| In recent years,deep water oil extraction has attracted widespread attentions.Microencapsulation technology is applied to the phase change sheath of pipeline transporting mixture of oil,gas,water and sand to deal with the cold environment in deep water.Two aspects of microcapsules performance are required: Melting enthalpy larger than 100 J/g,crystallization temperature ranging between 20-50℃.In-situ polymerization is used to fabricate phase change microcapsules and the main results are as follows:(1)The fabrication process of paraffin-poly(urea-formaldehyde)phase change microcapsules is optimized by adjusting the addition amounts of sodium chloride and crosslinker(a mixture of ammonium chloride and resorcinol with a weight ratio of 1:1).The thermal properties and morphology of products are characterized and working mechanisms of sodium chloride and crosslinker factors are studied in detail.The optimized microcapsules is obtained by adding 4 wt% sodium chloride and 0.25 wt%crosslinker,which exhibits diameter of several microns and melting enthalpy of 110 J/g.(2)Core material is prepared by mixing octadecane into paraffin,which helps widen the heat release temperature range of phase change below 50℃ due to the interaction between the two kinds of alkanes.The fabrication process of octadecane-poly(urea-formaldehyde)microcapusles is optimized to prepare the paraffin/octadecane-poly(urea-formaldehyde)products.Furthermore,multi-wall carbon nanotubes(MWCNT)is added to solve disadvantages,e.g.,large supercooling and low thermal conductivity,of core materials.With condition of 0.5 wt% MWCNTs,the microcapsules shows melting enthalpy of 104.5 J/g and crystallization temperature between 20-50℃. |
