Background


In the past decades, there has been growing interest in investigating the development and application of polymers with shape memory characteristic. Shape memory polymers were first developed in Japan in 1984. Shape Memory Materials are one group of very promising smart materials. They include shape-memory alloys, shape-memory ceramics and shape-memory polymers. These materials exhibit novel properties such as sensing (thermal, stress, optical, chemical), actuation, high damping, adaptive responses, super-elasticity capability and air permeability. Thus they are used in medical, textile, garments and footwear products, composites and electrical appliances.


From 1998, the many researchers started to work on the applications of shape memory polymers to smart textiles and clothing. During the past eight years, the synthesis, characterization, application, industrialization and modeling of different types of shape memory polymers such as Polyurethane, Pnipam and Polynorbornene for various purposes were carried out.


Comparatively, among all shape memory materials have limited development in apparel arid related areas. There are wider potential to apply shape memory polymer in the fields of textile and clothing such as fiber knitted and woven fabrics/garments.


In 2003, the Shape Memory Textiles Centre in The Hong Kong Polytechnic University was established and funded by the Innovation and Technology Fund of The Government of HKSAR. The shape memory fabrics were first prepared in 2003 by the project team led by Prof. Jinlian Hu of The Hong Kong Polytechnic University. In addition, the Shape Memory Fibre Spinning Laboratory in The Hong Kong Polytechnic University was also established. The relationships between synthesis procedures of shape memory polymers and the shape memory behavior of spun fibers are analyzed.


Prof. Jinlian Hu was achieved an silver award of 53rd World Exhibition of Innovation, Research and New Technology in Brussels Eureka In 2004 regarding the shape memory fabrics and their preparation methods. In 2006, she was achieved the First-Class Prize of Sang Ma Trust Fund Textile Science and Technology Award on the development of shape memory fabrics/garments.



Shape Memory Fabrics


Shape memory fabrics/garments so produced are novel fabrics which respond to the temperature stimulation. The concept of shape memory fabric is new and these fabrics were prepared by applying waterborne shape memory polymers in Polyurethane series (SMP) onto fabrics through specific finishing processes.


 

Shape Memory Polymers (SMP)


SMP generally characterized as a phase segregated statistically block copolymer having a hard segment and a soft segment. The hard segment acts as a frozen phase and the soft segment acts as a reversible phase. This frozen phase helps to memorize the original shape while the reversible phase acts as a switch responsible for shape recovering. Once the shape memory polymer is deformed, the original shape is recovered by heating the SMP at a switching temperature which equals to the melting temperature of soft segment, T ms.


Shape memory is the ability of a product to remember its original shape upon application of an external stimulus such as chemicals, temperature, or pH. A change in shape - return to the predetermined shape, caused by a change in temperature is called a thermally induced shape memory effect. To have this smart property in fabrics, a temperature sensitive shape memory polymer (SMP) is used in fabric finishing. There are 3 thermally sensitive cotton fabric shape memory effects.


Thermally Sensitive Shape Memory Effects


Flat appearance


The fabric shape memory effect of flat appearance could be defined as the ability of recovering an original flat shape from a deformed shape, after stimulation at switch temperature in different media.


Crease retention


The fabric shape memory effect of crease retention could be defined as the ability of recovering and retaining an original creased shape from a deformed shape, after stimulation at switch temperature in different media.


Bagging recovery


The fabric shape memory effect of bagging recovery could be defined as the ability of recovering an original flat shape from a deformed shape which likes a bag, after stimulation at switch temperature in different media.


Advantages:


  • Temperature Sensitive
  • Higher Fabric Breaking Strength and Tearing Strength
  • Better Washability & Performance.


Other Features


  • Different predetermined fabric shapes, e.g. flat, crease & bagging.
  • Formaldehyde level is low in fabric after SMP finishing.
  • Finishing formula can be tuned to change the shape recovering temperature of the fabric.
  • Different thermal triggering means
    • Hot water washing,
    • Tumble drying,
    • Steaming, etc.
  • Fabrics have improved color retention
  • Compatible with other softeners, whiteners, antibacterial finishings etc


In general, shape memory fabrics/garments treated with SMP were endowed with excellent hand, shape retention, dimensional stability, good durability, wrinkle free, flat appearance, bagging recovery, comfort to wear and easy care under the water and higher temperature.


 

The Application of Shape Memory Polymer on Textiles and Apparel


During application of Shape Memory Polymers on textiles and apparel, different types of shape memory polymers should be synthesized using different methods. For fabrics/ garments, different finishing methods will be used for treatment of the fabrics/garments using shape memory polymers under the different processes. For the fiber industry, they can be spun into shape memory fibers. The application fields o. shape memory polymers are:

  • Woven fabrics/ garments
  • Knitted fabrics/ garments
  • Fiber
  • Coating
  • Film
  • Intercalation


For application of Shape Memory Polymer on the fabrics/ garments to develop the smart textiles, it is a very promising area with tremendous potential that has attracted enormous attention, but technologically it is still very challenging. The important achievement and advancement in this field have been made by Shape Memory Research Groups. The applications of shape memory polymer on textiles can bring tremendous value to the Hong Kong Textile and Clothing industry in near and long term future.