Phase Change Materials (PCM) is a very important requirement in the textile industry to protect us from extreme environmental conditions like extreme heat, open fire, high voltage, toxic chemicals etc. Clothing made from such materials can make textile products more comfortable which are commonly used in defense wear, sportswear, bulletproof jackets, firefighting wear, and other professional wear. Currently, this intelligent material absorbs, stores or discharges heat according to different changes in temperature to meet the requirements and is often applied to make smart textiles.
What is Phase Change Materials?
A phase change material (PCM) is a special kind of substance that releases or absorbs sufficient energy at the phase transition to provide useful heat or cooling. In this process, the materials go from one stage to another [For example: from solid to liquid]. Any material which experiences this process of phase change is Called Phase Change Material or PCM. Phase change material is a substance that releases/absorbs sufficient energy in phase transition to provide useful heat/cooling. Generally, the human body temperature is 37⁰C which increases up to 38⁰C, 39⁰C, or 40⁰C during exercise. The most comfortable skin temperature is 33.4⁰C and when it changes more than 4.5⁰C below or above the comfort temperature, the human body feels uncomfortable. PCMs are attractive for storing energy in all the available heat energy storage techniques due to their high density, compact storage system and high latent heat. A large number of inorganic and organic PCMs are available in the temperature range of -5⁰C to 190⁰C. The organic phase change materials ranging from 18-65⁰C are used in textiles and buildings to enhance the thermal comfort effect. Among all the PCMs, n-octadecane is usually used for the textile application having a melting point of 28⁰C.
How PCM work?
Phase change materials are materials that change their phase upon absorbing or releasing latent heat. Among the different types of PCM, paraffins such as Eicosane, Octadecane, polyethylene glycol (PEG), Nonadecane, etc. are used for textile products which usually store and release heat using chemical bonds. Absorbs large amounts of latent heat from the body and melts away. Later the phase changes from solid to liquid creating a temporary cooling effect. Phase-change materials in textile products can significantly increase thermal conductivity. An increase in temperature breaks the chemical bonds in the molecules of the PCM material and melts the material, thereby saving heat energy. The preferred melting temperature of PCM used in clothing is about 15 to 35⁰C, close to the human body temperature. The thermal performance of PCM depends on several factors such as the amount of PCM that is encapsulated, the phase change temperature of the PCM material, how much energy it absorbs or releases during the phase change, etc. Phase change materials store energy as latent heat and when the previously stored latent heat is released the garment creates a temporary warming effect. Thus in the reverse cooling process, the stored energy is released to the surroundings. The organic phase change material is paraffin. It absorbs about 200 J/g of latent heat during the phase change and releases this high amount of heat to the surroundings during the reverse cooling process called crystallization.
Classification of PCM
1. Organic PCM
Organic PCMs with good properties are more expensive than inorganic PCMs which are classified into two groups:
A. Paraffinic compounds:
Due to its large temperature range, this compound is used for textile thermo-controlled fabric purposes. Some of the outstanding properties of paraffin are-
- large temperature range
- Easy to use
- This compound is chemically inert and stable below 500⁰C.
- They show little volume change on melting and the vapor pressure of the compound in molten form is low.
- Paraffin has some significant disadvantages such as incompatibility with plastic containers, low thermal conductivity and moderate flammability. These disadvantages can be overcome by changing the wax, storage unit.
B. Non-paraffinic compounds
These compounds form the largest group of phase change materials. Some notable features of the compound are:
- low flash point
- High temperature stability
- Low thermal conductivity.
- Higher heat of fusion than paraffinic. Fatty acids cost 2-2.5 times more than technical grade paraffin.
2. Inorganic PCM
Metallic inorganic, hydrated inorganic salts form the group of PCM. Their latent heat absorption and release temperature ranges from 20 to 40⁰C and melting temperature ranges from 8.1 to 130⁰C. Calcium chloride hexahydrate, Glauber’s salt are some notable examples of inorganic PCM. Some of its properties are
- high thermal conductivity
- limited life cycle
- Wide range of melting temperature etc.
Classification of inorganic pcm:
A. Salt hydrates
Salt hydrates represented as AB.n.H2O are crystalline solid mixtures of inorganic salts and water. The poor nucleating properties of most salt hydrates result in a supercooling of the liquid before crystallization begins, which can be overcome by adding nucleating agents. Some notable features of the compound are-
- almost twice as high thermal conductivity as paraffin
- high fusion per unit volume
- They have little change in volume after melting.
Eutectics and low melting metals belong to this group. Due to the weight penalty of compounds, PCM technology is not considered seriously. Some of their characteristics are:
- high heat per unit volume
- high thermal conductivity
- Low vapor pressure.
The group consists of a minimum-melting combination of two or more elements where each element freezes and melts together. They are of three types i.e. 1) Inorganic-Inorganic, 2) Organic-Organic, 3) Inorganic-Organic. They melt and freeze without any separation. Some examples of eutectics are triethylethane+water+urea, naphthalene+benzoic acid etc.
PCM in smart textile
During the summer when any vehicle is parked outside, the temperature inside the passenger compartment of an automobile can increase. Many cars are equipped with air conditioning to control the interior temperature while driving. Automobiles, like cars, can be equipped with air conditioning. But adequate cooling capacity requires a lot of energy so application of PCMs technology in automotive interior can save energy as well as comfort the car interior.
Phase change materials currently used in smart textiles are primarily developed for applications in space suits and gloves. PCM is applied to space suits to keep warm and applied to gloves to protect astronauts from high-temperature fluctuations when performing extravehicular operations in space. The utility of insulation primarily stems from microencapsulated phase change materials developed for warming the gloved hands of astronauts. The materials were adopted as glove liners to support during the extreme temperatures of the space environment.
Apparel active wears
This clothing is intended to provide a thermal balance between the heat produced by the body and the heat released to the environment during sports. The heat produced by the body during strenuous activities is often not released to the environment in sufficient quantities resulting in conditions of thermal stress. Therefore, typical active wear clothing cannot always meet this demand. On the other hand, hypothermia can occur due to less heat generation in the human body during resting periods considering the same heat release. For this reason, phase change materials are also used in consumer products. Thermal shock is controlled by the application of phase change materials in the clothing and helps the wearer to increase work efficiency under high stress.
Phase change materials textiles may soon be useful in the medical sector to enhance the thermo-physical comfort of various surgical garments such as caps, gowns, gloves. In addition, phase change materials used in patient bedding products such as mattresses, covers, blankets, etc. interact with the micro-climate around the human body and help in efforts to keep the patient warm enough during surgery by providing insulation that matches the body temperature.
PCM materials present in clothing coated with PCM react to changes in body temperature by absorbing large amounts of latent heat from the body. Thermo-controlled smart textiles and heat-storage can absorb, release, store and redistribute heat to prevent drastic changes in the human body. As a result, PCM applications are contributing to the smart textile industry such as elegant fleece vests, dresses, underwear, men’s and women’s hats, rainwear, gloves, socks, etc. in everyday life.
PCMs used in space suits and gloves as well as smart consumer products can provide a thermal balance between heat generated by the body and heat emitted to the environment in sportswear by applying phase change materials. If the heat generated by the body during sports is not released, thermal stress is likely to increase. When the excess body heat of the wearer increases, the encapsulated PCM absorbs and releases the temperature as needed. Activewear, ice climbing underwear, motorcycling, snowboard gloves and running sportswear are some of the notable applications of PCM in sportswear.