Functional Carbon Nanotubes,Graphene-reinforced Polyamide 66 Fibers

Nanocarbon materials,i.e.one-dimensional carbon nanotubes(CNTs)and two-dimensional graphenes(GNs),have been considered as ideal nanomaterials for reinforcement and functionalization of polymers due to their outstanding mechanical,electrical and thermal properties.However,as the sp~2 hybrid carbon atoms form a six-membered ring structure,and each carbon atom has a 2p orbital with a 2p electron in it.Also,these p orbitals are parallel to each other and perpendicular to the plane formed by sp~2 hybridization orbitals of carbon atoms,and thus forming largeπbonds.The formation of largeπbonds leads to strong van der Waals forces and super-strongπ-πinteraction between graphene surfaces.As a result,CNTs and GNs generally tend to agglomerate in polymer matrix and reduce the specific surface area between the carbon nanomaterials and the polymer matrix.Furthermore,due to the chemical inertia of CNTs and GNs,they cannot form strong interfacial adhesion with polymer matrix.Therefore,the poor compatibility of these carbon nanomaterials with polymer matrix result in stress concentration,which will in turn lower the performance of polymer nanocomposites.Recent years,many methods have been reported to improve the dispersion and compatibility of carbon nanomaterials in polymer matrix,which can be generally divided into mechanical dispersion and chemical dispersion.Mechanical dispersion usually improves the dispersion of carbon nanomaterials in the polymer matrix by means of mechanical stirring,ball milling,sonication,etc.,but such methods have low dispersion efficiency and thus are not conducive to the dispersion of carbon nanomaterials in target medium.Chemical dispersion usually uses covalent modification and non-covalent modification to modify carbon nanomaterials to improve their compatibility and dispersion in polymer matrix.However,most of the chemical dispersion methods reported in the literature rely on weak interactions,such as hydrogen bonding and van der Waals forces,to improve the interfacial interaction between carbon nanomaterials and polymer matrix.Moreover,the large size of carbon nanomaterials prevents their further uniform dispersion in polymer matrix.Therefore,these dispersion methods cannot efficiently improve the mechanical properties of polymer nanocomposites.In addition,chemical modification will destroy the inherent structure of carbon nanomaterials,and it will consume a large number of solvents and monomers,and the operation is complex,which is not suitable for industrial production.Therefore,the existing research on dispersion technologies of carbon nanomaterials is not enough to solve the problems encountered in production,and further research is needed.To solve these problems,in the process of preparing poly(hexamethylene adipamide)(PA66)based nanocomposites,carbon nanomaterials are functionalized by using mild reaction conditions,environmentally friendly condensation reaction and Diels-Alder reaction,which are less destructive to the inherent structure of carbon nanomaterials;reducing the size of carbon nanomaterials using high-power ultrasonic treatment systems;the carbon nanomaterials of different dimensions are mixed in a certain proportion,so that they are mutually constrained to achieve the purpose of synergistic dispersion.The three methods mentioned above effectively improve the dispersion and compatibility of carbon nanomaterials in PA66 matrix.Subsequently,the carbon nanomaterials reinforced PA66 nanocomposites are prepared by in-situ polymerization.The carbon nanomaterials form covalent connection with polymer matrix,which improves the interface interaction between them.Finally,high performance nanocomposite fibers are prepared by melt spinning.The main contents are summarized as follows:(1)In this work,functional carbon nanomaterials(FMWNTs)were prepared by ethylenediamine(EA),maleic acid diamine(MAD)and 3-aminopropyl-terminated poly(dimethylsiloxane)(APDMS)functional groups grafted onto the carboxylic multi-walled carbon nanotubes(CMWNTs)and multi-walled carbon nanotubes(MWNTs)by condensation reaction and Diels-Alder(D-A)reaction.The dispersion of FMWNTs in PA66 matrix was significantly improved by in-situ polymerization,and the interfacial adhesion between them was enhanced.Therefore,the mechanical properties of the nanocomposite fibers are obviously enhanced.Compared with EA and APDMS modified CNTs,the tensile strength and Young’s modulus of the nanocomposite fibers fabricated using MAD modified CNTs,which are 611 MPa and 7.4 GPa,respectively.(2)Small size GNs were prepared by high power ultrasonic processing system,mixed with MWNTs in a certain proportion and added to the hexanediamine adipate salts.PA66/GNs/MWNTs nanocomposites were fabricated by in-situ polymerization and the resultant was melt-spun into fibers.The results show that the mixture of MWNTs and GNs exhibits good dispersion in the PA66 matrix when the ratio of GNs to MWNTs is 1:1.The tensile strength and Young’s modulus of the PA66/GNs/MWNTs nanocomposite fibers are 703 MPa and 9.4 GPa as the total proportion of MWNTs and GNs is 0.5 wt.%,respectively.The mechanical properties of the nanocomposite fiber are significantly improved compared with the nanocomposite fiber by adding only single carbon nanomaterials.(3)Combining the advantages of small size,covalent modification and synergistic dispersion,PA66-F-GO-F-CMWNTs nanocomposite fibers were prepared by in-situ polymerization and melt spinning using melamine(M)functionalized graphene(F-GO)and MWNTs(F-CMWNTs)as reinforcing fillers.The PA66-F-GOs-F-CMWNTs nanocomposite fibers have better mechanical properties when the total proportion of F-GO and F-CMWNTs is 0.5 wt.%,especially when the ratio of F-GO to F-CMWNTs is1:1.The tensile strength and Young’s modulus of the fabricated nanocomposite fibers are 728 MPa and 9.6 GPa,respectively.The mechanical properties of the fabricated nanocomposite fibers are more superior to those of nanocomposite fibers with both GNs and MWNTs.The formation of the three-dimensional network structure of the functionalized carbon nanomaterials significantly promotes load transfer of nanofillers in the polymer matrix,which proves that the addition of different dimensional carbon nanomaterials plays a synergistic strengthening role,so the high-performance polymer nanocomposites are obtained.This study has important guiding significance for further expanding the application field of carbon nanomaterials reinforced polymer nanocomposites.