Development of Test Methods for Heating Textiles

The integration of electronic and data processing functions within textile products has given rise to e-textiles. They can sense variations in the environment, either external or from the wearer, react by performing an action, and even adapt their properties. E-textiles offer major opportunities in healthcare, protection, and sportswear among others. However, in order to further develop this thriving E-textile industry sector, standardized testing and quality control methods are crucial for safeguarding product quality, regulating performance consistency, and ensuring consumer safety.<br/><br/>In the specific case of Joule heating textiles, several products have already reached the market. However, issues have been reported in terms of efficiency, durability and safety. The lack of efficiency may be associated with a higher response time, heterogeneous heat distribution, and/or irregular heating levels during repeated applications. In addition, different factors associated with daily life use can lead to a premature decrease in performance and ultimately reduce the lifespan of heating textile. Such factors can be mechanical (abrasion and repeated stretching and bending), related to textile care processes (laundering, ironing) and environmental (e.g. corrosion due to perspiration). Heating textiles may also create safety issues to the wearer due to short circuits, overheating, and fire incidents.<br/><br/>A test protocol has been developed to quantitatively assess the heating efficiency of heating textiles in a repeatable way. It uses thermocouples to measure the change in temperature at the surface of the heating textile during the heating and cooling phases. Various boundary conditions were applied with different fabrics/flexible materials simulating realistic use scenarios of heating textiles. The robustness of the test protocol was assessed with different heating textile structures: a conductive nonwoven fabric combining silver-coated nylon and polyester fibers; the same nonwoven fabric encapsulated with a polyurethane film; a heating fabric with an embroidered carbon fibre yarn; and a silicone rubber heating pad incorporating copper wires. Mathematical models were also developed to describe quantitatively the heating and cooling effectiveness of the heating textiles.<br/><br/>In terms of durability, the work focuses on five damaging conditions that are relevant to heating textile use in consumer products: abrasion, laundering, exposure to perspiration, repeated stretching, and repeated bending. The effect of these damaging conditions on the heating textile performance is studied using different types of Joule heating textiles – knitted, woven, nonwoven, embroidered/stitched/inserted, coated, and laminated. The conditions of the damaging treatment are selected to simulate realistic product use situations, e.g. in terms of the frequency and number of cycles of the bending and stretching motion and number of laundering cycles applied. The durability of the heating textile is assessed by comparing its heating performance after exposure to the damaging treatment with its initial efficiency. For the safety assessment, the test protocols characterize the propensity of the heating textile products to short circuits, ignition, and overheating.<br/><br/>The test and quality control protocols developed as part of this research aim to be reliable and robust as well as applicable to a wide range of Joule heating textiles with different structures. They are intended for Standards Development Organizations such as ASTM International and the International Electrotechnical Commission (IEC). We hope that they will contribute to lifting some of the barriers that currently limit the growth of the e-textile industry.