(230n) Mechanical Properties of Polyhydroxyamide/Carbon Nanotube Composite Fibers: Experiment-Computation Collaborative Approach
Polymer composite fibers including carbon nanotubes (CNTs) have attracted great attention from industry and academia as a new class of composite fiber materials because of its excellent mechanical and thermal properties. CNTs have also remarkable electrical conductivity, in contrast to the commercial polymeric fibers exhibiting electrical insulation behavior. The structure and property of polymer/CNTs composite fibers are highly dependent on the amount, alignment, and dispersion of CNTs, and interfacial interaction between polymer and CNTs, which are affected not only by type, geometry and functional group of CNTs, but also by processing conditions such as spinning method and post-treatment. In particular, the interaction between polymer and CNTs is considered as a critical factor to be controlled and investigated, because it strongly influences the mechanical properties of final composite fibers. Although many experimental research results provide valuable and unique information about the structure-property relationship, it still needs to understand an atomistic-level behavior for interfacial interaction between polymer and CNTs. In order to delve the influences and reinforcing mechanism of CNTs on the mechanical properties of polymer composite fibers, in this study, polyhydroxyamide (PHA), a possible precursor which could be converted to polybenzoxazole (PBO), and multi-walled carbon nanotubes (MWCNTs) composite fibers are prepared by wet-spinning and their structural features, thermal properties and mechanical performances are then investigated as a function of various MWCNTs contents. Also, molecular dynamics simulations were performed to simulate and understand the influences and reinforcing mechanism of the CNTs on the mechanical properties of the composite fibers. In experimental results, SEM images show that the MWCNTs are well dispersed in the PHA matrix without forming aggregates. As a result, the mechanical properties such as initial modulus and tensile strength of the composite fibers were substantially enhanced compared with those of neat PHA fiber. For example, initial modulus, elongation at break, and tensile strength of the composite fibers were improved more than 19.6, 15.6, and 70.1%, respectively, by incorporating up to 2.0 wt% MWCNTs. In addition, an elastic loop test showed that the compressive strength of the composite fibers were noticeably higher than that of neat PHA fiber. The improved overall performances of the composite fibers were believed to be due to the good dispersion and specific interaction between the PHA and the MWCNTs.