Application of Nickel-Titanium alloys (NiTi-NOL) in smart textiles and clothes

Abstract

Nickel-titanium alloys (NiTi-NOLs) are responsive smart materials which change their shape and superelasticity also within the range of human body or environment temperature. By using shape memory alloys, it is possible to design and develop smart textiles and clothes with self-adapting functions for diverse fields of application - from medical textiles, personal protective equipment, interior decoration, sport textiles to geotextiles. Nitinol performs as a temperature sensor (for body and environment temperature) or as an actuator for the movement of the parts of textiles in animated kinetic dresses. A yarn core, made from pre-programmed Nitinol fibres which are less than 100 pm thick, is wrapped with textile fibres. Nitinol wires of thickness 100-300 pm and Nitinol springs are used as well. Due to low extensibility and high rigidity of Nitinol, it is difficult to bend the yarn to create loops, which makes knitting a highly demanding process. Another disadvantage of thin Nitinol fibres, in addition to the high price, is programming of the memory which is especially demanding when knitting pure Nitinol fibres. By exploiting a one-way memory of Nitinol, Velcro fasteners, self-ironing clothes, textiles which automatically regulate the body temperature or the lightening of rooms have been developed, while a two-way memory of Nitinol has been exploited in springs for self-adjustment of the firefighters suits thermo-insulating properties. Due to its superelasticity, Nitinol imparts elasticity to medical compressive stockings and self-adaptation properties to bras. The capacity of Nitinol to absorb impact energy is favourably utilized in anti-ballistic jackets.