Preparation And Performance Of Aramid Fiber/NFC-Mica Paper-based Composites

As a new type of paper-based composite,aramid fiber/mica paper-based composite is generally made from aramid fiber and mica by water-assisted paper-making process.And aramid fiber/mica paper-based composite has became an advanced insulating material for major normal engineering construction since it combines excellent insulating properties of mica and great mechanical properties of aramid fiber,which is widely used in various fields,such as ultra-high voltage transmission,rail transit,telecommunication,and national defense.However,the poor interfacial bonding between the mica and aramid fiber leads to loose structure of aramid fiber/mica paper-based composite,which restricted its further application.Therefore,looking for an effective way to improve the surface properties of aramid fiber or mica and the interface of paper-based composite is a key issue in the preparation of high-performance aramid fiber/mica paper-based composite.Nanofibers have been applied to adjust the micro-structure and improved the overall performance of composite because of their small size,large specific surface area,high strength and other excellent properties.Therefore,this study aimed to improve interfacial interaction between mica and aramid fibers by introducing nanofibers,so as to enhance the mechanical and dielectric properties of paper-based composite and achieve high performance insulating paper-based composite.First,the physical and chemical properties of aramid fibrid,mica and NFC,as well as the micro-structure,mechanical and dielectric properties of binary paper-based composites including AN,AM and MN paper-based composites,were comparatively analyzed.It was clear that there was poor bonding strength for paper-based composite due to simple physical covering between aramid fiber and mica.Fortunately,NFC could provide inferior interfacial bonding among aramid fiber and mica.Second,Aramid fiber/Mica-NFC composites were prepared by adding different contents of NFC into aramid/mica paper,and the properties of AMN paper-based composites were investigated.As a result,it was found that the tensile strength,strain at break and dielectric breakdown strength of AMN-30 paper-based composite reached the maximum value,29.0 MPa,3.3%,and 14.9 kV/mm,respectively.Importantly,NFC as interfacial layer was confirmed by the significantly decreased physical properties of NaOH-Urea treated Aramid/Mica-NFC composite.It was found that the tensile strength of the AMN-30 paper-based composite decreased by 54.2%,and the cross-section structure of composite became loose.Based on visualization of NFC by fluorescence tracking and EDS elemental analysis,NFC and mica were uniformly distributed in AMN paper-based composites,indicating that NFC was used as carrier/adhesion polymer,and favored well-ordered biomimetic multilayer structure.And adding a small amount of NFC is beneficial to form a single network multi-layer(SNM)structure,and the high addition of NFC helps to form a common continuous double network multi-layer(DNM)structure.At the same time,a small amount of NFC led to a single-network multilayer structure while high amount addition of NFC was favorable for a co-continuous double network multilayer structure.Finally,nano-fibrillation and hydrothermal treatment were combined to modify aramid fiber in order to obtain nano-aramid fiber(ANF).In addition,the various amounts of ANF was introduced into paper-based composite to improve the structure and properties of ANF-NFC/Mica paper-based composite.The results showed that there were some-COOH groups on the surface of the modified ANF,which was beneficial to its dispersion in the aqueous solution.Also,ANF tended to form physical interweaving and hydrogen bonding with NFC,and synergistically enhanced the mechanical and dielectric properties of AMN paper-based composite.Compared with ANM-0,ANM-3 paper-based composite showed excellent tensile strength(28.8 MPa)and dielectric breakdown strength(32.8 kV/mm),which increased by 111.8%and 63.1%than that of ANM-0.In addition,the dielectric constant and dielectric loss of ANM-3 paper-based composite had little change with the increase of temperature at the frequencies of10~5 Hz and 10~6 Hz,which maintained within 5.5-6.0 and 0-0.05,indicated ANM-3 paper-based composite process a good dielectric-temperature stability.