Phase Change Materials (PCM)
Every material absorbs heat during heating process and its temperature will rise constantly. The heat stored in the material is released into the environment through a reverse cooling process and the material temperature decreases continuously. A normal textile material absorbs about one kilo joule per kilogram of heat while its temperature rises by one degree Celsius. Phase Change Material (PCM) will absorb higher amount of heat when it melts. This thermo regulating effect of textiles can be obtained with the application of PCM.
Tthe PCM incorporated clothing action A paraffin-PCM, absorbs approximately 200 kilojoules per kilogram of heat if it undergoes a melting process. During the complete melting process, the temperature of the PCM and its surrounding area remains constant. The paraffin's are either in solid or liquid state. In order to prevent the paraffin's dissolution in the liquid state, it is enclosed into small plastic spheres with diameters of only a few micrometers. These microscopic spheres containing PCM are called PCM-microcapsules. The microencapsulated paraffin is either permanently locked in acrylic fibres and in polyurethane foams or coated onto the surface of a textile structure.
Normal garments do not balance the heat generated and released in to the environment from the body. PCM incorporated textiles provide good thermal balance due to its thermo regulating effect. PCM controls the heat flux through the garment layers and adjusts the heat flux to the thermal circumstances, for example, if the heat generation of the body exceeds the possible heat release through the garment layers into the environment, the PCM will absorb and store this excess heat. On the other hand, if the heat release through the garment layers exceeds the body's heat generation during lighter activities, the heat flux through the garment layers is reduced by the heat emission of the PCM. The figure2 shows the thermoregulation effect of PCM incorporated clothing over the conventional clothing.
Intensity and duration of the PCM's active thermal insulation effect depend mainly on the heat storage capacity of the PCM-microcapsules and the applied quantity. Thin high-density materials support for cooling process. Thick and less dense textile structure leads to more efficient heat release. To ensure a suitable and durable active thermal insulation effect in an active-wear garment, it is necessary to apply the correct PCM in the appropriate quantity. The selected PCM is normally microencapsulated and incorporated in a textile substrate. Requirements of the textile substrate in a garment application include sufficient breath ability, high flexibility and mechanical stability. The substrate incorporated with PCM-microcapsules needs to be integrated into a suitable location of the garment design and certain design principles need to be taken into account.
