Smart shape memory materials

Edited by Zhao Xinhua

Shape memory materials (SMMs) are smart materials that can remember and recover substan—tial programmed deformation upon activation and exposure to an external stimulus such as tempera—ture,magnetic field,electric field,pH value,and UV light.They can be used comfortably with human skin because of their low weight and softness.The appli—cation of both alloys and polymers of SMMs in textile has gained momentum to shape memory smart textiles and they have been used in many areas of textiles.The shape memory polymers have a wider application in textile applications and polymers are more advantageous than alloys in terms of their ease of use,aesthetics,and price.

Application in textile and clothing

An example of a natural shape memory textile material is cotton,which expands when exposed to humidity and shrinks back when dried.Such behavior has not been used for aesthetic effects because the changes,though physical,are generally not noticeable to the naked eye.

SMMs are useful in many technical textiles.One of the most well—known examples of SMPs is a clothing application,a membrane called Diaplex.The membrane is based on polyurethane—based SMPs developed by Mitsubishi Heavy Industries.Diaplex is laminated to the garment fabrics,which not only shows the high waterproof,but also responds intelligently to the heat released by the wearer's metabolism through the control of heat release.It is suitable for making multi—functional intelligent clothing with shape memory and can generate heat dissipation and moisture channel when the ambient temperature is high.At present,there are commercial products of this material,such as smart sportswear,mountaineering clothes,etc.

Shape memory polyurethane (SMPU) is an ex—ample of SMPs,which is based on the formation of a physical cross—linked network as a result of entangle—ments of the high molecular weight linear chains and on the transition from the glassy state to the rubberelastic state.It is a class of polyurethane that is dif—ferent from conventional polyurethane in that these have a segmented structure and a wide range of glass transition temperature (Tg).

For instance,in smart compression stocking us—ing shape memory polyurethane and nylon filaments,it allows externally controlling the pressure level in the wrapped position on the leg using the external heat stimuli.Compression stockings or bandages are the preferred choice for the management of venous ulcers and also for the prevention of recurrence ulcers.Nev—ertheless,current textile—based compression products have many shortcomings such as size fitting,and the shape control ability of the shape memory textile will promote the development of one size stocking that could be programmed to fit different leg sizes.

SMP—coated or —laminated materials can improve the thermophysiological comfort of surgical protective garments,bedding,and incontinence products because of their temperature—adaptive moisture management features.Films of SMPs can be incorporated in mul—tilayer garments,such as those that are often used in the protective clothing or leisurewear industry.The SMPs revert within a wide range of temperature.This offers great promise for making clothing with adapt—able features.Using a composite film of SMPs as an interlining in multilayer garments,outdoor clothing could have adaptable thermal insulation and be used as protective clothing.SMP membrane and insulation materials keep the wearer warm.Molecular pores open and close in response to air or water temperature to increase or minimize heat loss.

"Iron" flat clothes

SMA or SMP can be used in textile in accordance with needs for clothing and textile as fibers,yarns,and fabrics.They can be laminated,coated,foamed,and even straight converted to fibers.SMAs have some ap—plications such as in brassieres and flame—retardant laminates.

When SMAs are used in a wedding dress or cos—tume,the clothing is easy to fold during transportation and storage.Just blow it with a hair dryer before use and it will instantly return to its original shape.SMAs will also be used in scald resistant clothing,the incorpora—tion of the shape memory material into textile structure makes it possible to increase heat insulation because of the increase in the air layer thickness in the transverse direction of a flat textile fabric.With the increasing tem—perature in the layer,the air pocket expands,and then the garments of shape memory materials make the firefighter less susceptible to burn injuries.Other applica—tions include fishing yarn,shirt neck bands,cap edges,casual clothing,and sportswear.

Also,using a composite film of SMPs as an interlining provides apparel systems with variable tog values to protect against a variety of weather conditions.With the further development of currently avail—able SMPs and the emergence of new types of SMPs,the range of ap—plications is expected to expand more widely in the near future.

SMMs can be used in textile with different production methods,and their products can be made with finishing,coating,laminating,blending,and other innovative structures.SMM fabrics including wo—ven,knitted,braided,and nonwoven fabric easily returns to its original shape when heated above the switch temperature,even if it has been wrinkled or severely deformed.Therefore,the SMM fabric can be ap—plied in collars and cuffs,which need to keep their shape,and for el—bows and knees,which need to recover their shape if wrinkled.

Take the most common shape memory textile made by PTT as an example.It is a material that stimulates the function of shape memory by combining force and body temperature.It can "iron" flat clothes by body temperature or touch with hand.

As the concept of healthy life gradually becomes popular,SMM is applied to body—shaping clothes,which changes the sense of pressure of traditional shape—shaping clothes on the body.When the human body wearing no obvious sense of pressure,under the human body temperature conditions,body—shaping clothing gradually restored to the initial shape,so as to achieve perfect plasticity.Simply put,the fiber can automatically return to its original design shape at human body temperature,so it can be tailored to suit your body shape.

The product technology research and development of SMMs con—tinue to be developed,and has preliminarily realized industrialization.SMM textile and garment will be more and more popular in people's life.As a kind of smart high value—added textile fabric,SMM textiles will open up a new field for China's textile and garment industry.