Preparation of shape memory NiTiNOL filaments for smart textiles

Abstract

A nickel-titanium alloy (NiTiNOL, nitinol) filament with a diameter of 200 μm was used for preparing a smart knitted textile fabric with a shape memory effect within the range of human body temperatures. The annealing of the filament at 500 °C for 30 minutes was followed by air cooling at 20 °C to achieve a suitable transition temperature from martensite to austenite phase within the range between room temperature and 75 °C. The tensile properties of filaments before annealing and after it were analysed on Instron 6022 dynamometer. The measurements of exact transition temperatures from soft martensite state at room temperature to hard austenite state at heating were made on a dynamic mechanical analysis instrument. From the annealed filament a left-right knitted fabric was hand made. The fabric was trained into a selected 3D form by cyclic heating in a strained form at 75 °C for 10 minutes and then cooled at room temperature. For a stable two-way memory effect, the nitinol fabric needed to make fifteen cycles of heating and cooling.