High-performance ultrahigh molecular weight polyethylene (UHMWPE) fibers are the most preferred ballistic-proof fibers for using in the manufacture of body amours due to their high ductility and low density. In this study 5wt% acid-treated multi-walled carbon nanotube (MWCNT) have been adopted as the fillers and successfully developed a gel-spinning process using twins-extruder for fabricating highly oriented MWCNT/UHMWPE composite fibers. 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.

Systematic investigations were carried out to understand reinforcement mechanisms at different draw ratios by microstructure evolution and load transfers via transmission elec...[ Read more ]

High-performance ultrahigh molecular weight polyethylene (UHMWPE) fibers are the most preferred ballistic-proof fibers for using in the manufacture of body amours due to their high ductility and low density. In this study 5wt% acid-treated multi-walled carbon nanotube (MWCNT) have been adopted as the fillers and successfully developed a gel-spinning process using twins-extruder for fabricating highly oriented MWCNT/UHMWPE composite fibers. 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.

Systematic investigations were carried out to understand reinforcement mechanisms at different draw ratios by microstructure evolution and load transfers via transmission electron microscopy (TEM) and micro-Raman spectroscopy respectively. Three distinct mechanistic behaviors were concluded: (1) At low draw ratios, the dispersed CNTs were in the form of ellipsoidal nanoclusters with a thin UHMWPE absorption layer of lower crystallinity. UHMWPE molecules within the absorption layer were highly mobile, and exhibited larger elongation strain than those in the matrix whilst transferring the load between the matrix and the dispersed CNT clusters. Hence, the presence of CNTs led to a significant toughening effect. (2) At intermediate draw ratios, single CNT fibers were pulled out from the CNT clusters and the clusters formed a “tadpole” structure. In the meantime, the composite became highly inhomogeneous around the CNT clusters. The absorption layer behind the head of the “tadpole” remained at low crystallinity and poorly aligned, but those around the tales disappeared. Chains in the absorption layer formed the “bottleneck” zone during loading, and the CNT clusters effectively acted as defect centers within the composite fiber. Consequently, an adverse effect was observed with the incorporation of CNTs. (3) At high draw ratios, most of the CNT fibers were pulled out from the CNT clusters and aligned nearly perfectly along the fiber axis. The UHMWPE matrix showed uniform crystalline morphology both in the vicinity and away from the CNT clusters. Co-deformation of CNTs and the matrix was observed under micro-Raman, and hence the CNTs acted as an effective reinforcing fillers to arrested the bulk crack propagation.