Shape Memory Polymers(SMP)
These types of materials can revert from the current shape to a previously held shape, usually due to the action of heat. This technology has been extensively pioneered by the UK Defense Clothing and Textiles Agency. When these shape memory materials are activated in garments, the air gaps between adjacent layers of clothing are increased, in order to give better insulation. The incorporation of shape memory materials into garments thus confers greater versatility in the protection against extremes of heat or cold.
Shape memory alloys, such as nickel-titanium, used to provide increased protection against sources of heat, even extreme heat. A shape memory alloy possesses different properties below and above the temperature at which it is activated. Below this temperature, the alloy is easily deformed. At the activation temperature, the alloy exerts a force to return to a previously adopted shape and becomes much stiffer. The temperature of activation can be chosen by altering the ratio of nickel to titanium in the alloy.
Cuprous-zinc alloys are capable of a two-way activation and therefore can produce the reversible variation needed for protection from changeable weather conditions. They will also react to temperature changes brought about by variations in physical activity levels.
A shape memory alloy is usually in the shape of a spring.
flat below the activation temperature but becomes extended above it. By incorporating these alloys between the layers of a garment, the gap between the layers can be substantially increased above the activation temperature. In consequence, considerably improved protection against external heat is provided.
For clothing applications, the desirable temperatures for the shape memory effect to be triggered will be near body temperature. Polyurethane films, which can be incorporated between adjacent layers of clothing. With temperature of the outer layer of clothing has fallen sufficiently, then polyurethane film responds so that the air gap between the layers of clothing becomes broader. Bi-Material Film laminates rely on differing coefficients of thermal expansion to produce a reversible bending effect. Encapsulated Bi-Gels absorb liquid at differing rates according to temperature, which causes them to bend used to actuate variable insulation system. Other uses of SMPs in domestic purpose are in shower mixer valves, coffee makers, rice cookers, safety shut off valves for fuel lines in the event of fire and in air conditioning systems.
