Preparation And Tribological Performance Of Functionalized Carbon-based Modified Polyimide Composite Films

Polyimide(PI)is widely used in many fields due to its excellent properties.However,with development of technology,pure PI is difficult to meet requirements of high precision,load,temperature and wear resistance.The addition of fillers to PI matrix is an effective way to improve its performance.Graphene nanosheets(GNS)and multi-walled carbon nanotubes(MWCNT)have excellent physicochemical properties and are often used as reinforcement filler to modify polymers,but ease of agglomeration of GNS and MWCNT in polymers and weak interaction with polymer interfaces limits their application.In this paper,GNS and MWCNT were first modified by two different chemical modification methods to study their effect as reinforcing fillers on properties of PI composites.Then hybrid materials of graphene and multi-walled carbon nanotubes(GNS/MWCNT)were modified by Friedel-Crafts reaction,and the friction characteristics of PI composites with modified GNS/MWCNT were investigated.The main research contents are as follows:(1)Amimophenyl-functionalized graphene nanosheets(AGNS)was successfully prepared by condensation reaction and nitroreduction using GNS.Novel polyimide/amimophenyl-functionalized graphene nanosheets(PI/AGNS)nanocomposites were synthesized by in-situ polymerization using AGNS as nanofiller.The amimophenyl-functional groups introduced on surface of AGNS formed covalent bonds with carboxyl groups of polyamic acid(PAA),which avoid mentioned agglomeration of GNS in PI matrix.The tribological properties of PI/AGNS nanocomposites were investigated and found that addition of AGNS improved wear resistance of PI/AGNS nanocomposites.Simultaneously,PI/AGNS nanocomposites demonstrated lower friction coefficient and wear rate under seawater than that under dry friction conditions.In addition,compared with pure PI,mechanical and thermal properties of PI/AGNS nanocomposites have been improved to varying degrees.(2)Amine-functionalized multi-walled carbon nanotube(AMWCNT)was successfully obtained by Friedel-Crafts reaction using MWCNT.Novel polyimide/amine-functionalized multi-walled carbon nanotube(PI/AMWCNT)nanocomposites were synthesized by in-situ polymerization using AMWCNT.The amine-functional groups grafted on surface of AMWCNT can react with carboxyl groups of PAA to form strong chemical covalent bonds,which enhanced interfacial adhesion between AMWCNT and PI.Moreover,PI/AMWCNT nanocomposites exhibit superior tensile strength,degradation temperature and abrasion resistance compared to pure PI.Due to lubrication of seawater,PI/AMWCNT displayed lower friction coefficient and wear rate under seawater than that under dry friction.(3)Amine-functionalized graphene/multiwalled carbon nanotube(AGNS-MWCNT)hybrids were successfully prepared by Friedel-Crafts reaction using GNS/MWCNT.Novel polyimide/amine-functionalized graphene/multiwalled carbon nanotube(PI/AGNS-MWCNT)nanocomposites were synthesized by in-situ polymerization using AGNS-MWCNT hybrids.The presence of amine-functional groups on surface of AGNS-MWCNT hybrid improved dispersion of AGNS-MWCNT in PI matrix and enhanced interfacial interaction between two phases.The mechanical,thermal and tribological properties of PI/AGNS-MWCNT nanocomposites were investigated.The results showed that addition of AGNS-MWCNT hybrid fillers effectively enhanced comprehensive properties of PI/AGNS-MWCNT nanocomposites compared with pure PI.Due to synergistic effects between GNS and MWCNT,tensile properties and thermal stability of PI/AGNS-MWCNT nanocomposites are better than those of PI/AGNS and PI/AMWCNT nanocomposites reinforced by single filler.At the same time,AGNS-MWCNT hybrid combines excellent properties of AGNS and AMWCNT and significantly improved the wear resistance of PI.Compared with dry friction,lubricating performance of seawater reduced friction coefficient and wear rate of PI/AGNS-MWCNT nanocomposites during friction and improved antifriction resistance of PI/AGNS-MWCNT nanocomposites under seawater condition.