| With the rapid development of science and technology and people’s life quality,the way of controlling the thickness of the clothes to adjust temperature is difficult to meet the requirements for the comfort and functionality.Phase change material(PCM)can effectively release or store a great amount of latent heat during the phase transition.Microcapsules containing phase change material(microPCMs)by the microcapsule technology can overcome the problem of leak,poor compatibility and corrosivity in the process of PCM used in single.MicroPCMs are finished the fabric surface,and the core materials of microPCMs adjust the temperature of the fabric microenvironment by means of phase transition,which significantly reduced the thickness of the fabric and effectively mitigated the discomfort of the body because of the external environment temperature change,thereby improving the wearability.First,microPCMs containing n-octadecane as the core material and sodium alginate as the wall material were prepared by air-flow piercing-concreting method to green environmental protection.The influences of sodium alginate content.CaCl2 content,the mass ratio of core material and wall material and air pressure to microPCMs morphology,thermal performance and encapsulation were studied by using Optical Microscope(OM).Scanning Electron Microscope(SEM).Fourier Transform Infrared spectrometer(FT-IR),and Differential Scanning Calorimetry(DSC)analysis method.Through the Design-Expert 8.0,the multiple regression model of sodium alginate content,CaCl2 content,and the mass ratio of core material and wall material were established with the encapsulation efficiency as response value.Best preparation conditions of sodium alginate microcapsule:the mass fraction of sodium alginate was 2.6 wt%,CaCl2 dosage was 6.3 wt%,the mass ratio of core material and wall material was 0.35:1,and airflow pressure was 0.04 MPa.The response value and the optimal level of all the factors were obtained.Based on the results the microPCMs prepared was round,and had great dispersion.The melting latent heat of the microPCMs was 142.2 J/g,and encapsulation rate reached 64.76%.In conclusion,sodium alginate microcapsule has the advantages of green environmental protection,but the heat enthalpy value is low.Thus sodium alginate microcapsule could not significantly increase heat preservation performance of compound fabric.Next,In order to further increasing the thermal enthalpy of microcapsule,microPCMs containing n-alkane(n-tetradecane,n-hexadecane,n-octadecane and n-eicosane)as the core material and melamine-urea-formaldehyde(MUF)as the wall material were prepared by in-situ polymerization.MicroPCMs have the high phase change latent heat and more appropriate phase change temperature.The influences of emulsifying speed,emulsifiers type,emulsifier ratio,dosage of emulsifier,dosage of urea and the ratio of core material and wall material on microPCMs morphology,microPCMs thermal performance and encapsulation were studied by using Optical Microscope(OM),Field Emission Scanning Electron Microscope(FE-SEM)and Fourier Transform Infrared spectrometer(FT-IR),Differential Scanning Calorimetry(DSC),X-ray diffraction(XRD),and Thennogravimetric analyzer(TG)analysis methods.Through the Design-Expert 8.0.the multiple regression model of emulsifier content,the urea content,and the mass ratio of core material and wall material were established with encapsulation efficiency as response value.The response value and the optimal level of all the factors were obtained.Best preparation conditions of MUF microcapsule:the mix ratio of SDS and PVA as compound emulsifier was 4:1,the emulsifier mass fraction 6.9 wt%,the urea mass fraction 0.7 wt%,the mass ratio of core material and wall material 1.7:1.Based on the results the microPCMs prepared was round ball,the particle size 5～20 μm and had smooth surface,tight structure.The latent heat of phase change of microPCMs was 194.1 J/g,and encapsulation rate reached 88.75%.FT-IR analysis showed that n-alkanes were encapsulated by MUF resin successfully.Compared with sodium alginate microcapsule,MUF microcapsules with high heat enthalpy can be used for the preparation of low temperature protection fabric.Third,microPCMs coated to the surface of the fabric and low temperature protection composite fabric(LTPCF)was obtained by the intumescent coating method.The intumescent coating process was explored and LTPCF was tested by the low temperature protection test.The effect of foaming agent content,stabilizing foam agent content,foaming time,foaming density,clearance,WPU content,microPCMs content,and organization structure of fabric on coating finishing liquid and LTPCF and optimum foam coating process were researched.The optimum technological condition for finishing was the mass fraction of foaming agent SDS 3.0 wt%,the mass fraction of stabilizing foam agent PAM 2.5 wt%,the foaming time 4.5 min,foam density 100-150 g/L,clearance 1.5 mm and WPU content 20 wt%.Low temperature protective performance of plain weave fabric of is better than that of twill and weft plain fabric.Research showed the bigger microPCMs in the finishing liquor,the longer the low temperature resistance time of compound fabric,and the greater the low temperature protection performance.But when the mass fraction reached 20 wt%.microPCMs attached to the surface of fabric appeared obvious agglomerates.To further prolong low temperature resistance time of the composite fabric and improve the low temperature protection performance of fabric,microPCMs containing different PCM(n-tetradecane,n-hexadecane,n-octadecane and n-eicosane)in the study were coated to the surface of fabric,and hierarchical phase change low temperature protection composite fabric(HPC-LTPCF)was obtained.Compared with the composite fabric coated the single core material microPCMs,HPC-LTPCF can more significantly prolonged low temperature resistance time of composite fabric.Low temperature resistance time of HPC-LTPCF(optimum mixing ratio of n-tetradecane.n-hexadecane.n-octadecane for 1:1:2)was 6.9 min at-15 ℃,compared with the composite fabric coated the single n-octadecane microPCMs.and prolong 13.1%year-on-year.Further prolong the operating time of body work in low temperature environment.Finally,this study researched simulation of HPC-LTPCF by the finite volume analysis software FLUENT 16.0.The simplified geometric model of LTPCF was established by ANSYS Workbench in the beginning,and low temperature protection test of the fourth chapter was simulated.The temperature field cloud picture of HPC-LTPCF model at different times was described,intuitive showed the temperature field change of HPC-LTPCF.The simulation results were compared with the experimental results,and the error was less than 6.53%.The correctness of the model was verified.Based on the results the influence of environment temperature and wind speed on low temperature protection performance of compound fabric model were explored,and it can be used for optimization design of low temperature protection composite fabric and the low temperature protectivon performance of composite fabric in a real environment was analyzed and forecasted. |
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