True smart textiles should be washed, laundered and still wearable but this is not the case – yet. R&D is honing in on this prerequisite, reports Caroline Hayes

The two main beneficiaries of e-textiles will be the sports and fitness and medical and healthcare sectors. Emerging areas will be the use of e-textiles in wellness (e.g. bandages), home and lifestyle (e.g. bed linens), industrial, commercial and military, and fashion applications, and includes automotive use in a category called ‘others’.

The value of the worldwide e-textile market will grow from $100million in 2015 to over $3billion by 2026, according to IDTechEx, in its report E-textiles 2018-2018.

Figure 1: Off-the-peg wearable garments will need industry-wide manufacturing and test standards.

T-shirts and other clothing that can monitor the wearer’s heart rate or other physical parameters still require an additional unit that contains the transceiver to gather data. The concept of circuitry being as fine as cotton thread and woven into a garment is still some way off.

Du Pont introduced InTexar in 2017, which is probably the closest to an e-textile available today. It is layered on, rather than through a fabric and consists of a stretchable thermoplastic polyurethane (TPU), and a thin layer of carob on silver to sense electrical signals, which are transmitted through a layer of silver, topped by a thin, stretchable water resistant layer and a protective top layer, to protect the material and make it washable (Figure 1).

A project published by the American Chemical Society, demonstrates a washable fabric that can be a human machine interface using touch and gesture sensing. Using conductive carbon nanotubes (CNTs) and screen-printing technology, the team from Beijing, China and Atlanta, Georgia, USA, created an e-textile that is conductive (0.2kOhm/sq), and permeable to air (88.2mm/second), and able to be manufactured on common fabric on a large scale. The electrode was stable under harsh mechanical deformation and even after being washed, reports the research team.  Moreover, based on a single-electrode mode triboelectric nanogenerator and electrode pattern design, the e-textile was sensitive to touch/gesture for human machine interface activities.

Flexible sensors will be incorporated into textiles and this will accelerate adoption, but they are still ‘add-ons’. IDTechEx believes that new functionality will be achieved by integrating materials “such as carbon nanotubes, inorganic nanorods and piezoelectrics . . . within textile structures, introducing new properties. Systems combining the best in conventional electronics with flexible sensors and actuators via bespoke connectors enable new product options,” says its e-textile report.

Flexible, conductive yarn or thread at thicknesses close to traditional thread are being introduced and, when used with non-conductive threads, can be woven to create e-textiles; the conductive threads can also be incorporated with embroidery processes to concentrate the conductive area. Another alternative is to coat non-conductive yarn with metal or substances to make them conductive for use in e-textiles.

 

Figure 2: Du Pont’s InTexar is made of stretchable layers bonded onto a fabric. (Picture: Du Pont)

Identifying the real issue to the adoption of e-textiles, the PCB trade association, the IPC, has published a white paper looks at the manufacturing challenges to ensure materials are functional over a period of time, measured in years, and remain robust over that time. The IPC WP-024, IPC White Paper on Reliability and Washability of Smart Textile Structures – Readiness for the Market finds that challenges to this ‘wearability’ issue are air permeability, satisfactory washability, and the viability of large scale manufacturing.

Both traditional textile manufacturers and multi-national corporations are keen to include e-textiles in their offerings. A cross-pollination of skills – textile manufacture and chemical engineering – will ensure that production standards as well as a set of standard tests to ensure durability and reliability. If manufacturing time and costs can be reduced and the scale of manufacture increased, e-textiles could present new, as yet, unimagined, uses for garments that sense and monitor data from the wearer.