Phase change materials in textiles: synthesis,properties,types and applications

Abstract

Phase change properties of clothing gain attention of the researcher now for their significant unique ability to absorb, release, store, and deposit temperature during phase transition. Phase change materials have been widely used and utilized now in various fields, as well as in textiles. In apparel products, phase change materials are used to introduce various special features, especially its make garments smart or have technical functions. Various researchers pay attention to this area for its large organic and inorganic resources. This review paper summarizes the road map of phase change materials in textiles, including the way of synthesis, the characteristics of phase change materials, and their applications in smart textiles. In addition, the diverse usage of phase change materials in different textiles is discussed. It also tries to cover the principles of phase change behavior, phase change material types, and their thermal properties. After that, the paper will try to mention the potential benefits and challenges associated with utilizing phase change materials in various applications that have been discussed here. Finally, this paper concludes with the mass acceptance of phase change materials in various technological advancements, along with a short note about future research opportunities.

Keywords

Phase change materials PCM smart textiles modern textiles high-performing textiles

Introduction

In this era in the world, textiles play a vital role in our daily lives, and textiles have various applications in human life. Similar to other fields’ advancements, the day by day advancement of textiles has also occurred. In recent years, the integration of phase change materials (PCMs) in textiles is a significant achievement of science. Textile-associated PCMs change the properties of clothes by increasing flexibility and comfort, which has great applications in sportswear, bedding, automotive textiles, agrotextiles, aerospace textiles, and medical textiles, etc.^1,2

Multiple factors influence the successful integration of PCMs in textiles. Although the properties of PCM textiles depend on the formulations of PCM, PCM formulation directly influences thermal performance, durability and compatibility with the fabric manufacturing processes.^3,4

PCMs refer to substances that shift from one state to another, such as solids that turn into liquids or liquids that turn into solids depending on the circumstances. When compared with sensible heat storage materials, PCMs have outstanding thermal characteristics, and may accumulate potent heat enthalpy with a density (per unit volume or mass) of high storage.^1,5 PCM textiles respond to the changes of the environment like changes of temperature in the different bodies of humans. When temperature increases in the body, microcapsules used in textiles such as PCM absorb the heat and store energy in a different phase. The capacity of thermal insulation generally differs from the insulating qualities of any material. PCMs during heating incorporate energy and during cooling release energy, and are used to improve it.^2,5,6

In textiles, PCM is integrated into various forms, such as microencapsulation, fiber technology, coating, and lamination. The microclimate between garments and the human body can thus be controlled using microcapsules and packs, which has led to the development of thermal comfort by reducing heat stress. On the other hand, PCM textiles help to control body temperature, which is overheating, they also reduce shivering as well as helping to redistribute warmth equally, which ultimately increases comfort. Depending on time (day or night) the applications may vary.

Principle of phase change behavior

The mechanism of phase change in textiles shows the ways of interaction of the PCM with the environment, and phase transition within the structure of the textiles. The thermal characteristics and performance of the textile based PCMs were determined by these mechanisms. In addition, the design of the textiles was impacted by the mechanism of PCM.

Melting and solidification

Melting and solidification is the most common mechanism in the textile-based PCMs. In this mechanism, it works – it reaches the temperature of its melting point, then it absorbs heat from the surroundings, and changes its state from solid to liquid (see Figure 1). The energy which is absorbed in this transition phase is named latent heat of fusion. After that, by releasing heat PCM again solidifies, and also stores heat back into the environment. To provide thermal regulation and comfort to the wearer this phase change mechanism allows PCM to keep a constant temperature.^3,7

Figure 1.

Melting and solidification mechanism of phase change material (PCM).

Crystallization and fusion

Sometimes PCMs are developed by crystallization and fusion mechanisms. When the temperature of the PCM decreases below its freezing point then it goes to solidify a crystalline structure, which is called crystallization. In this mechanism during phase change the material releases heat. On the other hand, by absorbing heat crystalline PCM goes back into the liquid state, which is called fusion. Basically, this mechanism is used in a few inorganic PCMs.

Supercooling and nucleation

During phase change, materials remain in the liquid state at below-freezing temperatures then the supercooling mechanism has occurred. In the absence of the nucleation site this happens, also the nucleation site is responsible for forming solid crystals. Supercooling leads to unpredictable phase change behavior, and also it decreases the efficiency and creditability of PCM-based textiles. After all, to overcome this supercooling issue, a technique named nucleation or nucleation agents are applied to induce the formation of solid crystals at lower temperatures and facilitate more controlled and efficient phase change.

Microencapsulation and coating

The encapsulated or coated mechanism is the most popular to integrate PCMs into textiles. By this mechanism, it ensures a uniform distribution and stability of PCMs in the textile structure. Typically, microencapsulation is made of polymer, which induces encapsulating PCM droplets within microcapsules and formed composite materials. These droplets can be applied directly to the textile fibers or fabric. Another way for PCMs is coating techniques. By coating of the textile surface, phase change characteristics can be gained, these encapsulation and coating mechanisms provide protection to the PCM from leakage, and facilitate controlled heat transfer during the phase change process (see Figure 2).^5,6,8

Figure 2.

Flow diagram of a typical complex coacervation encapsulation process.

Types of PCMs

Organic PCMs

Organic PCMs have the ability to store and release thermal energy during phase transitions between solid and liquid states. These PCMs are composed of organic compounds such as hydrocarbons or fatty acids, which have induced thermal properties for various applications (as given by Table 1).

Table 1.

Properties of organic PCMs

Properties	Range
Melting point	−5–100°C
Latent Heat	100–400 J/g
Heat capacity	High
Cost	Relatively low cost
Availability	Available

The application of organic PCMs into textiles integrates thermal regulation properties, also by this temperature can be controlled in clothing, sportswear and bedding products.

In long term stability organic PCMs have low performance, in addition they need to be addressed separately because of potential leakage or subcooling issues.

Inorganic PCMs

Inorganic PCMs come from inorganic materials such as salts, metals, alloys, etc. In textiles the usage of inorganic PCMs gives unique advantages and opportunities for thermal regulation and energy management. In these, reversible phase transitions between the solid and liquid states occur, which is indicative of proficiency to reserve and release thermal energy during this process (as given by Table 2).

Table 2.

Properties of inorganic PCMs

Properties	Range
Thermal conductivity	High
Latent heat	High
Thermal stability	High

The application of Inorganic PCMs has various advantages. Inorganic PCMs achieve thermal regulation properties of clothing according to the requirement of the body. They can absorb and release heat by which comfort of the clothing will be increased. These inorganic PCM-based textiles can also respond to changes of environmental temperature, and by dynamic adjustments optimal comfort can be achieved. They are widely used in curtains, wall coverings, etc.

Inorganic PCMs may interact chemically with some textile materials; for that reason they have long-term stability and good performance. To prevent leakage of this type of PCMs, use in textiles by coating or the encapsulating method.

Thermal properties of PCMs

Melting point

Materials that undergo phase changes have a huge storage capacity of potential energy due to their ability to change state at constant temperatures.

Among the most efficient uses for these kinds of materials in textiles is thermal energy storage (TES), which is possible with phase transition materials with melting points ranging from 15°C to 35°C.¹ Temperatures ranging from 8.1°C to 130°C might cause inorganic PCMs to melt. The crystallization and melting rates for hydrocarbons with 16 to 21 carbon atoms have a range from 10°C to 40°C. Another kind of organic compound that could be utilized as a PCM is polyethylene glycol (PEG), which has a melting point of about 33°C.⁹ Alkanes and alkane mixtures (paraffin) are frequently used in PCMs for the storage of thermal energy at low to medium temperatures. Eicosane, among many alkenes, has gained popularity in technologies of passive thermal management, which is based on energy storage and is used in electronics, with a nominal melting temperature of 37°C.¹⁰ The microcapsule of PCM was developed by the Institute of Textiles and Apparel at the Hong Kong Polytechnic University, to evaluate the temperature regulating functionalities of PCM cloth items. The melting point of the PCM used in the experiment ranges from 26°C to 28°C,¹¹ and a specialized microclimate cooling vest that may be worn below clothing to guard against chemicals was experimented on and developed. Two different kinds of encapsulated phase transition materials, hexadecane, which has a melting point of 18°C and octadecane, which has a melting point of 28°C, were utilized as coolants in 3 mm diameter macrocapsules.¹²

Latent heat capacity

Among the finest techniques for the conservation of thermal energy is latent heat storage. In comparison with the sensible heat storage method, the latent heat storage method offers a significantly higher storage density, and a smaller temperature differential between heat storage and release. During the heating process, each substance absorbs heat, causing its temperature to grow constantly. The reverse cooling procedure involves releasing the heat from the material (where heat has been stored) into the environment. The temperature of the material continues to drop during the process of cooling.

According to research on heat absorption rates, PCMs absorb more heat when they melt than ordinary materials. During the process of melting, paraffin-PCM absorbs approximately 200 KJ/kg of heat.

When PCMs reach their crystallization temperature, a cooling process starts, and then the paraffin absorbs heat in large amounts, while melting is released into the environment. It is shown that the capacity of heat storage of normal PCM textiles compared with the paraffin used in PCM textiles has increased significantly the storage capacity of heat.¹ To investigate the thermal behavior of the storage systems of latent heat, numerous research teams have run experiments. Due to the storage density of high energy and fine thermal conductivity, inorganic salt hydrates initially held out the most promising hope in most early experiments on latent heat storage. Truth be told, however, one of their principal problems was that they were corrosive, incompatible with a number of materials, susceptible to supercooling, and segregated during phase changes during thermal cycling.¹³

Thermal conductivity

PCMs have an issue with poor thermal conductivity, which limits their ability to carry heat effectively. Increasing thermal conductivity can hasten the rate of heat being generated and released, thereby increasing the productivity of storage systems of thermal energy.¹⁴ The thermal conductivity can be raised by encapsulating phase transition materials or incorporating with higher thermal conductive materials. By using the additives of higher thermal conductivity, many experiments were conducted to improve the thermal conduction of PCMs. The main subject of this review study is the addition of metal and carbon-based materials. There are many alternative forms of carbon-based additives available, and they all have great thermal conductivity, consistent chemical and thermal properties, lower density, as well as good compatibility. There are many difficulties in producing and processing various carbon-based compounds, especially carbon fibers. The thermal conductivity of compounds containing metal atoms is significantly improved. Most of them have large densities, making uniform dispersion difficult. This causes unstable heat transfer, and because of their lively chemical composition, they are highly reactive with other materials. In terms of actual applications, they have several limitations. However, the review study is looking at ways to develop the thermal conductivity of PCMs, such as the addition of higher thermally conductive additives.¹⁵

Supercooling and nucleation

Materials that undergo phase transitions and stay liquid at temperatures below freezing have been subjected to supercooling. Supercooling results in unexpected phase change behavior in addition to decreasing the effectiveness and reputation of PCM-based textiles. Nucleation, or the use of nucleation agents, is a method used to solve this excessive cooling problem. Most of the liquid PCMs can be ‘supercooled’, or cooled much below the temperature of solidification, without freezing.^16,17 As it is undesirable, the supercooled condition must be reduced or eliminated. Phase transition materials include both inorganic and organic phase-change substances such as salts, salt hydrates, metals, and alloys. Examples of organic phase change substances include paraffin and alkanes.¹⁸

Generally, organic PCMs do not go through intense supercooling.¹⁹ On the other hand, encapsulated organic PCMs exhibit supercooling behavior, probably as a result of the lack or scarcity of nuclei in such a constrained area.¹⁸ Improving heterogeneous nucleation during melt crystallization by using nucleating agents such as alcohol, high-melting-point paraffin, and nanoparticles that are solid, for instance, found a way to reduce the supercooling of octadecane microcapsules using the derivatives of n-paraffin such as 1-octadecyl amine and also 1-octadecanol.²⁰ Using paraffin, which has a melting point of 60–65°C (20 weight percent of the core components), might avoid supercooling of n-octadecane in the microcapsules.^21,22 When the temperature exceeds the freeze temperatures of the additives, a heterogenous nucleation takes place because the nucleating additives precipitate out of the solution and mix into PCM alkanes that are in the center.²⁰

Properties of PCMs

The applications of PCMs in textiles were explained in the previous points. Basically, PCMs are classified as two types, and they are: organic, inorganic and eutectic PCMs.

Organic PCMs such as: hexadecane, heptadecane, lauric acid, PEG, etc. and inorganic PCMs such as: sodium nitrate, potassium nitrate, Al, Fe₃O₄, etc. and eutectic phase transition materials such as: Al and Zn, KNO₃ and NaNO₃, etc. are used.²³

In this review study, we will discuss some of the properties of the mentioned PCMs and also other PCMs (as presented in Tables 3, 4 and 5).

Table 3.

Properties of organic phase change materials, according to Wang et al.²³

PCM	Phase transition temperature (°C)	Density	Latent heat
Hexadecane	T_p: 18–20	–	H_p: 224 kJ/kg
Heptadecane	T_m: 22.91T_s: 21.75	–	H_m: 182.36 kJ/kgH_s: 209.62 kJ/kg
n-Eicosane	T_m: 37.27T_s: 28.87	–	H_p: 250.41 kJ/kg
Paraffin wax	T_p: 18T_m: 44	930 kg/m³ at solid830 kg/m³ at liquid
Lauric acid	T_m: 43.5–48.2	940 kg/m³ at solid885 kg/m³ at liquid	H_m: 187.21 kJ/kg
PEG	T_m: 52.48T_s: 19.18	–	H_m: 153 kJ/kgH_s: 151.46 kJ/kg

PEG: polyethylene glycol; PCM: phase change material.

Table 4.

Properties of inorganic phase change materials, according to Wang et al.²³

PCM	Phase transition temperature (°C)	Density	Latent heat
NaNO₃	T_m: 305–306	2260 kg/m³2110 kg/m³ at 304°C1908 kg/m³ at 306°C	H_m: 170–190 kJ/kg
Na₂SO₄H₂O	T_m: 32.4	1464 kg/m³	H_m: 252 kJ/kg
CaCl₂ 6H₂O	T_m: 28.84	–	H_m: 170.2 kJ/kg
CaCl₂ 6H₂O-CO(NH₂)₂	T_m: 24.18	–	H_m: 149.2 kJ/kg

PCM: phase change material.

Table 5.

Properties of eutectic phase change materials. according to Wang et al.²³

PCM	Phase transition temperature (°C)	Density	Latent heat
Zn-Al	Tp: 429.8–508.5	–	Hp: 166 kJ/kg
KNO₃: NaNO₃ = 4:6	Tm: 225.7	2290 kg/m³	Hm: 110 kJ/kg
KNO₃: NaNO₃ = 5:5	Tm: 220	–	–

An overview of the advantages and disadvantages of the three PCMs is presented in Table 6 below.^24,25

Table 6.

Advantages and Disadvantages of Organic, Inorganic and Eutectic PCMs

PCM types	Advantage	Disadvantages
Organic PCM	No supercooling No separation of phases Low pressure during vaporization Wide range of temperatures Self-nucleating Reusable	Combustible Insufficient thermal conductivity Low capacity for volumetric latent heat storage
Inorganic PCM	Greater heat conductivity compared to organic materials low cost Inflammability Sharp phase transition Low volume change High volumetric latent heat storage capacity	Corrosive to metals Supercooling Separation of phases Consistent melting Significant volume change
Eutectic PCM	Sharp melting point Properties can be customized to meet particular requirements. Higher density of volumetric thermal storage	Few thermophysical property data available for a wide range of combinations Expensive

PCM: phase change material.

Applications of PCMs in textiles

There is a lot of potential for textile applications with PCMs that change phases at temperatures close to those of human skin. All-season protective textiles can be developed because of their unique property. When PCMs are incorporated into fibers, textiles, or foams, they may both store and release body heat. This dynamic phase change method provides excellent thermoregulation by continuously adjusting to the body’s physical activity and the external temperature.

Before the fiber is extruded, PCM microcapsules are added to a solution of polymers to provide man-made fibers with this thermoregulating property.

The incorporation of microcapsules of PCM directly inside the structure of the fibers allows the textile to have the necessary thermoregulatory properties. Currently, heat-storage and thermoregulating textiles and cloths are made using the following techniques: (a) PCMs microcapsulated incorporation into fibers, fabrics, and foams; (b) spinning of fibers with various PCMs; (c) coating of fabrics with organic PCMs; and (d) impregnation of foams with PCMs.

PCMs are contained in small spheres with a diameter ranging from 1 µm to 30 µm before being applied to the textile structure. These microcapsules have high resistance to heat, mechanical action, and the largest number of chemicals.

They react to temperature changes as follows:

Rise of temperature: The microcapsules respond by absorbing heat when the temperature rises as a result of a higher surrounding temperature. The microcapsules’ PCMs melt. They absorb heat from the environment and store additional energy.

Fall of temperature: The heat that had been stored is released when the temperature drops as a result of a lower surrounding temperature.

When textile materials are treated with microcapsules such as PCMs for clothing applications, several thermal benefits are achieved:

Cooling effect: Heat absorption by the PCM provides a cooling effect.

Heating effect: Heat emission from the PCM creates a warming effect.

Thermoregulating effect: The PCMs’ heat absorption or emission helps maintain a nearly constant temperature in the surrounding substrate.

Active thermal barrier effect: The PCMs regulate the heat outflow from the wearer’s body into the surroundings, adapting to thermal needs.

The fabric treated with a 22.9% incorporation of microcapsules has a rate of 4.44 J/g heat absorption capacity when the microcapsules melt (the microcapsules are made by in situ polymerization of melamine-formaldehyde microcapsules containing eicosane). This heat absorption postpones the rise in the microclimate temperature of garments, enhancing thermophysiological comfort, and also preventing heat stress. Researchers Wang et al.²⁶ investigated the effect of PCMs on intelligent thermal-protective clothing.

When the temperature rises above its melting point (28.0°C), the PCM layer changes into a liquid state throughout the heating process, storing and absorbing thermal energy. The temperature keeps rising as the PCM completely transforms into liquid. The temperature of the layer of PCM drops when the conducting fabrics are powered off at 29.0°C. When the temperature of the layer of PCM goes below 27.0°C, the liquid PCM solidifies and starts releasing stored heat, acting as a thermal buffer. The PCM clothing assembly (coating of nonwoven fabric with PCM and having a conductive layer) consumes approximately 30.9% less electrical energy than the nonwoven fabric with a conductive layer assembly. This demonstrates how a conductive fabric may drastically raise the temperatures of numerous layers in an assembly, making it warmer.^1,26–29

Reyes et al.³⁰ developed a smart textile using polyester fabric coated in microencapsulated trimethylolethane (TME) hydrate as the phase transition material. Melamine-urea-formaldehyde (MUF) was polymerized in situ at different stirring rates, emulsification periods, and TME hydrate concentrations to create the TME microcapsules. To produce the smart fabric, a knife-over-roll coating technique was used, with polyester resin serving as the binder. According to the results, the maximum amount of microencapsulated TME PCM that was achieved was 18.883 mg. The presence of MUF resin and TME hydrate in the microcapsule at 3300, 2870, 1148, and 1390 cm⁻¹ was verified by Fourier transform infrared (FTIR) findings. The surface of the microcapsules was rough and amorphous, as seen in the scanning electron microscopy (SEM) data. The latent heat storage capacities of the microcapsules before and after application to the fabric were measured by the DSC results to be 205.1674 J/g and 224.7318 J/g, respectively, indicating excellent thermal properties. Ultimately, 64.715% was found for the encapsulation efficiency, suggesting possible uses for fabric thermal storage.³⁰ According to Zeighampour et al.,³¹ it was suggested to create a unique thermoresponsive shape-stable nanocomposite PCM to address the two primary issues with PEG as a PCM material: leakage and low Thermal Conductivity (TC). It makes use of a porous composite structure created when Reduced Graphene Oxide Nanoparticles (rGONPS) and Carbon Nano Fiber (CNF) are combined. Practical thermal energy storage requires an enhanced TC without PCM leakage throughout heat cycles, which is what the produced Shape Stabilized Phase Change Materials (SSPCM)-coated fabric offers. The produced samples also have the necessary thermal endurance, appropriate energy storage capacity, leakage-proof property, and appropriate phase transition temperature. To produce SSPCM fabric on an industrial scale another technique was created to adhere PEG/CNF-rGONP to a nonwoven polyester (PET) by coating, impregnation and dry-fixation. The binder vinyl acetate acrylic resin offers respectable laundering and abrasion durability without affecting the SSPCM coated fabric thermal characteristics. The new SSPCM showed more than four times better performance than previous ones. The fabric coated with SSPCM maintained a satisfactory degree of bending flexibility, with a decrease in bending length of less than 30%. In addition, it indicates that adding PEG to CNF-rGONP (50:50 weight percentage) supporting matrices provides a viable thermoregulating, dynamic insulating, and energy storage option for a range of uses. This covers consumer garments and defensive clothing, building cars, packaging, electronics, and energy-harvesting devices (see Figure 3).³¹

Figure 3.

Application of phase change material (PCM) incorporated textiles.

Space suits

PCMs were initially designed for space suits and protective gloves for the protection of astronauts from freezing temperatures while performing space tasks. The comfort of astronauts in the space environment is ensured by these materials.¹

PCMs store extra heat that is absorbed by them as latent heat from the environment or body when the temperature rises. The normal body temperature for thermophysiological comfort is 37°C, while the skin temperature is 33.4°C.^32–35 To keep the temperature at a comfortable level NASA employed PCMs to create thermoregulated clothes, and smart fabrics are used in clothing, interior design, and technological fields. The PCM composite exhibited satisfactory thermal stability.³²

Sportswear

PCMs, initially developed for space suits and protective gloves, are now used in consumer products, particularly in clothing textiles with thermoregulating properties. These textiles aim to enhance the thermal performance of activewear garments. By the addition of PCMs into sportswear, the excess body heat generated during physical activity is absorbed and released as needed, maintaining a thermal balance and reducing thermal stress. Examples of PCM applications in sportswear include underwear, snowboard gloves, active wear (cycling or running garments), and ice climbing gear.¹

Hassabo et al.,³⁶ in order to enhance the qualities of present apparel, developed smart knitted fabrics that are suitable with warm-up exercises before engaging in any activities. This was accomplished by utilizing raw materials, and creating structures that are ultimately used while wearing and using these fabrics. Experiments have been conducted to determine the optimal samples to use in the production of fabrics appropriate for athletic warm-up apparel. In this study from the 16 treated samples with various PCMs such as cotton 40/1, modal 40/1, bamboo-cotton (40–60%) 40/1, bamboo-cotton (70–30%) 40/1, etc., and examined the functional properties. The authors also discovered that using PCMs has increased the fabric’s resistance to ultraviolet rays, decreased the air permeability, increased the water permeability, increased the weight of the fabrics per square meter, decreased the thickness of the fabrics, decreased thermal insulation, and increased the bursting resistance of the fabric. Circular multitrack weft knitting (TERROT I3P 148) was used to produce different structured fabrics, and butane tetracarboxylic acid (BTCA), sodium hypophosphite (SHP), potassium carbonate (K₂CO₃), sodium lauryl sulfate, dichloromethane (DCM), dicyclohexyl carbamidimide (DCC), and octadecane were used as chemicals to treat the samples.³⁶

Shoes and accessories

Currently, PCMs find applications in various types of footwear, including ski boots, mountaineering boots, and boots of race car drivers. These PCMs, contained in microcapsules, react to temperature changes from both the garment’s exterior and the body. Depending on the end use, specific temperature ranges are targeted, such as 36°C temperature for a motorcycle helmet and 26°C temperature for gloves. The PCM-enabled heat-storage and thermoregulated fabrics are able to absorb, store, distribute, and release heat, keeping the wearer’s head, body, hands, and feet at a comfortable temperature. For instance, in ski boots, PCMs absorb excess heat generated by the feet, and release it back to colder areas when needed, ensuring comfort. Golf shoes, footwear, and ski boots are some examples of potential goods which are suitable for PCM incorporation.^1,37

Medical applications

Textiles treated with PCM microcapsules are suitable for a wide range of applications because PCMs react to changes in the temperature caused by modifications of their activity levels and external conditions.

Bandages, surgical clothing, bedding materials for patients, and items to regulate patient temperatures in intensive care units can all make use of these textiles.

Medical and hygiene applications that require fabric with PEG treatment, such as surgical gauze, diapers, and incontinence products, benefit from the fabric’s ability to transport liquids while still having antibacterial properties. Textiles that store heat and regulate temperature (heat storage and thermoregulating textiles) help keep skin at a comfortable level and make them suitable for bandages, burn treatments, and heat/cool therapy.^1,37

Shahid et al.³⁸ claim to have created a medical bed sheet made of cotton fabric combined with microencapsulated phase change material (MPCM). In order to achieve this, MPCM was incorporated into the printing paste and allowed to dry at room temperature after being applied to the fabric using the screen-printing method. After that thermal conductivity, thermal behavior, and thermal transition of the sample was examined. The outcome was the successful implementation of MPCM of 7.429 µm in cotton based medical bed sheets by the printing technique. The weight of the sample without MPCM decreased significantly with increasing temperature, according to the Thermo-gravimetric analysis (TGA) data, but the weight of the sample with MPCM kept a substantial amount of weight and delayed the rate of weight loss. The developed sample had the ability to absorb extra moisture from the environment, lowering the fabric’s humidity and temperature. Force and elongation were 502 N and 22.8 mm, respectively, before the addition of MPCM to the fabric. These values increased to 679 N and 22.9 mm, respectively, following the MPCM integration. In comparison with the sample without MPCM, the generated sample with MPCM demonstrated a higher thermal conductivity (0.1760822 wm⁻¹ k⁻¹). Patients’ overall comfort and the fabric’s ability to regulate their body temperature are both impacted by surface roughness. Nonetheless, the produced sample covers the end of the staple fiber, producing a comparatively uniform surface. Finally, this research may open up new avenues for developing hospital beds that shield patients from bed sores.³⁸

Bedding and accessories

In quilts, pillows and mattress covers microcapsules of PCM are inserted and the result was it provides active temperature control during sleep. During the rising of the body temperature, it absorbs excess heat and cools the body. Similarly, during temperature falls or drops from the body then the stored energy is released; the ultimate result was keeping the body warm.¹ PCM is used in hospital bedding for patients,³⁸ which is explained in the medical applications section.

Automotive textiles

Micro PCMs have potential applications in automotive textiles, particularly in seat covers. PCMs that are paraffin based are preferred for such uses because of their higher heat storage capacity, lower toxicity, lack of hygroscopic properties, and also their cost effectiveness. By blending these PCMs, the desired temperature range can be achieved. When PCM-incorporating textiles are used in car interiors and seat covers, they can offer excellent thermal control, enhancing the comfort of passengers.^1,39

Experimental testing was done at different discharge rates using a composite container for an electric vehicle battery module that was filled with PCM. In electric vehicle battery modules, PCMs can serve as passive defence against any possible thermal abuses; however, using a composite reinforcement material is highly recommended in terms of mechanical strength.⁴⁰ To increase thermal performance, lower energy consumption and gas emissions, and minimize energy gain or loss, PCMs can be installed in the roofs, doors, and side walls of automobiles and buses. This idea can have a favorable worldwide impact on transportation-related emissions and energy consumption.⁴¹

Nonwoven protective garments

Method

To protect employees from very dangerous chemicals, gases, and vapors, a nonwoven protective suit has been designed. The garments are made up of multiple layers of nonwoven fabrics bonded through lamination. It includes an overall with an integral hood, visor, and a self-contained breathing apparatus. During use, workers wear underwear and a normal work suit underneath. The garment’s purpose is for tasks such as transporting hazardous chemicals, cleaning chemical facilities, and handling contaminated soil.

Computer simulations were conducted to select a suitable PCM that absorbs heat within the temperature ranging from 23°C to 31°C. The PCM incorporated in a 0.3 mm thick polymeric film provides the required heat storage capacity of approximately 40–60 kJ for the desired cooling effect, and to prevent heat stress during the 1–2-hour wear period. While still providing a barrier function against hazardous elements, the polymeric film may be laminated to the inner side of the nonwoven fabric system, or replaced with the most inner layer.⁴²

Firefighter garments

Method

To ensure eicosane was in molten form and would better penetrate the nanoporous aerogel structure, it was heated to 80°C, which is double its melting temperature. To avoid particle aggregation, aerogel particles were gradually added to the hot, molten PCM while being continuously stirred at 80°C. The mixture was filtered using glass-filter paper and suction filtration after 2 hours. The residue was cleaned in heptane before being dried till the solvent evaporated under a fume hood at room temperature. To remove excessive eicosane and solvent, it was then further dried at 120°C in a vacuum oven, producing a powdered eicosane/aerogel composite.

The face cloth of the thermal liner was coated on one side with the prepared eicosane/aerogel composite powder (skin side), and on the other side with nanoporous aerogel particles (ambient side) using a laboratory coating machine. Another cloth piece was coated on both sides with a binder paste that did not contain aerogel or composite powder, dried, and cured for comparison.^13,33,43

According to McCarthy and di Marzo,⁴⁴ realistic firefighting conditions were simulated using bench-scale experiments conducted at varying radiant heat exposures. The specimens with PCMs showed lower overall temperatures in the results compared with those without. The phase change had some influence, but the extra material was mostly to blame for the temperature variations. When the temperature plots for the layers close to the PCM were closely examined, a shift in slope was seen, which suggested latent heat absorption. When the heat flux exposure was lower than when it was higher, the impacts of the latent heat were more noticeable. A PCM was included in a mathematical model of heat transport by firefighter protective clothing (FFPC) in order to explore better the impact of the PCMs. Excellent agreement was found between the model’s temperature display and the experimental data. It was possible to predict the phase change effect using the theoretical model, accurately reflecting the impact of various PCMs. Without the cost of experiments, the model offers a great tool for calculating the PCM’s influence, and comparing the outcomes with various specimen configurations and exposures. Using this model, the amount of batting needed to match the PCM’s thermal performance was calculated, and it was found that the batting would need to be around the clothes.⁴⁴

To produce garments for firefighters, flame retardancy by incorporating PCMs is a must. According to Diaconu et al.,⁴⁵ depending primarily on the PCM state (bulk, encapsulated, or composite, shape-stabilized PCMs) and the flame retardant nature, there are various methods for integrating flame retardants with PCMs. As a result of the abundance of techniques for making PCMs flame retardant, a systematization was created that separated the flame retardancy techniques into three primary classes:

Flame retardant integration inside the mass of the PCM: a. Integration of flame retardants for bulk PCMs; b. Flame retardants for PCMs with stable shapes; and c. Flame retardants for PCMs enclosed. 2. Surface coatings for flame retardancy. 3. Flame retardancy attained by changing the chemical bonding.

Benefits and challenges of PCM applications

To provide more protection from extremely cold conditions, PCM microcapsules are used in outdoors wear such as snowsuits, trousers, ear warmers, boots, and gloves. These microcapsules can be applied to the fabric surface or incorporated within the fibers, significantly increasing their capacity for thermal storage (up to 2.5–4.5 times compared with regular fabrics/fibers within specific temperature ranges). This microencapsulation process also results in lighter and softer PCM-infused textiles. The incorporation of PCM microcapsules into fibers or as coatings on fabrics improves thermal comfort and flame-retardant properties. Moreover, the distribution of PCM microcapsules on textile substrates is uniform and durable even after repeated washing.^46,47

PCMs utilize latent heat, storing or releasing energy within specific temperature ranges by changing their states. During the process of heating, they absorb energy through phase transition, but they release this energy to the surroundings during the process of cooling within the specified range.⁴⁷ N-paraffin waxes are ideal PCM prospects for cooling storage due to their significant heat storage capacity, nontoxicity, lack of corrosiveness, and hygroscopic properties, broad temperature responsiveness, and cost effectiveness.^47,48

Initially designed to protect astronauts from significant fluctuations in temperature in space, the current application of PCMs in everyday textiles has multiple challenges. Incorporating these remarkable materials into clothing demands the creation of novel testing methods and standards. A key obstacle lies in their limited thermal conductivity, exemplified by paraffin PCM with a conductivity of 0.22 W/m K which is compared with that of graphite powder of 2–90 W/m K.

This low conductivity makes it difficult to store and release heat quickly during melting and crystallization. To achieve swift responsive properties with changing temperatures, it may be necessary to enhance the thermal conductivity of both the core PCM microcapsules and their shell walls. In addition, assessing factors such as effective microencapsulation, mechanical durability, and flammability of organic PCMs is crucial.³⁹ The human body generates more heat with increased physical activity and metabolism. The metabolic rate at rest is 115 W, while the rates for low, moderate, high, and very high levels of activity range from 180 W to 520 W. The body must therefore emit more heat into the surroundings in order to maintain thermal comfort and balance. This calls for enhanced cooling capabilities in textiles or clothing with integrated PCMs. When PCM quantity is limited, the duration of the cooling or warming effect is constrained.

The cooling or warming effect would last for approximately 15.5, 9.9, 6.0, 4.3, and 3.4 minutes across the five activity levels, absorbing 30% of body heat production if clothing weighed 800 g, contained 20% PCM by weight, and had a latent heat of 200 J/g, and assuming PCM does not exchange heat with the environment. Absorbing 100% of body heat would shorten this duration further. Increasing PCM mass to 1 kg extends the functional duration sixfold, but this may impact fashion. Striking the right balance between fashion and function can indeed be challenging.⁴⁹

Future research directions

Novel PCM formulations

This review paper will focus on the recently developed formulations of phase transition materials. To assess the thermal properties a newly developed formulation of phase transition material is followed, which is called ‘epoxy composite’. This epoxy composite contains a thermally conductive phase and a thickening agent. The findings showed that the PCM phases might be contained by epoxy matrix without impacting the PCM’s used characteristics of heat absorption. Organic PCMs demonstrated reversible phase changes throughout several cycles, although their inorganic PCMs did not demonstrate this.

The organic PCM epoxy specimens’ enthalpy values increased linearly as the matrix’s PCM content increased. Using thickening agents enabled the fabrication of specimens with up to 40% PCM loading without obvious phase segregation, which is a considerably greater loading than had previously been recorded.

To prevent the melted paraffin from leaking out of the composites, epoxy resin is used as a supporting substance. In other words, the cost of these composite PCMs is lower because they do not need a container for encapsulation.⁵⁰ Other unique formulations have been discovered and manufactured effectively, such as a newly discovered method of microencapsulating PCMs (microPCMs) having thermochromic capacity. Thermochromic pigments were assembled with n-octadecane droplets after suspension-like polymerization to create microPCMs with an additional level of thermochromic performance, as well as a series of thermochromic microPCM samples. Each sample of the thermochromic microPCMs showed outstanding storage of thermal energy and discharging performance, higher encapsulation efficiency, and capacities of thermal storage. As a result of their temperatures being higher than the temperature at which colors change, and additionally it was also discovered that all thermochromic microPCMs were thermochromic and had exceptional thermal stability. This work’s dual functional microcapsules have significant promise in applications such as in the storage of solar energy, thermosensitive sensors, food and medication packaging, intelligent textiles or fabrics, and so on.⁵¹

However, there are some other possible research areas for developing microcapsule performance such as eutectic and metallic PCMs, sol-gel encapsulation techniques, complicated coacervation, and the spray drying method, etc.⁶

Optimization of PCM integration

There are numerous ways to add PCMs into textiles such as microencapsulation, nanoencapsulation, sol-gel encapsulation, etc. For improved application and endurance, PCMs should be microencapsulated, or nanoencapsulated to avoid leakage.¹ PCMs are encapsulated using small capsules that are inserted into textiles in the microencapsulation procedure. Spray drying, coacervation, in situ polymerization, and other processes are used to achieve microencapsulation.⁵ Among these approaches, in situ polymerization is the most extensively used due to the development of an efficient capsule appropriate for usage in textiles as well as quick wall formation.^1,52 The PCM is encapsulated at the nanoscale to produce nanocapsules. These capsules are smaller than microcapsules, and have superior features such as higher stability and dispersibility. Nanocapsules have 1 µm particle size, while microcapsules have sizes ranging from 1 µm to 1000 µm, and researchers are now paying close attention to the technique of nano encapsulating PCMs because of the tiny particle size with increased surface qualities, following their use on textile materials for the thermoregulating effect.¹³

Tinoson CEL is a product made by Ciba Company that is manufactured as nanocapsules containing antimicrobial agents in an aqueous media. When bonded to the product, these nanocapsules’ reactive groups with cotton fibers exhibit good washing stability. In the presence of sulfate and chloride, silver-polyamidoamine woody compounds, such as silver-polyamidoamine nanocomposite solutions, exhibit strong antibacterial activities without losing solubility or activity. It is simple to create the polyamide amine tree with silver by mixing silver acetate powder into the pre-made tree solution.

The synthesis of complexes with internal nitrogen and silver carboxylate salts are two steps in the production process. Its very high local concentration (256 groups of carboxylates around a sphere with a diameter of 54 angstroms) is thought to be responsible for its interesting antimicrobial properties; when microorganisms come into contact with nanoparticles with a very high specific surface area, silver compounds in the form of + Ag or AgO are formed.^53,54

PCM microencapsulation preparation techniques are presented in Table 7 below.^55–61

Table 7.

Preparation techniques of PCM micro-encapsulation

Polymerization	Preparation process
In situ polymerization	Paraffin after preparing 25 g of solid (core) and 0.66 mol/L of melamine in water, 14.5% formalin of 41.5% (wall) and 2.9 g of sodium dodecyl sulphate (SDS) per liter were added as an emulsifier. The pH was then lowered to 8.5–9 using an aqueous solution of 10% sodium hydroxide at 250 rpm for an hour at 70–75°C. Finally, the temperature was lowered to gather microcapsules.
Complex coacervation	N-hexadecane (core)/1 gum unit In 10 units of distilled water over 45°C, arabic gelatin (wall) was dissolved, and the mixture was agitated for 10 minutes at 1000 rpm. To dissociate the polyelectrolyte, a few drops of a 10% sodium carbonate solution were added. A pH adjustment was made to 9–10. After then, the coacervate was found.
Spray dryer	To create the emulsion solution, paraffin wax (core), 10% w/w gelatin, and acacia (wall) were combined. Subsequently, the spray dryer was supplied with the produced solutions. Emulsions were atomized at a feed rate of 20 ml per minute using a centrifugal atomizer running at 25,000 rpm and 130 to 80°C. At the bottom, the microcapsules were gathered.

Figure 4 shows the encapsulation techniques.

Figure 4.

Encapsulation techniques of phase change materials (PCMs).

A study demonstrated the thermoregulated and sensory effects of smart textiles for workers in extreme weather circumstances using artificial composite PCMs integrated with carbon nanoconductive materials. Carbon nanoparticles and synthetic polymers such as polyurethane and ammonia formaldehyde, when combined with an electrospraying coating process, can function as a protective layer and enhance the performance of thermoregulated composite PCM coated textiles. This protective layer can withstand a maximum of heating and cooling cycles from wearers in a variety of settings, including sports, space exploration, underwater low temperature rescue, automobiles, medical applications, military use, extreme weather, and special health and safety users. In addition, the electrical conductivity of the carbon nanoparticles provides a sensory effect, without compromising the physical and chemical properties of the fabric structure, and the anticipated special characteristics of smart textiles will include breathability, water resistance, soil resistance, wrinkle resistance, flame retardancy, antistatic qualities, ultraviolet protection, and wicking capabilities (see Figure 5).³²

Figure 5.

Preparation of composite phase change materials (PCMs).

Techniques for Incorporating PCMs in textiles with important elements:^62–65 (a) Fiber technology: the fiber’s structure contains sealed PCMs. Through doping, it could be integrated during the polymerization stage. (b) Coating: the used binder is covered in PCMs. Several machines could be used to apply the coating on the fabric. (c) Lamination: it starts off as a thin film laminating process. The fabric is treated with a foam mixture.

A study stated that there are four standard methods for adding PCMs to textiles: The four approaches include laminating, adding PCM during fiber spinning, filling a hollow fiber with PCM, and coating textiles with PCM that acts as a cross-linking agent. Before being laminated onto the textile’s surface, the PCM is first combined into a thin layer.^1,65–69

The following benefits of using PCM fibers by lamination are:⁶¹ (a) A high concentration of PCMs per unit area; (b) low production process costs and reduced textile weight.

Many studies have been conducted on the application of PCMs in coating procedures. In order to dip-coat nylon fabric with polyurethane-urea microcapsulated PCMs, Kwon and Kim⁷⁰ utilized a waterborne binder and let it sit at room temperature for one hour.

Long-term durability and stability

The PCM utilized determines the long-term stability and durability of PCMs in textiles, which plays an important role in defining the textile’s longevity and stability, because certain PCMs have higher long-term stability than others. Durability and stability also depend on PCM encapsulation. PCMs are frequently enclosed in textiles to avoid direct contact with the fibers. Encapsulation protects the PCM from physical damage, chemical interactions, and leaking, potentially increasing its longevity.

The stability of a MPCM may be assessed by analyzing changes in parameters such as microcapsule sizes and shapes, viscosity, and thermophysical properties.⁷¹ Typically, the longevity of MPCMs may be assessed using a continuous pumping test. There are also some parameters influencing the longevity of MPCMs such as the distribution of size, ratio of core-to-shell, etc.⁷² The microencapsulating process and parameters used also influence the thermal stability of MPCMs. Zhang et al. discovered that increasing the agitation speed and emulsifier concentration enhanced the thermal stability of the macrocapsules.⁷³

Standardization and regulations

At this point, the PCM testing methods used in applications will be discussed. Standardized test procedures are proposed to assess the stability of microcapsules throughout the usage and maintenance of textiles, particularly the wash fastness standards ISO 105-C06, ISO 105-C08, ISO 105-C09, ISO 105-C10 and ISO 6330.⁷⁴

Podgornik et al.⁷⁴ used the following test techniques to assess the biodegradability of textile materials:

21701:2019 Textiles – Test procedure for efficient textile hydrolysis and controlled composting conditions for the hydrolysate’s biodegradation.

ISO 11721-1:2001 Textiles – Analyzing the cellulose-containing textiles’ resistance to microorganisms – Soil burial test. Part 1: Evaluation of rot-retardant finishing.

ISO 11721-2:2003 Textiles – Analyzing the cellulose-containing textiles’ resistance to microorganisms – Soil burial test. Part 2: Identifying a rot-retardant finish’s long-term resistance.

AATCC TM30:2013 Antifungal activity on textile materials: Their resistance to mildew and rot. Test 1: soil burial.

ASTM D 5988-18 Standardized test procedure to measure aerobic biodegradation of plastics materials in soil.

Shim et al.³ conducted a PCM clothing test in both a warm and cold environment. A thermal manikin’s heat loss was monitored and utilized to assess the influence of PCMs in clothes on the transfer of heat from the human body during temperature transients. A technique makes use of a fabric intelligent hand tester to evaluate and determine the PCM textiles’ index of thermally regulated capabilities, based on how they relate to the rate of temperature change.³⁷

A guarded hot plate is another way of assessing and testing the thermally regulated performance of PCM textiles.⁷⁵ In summary, several methods are used for testing the performance of PCM textiles. Specific standards and regulations relevant to these materials may be developed in the future.

Zeighampour et al.³¹ studied the characterization methods of fabric using shape stabilized PCMs, using methods such as:

Morphological analysis of the fabrics was conducted using a stereo microscope (2CE-MU, HP, USA) operating at a magnification of 10–40. A field emission scanning electron microscope (FESEM, Quanta FEG 450; FEI, USA) operating at 15 kV acceleration voltage and magnification of 100–60,000. The specimens’ surface topography and cross-section were inspected both before and after coating. The samples were coated with a thin layer of gold before being subjected to FESEM examination.

Weight change measurement: A laboratory balance (GR-120; A&D, Japan) was used to assess the fabric samples’ weight. Before being weighed, the specimens were conditioned for 24 hours at 20°C and 65% relative humidity in a conditioning room. The following equation was used to compute the weight change: Add-on (%): Wb-Wa/Wb $\times$ 100; where Wb represents the specimen’s weight following coating, abrasion, or washing cycles, and Wa is the specimen’s initial weight.

Measurement of thickness: At a constant pressure level of 1 kPa, the specimens’ thickness was determined using the ASTM D5729-97 (2004) test technique. At least five measurements were done for each sample at various positions on the various specimens, and the average was then reported.

Measurement of air permeability: Using an air permeability tester (MO 215; SDL Atlas, USA), the sample’s capacity to let air flow was assessed in accordance with the BS 9237–1995 test protocol. There was a pressure drop of 100 Pa and a test surface area of 0.785 cm². For each sample, 10 measurements were made. The following equation was used to compute the air permeability (R, in mm/s): R = qv/A $\times$ 167; The air flow rate in cm³/m is represented by the symbol qv in this instance, the conversion factor between mm/s and dm³/min.cm² is represented by the number 167, A is the sample area in cm².

Bending property measurement: A Shirley fabric stiffness tester (Stiffness Tester; SDL, UK) was used to measure the bending properties in accordance with the ASTM D 1388–96 (2002) test procedure. Equations were used to calculate the specimen’s bending modulus (q) and ending rigidity (G), respectively: G = WC3 $\times$ 10³; where G is the bending rigidity in mg.cm, W is the samples’ weight per unit surface in g/cm², and C is the bending length in cm and q = 12 $\times$ G $\times$ 10⁻⁶/d3; where q is the samples’ bending modulus in kilograms, and d is the samples’ average thickness in centimeters (cm²).

Thermal conductivity: In accordance with ISO 5085-1:1989 (part 1, low thermal resistance), a tog meter (IUT, Iran) was utilized to measure the samples’ thermal conductivity. The tog meter is made up of a forced-air cabinet, a circular hotplate, and a cold plate. It is intended to rest on top of the sample and be in good contact by applying 6.9 Pa of pressure across the entire 855 cm² surface. The 330-mm diameter specimens were conditioned for 24 hours at 20°C and 65% relative humidity before testing. The thermal resistance (Rf) was measured using the procedure outlined in ISO 5085-1:1989 (part 1, low thermal resistance). The following equation was used to calculate the TC (k, in W/m K) (Standardization, 1989): k = d $\times$ 10⁻³/Rf; where Rf represents the samples’ thermal resistance in m².K/W, and d denotes the specimen’s thickness (mm) at a pressure of 6.9 Pa.

Cost of PCMs and PCM incorporated fabrics

Prices for specific fabrics with PCM incorporation and PCMs are higher. The price range of PCM and PCMs incorporated fabrics are presented in Table 8.

Table 8.

A summary about the price range of PCM and PCM’s incorporated fabrics

Type	Description	Price (US dollar/kg)	References
PCM chemicals	Paraffin wax PCM	$1.88–2.00	[76], [77], [78]
	TiO₂	$1342.3
	Oleic acid	$1.67–1.76
	Palmitic acid	$1.61–1.72
	Calcium chloride	$0.20
Types	Description	Price (US dollar/yards)	References
PCM incorporated fabric	PCM microencapsulated fabric for temperature control	$5.00–50.00	[65], [79]
	PCM cooling vest soft and comfortable	$5.00–50.00
	Nonwoven special functional fabric	$3.80–4.50
	Sports wear	$5.00–12.00
	Cooling polyester	$5.00–7.50

PCM: phase change material.

Fibers that are used in textiles to add PCMs

According to a study, PCM microcapsules can be contained in a coating compound and coated onto fabrics, or they can be included into the structure of foams and applied to fabric in a lamination process. Examples of these applications include the spinning polymer of produced fibers (such as acrylic and viscose). Another way to add PCMs to textiles is to fill hollow fibers.⁹

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) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Md. Mubashwir Moshwan

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Phase change materials in textiles: synthesis,properties,types and applications – a critical review

Abstract

Keywords

Introduction

Principle of phase change behavior

Melting and solidification

Crystallization and fusion

Supercooling and nucleation

Microencapsulation and coating

Types of PCMs

Organic PCMs

Inorganic PCMs

Thermal properties of PCMs

Melting point

Latent heat capacity

Thermal conductivity

Supercooling and nucleation

Properties of PCMs

Applications of PCMs in textiles

Space suits

Sportswear

Shoes and accessories

Medical applications

Bedding and accessories

Automotive textiles

Nonwoven protective garments

Method

Firefighter garments

Method

Benefits and challenges of PCM applications

Future research directions

Novel PCM formulations

Optimization of PCM integration

Long-term durability and stability

Standardization and regulations

Cost of PCMs and PCM incorporated fabrics

Fibers that are used in textiles to add PCMs

Footnotes

Declaration of conflicting interests

Funding

ORCID iD

References