Study On Modification Of Polyimide Fiber With Nanosilica And The Properties Of Its Paper-based Materials

Polyimide(PI)fiber exhibits numerous excellent properties such as excellent mechanical properties,thermal stability and insulation with light-weight,so it can be widely applied in many fields including aerospace,national defense and satellites communication,transportation and electricity.However,PI fiber shows apparent isotropy,rigid molecular chain and stable properties,which leads to surface passivation,shortage of active groups,weak hydrophilicity on PI fiber and poor sheet formation.Hence,modification of PI fiber can be used to improve surface activity and the integrated performance of its paper-based materials.Researchers pay more attention to modify PI fiber in synthetic process,but surface modification on PI fiber is few at home and abroad.Firstly,the morphology parameter,chemical structure and thermal stability of PI fiber and p-aramid fibrid were analyzed,which would provide the theoretical basis for the preparation of polyimide fiber paper-based material and its property analysis.The results showed that PI fiber had smooth surface,no hydrophilic groups,uniform length,a small amount of micro fibers and longer than wood fiber,which led to flocculation of PI fibers in water phase.There existed unique tertiary amide group in the molecular chain of PI fibers,its initial decomposition temperature was 530?,TG10% was 560? and the loss of PI fiber was 45.19%.P-aramid fibrid had apparent fibrillation,light and soft,good water absorption and dispersion,and the content of micro fibers was 35.3%.There exsited secondary amide group in the molecular chain of p-aramid fibrid,its initial degradation temperature was 500?,TG10% was 525? and the loss of PI fiber was 54.02%.Secondly,PI fiber was modified with ethanediamine,and the morphology,chemical structure,thermal stability and mechanical,dielectric properties and wettability of its paper-based materials were analyzed after modification.The results showed that the tensile index,tearing index,interlayer bonding strength and dielectric strength of PI fiber paper-based material appeared an increasing trend initially,then declined.The tensile index,internal bonding strength and dielectric strength of paper sheet all reached maximum and the figures were 37.4 N?m/g,0.57J/m2,8.77Kv/mm respectively when the modifying time was 4h,the maximum of tearing index of paper sheet was 22.1 mN?m2/g when the modifying time was 2h.FT-IR spector showed that the peak intensity of tertiary amide group weakened and appeared the absorption peak of secondary amide group and N-H bonding in the molecular chain of ethanediamine at 1650cm-1,1550cm-1 and 3500-3000cm-1.The wettability of PI fiber paper-based material improved and the contact angle decreased from 116°to 66.8°.TG-DSC curves showed that the initial decomposition temperature decreased from 530? to 480?,TG10% also decreased from 560? to 515??Thirdly,the mechanical and dielectric properties of PI fiber paper-based material were enhanced by adding nanosilica.The tensile index and dielectric strength of paper sheet all reached maximum and the figures were 32.6N?m/g,8.45Kv/mm respectively,while the dielectric contant and dielectric loss were minimum,with 1.02 F/m and 0.1429 respectively when the dosage of nanosilica was 10%,and the maximum of tearing index of paper sheet was 23.9 mN?m2/g when the dosage of nanosilica was 20%.The tensile index,tearing index and dielectric strength improved by 32.8%,28.4%,17.5% after adding nanosilica modified with KH550.SEM images showed that the nanosilica presented good dispersion in the sheet structure when its content was less than 10%,while it appeared severe flocculation when the content of nanosilica was more than 10%.The wettability of PI fiber paper-based material improved by adding nanosilica modified with KH550 and the contact angle decreased from 116°to 51°?Finally,PI fiber was modified with nanosilica by in situ deposition,and the morphology,chemical structure,thermal stability,mechanical,dielectric properties and wettability of its paper-based materials were analyzed after modification.The results showed that the tensile index,tearing index,internal bonding strength and dielectric strength of PI fiber paper-based material appeared an increasing trend initially,then declined.The tensile index,internal bonding strength and dielectric strength of paper sheet all reached maximum and the figures were 31.3 N?m/g,0.42J/m2,11.24Kv/mm respectively when the modifying time was 4h,the maximum of tearing index of paper sheet was 20.4 mN?m2/g when the modifying time was 2h.SEM-EDS images showed that numerous nanosilica deposited on PI fiber.FT-IR spector showed that the peak intensity of tertiary amide group weakened and appeared the absorption peak of secondary amide group,hydroxyl group and C-O-Si bonding at 1650cm-1,1550cm-1,3200-2500cm-1 and 1073cm-1 respectively.The wettability of PI fiber paper-based material improved and the contact angle decreased from 116°to 78 °.TG curves showed that thermal stability of PI fiber weakened after pretreatment with alkali and acetic acid,surprisely,it improved with the increase of nanosilica on PI fiber.