule content in the finishing agent,the hand feel and air permeability of the fabric decrease continuously,and the hand feel decline can be improved by adding softener.Temperature-regulated fabrics have obvious cushioning effect on the change of ambient temperature,good temperature control effect and washing resistance.This paper contains 40 figures,17 tables and 93 references.