Study On The Alkylation Of Aramid Nanofibers And Their Properties

Aramid nanofibers?ANFs?is a kind of one-dimensional nanomaterials with similar form of carbon nanotubes with high-strength.ANFs are considered as essential "building blocks" of the nanoscale toolset and possess equally high or better properties of macroscale PPTA fiber.While,the present applications of ANFs are limited to the reinforcement of those polymer that contain similar structures or groups that can be acted with ANFs.In order to overcome this constrain,broaden its application to non-polar or weakly polar polymers such as PE,PP and PVC materials of wide use,this paper proposes design ideas for functionalizing the surfaces of ANFs with different chain length of alkyl groups,while turning its surface to be electrically neutral,changed the polarity of the material surface,increasing its affinity with the interface of the weakly polar polymer matrix,and realizing the application of aramid nanomaterials in the field of weakly polar polymer materials such as PVC.In this paper,the amide groups of PPTA can be deprotonated in DMSO/KOH firstly to obtain ANFs.TEM showed that ANFs were fibrous,with a diameter of about25 nm,and they were intertwined with each other into network structure.Then,the surface of ANFs were functionalized moderately and controllably with five types of bromoalkanes?bromoethane,1-bromobutane,1-bromohexane,1-bromooctane,and1-bromododecane?.By controlling the molar ratio of brominated alkanes and amide groups in ANFs,30 kinds of resulting alkyl-derivatized aramid nanomaterials?R-ANMs?with different surface properties and morphologies were prepared.The products were characterized through EA,FT-IR and XRD.TEM showed that R-ANMs had different morphological characteristics,with the change of the alkyl functional group chain length and the degree of substitution?DS?,R-ANMs maintained the nanofibrous form no longer,but gradually appeared short nanofibers,nanobranches,nanospheres,nanosheets and other different forms.Subsequently,this work selects a common polymer material—PVC polymer as the matrix,exploring the interface mechanism between the obtained R-ANMs and the PVC matrix as well as the influence rules of different forms of R-ANMs on the mechanical properties of PVC.Represented by a series of bromoethane modified?ANMs-C₂H₅-X?,octyl bromide modified(ANMs-C₈H₁₇-X)and dodecyl bromide modified(ANMs-C₁₂H₂₅-X)aramid nanomaterials,which were added to the PVC matrix as reinforcing phases,mainly including:?1?Research on dispersibility of R-ANMs.Experiments showed that R-ANMs can be uniformly dispersed in common organic solvents.Compared with unmodified ANFs,its solvent selection range was wide,and DMF was the ideal dispersion solvent.?2?Preparation and characterization of R-ANMs/PVC composite films.A simple solution mixing method was adopted,and 108 kinds of R-ANMs/PVC composite films were prepared through changing the weight ratio of the three R-ANMs.FT-IR confirmed the existence of hydrogen bonding between R-ANMs and PVC matrix.SEM showed that the addition of R-ANMs results in the fracture morphology to change from flattening to tensile deformation compared with pure PVC film.?3?Testing of mechanical properties of composite films.Mechanical property test of three kinds of R-ANMs/PVC composite films demonstrated that ANMs-C₁₂H₂₅-X/PVC composite films have the excellent reinforcement effect,with a maximum tensile strength of 44.27 MPa,a maximum toughness of 99.72 N/mm² and a maximum Young's modulus of 2057.38 MPa,which was 96.15%,236.78%and 57.91%higher than pure PVC respectively.Among them,the toughness increasing was the most significant,showing its great application potential as a nano-toughener.The research in this paper wides the application of ANFs to the field of non-polar/weak polar polymers,and at the same time provides new ideas and important theoretical guidance for the development of new nano-functional materials based on aramid.