Preparation And Properties Of Phase-Change Energy Storage Polymer Microcapsules Under The Auxiliary Fields

In recent years,the research and application of polymer phase-change energy storage microcapsules have been drawing more and more attention all over the world.And in this field,it is very necessary to develop a simple,clean and efficient method for preparing polymer capsules with high latent heat.Both ultrasonics sonochemistry and microwave chemistry are in the ascendant in the field of polymer science.The former has the main advantages of fast reaction rate and multiple effects of dispersing,stirring,emulsifying and initiating in the reaction process.In addition,the sonochemical reaction can be carried out at low temperature(room temperature)without external initiator.The latter has advantages of fast reaction rate,low energy consumption and few side reactions.Both belong to the category of"green chemistry".In this paper,ultrasonically initiated in situ encapsultion polymerization and microwave-assisted in situ encapsulation polymerization were employed to prepare polymer phase-change energy storage microcapsule,which was applied to spin energy storage thermo-regulated fibers.Poly(methyl methacrylate)/stearic acid phase-change energy storage nanocapsules(PMS-PCESNs)were prepared by ultrasonically initiated in situ encapsulation polymerization.The effects of ultrasonic time,ultrasonic intensity,reaction temperature,nitrogen flow rate and emulsifier dosage on the monomer conversion were investigated through parallel experiments.The results showed that the conversion rate of monomer reached 90%after 30 min under the field of ultrasound.And it could reach 80%when the ultrasonic power was 750 W.The conversion of monomer was ideal at room temperature.The reaction rate and monomer conversion rate were good with nitrogen flow rate of 50 mL/min and 1.0 wt%emulsifier(based on the monomer),respectively.The effects of ultrasonic power,ultrasonic time,nitrogen flow rate and emulsifier dosage on the phase-change energy storage latent heat(encapsulation efficiency)were investigated by two cycles of orthogonal experiments.The results showed that the order of importance was emulsifier dosage,ultrasonic power,nitrogen flow rate and ultrasonic time,respectively.The optimal parameters were:ultrasonic power 750 W,ultrasonic time 50-60 min,emulsifier dosage 1.0 wt%and N2 flow rate 50 mL/min.According to the theory of three-phase interface,the thermodynamic analysis of ultrasonically initiated in situ encapsulation polymerization showed that why a perfect core-shell structure could be formed.The kinetic analysis showed that there was no constant period in ultrasonically initiated in situ encapsulation polymerization.The results of DLS showed that the particle size of PMS-PCESNs was below 100 nm and monodispersed.The results of TEM,SEM and AFM showed that PMS-PCESNs gave obvious core-shell structure with a narrow size distribution.The results of DSC showed that the initial phase transition temperature,peak temperature and latent heat of PMS-PCESNs was 53.11 ℃,55.57℃ and 155.6 J/g,respectively.The polymerization encapsulation efficiency reached 83.0%.And the results of XPS confirmed the successful encapsulation of PMMA to SA according to the change of C/O value before and after ultrasonically initiated in situ encapsulation polymerization.Poly(urea-formaldehyde)/lauryl alcohol phase-change energy storage microcapsules(UF/LA-PCESMs)were prepared by microwave-assisted in situ encapsulation polymerization.In the reaction,the microwave power has a significant effect on the phase-change energy storage latent heat(encapsulation efficiency),with the best effect at 300 W.The encapsulation efficiency reached 80%after 35 min under the field of microwave.Both the homogenization rate and stirring rate have significant influence on the encapsulation efficiency.The latent heat of UF/LA-PCESMs would reach a maximum value when the homogenization rate was 3000 rpm and the stirring rate was 800 rpm.Compared with a single emulsifier,the composite emulsifier is beneficial to increase the latent heat of phase-change microcapsules.And the result is ideal when the composite emulsifier dosage is 3.5 wt%.The results of DLS showed that the particle size of UF/LA-PCESMs was 170 nm-180 nm and monodispersed.The results of TEM,SEM and AFM showed that the shell structure of the UF/LA-PCESMs was non-porous,dense and smooth.The results of DSC showed that the initial phase transition temperature,peak temperature and latent heat of UF/LA-PCESMs was 22.64 ℃,26.84 ℃ and 156.0 J/g,respectively.The polymerization encapsulation efficiency reached 75.0%.And the results of XPS confirmed the successful encapsulation of UF to LA.Polyethylene energy storage thermo-regulated fibers(UF/LA-PCESMs-PE fibers)were obtained by the process of blending(UF/LA PCESMs and PE),granulating and spinning.The latent heat of UF/LA-PCESMs-PE fibers increased steadily with the increase of UF/LA-PCESMs contents and reached 74.52 J/g.The results of TG showed that the maximum weight loss rate of fibers moved to high temperature with the increase of UF/LA-PCESMs contents.This meant that UF/LA-PCESMs could improve the thermal stability of PE fibers.The results of mechanical test showed that the tensile strength decreased with the increase of UF/LA-PCESMs contents.However,the mechanical properties of UF/LA-PCESMs-PE fibers could still meet the requirements of textile(UF/LA-PCESMs contents ranged from 0 to 20 wt%).The results of SEM showed that UF/LA-PCESMs were well distributed in PE matrix.And the structure remained intact after blending,granulating and spinning.The application of ultrasonics sonochemistry and microwave chemistry was further developed and deepened in the field of materials science,which laid a theoretical and experimental foundation for the related research.