A remarkable mechanical property of 5wt% acid-treated MWCNTs/UHMWPE nanocomposite fiber have been fabricated with the modulus and the strength of the fibers enhanced to 137 GPa and 4.2 GPa respectively, which are the best specific mechanical properties among the current commercial fibers. An extensive TEM analysis was carried out to study the mechanisms of microstructures formation and the reinforcements....[ Read more ]

A remarkable mechanical property of 5wt% acid-treated MWCNTs/UHMWPE nanocomposite fiber have been fabricated with the modulus and the strength of the fibers enhanced to 137 GPa and 4.2 GPa respectively, which are the best specific mechanical properties among the current commercial fibers. An extensive TEM analysis was carried out to study the mechanisms of microstructures formation and the reinforcements.

The change of CNTs dispersion and alignment, PE morphology and CNTs/PE interface was studied by in situ observations on the TEM micrographs after each process. CNTs dispersion and alignment, PE chains orientation and crystallinity of CNTs/PE interface increase with draw ratio (DR). The relationships between them were investigated and concluded the mechanisms of CNTs alignment and dispersion. During the hot-drawing, the crystallinity of interfacial PE increases first, then loads transfer from the PE matrix to the CNTs cluster for pulling out and orienting the single CNT through a good adhesion interface.

The mechanical properties of composite fibers at different DRs were tested to characterize the relationship between the morphologies and mechanical properties of fibers for studying the reinforcement mechanisms. There are three different mechanical enhancements of 5 wt% MWCNTs/UHMWPE composites fibers comparing with the pure UHMWPE fibers at different DRs. At low DRs, the toughening effect with higher EAB is due to the present of relatively elastic “absorption layers” around the CNTs clusters. At middle DRs, the “bottle-neck regions” are relatively soft regions which cannot support enough force for load transfer. So the addition of MWCNTs causes no/reverse mechanical effect. At high DRs, homogenous high crystallinity PE matrix is strong enough for load transfer from PE matrix to MWCNTs. And at such high DRs, isolated MWCNTs align perfectly along the fiber axis. The degree of MWCNTs dispersion and alignment reaches the maximum which benefit the mostly even stress distribution in the matrix and the large amount load transfers to CNTs. This is the most reasonable explanation for excellent mechanical properties of highly oriented nanocomposite fibers at DR of 30.