Functionalization Of Partially Unzipped Carbon Nanotubes And Preparation Of Its Composite Fibers With Polyimide

As an important member of high-performance fibers,polyimide(PI)fiber is widely used in many application fields,such as high temperature filtration,flame retardant protection,fiber reinforcement and electromagnetic shielding.However,due to the limitation of the polymer synthesis and fiber formation process,the properties of PI fiber especially the mechanical properties are hard to be improved.So increasing the properties of PI fiber by its modification is of great practical significance,and addition of reinforcements,as an efficient and economical approach,has been widely studied in recent decades.Particularly,carbon nanotubes(CNTs)and graphene attracted people’s great attentions for their unique performance.The majority of the research efforts has been concentrated on the reinforcement of either CNTs or graphene to polymer matrix,but researchers showed more interest in the synergetic reinforcement of CNTs and graphene on polymer in recent years.Partially unzipped carbon nanotubes(PUCNTs)possess both large specific area of graphene and high aspect ratios of CNTs,and therefore are quite suitable to be used as reinforcements of polymer fibers.In this work,PUCNTs were prepared by longitudinally unzipping the outer wall of multi-wall carbon nanotubes(MWCNTs)and then were modified to form functionalized PUCNTs(f-PUCNTs)which provide reaction sites for the covalent connection with polyamide acid(PAA)matrix.Finally,a series of f-PUCNTs/PI composite fibers were prepared by wet spinning and thereafter heat treatment.The structure of f-PUCNTs and the properties of the composite fibers were discussed.The main research contents and conclusions are as follows:1.PUCNTs which contain outer-wall graphene and inner-wall CNTs were successfully prepared by longitudinally unzipping MWCNTs,and 4,4′,4"-triaminotriphenylamine(TAPA)reacted with the oxygen-containing groups of outer-wall graphene to form f-PUCNTs,which was done for the first time.Then the reaction of unzipping and the functionalization,the structure,the dispersibility and the surface topography were studied,respectively.f-PUCNTs showed distinctly improved dispersibility in DMAc solution,and the outer-wall graphene and the inner-wall CNTs exhibited strong interface interaction between each other.2.The f-PUCNTs/PAA composite solutions prepared by using in situ polymerization were wet-spun to obtain composite fibers which were finally transferred into f-PUCNTs/PI composite fibers after heat treatment.The mechanical properties of the composite fibers were focused on in the discussion,and the thermal properties of the composite fibers were also investigated.f-PUCNTs possessed both large specific area of graphene and high aspect ratios of CNTs,which benefited not only to the interaction between f-PUCNTs and polymer matrix,but also to orientation of f-PUCNTs in composites.Moreover,the interaction was beneficial to the stress transfer from the matrix to f-PUCNTs.With the increase of the dosage of f-PUCNTs,the mechanical properties of f-PUCNTs/PI composite fibers increased at first and then decreased,and reached the maximum at a dosage of 1.0 wt%.The tensile strength and Young’s modulus of f-PUCNTs/PI composite fiber containing 1.0 wt%f-PUCNTs were165%and 208%those of PI fiber,respectively,and were 137%and 153%those of the composite fiber containing the same amount of PUCNTs,respectively.Moreover,5%weight loss temperature and glass transition temperature of 1.0 wt%f-PUCNTs/PI composite fiber were 50 ~oC and 13 ~oC higher than those of PI fiber,respectively.