Edinburgh Napier University

  The influence of the concentration of a commercial photochromic dye, incorporated into as-spun and drawn fibres produced from polyethylene and polypropylene, on their mechanical properties was investigated. As-spun fibres were produced by incorporating a commercial photochromic dye at different concentrations at the extrusion stage of the production process of polypropylene, polyethylene and polyester. The fibres from polypropylene and polyethylene, which showed photochromism when exposed to UV light, were then drawn, and their mechanical properties evaluated and analysed using a factorial experimental design, applying appropriate statistical methods. No further investigation was carried out on the polyester as the dye appeared to degrade at the higher temperatures required for its extrusion, leading to a brown fibre, which was not photochromic. According to the analyses, the most significant parameter influencing the mechanical properties of the as-spun fibres was the polymer type; the effect of the dye concentration was dominated by the significance of the polymer type. The effects of the multi-stage hot-drawing process used to produce the fibres on the mechanical properties of the drawn polypropylene and polyethylene fibres were characterised and statistically modelled. It was found that the dyeing concentration had a negative effect on the tenacity and the modulus of the drawn polypropylene fibres but a positive effect on the tenacity and the modulus of the drawn polyethylene fibres. A dye concentration of 0.2% on mass of polymer had a positive effect on the elongation of the drawn polypropylene and polyethylene fibres, whereas the higher dye concentration of 0.4% had a negative effect on the elongation of both drawn fibres. A new forecasting data source was obtained to optimise the selection of the polymer and the dye concentration and to specify the direction of modification, either increasing or decreasing, the significant process parameters.