An investigation of the mechanical and biological properties of nylon coated ultra-high-molecular-weight polyethylene

In spite of considerable improvements in the manufacturing of body armor using lightweight and high-strength fibres, demands for lighter and more flexible products capable of providing sufficient protection against various types of threats has not waned. Among high strength fibres, ultra high molecular weight polyethylene (UHMWPE) possesses superior mechanical and physical properties. Nevertheless, the use of UHMWPE fabric with a shear thickening fluid (STF) materials for the manufacture advanced liquid body armors has been unsuccessful as this polymer is inherently inert and cannot bond or readily interact with other materials. To address these challenges, this research thesis focused on the development of a new method to increase the performance of UHMWPE fibre/fabric for high impact applications and improve its capability to bond with silica-based STF materials. A novel coating technique was developed using a nylon solution with UHMWPE fibre which results in a strong interlocking mechanism and the creation of a uniform coating without adding extra thickness to the fibre. Standard penetration tests showed considerable improvement in puncture/stab resistance of a nylon coated UHMWPE fabric compared with the uncoated fabric (with equivalent areal density) in terms of energy absorption, which was also explained by the scanning electron microscope (SEM) images of ruptured areas. In order to further improve the penetration resistance of UHMWPE fabric, a dispersion of fumed silica particles in polyethylene glycol (PEG) was synthesized exclusively via a novel sequential ultrasonication technique to incorporate with a multilayer stack of UHMWPE fabric. A complete set of rheological measurements, zeta potential and SEM analysis were done to study the viscoelastic characteristics and tune the stability of the synthesized STF samples. Evidence of the improved adhesion of STF materials to UHMWPE fibres coated with nylon from the SEM images was observed. Finally, while the evidence of improved mechanical properties of nylon coated UHMWPE were provided (e.g. higher creep resistance and toughness), its potential application for the manufacturing of medical devices was also explored. As a result, from the preliminary cytotoxicity and osteolysis assessments, it was shown that the biological compatibility of UHMWPE was improved when it was coated with nylon.