SMM creates more sensing, adapting and reacting capabilities of Smart Textile

Md Abdullah Al Rumon

Technical Textile is becoming a robustious field nowadays. Fibre, yarn, fabrics and other structures with functional and technical properties inlaid as a substitute material with an endless range of applications. Generally the word “smart material” that refers those that can sense and response in a regulated and predicted manner to environment stimuli which may got from mechanical, chemical, thermal, magnetic or other form. Here just not only direct visible responses are included rather invisible responses for instance molecular, magnetic or electrical level which may not be apparent to the naked eye.

Today’s textile concept isn’t as similar as past and expectations around on textile have been changing more and more. At this point, shape memory materials can drive to solve these needs in textile due to its exclusive smart features. Shape memory materials (SMM) are exclusive materials that can remember and recover according to programmed deformation upon external stimulus such as chemicals, temperature, pH, light, a magnetic field, etc. Shape memory materials have been used in many areas and application on textiles of this technology has covered a wide range of usage recently. Shape-memory materials can be used in textile as clothing, yarn, fabric and sophisticated garment designing. The Applications and possibilities are huge by our imagination and creativity.

Principle of SMM

It’s an interesting technical behaviour of material that can be able to return or form a pre-programmed shape with a certain stimuli like temperature. It is a kind of mechanical action done through molecular rearrangement. There are two phase, Martensite and Austensite. In Martensite at low temperature the structure of a material changes and can be easily deformed. And upon heating, the structure changes to an Austensite phase and the programmed shape is recovered as the material remembers its original shape. SMP and SMA are the most common forms of shape memory materials.

Shape Memory Alloy (SMA)

Figure 2: Two way shape memory effect of SMA.

SMA comes with two-way shape memory effect where the martensitic phase occurs at a lower temperature and austenite phase acts at high temperature. Both phase can be memorised in a certain condition. In that case it can be used as actuator. Here it is possible to recover 100% of the original programmed shape. Generally combination of Nickel-Titanium alloys used but copper based alloy can be used as cheaper alternative.

In terms of Textile it’s a challenge because incorporating excessive use of alloy will diminish handle and touch effect of ordinary fabric.

Shape Memory Polymer (SMP):

Figure 3: Shape changing pattern of SMP in different temperature stages.

SMP comes with some extra features comparing with SMA. It has higher extensibility, softer handle, bendability, and lower in weight where these are the reasons to be considered very suitable for clothing industry. Its behaviour is defined by four temperature. Glass Transition (Tg), Deformation Temperature (Td), Storage Temperature (Ts), and Recovery Temperature (Tr). SMP is categorised by 4 classes, chemically crosslinked- glassy thermosets, semi-crystalline rubbers, physically crosslinked thermoplastics and block co-polymers.

Typical example of SMPs are segmented polyurethane based ones, that has a wide range of shape recovery temperature, low manufacturing cost with very high recoverable strains (up to 400%). The use of shape memory in textile opens up new dimensions and horizons for functional textile designing and use. For instance, Blending of SMP and polyester fibre may give an extraordinary behaviour like with a certain body temperature SMP will change its molecular structure that will assist air permeability so that the fabric would be more comfortable.

Shape-Memory Applications in Textile

Shape-memory fibres based on SMPs can be implemented to develop smart textiles which are respond to thermal stimulus besides that SMA or SMP can be used in accordance with needs.

Figure 4: An example of shape-memory smart garment.

SMAs have some applications on different field of garments such as in brassieres and flame retardant laminates. SMPs have better potential and more effectivity for textile and clothing and related products. These products are shoes, diversified breathable fabrics, thermal insulating fabrics and crease, shrink-resistant for apparel fabrics etc. These products can be made with finishing, coating, laminating, blending, and other innovative structures.

Shape-Memory textiles can be used as technical garments. Figure 4 is a schematic drawing. At low temperature, the smart garment assumes the configuration shown in Figure 4 (a). Here, shape memory fibres are saturated to this structure by such a way. With the increasing temperature in the layer, the air pocket expands (Figure 4 (b) and figure 4 (c)). Hence, this garment makes the firefighter less capable to burn injuries.

The other study is about bra designing of SMM. Women’s brassieres have both aesthetic as well as structural requirements. The application of superelastic NiTi alloy to the wire re-enforcement, called the underwire. NiTi underwires offer elevated comfort due to the enormous lower elastic modulus than the conventional steel wires. An additional advantage is the fact that the superelastic NiTi wires are counteraction to permanent deformation which can be the result of washing and drying cycles.

A recent application for SMA was a shirt designed by Corpo Nove, a fashion house in Italy, which shortens its sleeves when the temperature rises and does not require ironing when incited. Mitsubishi Heavy Industries have produced their own range of active sports clothing called “Diaplex” by applying a shape memory polymer (SMP) laminate. The SMP laminate is placed between two layers of fabric, to create a membrane, which is simultaneously waterproof, windproof and breathable.

The continued improvement of the SMM mechanical Properties would enable an extensive range of textile designs and applications as demand of technological innovative textiles and its significance is increasing rapidly. SMP is a challenging polymer to process. Although a preliminary investigation is still needed to improve as mechanical properties are not as successful as anticipated. Its potential has yet to be fully explored as SMM can be further developed by incorporating pigment into the different materials. Methods that could be investigated to achieve this with incorporating thermochromic and photochromic dyes into the SMP to get more access in different use. These concepts for SMM would inevitably lead to unique, exciting smart woven textile designs.

Reference:

1. Yvonne Y. F. Chan Vili Investigating Smart Textiles Based on Shape Memory Materials, Yvonne Y. F. Chan Vili Textile Research Journal, Vol 77, Issue 5, 2007

2. Mostafa O. Gok, Mehmet Z. Bilir, Banu H. Gurcum, Shape-Memory Applications in Textile Design, Procidia- Social and Behavioral Sciences, July 2015.