Initial insights of laundry detergent and additive impact on e-textile surface resistivity

Abstract

Smart clothing represents less than 1% of the multibillion dollar wearables market. This lagging representation is due to many factors; one predominant challenge which includes performance reliability post-laundering/care. Due to smart clothing intimately contacting the human body, it naturally becomes soiled and requires laundering. However, insight into the impact of consumer detergents and other additives on e-textile conductive functionality post laundering has yet to be explored. The purpose of this research was to study laundering conditions, specifically the influence of select laundry detergents and additives, on surface resistivity of select e-textiles to provide initial insights into the impact of consumer-available laundering treatments to contribute to knowledge around laundering of e-textiles. Understanding initial impacts of laundering conditions, particularly detergents and other common laundry additives can inform future studies, laundering text methods of e-textiles, and care label development.

Keywords

E-textiles smart garments launderability wash fidelity resistivity detergent

Wearables are electronic devices worn on the body, either as an accessory or integrated into clothing that have conductivity capabilities, advanced circuitry, and data communication functions.¹ The market for wearable technology has been rapidly growing in recent years as smartwatches or other smart wearable devices are being deployed to monitor movement and body rhythms. Wearables are now evolving to move data collection, analysis, and communication from the external smart device directly to the body by sensors and electronic textiles (also called e-textiles). When this wearable technology is fully integrated into clothing, products are called ‘smart clothing’ or ‘smart garments’. Although the wearables market is now a $32.63 billion industry² ‘smart clothing’ represents less than 1%.³ This lagging integration of the smart clothing category is due to many factors, some of which include technical challenges with sensor size, consistent conductivity, and performance with garment style.⁴ One of the most significant challenges of e-textiles is performance reliability after laundering,^5–7 which includes functional conductivity. This electrical challenge of conductive woven and knitted e-textiles, in which metallic components are embedded into yarn structure or applied as a coating, is due to intimate contact with the human body, which naturally becomes soiled, and must be cleaned. Washability, or launderability, has been identified as one of the key aspects for the widespread use of e-textiles for the integration of smart garment design.⁸ However, the performance of e-textiles after-laundering requires continued research, particularly related to the impact of laundering detergents and additives.

Background

An e-textile is a fiber, yarn, fabric, or end product that results in an electrical or electronic circuit, with or without processing capability.¹ E-textile structures are often knitted/woven from electrically conductive yarns, or nonconductive textiles may be made electrically conductive through the surface application of a metallic coating, metallic ink-printing, or embroidery with metallic threads.⁴ Most e-textile products are still in the research and product development stage,⁹ falling short in either functional performance, ease of use, production capability, price point, comfort, and/or maintenance, which includes launderability.^8,10 To achieve their full potential, wearable e-textiles (‘smart’ garments, bags, shoes, and other wearable soft accessories) must overcome these challenges to be worn/used and properly cared for by consumers on a daily or routine basis.¹¹

Conductivity and surface resistivity

Electrical conductivity is essential for functional e-textile products. The counterpart of conductivity is resistivity, which is the measure for how strongly a material resists an electric current. For conductive textiles, electrical surface resistivity is the common measurement for communicating electrical parameters¹² as it indicates the effectiveness of the textile to carry electrical currents and function within specific wavelength frequencies. When evaluating e-textile conductivity, a low surface resistivity reading indicates a textile that readily allows electrical current to transmit across the surface of the fabric effectively at the frequency deemed appropriate for its end use (e.g. operating in the 2.54 GHz ISM band).

Soiling and laundering

There are many environmental conditions that may degrade or compromise electronic devices, including the presence of dust and particulate matter, air pollution, and high temperature and humidity levels.¹³ When worn on the body, additional and inevitable soiling occurs by hair, dandruff, tears, earwax, mucus, saliva, sweat, dead skin, and other intimate bodily secretions, much of which is transferred to clothing and textiles and needs to be removed for hygienic reasons.¹¹ Presently, it is unknown if and how bodily soils may impact smart garment functionality. Thus, it is important to understand the effect of washing on the performance of wearable e-textiles^6–10 followed by exploring the impact of soiling (future research opportunity).

Laundering garments, in general, may occur through wet or dry cleaning. Wet cleaning occurs by hand or as means by mechanical washing machines (either in the home or laundromat) with mechanical machine laundering being the preferred and most utilized method.¹⁴ Laundry washing machines are harsh, potentially damaging environments for e-textiles. Mechanical stress (abrasion, bending, torsion), thermal stress (temperature), water stress, and chemical influence (detergents and additives) have been identified as key damaging actions of laundering.^5,15–18 Depending on the integrated e-textile (LED, sensor, antenna, laminations, wired circuitry, etc.) as well as appearance (coloration, pilling, wrinkling, etc.), the impact of laundering can damage varying aspects of an e-textile system. Commonly, when exploring the impact of different parameters (such as launderability/washability)⁷ on conductive textiles a change in surface resistance is measured before and after the intervening procedure. Maintaining functional conductivity (within end-specified tolerances) is viewed as the initial challenge to overcome before addressing other negative laundering impacts such as textile integrity and appearance; however, in some cases all challenges are experienced in a single laundering scenario.¹⁹

Laundering e-textiles and related performance failure

Recent studies have provided a strong start to better understanding the impact of washing e-textiles. In particular, Rotzler and Schneider-Ramelow provided a review summary of common failure modes in e-textiles to continue building scholarly work that advances the development of reliable, washable e-textiles, that can then be utilized in smart garments.⁶ Focusing on e-textile fabrics (metallized yarns and textiles), a gradual loss of metallization layers occurs with each cycle of laundering^19–22 (see examples in Figures 1 and 2), with some researchers suggesting the impact of bleach in the laundering programme²³ and/or friction^24–27 between e-textiles samples (i.e. the mechanical stress of laundering textiles together) as major influencers of poor or failed conductive performance.

Figure 1.

Progressive metal loss through wash cycles of silver-plated polyamide thread. Scanning electron microscope (SEM) images of silver-plated polyamide thread without thermoplastic polyurethane (TPU) protection during wash tests: (a) Before wash test; (b) five cycles of wash test; (c) 10 cycles of wash test; (d) 20 cycles of wash test; (e) 40 cycles of wash test and (f) 50 cycles of wash test.²²

Figure 2.

Progression of metallization loss through wash cycles (with detergent) of silver-plated-nylon fabric electrodes. Scanning electron microscope (SEM) observations of silver-plated-nylon fabric electrodes visualizing progression of metallization loss over washing cycles with use of powder detergent with bleaching agent (a), liquid detergent without bleaching agents (b), no detergent/tap water only (c), and no detergent/tap water plus sodium percarbonate (d). M = machine washed; S = Soaked. (Figure adapted from Gaubert et al.).¹⁹

In response to mechanical stresses observed, researchers have suggested a protective layer of thermoplastic polyurethane to cover conductive components of an e-textile, but cracks and undesirable performance were still observed post-washing,²³ suggesting cyclical temperature changes of laundering procedures lead to thermal responses of materials.⁶

As mentioned by other researchers working in the area of laundering and e-textiles, there are many factors that impact the end performance conductivity of an e-textile, from the textile substrate composition to the use of protective layers/elements and thickness of supporting structures to washing programme (time, temperature, mechanical action, and laundering agent). It has been suggested, and therefore adopted in this study, that a gentle washing programme can lead to better washability for most e-textiles and to approach conducting research with the aim of addressing a single factor (e.g. laundering detergents/additives) in a laundering programme to evaluate e-textile performance.⁶

Detergent composition: surfactants and builders

Surfactants or ‘surface-active agents’ are the primary component of cleaning detergents (in general) and the crucial laundering additive(s) that interact with different surfaces to draw oil, dirt, and other residue out of textiles. Surfactants have a hydrophobic tail and a hydrophilic head. When there is a sufficient amount of surfactant molecules present in a cleaning solution, they combine together to form a structure to remove residues/soil. The hydrophilic head of each surfactant molecule can be electrically charges through ions (positive or negative) or be without charge (neutral). Depending on the charge of the hydrophilic head, the surfactant is classified as anionic, nonionic, or cationic. Chemistry informs that ions are charged particles due to a loss or excess of electrons. First, anionic surfactants are negatively charged. The negative charge helps the surfactant molecules lift soils, thus they are frequently used in detergents. Negatively charged particles are attracted to positively charged particle, such as those found in hard water. This makes them less effective in hard water because the surfactants bind to the water minerals rather than textile surface grime. Next, nonionic surfactants have no charge. Nonionic surfactants are good at emulsifying oils and removing organic soils, therefore, are commonly used together to create multi-purpose cleaners. Finally, cationic surfactants have a positive charge. Cationic acts opposite to anionic and attracts to negative charges, making them good surfactants for anti-static products (such as softeners). However, if cationic surfactants are mixed with anionic surfactants, the charges that each surfactant brings to the detergent environment is cancelled out and no longer effective (or effective as desired). Briefly and directly, ion interactions can highly impact surface resistivity. A loss of electrons to ionic interactions will result in increased surface resistivity.

Builders are chemical compounds used to enhance the cleaning efficiency of surfactants by softening water through ionic interactions. The builders bind to hard water minerals (ions such as calcium and magnesium) in place of the surfactants. Builders are also bases, meaning they work to neutralize acid – providing more stability to the pH – and help disrupt chemical bond. Ionic interactions are the basis of chemical reactions. Limiting the ionic interaction can reduce the laundering effect on surface resistivity. Please see the detergent/additive list detailed in Appendix A to review each ingredient and its corresponding electrically charge by way of the ion label.

Care labels and e-textiles

The Federal Trade Commission requires that garments be labeled with instructions for how to launder/care for the product and to provide warnings that will prevent substantial damage.²⁸ If a detergent or additive, refurbishment method, or other process can damage the product, it must be specified on the care label. There are five key conditions addressed on a garment label specifically involving care:

washing method (mechanical) and wash temperature (water; thermal);

bleaching (chemical);

drying method (mechanical or other method) and temperature (thermal);

ironing (mechanical; thermal);

warnings against other harmful procedures.¹⁸

Current care instructions for e-textiles are quite limiting in terms of wash/laundering conditions. Some e-textile suppliers and manufacturers recommend gentle hand washing with neutral detergents at temperatures below 40°C. This wash temperature aligns with ‘very cold’, ‘cold’, and low parameters of ‘warm’ washes as defined by industry standards.^29,30 According to the e-textile manufacturers’ specification sheets (provided with material purchase), care instructions advise against the use of bleach or laundry additives containing any concentration of bleach, avoid machine drying, wringing, ironing, and placing into direct sunlight (resulting in a high heat drying condition). E-textile specification sheets note that washing of any type (wet or dry) will eventually degrade metallic coatings and thus reduce functionality. For the most delicate e-textile materials, manufacturers instruct users to ‘not wash’ the textile and advise to ‘dry brush or wipe clean only’. However, little scientific evidence regarding the measurable impact of laundry additives on e-textile performance exists. Therefore, accurately informed care label parameters are lacking, and accordingly, consumer practice for proper e-textile laundering care. Understanding laundering condition impact on e-textile performance, to inform and guide textile care label development, may influence proper consumer care and satisfaction with their smart clothing product.

Research purpose and scope

As demand for smart garments intensifies, there is growing urgency to address laundering procedures of e-textiles. Although a considerable amount of research has been conducted on the washability of e-textiles, there are vast variations in test procedures, inconsistencies in laundering conditions, and a lack of specification of detergents and equipment used in research protocols⁸ that allow for replicability and advancement of scientific research. When e-textiles are fully integrated into smart clothing, laundry practices need to provide adequate hygienic cleaning and align with consistent care behaviors of apparel consumers in order to ensure garment longevity.¹⁴ It is therefore crucial to detail machine laundering conditions so effective e-textile machine laundering test methods may be established for realistic and repeatable care. Understanding the impact of laundering conditions, particularly detergents and other common laundry additives, will help inform care label development, and thus promote consumer actions for proper care of their smart clothing items. Proper care that ensures product performance also contributes to the product’s longevity and consumer satisfaction, which further fuels product consumption that allows and encourages smart garment advancements. The findings of this study have the potential directly to inform care label development for products that integrate the e-textiles examined in this study while contributing to the development of industry standards.

Therefore, the purpose of this research was to study laundering conditions to provide initial insights into the impact of select laundering additives (from a general detergent/additive perspective) on different e-textiles to provide a baseline direction for future studies and further build the scientific body of knowledge around laundering of e-textiles. With this main purpose of research in mind, an additional goal of the study was to propose a replicable protocol that may inform and assist with the development of standardized laundering methods for e-textile testing. Finally, outcomes of this study aim to recommend guidelines for appropriate care labeling of e-textile products, particularly contributing to the care label item of ‘warnings against other harmful procedures’ as a result of detergents/additives explored in this study. The authors note that in wearable apparel often textiles are placed alongside or layered with other textiles within a single garment to meet a predetermined set of end purpose parameters and assume that this would be a similar approach for e-textiles. However, studying the launderability of e-textiles alongside other textiles (e-textiles or other) to detail clothing physiology or outlining end purpose/intended use (for contamination or soiling specifics) is outside the scope of this study.

Materials and methods

In the experimental study, five laundry additives across seven e-textiles of various structures, fiber contents, and conductive materials were assessed. The work outlined in this research builds on previous studies involving e-textile performance to user/wear conditions.⁷ Methods are organized to share detailed materials, additives, and procedures of this study.

E-textiles

The e-textiles sampled in this study are not fully functional systems but are considered components for potential use in the construction of smart clothing or other wearable smart soft good products (bags, shoes, accessories, etc.). For these types of components, testing for a change in surface resistivity is a valid method to assess their launderability or washability.⁸ In this study, seven commercially available e-textiles with differing material properties were sampled and initial surface resistivity measurements gathered before laundering procedures were performed (see Table 1). The sample set includes base fibers of nylon, polyester, and a cotton/polyester blend. Woven and knit fabrics are represented, all of which fall within the ‘lightweight’ textile category. Five of the seven e-textiles have initial surface resistivity measurements less than 1 Ω/square, making them appropriate for use in applications conveying electrical signals, while the remaining two read between 1 and 2 Ω/square, making them appropriate for use as textile-based sensors.^31,32 Surface resistivity tests were conducted according to AATCC test method 76.³³ The square sample units used in the paper have a size of 2 inches by 2 inches, or 51 mm by 51 mm.

Table 1.

Material properties of e-textile samples

Product	Basic structure	Base fiber	Surface mass in kg/m²	Conductor	Site of conductor application	Surface resistivity in Ω/sq
ArgenMesh	Woven	Nylon	0.071	Silver	Yarns	0.24
Cobaltex	Woven	Polyester	0.084	Nickel, copper, cobalt	Fabric	0.06
Circuitex	Woven	Nylon	0.099	Silver	Yarns	0.13
Nickel Copper Ripstop	Woven	Polyester	0.081	Nickel, copper	Fabric	0.05
Silver Jersey	Knit	Cotton/polyester	0.145	Silver	Yarns	1.11
High-performance Silver Mesh	Knit	Nylon	0.031	Silver	Yarns	1.53
Ripstop Silver	Woven	Nylon	0.074	Silver	Fabric	0.21

^aElectronic microscope magnification power 3X; standard microscope with camera attachment.

The silver jersey, cotton/polyester blend is one comfortable e-textile sampled. It exhibits handle, drape, and stretch, making it compatible with apparel products, but it is limited to textile-based sensors due to its initial surface resistivity. The nickel copper ripstop has the lowest initial surface resistivity, which is ideal for end products conveying electrical signals. However, this particular e-textile may be less desirable for integrating into a smart garment where the e-textile comes in direct contact with the skin because users may experience a negative reaction (i.e. skin irritation) due to possible nickel allergy. However, it is valuable to report all surface resistivity measurements to advance e-textile research (in general). In addition, as e-textiles have the potential to be integrated into a variety of wearable products, findings from e-textiles that may not necessarily be suitable for direct contact with the skin (e.g. cobaltex and nickel–copper ripstop) may be a good fit for other innovative end products. Regardless of potential end use, any measurable change in surface resistivity after laundering will speak to the impacts of the particular detergents/additives in the wash water.

Laundry detergents and additives

Detergent is an important factor to consider during wash fidelity testing.¹¹ In this research, detergents and other laundry additives are the independent variables for experimentation and were selected to represent a range of formulations to simulate common laundering conditions of an average household/consumer (see Table 2) to provide initial insights into detergents and additives and guide future research. These additives include a standard reference detergent, a detergent suggested by e-textile supplier (Texcare), a plant-based detergent, color-safe bleach, and fabric softener. The plant-based detergent and Texcare detergent are commercially available and the standard detergent is reflective of consumer laundering detergent products currently on the market.³⁴ A plant-based detergent was selected due to increasing consumer preference for ecofriendly detergents.³⁵ The authors recognize that using the term ‘plant-based’ may not accurately represent the composition of ingredients that make up the detergent, but use this term to identify the detergent when writing/referencing as this is how the detergent ingredients are labeled and communicated to the consumer (by way of the product packaging; other terms used to describe ingredients include plant-derived and mineral-based). The ingredients (including amounts) for each detergent/additive (as provided by the product label) are outlined in Appendix A. While laundry detergents were of primary interest, color-safe bleach and fabric softener are also important to investigate because they are commonly used laundering additives that could potentially impact conductive functionality and would need to be identified on the care label.

Table 2.

Laundry additives/treatments and formulations

Additive	Product/brand	Formulation
Standard detergent	AATCC 1993 standard reference detergent without optical brighteners	Powder
Texcare	Y-Shield EMR Protection Texcare detergent	Liquid
Plant-based detergent	Seventh Generation Free and Clear detergent	Liquid
Color-safe bleach	Clorox2 Free and Clear Stain Remover and Color Brightener	Liquid
Fabric softener	Ultra Downy Free and Gentle Liquid Fabric Conditioner	Liquid

All detergents and additives selected for use in this research study are free of colorants and perfumes. Although color-safe bleach and fabric softener are designed to be used in combination with detergent, they are isolated in this experimentation.

Laundering procedure: Rotawash

The Rotawash accelerated laundering system was utilized in this study to carry out the washing simulation of five home launderings in one wash cycle. The Rotawash simulation of five home launderings is a sufficient simulation, as consumers will generally reject apparel products which fail after being used/washed only five or six times.⁶ Small textile specimens (rather than whole garments) were laundered in individual rotating canisters which allows for the control of water in conjunction with textile and additive.

Home, commercial, and most laboratory wash systems use tap water, which varies in mineral content, chlorine content, water hardness, and other factors that affect laundered textiles.³⁶ In order to reduce confounding factors related to wash water quality, which may have a substantial effect on end conductivity results,¹⁵ distilled water was used to carry out the laundering tests by the Rotawash accelerated laundering system as opposed to traditional washing machines that require a tap water supply line.

Specimen preparation

Specimen preparation protocols were adapted from AATCC test method 61 procedure 1B,²⁹ which calls for 2 × 6-inch textile specimens. This size was adjusted to 3 × 4 inches to provide adequate width for measuring resistivity post-laundering procedure. This adjusted size maintains the standard recommended fabric surface area of 12 square inches (305 mm). From each of the seven e-textile samples, 14 specimens were cut for a total of 98 specimens. Thus, each laundering condition received 14 replications across seven fabric samples.

E-textile specimens were cut from fabric areas not sharing warp or weft yarns and at least 2 inches (51 mm) from the selvedge (see Figure 3(a)). Fabrics most prone to fraying were cut on the bias to minimize fraying during the wash process (see Figure 3(b)). After laundering, specimens were cut down to 2 × 2 inches (51 × 51 mm) with fabric edges aligned to warp/wales and weft/courses directions (see Figure 3, (a)2 and (b)2). This allowed for testing surface resistivity across the specimen, on grain, in both structural directions. Specimen preparation was modified from AATCC test method (TM) 76 to align with previous research.³³ Care was taken to ensure that e-textiles were handled only with gloved hands and nonconductive tweezers to avoid soiling and contamination that could skew results.

Figure 3.

On-grain (a) and bias-cut and (b) specimens cut down to 2 × 2 inches/51 × 51 mm after laundering.

Measuring surface resistivity (i.e. sheet resistivity)

To accommodate the wash procedure, surface resistivity data were gathered following a combination of AATCC test method 76³³ (AATCC test method 76: Electrical surface resistivity of fabrics) using parallel plate electrodes (see Figure 4) and test method 210³⁷ (AATCC test method 210: Electrical resistance before and after various exposure conditions). Surface resistivity measurements were performed on 2 × 2-inch specimens to align the apparatus and materials used in this study in accordance with section 5 of AATCC TM 76.³³ From each e-textile sample, one set was cut and left unlaundered to serve as the baseline for comparison. The remainder were exposed to laundering, air-dried, trimmed-down (as indicated above), then measured for the surface resistivity post-laundering procedure.

Figure 4.

Testing surface resistivity using parallel plate electrodes.

The procedure for measuring resistivity was modified from AATCC TM 76 to align with previous research.³¹ Surface resistivity was measured using a Fluke 289 multimeter with an accuracy of 0.02 Ω using the two probe two wire method. Before each round of data collection, the resistance of the leads was cancelled/removed using the multimeter’s relative mode function. Laboratory conditions were maintained at 20°C to 22.22°C and 40 ± 2% relative humidity throughout the data collection process. Resistivity measurements were performed on each specimen in warp/wales and weft/course yarn directions as outlined in the test method. Averages of each resistivity measurement per e-textile specimen are reported.

Rotawash test conditions

The accelerated laundering procedure follows AATCC test method 61.^29,30 This method offers six optional test conditions with variations in temperature, liquid volume, concentration of detergent, and levels of agitation by steel or rubber balls. In this research, test condition 1B was selected for its gentler mechanical action, lower water temperature, and higher concentration of additives (our independent variable) to align with the (limited) care recommendations outlined by e-textile manufacturers. This test condition was most similar to a delicate home washing machine cycle. The selected 31°C temperature was considered a ‘cold’ wash temperature.^29,30 Table 3 outlines the specific parameters.

Table 3.

Optional test conditions of AATCC TM 61 with selected method 1B highlighted

	Temperature (°C)	Total liquor volume (mL)	% Powder detergent of total volume	% Liquid detergent of total volume	% Available chlorine of total volume	No. of steel balls	No. of rubber balls	Time (s)
Test no.
1A	40	200	0.37	0.56	None	10	0	2700
1B	31	150	0.37	0.56	None	0	10	1200
2A	49	150	0.15	0.23	None	50	0	2700
3A	71	50	0.15	0.23	None	100	0	2700
4A	71	50	0.15	0.23	0.015	100	0	2700
5A	49	150	0.15	0.23	0.027	50	0	2700

The Rotawash accelerated laundering system simulates the abrasive effects and color change of five traditional home launderings in one wash cycle. In this study, changes in resistivity were assessed and surface appearance changes were observed, rather than abrasive effects or color change/transfer.

Preparation of Rotawash canisters, washing, rinsing, and drying

Each textile specimen was laundered separately in its own dedicated canister with a 150 mL solution of distilled water and laundering additive, plus 10 rubber balls. Standard detergent, Texcare detergent, and plant-based detergent amounts were determined by AATCC TM 61 test condition 1B as described in Table 4. Color-safe bleach and softener volumes were calculated in relation to the percentage of additive to water ratio within a home laundering machine. This calculation was determined by measuring the additive as prescribed in the directions on the label of the bottle (e.g. filling to specified line marked on the cap). Once this volume was determined, the ratio of additive to water was calculated using the standard volume for home laundering machines (19 ± 1 gallon; 68137.4–75708.2 mL) as informed by the AATCC laboratory procedure for home laundering: machine washing (LP1-2018e).³⁸ [Note: values used in calculation reflected water volume in nonhigh efficiency (HE) home laundering machines.] Once this ratio was determined for a home laundering machine, the calculation was modified to reflect the total volume within the Rotawash canister. To ensure uniformity in concentrations, a stock solution of each laundry additive was prepared and measured out into 150 mL volumes per canister. E-textiles tumbled in Rotawash canisters for 20 min at 31°C. After the Rotawash procedure, each specimen was rinsed in room temperature distilled water and gentle massaged with hands underneath a slow-flow faucet stream of water for 90 s. Following the rinsing procedure, the specimens were air-dried on racks.

Table 4.

Average electrical surface resistivity (Ω/in²) by laundering condition

	Unlaundered	Water only	Standard detergent PB; AS	Texcare detergent AS; SS; SB	Plant-based detergent NS; AS; SB	Color-safe bleach SS; NS	Fabric softener CS; SS
Argenmesh	0.24	0.31	0.37	0.31	0.32	0.34	0.23
Cobaltex	0.06	0.29	0.08	0.07	0.08	0.15	0.36
Circuitex	0.13	0.30	0.15	0.39	0.56	0.17	0.19
Nickle–copper Ripstop	0.05	0.05	0.05	0.05	0.14	0.09	0.12
Silver Jersey	1.11	1.58	1.60	1.47	1.64	1.77	1.87
Silver Mesh	1.53	3.23	2.57	2.23	3.98	3.11	1.64
Silver Ripstop	0.21	0.30	0.30	0.31	0.71	0.43	0.24

AS: anionic surfactants; SS: synthetic surfactants; NS: nonionic surfactants; CS: cationic surfactants; PB: precipitating builders; SB: sequestering builders.

Results and discussion

Resistivity measurements were recorded in both warp/wales and weft/courses directions for seven e-textile samples with two replications of seven different laundering conditions (unlaundered and six different additives), resulting in 196 data points. For each combination of e-textile plus laundering condition, the average resistivity was calculated and reported (see Table 4). A paired-samples t-test using the averages was conducted to evaluate the impact the different laundering conditions had on the e-textiles. There was no statistically significant difference between the pairs.

Then, the percentage change was calculated and averaged across each laundering condition to compare the average resistivity of the unlaundered e-textiles and communicated by way of the chart (see Figure 5).

Figure 5:

Percentage change in surface resistivity for each laundry condition.

Texcare detergent, plant-based detergent, color-safe bleach, or fabric softener were ranked from one to six with one showing the least change in surface resistivity and six showing the greatest increase in surface resistivity after laundering. Across all e-textiles assessed in this study standard detergent ranked in the first position with the least change (or increase) in surface resistivity, followed by Texcare detergent, then color-safe bleach, water only, fabric softener, and then plant-based detergent receiving the ranking of six as it had the greatest change (greatest increase in resistivity) post-laundering condition. The authors want to point out that if the cobalt textile was removed from the analyses the ranked order of laundering additives would adjust. However, to advance understanding of laundering parameters on conductive e-textiles and encourage innovative solutions to research and develop wearable garments and other soft products, all e-textiles under study are included in the ranking. It is suggested that future research considers alternative textiles (or insulative/protective coating on the cobalt e-textile) or further exploration into laundering parameters to account for this particular textile.

This study and its findings may also aid in the development of accurate care labeling of smart garments and further develop standardized test methods for laundering of e-textiles. The discussion below first overviews the resistivity findings from the different laundering conditions, as organized by washing solution (water-only, detergent, and additive), then shares results regarding discoloration observed. After this discussion, suggestions for formal e-textile laundering test method development are presented. Finally, recommendations for care label guidelines for smart clothing are outlined, guided by the post-laundering surface resistivity findings of this study. To assist in understanding the findings, please review the detergent/additive ingredient list detailed in Appendix A as desired.

Unlaundered

Surface resistivity measurements of unlaundered specimens served as a baseline for comparison with laundered e-textiles. The percentage change in resistivity before and after laundering speaks to the impact of the laundering detergent or additive treatment (see Table 4).

Water only

E-textiles laundered in water only show the effects of pure, pH neutral, distilled water in the absence of laundering additive. This condition was expected to have the least effect on e-textile surface resistivity; however, water-only ranked fourth out of the six laundering conditions. This may be partially explained by a creasing of specimens that was observed only in samples laundered in water only. In these creased specimens, a very high resistivity was recorded because wrinkling or creasing creates a disturbance to the flow of electricity.³² The water-only laundering condition is the only condition in this study that lacks surfactants, which aid in cleaning by reducing the surface tension of water. Some surfactants, such as the above concentrations in which they form a lamellar phase, can lead to slippery surfaces, therefore decreasing friction. The absence of surfactants in this laundering condition may have allowed specimens to stick to the sides of the canisters, which often results in creasing. In addition, this wet environment without slippery surfactants may have contributed to frictional/mechanical stress that increases e-textile surface resistivity. As it was not possible to observe the happenings of each e-textile within the tumbling canister, the adherence to the sides of the canister is a speculation to account for the textile creasing and recorded resistivity.

Detergents

The plant-based detergent ranked fifth (i.e. the poorest performing) of the five additives evaluated in this study. A defining characteristic of plant-based detergents is their enzymatic cleaning action. The laundry enzyme in this plant-based detergent is protease. Protease acts as a catalyst for the biochemical breakdown of complex soils.³⁹ Also, silver and copper (found in select e-textiles) have specific properties which allows them to bind to cellular components, such as those found in plant-based, plant-derived, and/or mineral-based detergent ingredients. Based on the findings of this study, it is theorized that the biocatalyst’s interaction with the metallic coatings contributed to a greater increase in resistivity than other additive ingredients.

The Texcare detergent performed the second best out of the three detergents. This was unexpected as the Texcare detergent is most often recommended by the e-textile manufacturers for washing and was therefore expected to perform the best. The Texcare detergent includes mainly anionic surfactants. Due to strong electrostatic repulsion, e-textiles surface resistivity can be more stable in the presence of a negatively charged anionic surfactant. Therefore, anionic surfactants, such as Texcare, were an appropriate detergent selection for e-textile laundering because the detergent’s surfactant can solubilize dirt while facilitating less ionic interactions with the metallic coating. It is important to note that the standard detergent used in this study was also an anionic surfactant.

Standard detergent performed the best out of all additives. The standard detergent includes the highest concentration of builders in its formula. As a gentle reminder, builders are chemical compounds used to enhance cleaning efficiency of surfactants and to soften water by binding to water minerals (metal ions such as calcium and magnesium). This deliberate presence of ions, in the form of builders, was perhaps the reason why standard detergent was more effective at stabilizing e-textile surface resistivity than the recommended Texcare. Or a change in surface chemistry of the specimens may have accounted for the changes observed, such as a build-up of an insulating oxide layer or dissolution of such a layer (by the builder).

Fabric softener and color-safe bleach

The fabric softener ranked fourth out of the five additives evaluated. The fabric softener was also the only additive to list a cationic surfactant as its main cleaning agent. The positively charged cationic surfactant has a strong electrostatic attraction to negatively charged ions in the e-textile (opposite of the Texcare surfactant). The loss of these e-textile ions to the interactions with the surfactant may have led to the observed increased resistivity.

Color-safe bleach ranked third. The main cleaning agent in color-safe bleach was hydrogen peroxide. Hydrogen peroxide itself is unstable and decomposes to become water and oxygen. To explain briefly the hydrogen peroxide decomposition process, hydrogen peroxide reacts to form peroxides with certain organic compounds, several of which are used to initiate polymerization reactions. In most of these reactions, hydrogen peroxide oxidizes other substances, forming a catalyst reaction, which in turn decomposes the hydrogen peroxide in a low-activation energy (increased reaction rate) pathway. When hydrogen peroxide comes into contact with copper or silver (metals within select e-textiles), the copper or silver can act as a catalyst, speeding up the decomposition. Catalysts decompose over time, so this interaction could compromise the e-textile's metallic coating and increase the surface resistivity.

Laundering additive effects on appearance: discoloration

Discoloration was found on the high-performance silver mesh when washed in water only and the plant-based detergent. It was also found on the ripstop silver when washed in water only, standard detergent, and the plant-based detergent. The discoloration was more severe when washed in the plant-based detergent and uneven in its discoloration (see Figure 6).

Figure 6.

Example of e-textile discoloration: silver ripstop laundered with plant-based detergent: Close-up (left) and full view (right). Dashed line indicates where close-up image was taken within the larger sample.

One possible reason for this discoloration is an electrochemical process called ‘galvanic corrosion’. Briefly, galvanic action occurs when two (or more) electrochemically dissimilar metals come in contact with each other and a conductive path is formed for electrons and ions to transfer and move from one metal to another. When this transfer/movement occurs, one metal corrodes as its ions are deposited onto the other metal(s). To provide an example, the same process occurs if/when genuine silver silverware is washed in a dishwasher (made from steel) rather than by hand. When two metals or alloys of different electrolyte potentials – such as silver and stainless steel – form an electrical conducting path (are in contact) and in the presence of an electrolyte (any weak acid, including the carbonic acid found in water), the more reactive metal (silver) acts as anode and the less reactive (stainless steel) acts as cathode. This leads to ion migration through the electrolyte. The greater the electrochemical difference, the faster the corrosion and resulting discoloration. E-textile fabrics have potentially greater ion migration; however, when in contact with the stainless steel canister used in the Rotawash procedure; the more acidic additives were present and the galvanic corrosion was accelerated.

It is important to note that metals within e-textiles will undergo a variety of different chemistry experiences when incorporated into a product and used in an array of environmental conditions. At this point in research and development of e-textiles and other smart garment wearables, it is important for developers to consider potential chemical interactions with metallic components (integrated or applied) used to fabricate currently available e-textiles to consider an insulative or protective layer/coating from environmental elements that may cause adverse chemical reactions, such as decomposition or discoloration, as connected to laundering additives.

Test method development reflection

Based on the results of this study, the following suggestions are outlined to provide standard organizations, such as AATCC, ASTM, ISO, and/or IPC with points to consider when developing formal test method protocols connected to e-textile laundering procedures. These suggestions are based solely on the findings of this study and may or may not be deemed appropriate for consideration for standardized test method development.

Water: In order to evaluate the impact of additives, the water source was controlled in this study. However, use of distilled water to launder smart garments is not realistic for consumers. Therefore, it is recommended that a new laboratory method for wet laundering e-textiles be developed in which tap water composition (mineral and/or water hardness)³⁶ is reported and calculated for testing to be able to inform the consumer accurately how to care for their smart garment properly.

Standard detergent: In order to establish a baseline for detergent comparison and serve as a representative of common detergents available for consumer purchase and use, AATCC standard detergent was used in this study. As indicated in the results, standard detergent showed minimal change on the surface resistivity of the e-textiles, thus suggesting that the e-textiles will continue to perform as expected over multiple launderings when using a standard detergent (with a high concentration of builders in its formula). Therefore, based on the findings of this study we support the continuation of promoting industry standard detergent use in future e-textile-focused laundering procedure development. However, as many consumers may prefer to use liquid detergents (or pods),⁴⁰ standard developing organizations may consider developing a liquid equivalent to the standard power. This is especially important as some new laundering machines offer a ‘self-filling detergent’ feature (‘smart dispense’; ‘load and go’) that require use of a liquid detergent.

Reporting: As research and development around e-textiles are evolving, discussing different aspects of the e-textile within the study, manuscript, and/or standard test method are important for continued advancement of this field. The following bullet points were developed to serve as considerations for individuals involved in establishing standard testing procedures and/or best practices involving e-textiles and smart garments:

Specimen reporting of metallic components: This may be at the yarn or textile level. Reporting how metal is added to the product (e.g. dipped, plated, etc.) may assist in explaining study results and may also lead to changes in content/processes shared from e-textile manufacturers. An additional point to consider is how coated metallic components may influence other performance tests (such as abrasion).

Data reporting: Reporting percentage change in addition to raw resistivity readings may be viewed as an advantageous reporting structure that expands different data collection values. Another idea may involve the reporting (based on development) of a threshold (or resistivity range) for laundering of e-textiles based on end purpose or product. This may assist researchers and product developers to select materials (and place into products) more intentionally, which may result in improved product performance and longevity.

Wash water reporting: Water from home laundering is typically routed through a series of treatment procedures that can then be returned to serve as drinking water, water for irrigating crops, water for livestock or sustaining aquatic life, or back into the home to re-wash laundry. Therefore, it is worthy to consider development (and reporting) of metallic particle release (change in water composition – before, during, and after the laundering procedure) experienced in e-textile laundering. The impact of metallic particles in water is unknown, but is worthwhile to consider as the wearables market continues to expand.

Suggestions for smart garment care labels

As mentioned earlier, the Federal Trade Commission requires that all garments, which include smart garments (that include e-textiles in the product), are labeled with fiber content and instructions for how to launder or care for the product. In addition, if warnings exist that may damage the product, these need to be stated so that consumers/users understand what they need to do (or not do) to ensure product performance and longevity. The five key conditions addressed on a garment label involving care are: (a) washing method and temperature; (b) use of bleach; (c) drying method and temperature; (d) use of iron (temperature and steam compatible); and (e) warning about harmful procedures. Based on the findings of this study, suggestions for care labels can be proposed for labeling development regarding bleach and warnings. The other care label conditions (washing method, drying method, and ironing) were not included in the study’s experimental structure, but are worth noting as potential future areas to study.

Bleach

In this study, color-safe bleach on e-textile surface resistivity was explored as a laundering additive. Based on the findings, bleach is not recommended to combine with e-textiles as metallic components can act as catalysts for hydrogen peroxide decomposition. There are different types of ‘bleach’ on the market so care labels need to specify active ingredients of specific ‘bleaches’ to avoid. For example, care labels may state ‘do not wash in x, y, z specific bases’ (bleaches).

Care warnings

Large increases in surface resistivity after laundering suggest that the associated laundry additive is unsuitable for laundering e-textiles and may require new content to be developed for smart garment care labels. For example, in this study, the plant-based detergent yielded the poorest performing surface resistivity. In order for consumers to ensure optimal performance of their smart garment it is recommended that plant-based detergents are not used to launder these items. Therefore, care label developers may find it helpful to develop a new care symbol (or icon) that communicates this warning so that consumers do not use an eco-laundering detergent. It is important to note that descriptions of newly developed icons/symbols will need to be shared with the consumer in some way (perhaps on the garments hangtag in proper language options).

Overall, this study provided a greater understanding of the impact of laundering conditions, in the form of laundering additives, on e-textile performance. The findings provided further insight into aspects of e-textiles that consumers will need to understand to ensure proper care, satisfaction, and longevity of their smart clothing product.

Conclusions and future work

E-textiles are complex materials that require meticulous design, engineering, and manufacturing processes. Smart garments made from e-textiles will likely be expensive; thus, consumers will expect garment longevity. Washability is critical to the success of a smart garment because wash conditions determine garment longevity.¹⁰ Thus, designers and manufacturers of smart clothing must consider the effects of laundering, considering processes and well as additives^39–41 in the product development process. Overall, the findings of this study provide insight into understanding the impact of laundering, with a focus on additives such as detergents, bleach, and softener, on the surface resistivity performance of select e-textiles.

ArgenMesh, Cobaltex, Circuitex, Nickel Copper Ripstop, and Silver Ripstop have initial surface resistivity less than 1 Ω/square, making them appropriate for use in applications conveying electrical signals. If we consider 1 Ω/square the highest acceptable surface resistivity for these e-textiles (as all e-textiles in this study recorded values within this limit), none reached a point of failure after the simulated five launderings with any of the laundry additives examined; however, a garment would endure many more launderings in its lifespan. All seven e-textile retained functional conductive properties; however, the end application and corresponding target surface resistivity threshold should be considered in the product development process. Once end products have been developed, the whole garment must then be tested in order to develop further appropriate and accurate care instructions.¹¹

It should be noted that Cobaltex showed a spike in resistivity after laundering with distilled water only, but this specimen sustained a rigid crease during laundering. It has been shown that wrinkling may cause increased resistance.³¹ This creasing may explain the increase in resistivity, rather than exposure to water, and is noteworthy for future research.

Looking across all specimens and resistivity changes post-laundering, it was observed that standard detergent produced the least percentage change in surface resistivity. Observing trends in home laundering machine style and consumer options and use preference for detergents, researchers involved in this study call for the development of a synthetic liquid detergent similar to the formula of the powder/dry standard detergent used in this study to wet launder e-textiles, or products made from e-textiles, reviewed in this study. Findings from future research with the proposed detergent may then inform more accurate care instructions.

As with many experimental structured research studies there are limitations due to the need to control the variables under review and carry out a measurable and digestible study. In this study, a limited number of e-textiles and laundering products was examined. The e-textiles were selected for inclusion based on the fact that these particular textiles were available for purchase and showed potential for wearable garment integration (or application). This study also only focused on one type of laundering condition. Future studies are warranted to explore the surface resistivity impact from dry cleaning or other nonwet laundering conditions. Likewise, while this study explored a variety of care additives, many more are available on the market and are worthy of study. Another limitation that lends itself to future research opportunities involves the test method employed. In this study, the Rotawash was used which allowed for great control of the wet laundering conditions; however, it produces a highly atypical wet laundering environment for a smart garment. The researchers recommend expanding work to include wet laundering studies to measure the resistivity impact and chemical influence from different municipal water sources and home laundering machine equipment (such as AATCC TM 143; note that other TMs exist that involve home laundering). Finally, a limitation of this study was the testing of specimens, rather than a full product. As research and product development continues to advance the smart clothing wearables market, future research opportunities exist at the product level.

Looking beyond the limitations of this experimental study to focus on opportunities to build on the work and findings reported, the following future research recommendations are outlined. This research could be expanded on by furthering the number of washes and measuring resistivity after multiple Rotawash launderings using controlled hardness water. This would provide data at 5, 10, 15, 20+ simulated launderings, which would speak to the longevity of e-textiles. Future studies should measure resistivity incrementally after each wash in a succession of launderings to determine the point of conductive failure. Future research should investigate the combination of detergent with fabric softener and bleach as these products are commonly used together in home laundering. It may also be advantageous to evaluate the effects of laundry additives containing dyes and perfumes. Fragrance boosters are relatively new laundry additives that could affect the functionality of e-textiles and may be worthy of study. Future wash fidelity studies should also focus on the potentially detrimental environmental effects of metallic shedding from e-textile materials. The environmental impact of laundering smart garments, that embody e-textiles, must be considered as harmful metals may be entering the water supply system through wash water effluent.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Additional details and data from this study may be acquired by contacting the corresponding author.

ORCID iDs

Rachel J Eike

Dawn Michaelson

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