Preparation Of Modified Polyacrylonitrile Fiber Composite Membrane And Its Thermal Insulation Property

With the rapid development of human society,energy shortage and environmental problems are becoming more and more obvious.Heat energy is one of the most important energy sources for human survival,it has become a common goal for scholars to improve the utilization efficiency of heat energy.Nowadays,there is still a large loss of heat in the process of using and transmitting heat energy,so the heat insulation materials that can prevent heat loss and reduce energy loss are getting more and more attention from scholars.Composite insulation materials can combine the advantages of multiple materials and give them multiple properties to meet the needs of complex environments.The fiber insulation materials prepared by electrostatic spinning technology have the advantages of being light weight,good flexibility and good air permeability,and can be compounded with other materials to obtain multi-functional fiber membranes according to the demand,which has significant application prospects in the field of thermal insulation composite materials.The subject of this thesis is an enterprise commissioned project.In the development of textile insulation lining by electrostatic spinning technology,the commissioned company found that the thermal conductivity of the prepared nano-fiber membrane was greater than 51m W?m^-1?K^-1and the limited oxygen index was less than 18%,which made the product flammable.It was necessary to make the thermal conductivity of the fiber membrane less than the enterprise’s internal control standard(thermal conductivity less than 45 m W?m^-1?K^-1)and to improve its flame resistance,so as to upgrade it from a flammable product to a combustible product（limited oxygen index more than 22%）through systematic research.In order to solve the practical problems in the process of product development,this paper designed a method to modify polyacrylonitrile（PAN）fiber membrane by hollow silica microspheres（HSM）and flame retardants,and systematically studied the effect of the modification process on the thermal insulation performance,flame resistance and mechanical properties of PAN fiber membrane.The effects of the modification process on the thermal insulation performance,combustion resistance and mechanical properties of PAN fiber membrane were systematically investigated to improve the thermal insulation performance and combustion resistance of PAN fiber membrane.The specific research contents and results are as follows:（1）HSM with different particle sizes were prepared to modify PAN fiber membranes to study the effect of particle size on the thermal insulation properties of the membranes in order to achieve better modification effects at the same volume fraction.HSM were prepared by adjusting the ratio of water to ethanol in the raw material using ethyl orthosilicate as the precursor,with the average particle size distribution of 130 nm,250 nm and 380 nm.The bulk density of the three types of microspheres was tested,and all three types of microspheres were mixed with polyacrylonitrile solution at 1%volume fraction.HSM/PAN composite fiber membranes with HSM embedded inside the fiber were produced by uniaxial electrostatic spinning.The thermal conductivity of the three composite fiber membranes was analyzed,and the results showed that the 130 nm HSM-modified composite fiber membrane（HSM-1/PAN）had the lowest thermal conductivity of 38.05 m W?m^-1?K^-1,which was 25.7%lower than that of the PAN fiber membrane of 51.2 m W?m^-1?K^-1.And the mechanical and soft properties are better than the other two particle size modified fiber membranes.However,the improvement of the combustion resistance of PAN fiber membrane is not obvious,and the modified composite fiber membrane is still a flammable product.（2）In order to further improve the combustion resistance of HSM-1/PAN composite fiber membrane,using flame retardant 9,10-dihydro-9-oxa-10-phosphafi-10-oxide（DOPO）and HSM to modify PAN fiber at the same time,and the thermal conductivity,limiting oxygen index,mechanical properties,etc.of the prepared composite fiber membrane were investigated,The results show that when the concentration of DOPO in the spinning solution is 9 wt%,the thermal conductivity of the prepared HSM/PAN/DOPO（HPD）composite fiber membrane is39.9 m W?m^-1?K^-1,and the ultimate oxygen index is reaching 24.1%,which means the fiber membrane had upgraded from flammable product to combustible product.Therefore,the modification of PAN fiber membrane effectively improved the thermal insulation performance and combustion resistance,and achieved the research objectives set by the commissioned company.However,when DOPO concentration of 9 wt%in the spinning solution,the test results of the tensile properties of the prepared HPD composite fiber membrane showed a strength of 2.12 MPa and an elongation at break of 3.28%.This is sufficient for the use of the textile laminated thermal insulation membrane for the target product,but the mechanical properties are to be further improved for other applications.（3）In order to further improve the mechanical properties of the HPD composite fiber membrane,it is expected that it can be used in applications other than textile interlayer insulation liner.The HPD fiber membrane was modified with waterborne polyurethane（WPU）,magnesium hydroxide and hollow glass beads as modifiers to obtain the HPD/WMS composite membrane.And the structural properties of HPD/WMS composite membrane were studied.The results showed that the thermal conductivity of the prepared HPD/WMS composite membrane was 39.79 m W?m^-1?K^-1when the HPD composite membrane was modified by the impregnating solution composed of WPU solids∶Mg（OH）₂:hollow glass beads=3∶1∶1.The HPD/WMS composite membrane with a thickness of 1.1 mm could achieve a thermal insulation effect of15℃under the temperature field of 60℃,which is better than that of HSM-1/PAN composite membrane.It has better thermal insulation effect than HSM-1/PAN fiber membrane,and the tensile performance has been significantly improved too,with tensile strength of 11.09 MPa and elongation at break of 35.11%,which created conditions for the application of modified PAN composite fiber membrane in other applications.