Abstract
We have investigated strain hardening behavior of ultrahigh molecular weight polyethylene (UHMWPE) reinforced with 2.0 wt% loading of multiwalled carbon nanotubes (MWCNTs). A solution spinning process was used to produce neat and MWCNT-reinforced filaments of UHMWPE. Tensile tests of filaments showed 62% and 114% improvement in strength and modulus, respectively. Strain hardening tests on filaments revealed spectacular contribution by MWCNTs in enhancing strength and modulus by more than one order of magnitude. SEM micrographs showed sufficient coating of nanotube surface with the polymer that promoted interface adhesion. This intimate interfacial interaction enforced alignment of nanotubes during repeated loading-unloading sequences and allowed effective load transfer to nanotubes. Close interaction between UHMWPE and nanotubes was further evidenced by Raman spectral distribution as a positive shift in the D-band suggesting compressive stress on nanotubes by lateral compression of polymer. Nanotubes thus deformed induced the desired strain hardening ability in the UHMWPE filament. Differential scanning calorimetry (DSC) tests indicated around 15% increase in crystallinity after strain hardening—which together with nanotube alignment resulted in such dramatic improvement in properties.
Highlights
ultrahigh molecular weight polyethylene (UHMWPE) is regarded as one of the most promising high performance fibers because of its low density, excellent strength to weight ratio, and outstanding impact property
At identical draw ratio (∼30) the strength and modulus of UHMWPE can be increased by 19% and 12%, respectively when, reinforced with 5 wt% of multiwalled carbon nanotubes (MWCNTs) [5]
Once we found a workable concentration of MWCNTs at 2.0 wt%, and a good improvement in properties was achieved, we concentrated on evaluating the strain hardening behavior
Summary
UHMWPE is regarded as one of the most promising high performance fibers because of its low density, excellent strength to weight ratio, and outstanding impact property. Applications of this fiber have significantly increased in recent years in defense industries in manufacturing light weight ballistic plates, bulletproof helmet and vest, and shielding for armored vehicles. Strain hardening sequences of repeated loading and unloading are effective mechanisms to enhance tensile properties by uniaxially arranging the polymer chains and increasing the crystallinity. Strain hardening process can cause improved alignment of embedded nanotubes along the filament length Such alignment will be useful in transferring load from polymer chains to nanotubes. Details for filament fabrication, strain hardening experiments, and morphological characterizations are described
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