Feature: Wearables
Figure 6: The customised electrostatic force microscope we used to measure the electricity generated on the surface of the PIECLEX fabric and final textile for wearable applications
the wearables. At Murata, we thought if we took away all the electrodes from the sensor, leaving just the conductive threads that make the fabric, bacteria could then be destroyed with electricity. Tis is when the idea of PIECLEX was born. Te voltage generated by PIECLEX
ranges from single-digit to tens of volts, a level not easily noticed by humans, yet sufficiently high to inhibit microbial growth, giving the fabric antimicrobial properties. For comparison, static electricity
can reach about 3,000V, so the fabric’s generated low-level electricity is an extremely small amount of energy; see Table 1. In addition, the safety of the fabric
regarding cytotoxicity and sensitising potential was verified by the Japanese Food Research Laboratories.
PIECLEX Several volts to tens of volts Static electricity 1,000 V 2,000 V 3,000 V
PIECLEX advantages Tere are many products that are claimed to be antimicrobial and deodorising, but PIECLEX offers two major advantages: Te first is a semi- permanent antimicrobial effect. Some materials are known to generate voltage in response to an applied stress, called “piezoelectric effect”. PIECLEX is a fibre that realises antibacterial and deodorising properties through electricity generated by the piezoelectric effect when the fibre is stretched or contracted. Compared to antimicrobial treatments introduced through chemical agents, which can degrade from washing and ageing, the piezoelectric effect is degradation-free; see Figure 1. Another advantage of PIECLEX
Don’t feel at all Feel slightly Feel a sting
Table 1: Comparison of voltages generated by PIECLEX and static electricity
26 October 2023
www.electronicsworld.co.uk
is that it is environmentally friendly, since no chemical agents are used in its manufacture. Also, like Murata’s Picoleaf, PIECLEX is made of polylactic acid (PLA) – a plant-derived biodegradable plastic; see Figure 2. Tis, too, makes PIECLEX environmentally friendly, since if it ends up buried in soil it is degraded by soil bacteria and microorganisms, i.e., biodegraded. Fabric analysis shows that 70-80% of PIECLEX biodegrades within six weeks. Equally, because PIECLEX can be circulated back to nature quite
quickly, there’s no need for its incineration, a process notorious for its heavy CO2 emissions. Overall, this makes PIECLEX a highly-functional material, suitable for everyday use.
Development challenges One of the challenges with the PIECLEX fabric was how to best evaluate its feel and texture, but also its response to weather conditions – i.e., when it gets wet, hot or cold. Numerical data didn’t quite help, so we obtained our correlation data for different fabric samples. We also had to measure the electric discharge generated by stretch and contract for each fabric sample. Generally, conventional antimicrobial
evaluations are performed on a fabric when static, which is not suitable for our “stretch-to-antimicrobial” type material. Tis meant we had to devise our own measurement equipment and setup; see Figures 4-6. We developed the test equipment
based on a particular jig, and then successfully established the testing method. We established a collaborative setup where Murata evaluates the electrical characteristics and antibacterial functions of the PIECLEX fabric, and Teijin Frontier further tweaks the material based on those evaluations.
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