| A dual inclusion strategy for textile polymers has been investigated to increase elastic energy storage capacity of fibers used in high velocity impact applications. Commercial fibers such as Spectra and Dyneema are made from ultra high molecular weight polyethylene (UHMWPE). Dynamic elastic energy of these fibers is still low therefore limiting their wholesale application without a secondary metallic or ceramic component. The idea in this investigation is to develop methodologies so that the elastic energy of polyethylene based fibers can be increased by several folds. This would allow manufacturing of an all-fabric system for high impact applications.;The dual inclusion consists of a polymer phase and a nanoscale inorganic phase to polyethylene. The polymer phase was nylon-6 and the inorganic phase was carbon nanotubes (CNTs). Nylon-6 was blended as a minor phase into UHMWPE and was chosen because of its large fracture strain -- almost one order higher than that of UHMWPE. On the other hand, CNTs with their very high strength, modulus, and aspect ratio, contributed to sharing of load and sliding of polymer interfaces as they aligned during extrusion and strain hardening processes.;A solution spinning process was developed to produce UHMWPE filaments reinforced with CNTs and nylon-6. The procedure involved dispersing of CNTs into paraffin oil through sonication followed by dissolving polymers into paraffin-CNT solution using a homogenizer. The admixture was fed into a single screw extruder for melt mixing and extrusion through an orifice. The extrudate was rinsed via a hexane bath, stabilized through a heater, and then drawn into a filament winder with controlled stretching. In the next step, the as produced filaments were strain-hardened through repeated loading unloading cycles under tension. Neat and reinforced filaments were characterized through DSC (Differential Scanning Calorimetry), XRD (X-ray Diffraction), Raman Spectroscopy, SEM (Scanning Electron Microscope), and mechanical tests. Phenomenal improvement in properties was found; modulus, strength, fracture strain, and elastic energy increased by 219%, 100%, 107%, and 88%, respectively before strain hardening. Once strain hardened the strength, modulus and elastic energy increased by almost one order of magnitude. Source of these improvements were traced to increase in crystallinity and rate of crystallization, formation of microdroplets as a minor phase, sliding between minor and major phases, coating of nanotubes with polymer and alignment of nanotubes. |
