Liquid Sweat Research Articles

Double-side super-hydrophilic/superspreading fabric for ultrafast asymmetric sweat transport and in-situ power generation

Asymmetric (viz. Janus or one-way transport) fabrics that can promote directional sweat transport from the next-to-the-skin surface to the outer surface by the hydrophobic-hydrophilic difference across the fabric thickness have been developed. However, the hydrophobic next-to-the-skin surface inevitably increases the inherent resistance to sweat transportation into the fabric, fundamentally hampering its moisture management property. In this work, by selectively coating a poly-pyrrole (ppy) film with Turing patterns on one side of the fabric to achieve superspreading property, we demonstrated an all-hydrophilic asymmetric fabric with outstanding one-way liquid sweat transport property. Benefiting from the low resistance of sweat absorption, the all-hydrophilic fabric exhibited a dramatically increased directional sweat transport rate of 13.6 mm/s, which is 5.9 times that of the untreated fabric, and significantly enhanced sweat evaporation rate (1.56 times of the untreated fabric) and cooling performance. Furthermore, the conductive ppy-fabric, during the process of ultra-fast sweat transport, generated a potential of 150 mV over an area of 2×2 cm2 or scalable electrical energy output of 2.5 mW/m2 under continuous sweat transportation. The finding in this work not only provided new insight into the design and development of asymmetric fabric for ultrafast sweat transport but also proposed a novel method for the in-situ energy harvesting during the sweat transportation process, which has potential applications in self-powered smart wearables and functional clothing.

Textile sorption and release of odorous volatile organic compounds from a synthetic sweat solution

Body odorants typically transfer to clothing fabrics by way of liquid sweat, yet investigations of odor retention in textiles often neglect this route of exposure in their test procedures. This paper describes a novel method for transferring selected odorous volatile organic compounds to six types of textile fibers in yarn bundle form by an aqueous sweat solution. Headspace volatile organic compounds varying by chemical class (ketones, aldehydes, carboxylic acids) were monitored at discrete time intervals (30 min, 3 h, 24 h) using proton transfer reaction mass spectrometry. Lower intensities of ketones and aldehydes were detected in the headspace above cellulosic fibers (cotton, mercerized cotton, viscose) than above wool, nylon, and polyester fibers at 30 min. A rapid decrease in ketones occurred for all fibers, but lower intensities of ketones were released after 3 h for cellulosic and wool fibers. Nylon fibers typically released the highest amounts of ketones and aldehydes at 30 min, but by 24 h higher intensities of these compounds were released from polyester. Carboxylic acids exhibited minimal differences in intensities between 30 min and 3 h, with few differences evident among fiber types. Understanding the preferential sorption of odorants when clothing is exposed to volatile organic compounds in aqueous solutions such as sweat is enhanced from the results of this investigation.

Sweat and microwave manageable textiles for efficient personal thermal comfort and electromagnetic radiation defend

Although electromagnetic interference (EMI) shielding fabrics integrated with absorption and reflection have recently shown attractive defense performance, effective sweat management is still scarce for simultaneously achieving sustainable personal comfort. Here, we demonstrate a hierarchically arrayed fabric for personal EMI shielding and thermal comfort management. By integrating EMI shielding interfaces and spatially distributed channels, the fabric exhibits high-efficiency EMI shielding ability and enhanced sweat transportation. We demonstrate the tuning electromagnetic response with maximum EMI shielding efficiency value of ∼118 dB and continuous one-way liquid sweat flow with a temperature of ∼3.5 °C lower than that of conventional EMI shielding fabrics. In addition, the fabric shows substantially stabilized EMI shielding performance for long-term use by transporting and repelling internal liquid sweat. The high performance of our fabric makes it a promising design paradigm for personal electromagnetic interference shielding and thermal management.

High-Performance Liquid-Repellent and Thermal-Wet Comfortable Membranes Using Triboelectric Nanostructured Nanofiber/Meshes.

Skin-like functional membranes with liquid resistance and moisture permeability are in growing demand in various applications. However, the membranes have been facing a long-term dilemma in balancing waterproofness and breathability, as well as resisting internal liquid sweat transport, resulting in poor thermal-wet comfort. Herein, a novel electromeshing technique, based on manipulating the ejection and phase separation of charged liquids, is developed to create triboelectric nanostructured nano-mesh consisting of hydrophobic ferroelectric nanofiber/meshes and hydrophilic nanofiber/meshes. By combining the true nanoscale diameter (≈22nm), small pore size, and high porosity, high waterproofness (129kPa) and breathability (3736g m-2 per day) for the membranes are achieved. Moreover, the membranes can break large water clusters into small water molecules to promote sweat absorption and release by coupling hydrophilic wicking and triboelectric field polarization, exhibiting a satisfactory water evaporation rate (0.64g h-1 ) and thermal-wet comfort (0.7°C cooler than the cutting-edge poly(tetrafluoroethylene) protective membranes). This work may shed new light on the design and development of advanced protective textiles.

Evaluation of fabric liquid and moisture management properties at simulated skin and sweat temperatures using an advanced novel sweating simulator

The moisture management performance of fabrics under profuse sweating (i.e. the ability to sweat absorb, spread, evaporate, drip, and dry) is crucial to the wearer’s comfort and performance, and should therefore be accurately and realistically tested for quality evaluation and product development. However, it is challenging to measure these properties simultaneously under realistic conditions using current evaluation techniques or testing standards. In this article an advanced version of the novel sweating simulator (NSS) is presented with which the skin temperature, sweat temperature, active body posture, and varying sweating rates can be simulated and multiple fabric moisture management properties including liquid sweat accumulation rate, multi-directional spreading rates, variations in downflow rates caused by increasing liquid accumulation, discharge rate, evaporation rate, drying rate, and drying time can be measured concurrently and in real-time during the simulated sweating and drying phases. The high accuracy and excellent reproducibility of NSS measurements were demonstrated through testing eight different kinds of commercial moisture management fabrics to show the potential applications of the NSS. It is believed that the novel sweating simulator, owing to its comprehensive testing capability, will play a key role in the development of next-generation moisture management fabrics for numerous apparel and technical applications.

Influence of Stretching on Liquid Transport in Knitted Fabrics

The transport of liquid sweat in clothing worn close to human skin is very important from the point of view of the thermo-physiological comfort of clothing users. It ensures the drainage of sweat secreted by the human body and condensed on the human skin. In the presented work, knitted fabrics made of cotton and cotton blends with other fibers (elastane, viscose, polyester) were measured in the range of liquid moisture transport using the Moisture Management Tester MMT M290. The fabrics were measured in unstretched form and stretched to 15%. Stretching of the fabrics was performed using the MMT Stretch Fabric Fixture. Obtained results confirmed that stretching significantly changed the values of parameters characterizing the liquid moisture transport in the fabrics. Before stretching, the best liquid sweat transport performance was stated for the KF5 knitted fabric made of 54% cotton and 46% polyester. For this, the greatest value (10 mm) of maximum wetted radius for the bottom surface was obtained. The Overall Moisture Management Capacity (OMMC) of the KF5 fabric was 0.76. This was the highest value among all values obtained for the unstretched fabrics. The lowest value of the OMMC parameter (0.18) was stated for the KF3 knitted fabric. After stretching, the KF4 fabric variant was assessed as the best one. Its OMMC improved from 0.71 before stretching to 0.80 after stretching. The value of the OMMC for the KF5 fabric remained after stretching at the same level (0.77) than before stretching. The most significant improvement was observed for the KF2 fabric. Before stretching, the value of the OMMC parameter for the KF2 fabric was 0.27. After stretching, the OMMC value increased to 0.72. It was also stated that the changes in the liquid moisture transport performance of the investigated knitted fabrics were different for the particular fabrics being investigated. Generally, in all cases, the ability of the investigated knitted fabrics to transfer liquid sweat was improved after stretching.

Liquid Moisture Transport in Cotton Woven Fabrics with Different Weft Yarns.

Moisture transport in fabrics influences the thermal comfort of clothing due to drainage of sweat secreted by the human body. The moisture transport through textile materials takes place in two ways: water-vapor transport and liquid moisture transport. Both ways are equally important. In the present work, liquid moisture transport in cotton woven fabrics with different weft yarns was investigated. Measurement was done using the Moisture Management Tester MMT M290. The obtained results confirmed that the linear density of weft yarn significantly influenced the values of all parameters characterizing liquid moisture transport in the investigated fabrics. The best performance in liquid moisture transport was achieved by weft yarn of linear density 30 tex. For this fabric variant, the maximum wetted radius for both surfaces was the biggest: 25 mm for the inner and 26.6 mm for the outer surface of the fabric. This means that the fabric spread the liquid on the biggest area compared to the other variants being investigated to facilitate an evaporation of liquid sweat. The fabric variant with 30 tex weft yarn showed the highest spreading speed: 5.83 mm/s for both sides, and the shortest wetting time: 2.83 s for the inner and 3.00 s for the outer side of the fabric. The higher the linear density of weft yarn, the worse the ability of cotton woven fabrics to ensure liquid moisture transport.

A new test method for evaluating the evaporative cooling efficiency of fabrics using a dynamic sweating hot plate

The lack of direct measures of the ability of a fabric to cool the skin by liquid sweat evaporation is a critical gap in available laboratory tests for evaluating the comfort of active wear clothing materials. This paper describes a novel method designed to evaluate the evaporative cooling performance of fabrics in a protocol that simulates active wear, including sweating and drying periods, in a continuous one-step procedure. It uses a dynamic sweating hot plate to measure the latent heat absorbed by fabrics in sweat evaporation, and in drying after sweat absorption. The efficacy of the method is demonstrated using a selected set of high-wicking polyester and a cotton knit t-shirt material that have different moisture absorption, wicking and drying properties. The cooling efficiency test shows that high-wicking polyester fabrics provide larger evaporative cooling in the sweating phase, where it is more likely to convey cooling benefits to the skin. Cotton fabrics absorb more latent heat in the drying phase, where the cooling effect may contribute to chilling effects. It provides an ideal platform to observe the dynamic relationship between patterns of wicking and liquid moisture spreading in fabrics and the evaporative cooling provided by the test materials. It shows that the location of wicked moisture in the fabric is a critical determinant of potential cooling effects. It also shows that a fabric’s wicking ability is not always an accurate predictor of its cooling efficiency. This new test method has provided a unique tool for directly characterizing the cooling efficiency of clothing materials using a protocol that accurately simulates sweating generation and drying in actual active wear scenarios.

Omniphobic polyurethane – superabsorbent polymer – fluoropolymer surface coating on cotton fabric for chemical protection and thermal comfort

This research aims to develop chemical protective clothing via a functionalised surface coating on cotton fabric for simultaneous barrier performance and thermal comfort. An omniphobic protective layer on the cotton fabric was developed through a polyurethane – superabsorbent polymer – fluoropolymer coating to protect the penetration of water, oils and liquid chemicals. It was found that the padding of coated specimens with fluoropolymer provided a substantial improvement of hydrophobicity, and therefore, exhibited a high-water contact angle (114.06°) and a maximum water repellency rating of 100. The highest aqueous liquid repellency (8.0) and satisfactory oil repellency (7.5) with resistance against liquid chemical penetration were also achieved after the treatment with fluoropolymer. Moreover, the coated fabrics integrated with superabsorbent polymer showed an improved dry heat resistance and moisture vapour transmittance, consequently a high evaporative cooling index to create a favourable thermal comfort between the skin and the apparel in hot and humid conditions. Other comfort parameters, including air permeability and moisture management performance were compromised to a certain level due to a continuous and hydrophobic barrier layer on the fabric surface that hindered the transferring of air and liquid sweat through the coating.

Integrated cooling (i-Cool) textile of heat conduction and sweat transportation for personal perspiration management

Perspiration evaporation plays an indispensable role in human body heat dissipation. However, conventional textiles tend to focus on sweat removal and pay little attention to the basic thermoregulation function of sweat, showing limited evaporation ability and cooling efficiency in moderate/profuse perspiration scenarios. Here, we propose an integrated cooling (i-Cool) textile with unique functional structure design for personal perspiration management. By integrating heat conductive pathways and water transport channels decently, i-Cool exhibits enhanced evaporation ability and high sweat evaporative cooling efficiency, not merely liquid sweat wicking function. In the steady-state evaporation test, compared to cotton, up to over 100% reduction in water mass gain ratio, and 3 times higher skin power density increment for every unit of sweat evaporation are demonstrated. Besides, i-Cool shows about 3 °C cooling effect with greatly reduced sweat consumption than cotton in the artificial sweating skin test. The practical application feasibility of i-Cool design principles is well validated based on commercial fabrics. Owing to its exceptional personal perspiration management performance, we expect the i-Cool concept can provide promising design guidelines for next-generation perspiration management textiles.

Nature-inspired moisture management fabric for unidirectional liquid transport and surface repellence and resistance

Humans sweat to cool down and dissipate heat in indoor and outdoor environments. The evaporation of liquid sweat absorbs body heat and reduces skin temperature. However, when the wearer sweats a lot or is fully wet by external liquids such as rain, even the best moisture management fabrics can be soaked and saturated, becoming unbreathable, heavy, and clingy, and imposing significant reduction in wearer’s comfort and performance. Herein, inspired by liquid collection and release processes on the desert beetle’s skin, we develop an innovative moisture management fabric, transferring excessive sweat from the skin side to the outer surface of the fabric and dissipating it in terms of droplets, while blocking and repelling the external liquids. The completely unidirectional liquid transport is achieved in the developed nature-inspired fabric, which is treated with global hydrophobicity and discrete localized wettability gradient by a sustainable plasma treatment method. Moreover, the proposed fabric shows improved thermal comfort with high breathability, reduced clinginess, and dry skin surface. Specifically, a highly directional water transport capability of 1647.9% is obtained using a Moisture Management Tester, while the water resistance from the external side is equivalent to a water column of 15 mm height. The water flow rate from the inner skin side to the environment is equal to 91.44 g/min∙m2, which is much higher than that of the high sweating rate of an adult (i.e., 15 g/min∙m2). Regulation of liquid movement in the proposed fabric will attract wide potential applications, including sportswear, worker uniform, casualwear, protective clothing, firefighter apparel, and military clothing. Maintaining moisture and thermal comfort while adapting to the expanded ambient temperature range of the air-conditioning system will also be desirable in building energy conservation.

A study on porosity related aspects of cotton knitted fabric with single jersey structure for improved comfort application for garment

Knitted fabrics are the preferred structures in athletic wear in which demand for comfort is a key requirement. Heat and liquid sweat generation during athletic & exercise activities must be transported out and dissipated to the atmosphere. A key property influencing such behaviors is porosity. Two parameters that characterize it are pore size and pore volume. One of the objectives in this research was to come up with models that can predict inter yarn pore size and pore volume for simple weft knitted structures, from fabric particulars, such as courses and Wales, count, yarn size, stitch density, thickness and other geometrical details of the fabric, which characterize the structure. Such a model was developed that was based on the geometry of the unit cell of a single loop. The experimental work in this project involved using a set of 16 knitted fabrics that differ in course count and examining their pore structure and porosity related characteristics. The values of pore size and pore volume were calculated, those of pore size were measured with image analysis, and other parameters. The effects of course count and washing on stitch density, stitch length, fabric thickness and pore size are examined in details.

Moisture transfer of the clothing–human body system during continuous sweating under radiant heat

Mass transfer due to perspired moisture in a clothing system is critical for the understanding of thermo-physiology and thermal protection of a clothed body. Previous studies usually investigated moisture transfer without considering the effect of liquid sweating or external heat hazards. To understand the mechanisms of sweat evaporation, accumulation and dripping with continuous sweating under radiant heat, a multi-phase experiment was designed with a sweating Torso. The concept of clothed wettedness was proposed to understand sweat evaporation of the clothed body. Results showed that the evaporation rate of the clothed body increased with increasing perspiration rate and the rate increase can be explained by the material properties (e.g., material composition, hydrophilicity and evaporative resistance ([Formula: see text])), which affected the sweat accumulation ability. Results also demonstrated a dual relationship of [Formula: see text] with the evaporation rate of the clothed body. Firstly, the evaporation rate was increased for greater [Formula: see text] due to the higher moisture accumulation. Secondly, when [Formula: see text] exceeded a certain value, the evaporation rate decreased with greater [Formula: see text] due to the reduction in the mass transfer coefficient. For radiant heat exposure, evaporated sweat may condense on the skin surface, decreasing the evaporation rate and increasing the dripping rate. The sweat transfer process was also investigated in detail by the combined analysis of the sweat transfer rate and the evaporative cooling efficiency. This study provides insights into how continuous liquid sweat transfers and evaporates in the clothed body and its interaction with clothing material and environment radiant heat, contributing to the understanding of thermo-physiological burden and thermal protection of the clothed body with intensive activities.

Breathable dual-layer textile composed of cellulose dense membrane and plasma-treated fabric with enhanced comfort

The superiority of dense polymer membranes intended for protective clothing has been well demonstrated in literature. However, the best protection provided by dense membranes may be balanced out by less breathability and retention of liquid sweat on the skin surface, both of which contribute to wearer discomfort. Despite being imperative, the simultaneous investigation of breathability and liquid sweat transfer in dual-layer textiles composed of a dense membrane and a fabric has received less attention. This issue is addressed in the present work through developing dual-layer textiles composed of commercially available as-received fabric with slow water absorption rate and cellulose dense membrane. To this end, three cellulose dense membranes are produced through two different techniques: (1) solution casting of linter/(4-methylmorpholine N-oxide monohydrate (NMMO)/water) and linter/(LiCl/N,N-Dimethylacetamide (DMAc)) solutions, (2) Treatment of dry cast cellulose acetate (CA) solution with NaOH aqueous solution to convert CA dense membrane to cellulose dense membrane. The prepared dense membranes are integrated with fabric to develop dual-layer textiles. It is demonstrated that although the developed dual-layer textiles have acceptable breathability (water vapor transmission rate > 400 g/(m2 day)), however, they perform poorly to transfer liquid sweat from the inner layer (fabric with slow water absorption rate) to the outer layer (cellulose dense membrane) where the transferred sweat is air-dried. Through implementing moisture management test, it is shown that cost-effective and non-destructive treatment of the inner layer by O2 plasma imparts excellent moisture management properties to the produced dual-layer textile. Therefore, it can be said that the developed dual-layer textile may be considered to represent the best compromise between wearer comfort (breathability and liquid sweat transfer) and protection.

Skin Capacitance Mapping of Eccrine Sweat Gland Activity during Pregnancy

Skin capacitance mapping is a real-time non-invasive method useful in the assessment of eccrine gland activity. We presently revisit and explore the sweat gland production in pregnant women. Sprouts of sweat vapour are progressively increased during pregnancy by recruiting increasing numbers of active sweat pores. An overall moisturization of the stratum corneum ensues in absence of increased liquid sweat production. These aspects are conveniently assessed using skin capacitance mapping. The sweat duct opening could represent an increased way for percutaneous penetration of some xenobiotics during pregnancy.

Sweat Gland Awakening on Physical Training: A Skin Capacitance Mapping Observation

Skin capacitance mapping (SCM) is an established real-time non- invasive method useful in the assessment of sweat production. We presently review and explore the sweat gland production following a mild 10-min physical training on a cycloergometer. Sprouts of sweat vapor are progressively increased by recruiting increasing numbers of active sweat pores. An overall moisturization of the stratum corneum ensues, and liquid sweat appears in a further step. These aspects are conveniently assessed using SCM while blind assessments of the skin surface water loss cannot distinguish these functional features.

Moisture management properties of plain knitted fabrics made of natural and regenerated cellulose fibres

Moisture management is a complicated process which is known to be influenced by a variety of fabric characteristics such as fibre nature (hydrophilic or hydrophobic), porosity and thickness. There are different aspects of the moisture management properties of textile materials since water transport in textile materials can be in the form of liquid and vapour. The ability of textile materials to transfer water vapour allows the human body to keep thermal balance due to evaporation. With stronger physical activity of a person when the body produces a large amount of heat, the skin perspiration increases (in order to regulate the body temperature) and liquid sweat should be taken from the skin, otherwise it will worsen the sense of comfort. The aim of this research was to investigate the factors influencing moisture management properties of plain knitted fabrics at the three scale levels, i.e. microscopic (fibre type), mesoscopic (yarn geometry) and macroscopic (fabric porosity) levels. Plain knitted fabrics were produced from the two-assembled hemp, cotton and viscose yarns under controlled conditions so as to be comparable in basic construction characteristics, but varying in yarns geometry. Evaporative resistance test reflecting vapour transport and water distribution test reflecting liquid transport in the knitted fabrics were conducted. To determine the statistical importance of the results, analysis of variance (ANOVA) was applied. As a consequence of the geometry and deformation behaviour of the fibres used and spinning techniques applied, the yarns differed in both packing density and surface geometry, thus determining the pore distribution. Due to loose structure of the cotton yarn, the cotton knitted fabric was characterised by the lowest free open surface (macroporosity) exhibiting the lowest both water vapour and liquid permeability. Although having the highest macroporosity, the water vapour and liquid transport capability of the hemp knitted fabric was lower than that of the viscose knit. The best moisture management properties of the viscose knitted fabric were resulted from viscose affinity for water absorption and increased surface area of the viscose yarn. The results obtained proved that variations in any of the hierarchical structure levels can modify moisture transport ability of textile fabrics. Therefore, the moisture management properties of textile materials can be guided in a desired direction by the appropriate selection of fibres and careful design of yarn structure.

Effect of fiber count and knit structure on intra- and inter-yarn transport of liquid water

The moisture transport in fabrics determines its cooling effect and therefore the wearing comfort during sudorific activities. When liquid sweat is present, the moisture absorption by a fabric is characterized by the in-plane and transplanar wicking. We investigated the effect of fabric structure and fiber count on wicking by X-ray projection images using four different polyester knit structures (rib, eyelet, interlock and modified interlock, all hydrophilic), as well as five rib knits with different fiber counts per yarn (24–192, all quasi-hydrophobic with water contact angles 89 ± 1). Experiments were conducted with two-layer samples of the same fabric exposed to different external pressures. The liquid was transported in recognizable waterfronts, which can be interpreted as distinct intra-yarn and inter-yarn in-plane wicking fronts. For layer-to-layer wicking in hydrophilic samples, pressure-dependent time delays were observed; the delays correlated negatively with the relative void area at the interface, and were shortest for the rib knits. For the quasi-hydrophobic samples, however, the liquid wicked up to the upper layer without time delays, which was due to the liquid being pressed into the fabric, that is, due to the supply-driven flow. We distinguish this from the supply-limited flow, which is driven by capillary forces. The presented results have implications for the design of clothing systems for sudorific activities.

Analysis of water absorbency into knitted spacer structures

The absorbency properties of knitted structures are very important in designing garments that both remove liquid sweat from the skin and provide tactile and sensorial comfort to the wearer. Water absorbency by knitted spacer structures was experimentally investigated using a gravimetric absorbency tester to record absorbency rate, total absorbency and time taken to saturate the structure. The geometry of spacer structures was analysed and a model created to define the capillary characteristic in the spacer yarn. Absorbency into the spacer structures was modelled using the fabric parameters, the capillary radius and the properties of water. Experimental and theoretical results were compared to validate the models.

Impact of Fabric Moisture Transport Properties on Physiological Responses when Wearing Protective Clothing

This purpose of this study was to investigate the impact of fabric moisture transport properties (MTP) on physiological responses when wearing protective clothing. Ten healthy subjects wore two kinds of personal protective equipment (PPE) ensembles and exercised on a treadmill, worked on a computer, and moved a mannequin in an environment that simulated where health carers work. PPE1 consisted of cotton underwear and 100% polyethylene outerwear. PPE2 consisted of cotton underwear with moisture management function and outerwear made of waterproof breathable fabric. The results showed that there were significantly higher cumulative one-way transport capacity, liquid moisture management capacity, and wetting time in PPE2 than in PPE1 underwear. There was significantly higher water vapor permeability (WVP) in PPE2 than in PPE1 outerwear. Deep ear canal temperature, mean skin temperature, and chest wall skin and clothing microclimates (temperature and humidity) were significantly lower with PPE2 than PPE1. The level of plasma oxygen saturation was significantly higher with PPE 2 than PPE1. In the present study, due to the MTP of the fabrics, liquid sweat transferred from the skin surface to the opposite surface quickly and speeded up the processes of evaporation and heat dissipation. It was concluded that the fabric's MTP, when incorporated into protective clothing, is the main physiological mechanism for reduced heat stress.