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Abstract
Aramid nanofibers (ANFs) are a novel type of promising nanoscale building blocks for high-performance nanocomposites. Conventionally, ANFs are used to composite with polymers containing polar groups such as –OH and –NH2 since those polymers can interact with the amide groups in ANFs through polar-polar interaction such as hydrogen bonding. In this study, ANFs were derivatized with non-polar alkyl groups including ethyl, octyl and dodecyl groups and used as a performance-enhancing additive to polyvinyl chloride (PVC) with weak polarity. Interestingly, it was observed that the morphologies of the resulting alkyl-derivatized aramid nanomaterials (R-ANMs) varied significantly including nanofibers, nanobranches, nanosheets, and nanospheres, all of which depended on the degree of substitution (DS) and the chain length of the alkyl group. As an additive, R-ANMs improved the Young's modulus, toughness and yield strength of the PVC films. This study proves the concept that ANFs can be used to composite weakly polar or non-polar polymers.
Highlights
Poly(p-phenylene terephthalamide) (PPTA), known by its trade name Kevlar, is a type of aromatic polyamide material with high strength, stiffness and thermal stability (Tanner et al, 1989; O’Connor et al, 2008, 2009a)
The simultaneous increases in both tensile strength and toughness of resulting alkyl-derivatized aramid nanomaterials (R-ANMs)/polyvinyl chloride (PVC) films were attributed to the following: Firstly, the alkyl group grafted on the surface of Aramid nanofibers (ANFs) could facilitate the dispersion of ANFs in the polymer matrix, which could prevent stresses concentrating at certain points
ANFs were successfully derivatized with alkyl groups by the N-substitution reaction to form R-ANMs with morphologies ranging from nanofibers to nanosheets
Summary
Poly(p-phenylene terephthalamide) (PPTA), known by its trade name Kevlar, is a type of aromatic polyamide (aramid) material with high strength, stiffness and thermal stability (Tanner et al, 1989; O’Connor et al, 2008, 2009a). Negatively charged, uniformly sized ANFs were successfully prepared in DMSO as a stable dispersion by controlled deprotonation with KOH (Yang et al, 2011). Such dispersion represents the first example of nanofiber dispersion of synthetic polymers. ANMs-C2H5-X samples with different degrees of ethyl substitution were prepared according to the methods described in Takayanagi and Katayose (1981). R-ANMs/PVC nanocomposite films were prepared by a simple solution casting method (Figure 2). The R-ANMs/PVC films were denoted as ANMs-C2H5-X/PVC, ANMs-C8H17-X/PVC, and ANMs-C12H25-X/PVC
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