Preparation And Properties Of Nano-SiO₂ Modified Urea Formaldehyde Resin/Phase Change Microcapsules

Today,energy supply and demand is not balance.Increasing energy efficiency and exploiting new energy is paid more attentions.Phase change energy storage is the use of thermal storage properties of phase change materials to absorb or release the heat.It will achieve certain regulation and control of the ambient temperature around the phase-change material.It can change the spatio-temporal distribution of energy use and improve the efficiency of energy utilization.A binary eutectic phase change material is prepared by melt blending method with lauric acid（LA）and myristic acid（MA）in this work.The effect of mass fraction on the crystallization temperature of the LA-MA composite is determined by step-cooling curve means and the low hypoeutectic point of LA-MA composite is acquired by drawing the phase diagram,where the mass ratio of LA to MA is 3:1 and the eutectic temperature is 32.7℃,the latent heat of the eutectic composite is 160.5J.g^-1.FT-IR experimental results indicate that LA and MA are combined in the binary composite by molecular force,there is no chemical reaction during preparing composite phase change materials.After 500 cycles of 20-70℃thermal cycling,the phase change temperature of the composite has little variation,which indicates that the LA-MA mixture is stable.When the temperature is less than 100℃,TG experimental results display no apparent mass loss appears and further verify the stability of the LA-MA mixture.O/W emulsions are prepared using the binary low eutectic mixture of LA-MA as oil phase,the effect of emulsifier,addition of emulsifier time,temperature and speed on the stability and dispersibility of the emulsions are investigated and analyzed.The stability and dispersibility of the emulsions are determined by the resting method and particle size analysis.The experimental results show that the best stability and dispersion of the emulsions are produced with 5wt%addition of Tween80-sodium oleate as the compound emulsifier,1200r/min emulsification speed,60min emulsification time and emulsification temperature at 65℃.Organic PCMs have the advantages of high latent heat,good stability,non-toxic and non-hazardous,but in the process of phase change,there are shortcomings such as material melting and leakage.Microencapsulation may be used to package phase change materials to effectively solve the problems above.The phase change microcapsules are prepared by in-situ polymerization,where LA-MA is used as the core material and urea-formaldehyde resin as the wall material.The effects mass ratio of core material to wall material,polymerization speeds,temperature,time and the addition of nano-Si O₂ on the morphology and thermal properties of the microcapsules are investigated.The experimental results suggest that the microcapsule has an optimal appearance and performance at a core material to wall material mass ratio of 1:2,800r/min polymerization speed,65℃polymerization temperature,a 4h polymerization time and the addition of Si O₂ nanoparticles whose amount is 4wt%of the core material mass.