Preparation Of Low-temperature Phase Change Microcapsules Based On Long Chain Alkanes And Their Cold Storage Performance

In the process of rapid economic development and globalization,logistics and express delivery have become the important means of effective circulation of goods.Amongst,the transportation processes of food,medicine and biological products need fresh-keeping or freezing to prevent their decay and failure,so the main approach to solve this problem is the cold chain transportation.In the view of the"first mile","last mile",multiple small quantities of low-temperature distribution and different low-temperature requirements in cold chain transportation,low-temperature phase change microcapsules(LTPCMs)can rationally solve the low-temperature transportation problems between goods and users.The purpose of this project is to prepare LTPCMs with suitable temperature(especially subzero),high phase change enthalpy,high yield,high encapsulation rate,non-toxic,environmental-friendly and long temperature-holding period.And they can be applied to short-distance cold chain transportation of goods with different temperature requirements.In this paper,the n-tridecane low-temperature phase change microcapsule(n-tri-LTPCM)for cold storage was prepared by suspension polymerization using the cheaper n-tridecane as core material and the copolymer of styrene and methyl methacrylate(PS/PMMA)as shell material.With the help of TG,DSC,POM,SEM,IR and other test methods,the performances of LTPCMs were studied systematically under different conditions,such as mass ratio of styrene to methyl methacrylate,mass ratio of water to oil and the content of n-tridecane.And the structural composition,phase change enthalpy,stability,particle size distribution,apparent morphology and cold storage performance were analyzed and discussed.The results show that the best preparation conditions of LTPCMs are the mass ratio of styrene to methyl methacrylate of 40/60,the mass ratio of water to oil of 2/1,and the content of n-tridecane of 65wt%.Under the optimal condition,the n-tri-LTPCM has two phase change peaks,where the solid-solid phase change temperature is-17.61?with the phase change enthalpy of 38.33 J/g,and the solid-liquid phase temperature is-4.96? with the phase change enthalpy of 93.71 J/g.The yield can reach 90.87%and its temperature-holding period for cold storage can reach 40 min,which has a certain cold storage effect.Secondly,under the optimal preparation condition of n-tri-LTPCM,LTPCM for cold storage with different phase change temperatures were prepared by suspension polymerization,using n-dodecane and n-tetradecane of 50wt%as core materials and the PS/PMMA copolymer as shell material.The phase change enthalpy,stability,particle size distribution,apparent morphology and cold storage performance of three series of LTPCMs were compared and discussed to determine the best LTPCMs.The results show that the n-dodecane low-temperature phase change microcapsule(n-do-LTPCM)has one melting peak with the phase change temperature of-8.69? and with the phase change enthalpy of 110.53 J/g.The yield can reach 86.29%and the temperature-holding period for cold storage can reach 30 min.The n-tetradecane low-temperature phase change microcapsule(n-tetra-LTPCM)has one melting peak with the phase change temperature of 6.65?and with the phase change enthalpy of 116.19 J/g.Additionally,its yield is 91.83%and the temperature-holding period is 80 min.As a whole,the n-tetra-LTPCM has the best temperature-holding performance.Finally,the phase change enthalpy of n-tetra-LTPCM was increased with the content increase of n-tetradecane.The results show that the optimal temperature-holding performance of n-tetra-LTPCM is achieved when the content of n-tetradecane is 65wt%.And the best phase change microcapsules have a phase change temperature of 8.59?,a phase change enthalpy of 166.79 J/g,a yield of 88.48%,an actual encapsulation rate of 60.32%,an encapsulation efficiency of 92.80%,and a temperature-holding period for 140 min.The three series of LTPCMs prepared by this subject have achieved the goals of high yield,high enthalpy,high encapsulation rate and long temperature-holding period,and have met the demand for multiple small quantities of low-temperature distribution of food,medicine and biological products within 0.5-2 hours.It has potential application value in express delivery and short-distance cold chain transportation.