Heat Storage and Release Characteristics of Ceramic-Imbedded Woven Fabric for Emotional Clothing

Abstract This study examined the heat storage and release characteristics of ZrC-imbedded woven fabrics by light emission and thermal manikin experiments. The surface temperature of the ZrC-imbedded fabric was higher than that of the regular PET fabric. Furthermore, the Clo values of both the total and torso of the ZrC-imbedded fabric by the thermal manikin experiment were higher than those of the regular PET fabric, which suggests that the heat release is caused by far infrared rays emitted from the ZrC particles imbedded in the yarns as they receive light. This was confirmed by the higher emissivity and emissive power of the ZrC-imbedded fabric. However, the tactile hand of the ZrC-imbedded fabric needs to be improved by adjusting the structural parameters of the fabric and finishing process factors.


Introduction
The heat release property of fabrics used for warm-up suits has mainly been studied using three types of methods. Textile goods, such as Moiscare ® (Toyobo) and Heattech ® (Uniqlo), are made using the heat of wetting. Phase change materials (PCMs) undergo a change in physical state (liquid-solid) over a certain range of temperatures [5]. Therefore, nanocapsule PCM materials have been commercialized into different heat-release textile goods. In the recent years, Thermotron ® (Unitika), Megatron ® (Toray), and Reothermo ® (Asahi Kasei) brands have been sold as fabrics composed of ceramicimbedded yarns, which have the heat keepability as a result of their far-infrared emission characteristics. In previous studies [4,7,8,9], the carbonized powder of the charcoal fibers was used to obtain the far-infrared emission characteristics [7]. On the other hand, Lin et al. [8] used Al 2 O 3 , TiO 2 , and SiO 2 as ceramic powders for obtaining a far-infrared emissive polypropylene master batch. They reported the effects of the contents of the far-infrared master batches on the far-infrared emissivity using Al 2 O 3 , TiO 2 , and SiO 2 ceramic powders. Kuo et al. [4] examined nanocomposite fiber process optimization for SiO 2 -and TiO 2 -imbedded polypropylene with antibacterial and far-infrared ray emission properties. They reported that the far-infrared ray emission of the SiO 2 -and TiO 2 -imbedded polypropylene fibers was 85%, and the temperature rise by far-infrared ray emission was 8.6°C, which was much higher than that of regular polypropylene fibers. Lin et al. [9] examined the far-infrared emissivity of PET filaments wrapped with bamboo charcoal nylon fibers. These studies investigated the far-infrared emissivity characteristics according to the contents of the different ceramic powders. Furthermore, the findings of these studies were focused on the far infrared emissivity and temperature rise because of the high far-infrared emissivity. On the other hand, the wear comfort properties, such as wicking, drying, water vapor permeability, and heat keepability rate, of the ceramic-imbedded yarns and their fabrics have been studied by many researchers. Furata et al. [2] reported an increase in the moisture permeability of the ZrC-imbedded PET fabrics. Bahng et al. [1] examined the superior moisture absorption and fast dry characteristics of the ceramic-imbedded PET fabrics, which were assumed to be caused by the rapid evaporation of perspiration from the human body by the heat produced from the ceramic-imbedded filament. Negish et al. [10] reported that the ZrC in the yarns absorbs the heat emitted from the human body and/or reflects far-infrared radiation, which prevents the heat from flowing out. Shim et al. [11] examined the heatinsulating water-vapor-permeable property of a warm-up suit with good thermal performance because of the application of ceramic powders. In addition, Kim et al. [3] reported the farinfrared emission characteristics and wear comfort property of ZrC-imbedded heat storage knitted fabrics for emotional garments. ZrC-imbedded PET was spun with high-viscosity PET imbedded with ZrC powder on the core part and low-viscosity PET on the sheath part by conjugated spinning. They measured the wicking, drying, and thermal properties of the knitted fabrics composed of this ZrC-imbedded yarn and compared them with the emissivity and emissive power of the ZrC-imbedded knitted fabrics. On the other hand, these studies did not provide objective measurement data of the fabric worn by a thermal manikin related to heat storage and release emitted from the ceramics imbedded in the yarns, that is, the heat keepability rate was only assessed by the fabric specimens. Therefore, a thermal manikin test as a quantitative evaluation of the actual wearing performance is required. In this study, ZrC-imbedded fabrics were prepared using the sheath/core composite yarns spun by a conjugated spinning and the temperature rise by heat emitted from ZrC in the yarns was measured using a light heat This POY was texturized into draw textured yarn (DTY) 75d/36f with the following texturing conditions: draw ratio (1.65), heat temperature (190°C), and velocity ratio (1.75), which is defined as belt speed/feed speed on a Murata 33H (Japan) draw-textured machine. In addition, regular PET was prepared as a control yarn to compare with the ZrC-imbedded yarn specimens. Table 1 provides details of the physical properties of the yarn [3].

Woven fabric preparation
Two types of fabrics were woven on a rapier loom (Omni Picanol, Belgium) using PET 75d/72f in the warp with two kinds of weft yarns, 75d/36f ZrC-imbedded PET and 75d/72f regular PET. Table 2 lists the specifications of the fabric specimens.

Thermal radiation measurement
Thermal radiation measurements by light emission were taken using a light heat emission apparatus (UL chemical, Korea). Figure 2 shows a schematic diagram and measuring images of this apparatus. The specimens, 10 cm × 10 cm in size, were prepared at a temperature of 20 ± 2°C and relative humidity (RH) of 64 ± 4%, and a thermometer was placed on the specimen die, as shown in Figure 2. The heat emission bulb (220 V/500 W/3200 K) placed 50 cm away from specimen was switched on and the temperature change in the specimen was assessed using a thermometer according to the measuring time.

Prototype garment fabrication
Prototype garments worn by a thermal manikin were made using ZrC-imbedded and regular PET fabrics, as listed in Table  2. The different fabrics were made into long-sleeved jackets and trousers, as shown in Figure 3.

Thermal manikin measurement
The skin temperatures of the ZrC-imbedded and regular PET fabric garments were measured using a thermal manikin (MTNW-Huey, USA) according to the KSK ISO 15831:2005 standard measuring method in a climatic chamber. The emission apparatus. In addition, a thermal manikin test was carried out, and the heat storage and release characteristics of the ZrC-imbedded fabrics were verified by the Clo value from the thermal manikin experiment. The results are discussed with the far-infrared emission property and compared with that of a regular PET fabric.

Yarn preparation
ZrC-imbedded PET was prepared using a conjugated spinning method on a melt spinning pilot machine in Huvis Co. Ltd in Korea [3]. Partially oriented yarn (POY) 125d/36f with a lowviscosity PET on the sheath part and ZrC-mixed high-viscosity PET on the core part was spun on a bicomponent spinning machine. The spinning temperature was 285°C, and the spinning speed was 3000 m/min. The ZrC content in the yarn was 1.2 wt.%, which was mixed with high-viscosity PET at the core position in the extruder as a master batch chip. Figure  1 presents a schematic diagram of the conjugated spinning machine and cross section of the bicomponent yarn used in this study.
where I t is the total thermal insulation of the clothing and air layer, H is the total dry heat loss from the manikin, A s is the surface area of the manikin, T s is the mean skin temperature,

Tactile hand and measurement of the mechanical properties of the fabric
The mechanical properties of the ceramic-imbedded fabric specimens were measured using a fabric assurance simple testing (FAST) system [3]. The shear rigidity (G) was calculated using EB5, as shown in Eq. (2), which was measured using a FAST-3 measuring device.
experimental garments were made using two types of fabric specimens listed in Table 2. Figure 3 shows the jacket and trouser size specifications and their block patterns. The areas of the skin temperature measurements included 8 points (torso, forearm, thigh, calf, upper arm, hand, foot, and head) and temperature measuring sensors were attached to the 15 skin surfaces of the thermal manikin, as shown in Figure 4. The light emission apparatus was used for detecting the heat storage and release characteristics by far-infrared emission of the ceramic-imbedded yarns and fabrics. Figure 5 shows the garment worn by the thermal manikin with the light on and light off. The skin temperature of the manikin was set to 37°C for each body part. The ambient temperature (T a ) in the climatic chamber was 20 ± 0.5°C at 65 ± 2% RH and an air velocity of 0.1 m/s. The thermal manikin had no movement during the entire experiment. The average skin temperature (T s ) on 15 points was measured, and the total dry heat loss (H) from the manikin was also measured after 60 min since the thermal manikin was started. Thermal insulation value (I t ) was calculated using Eq.
(1). Finally, the Clo value was calculated using I t . distance, that is, the surface temperature of the ZrC-imbedded fabric specimen increased nonlinearly to 38°C during 10 min of light emission. When the light was off after 10 min, the surface temperature was decreased rapidly to 24°C after 20 min. On the other hand, the temperature rise on the fabric surface of the regular PET fabric was increased to 34.8°C and decreased to 24°C, which showed a similar increasing and decreasing shape to the ZrC-imbedded fabric. In addition, the heat-release temperature of the ZrC-imbedded fabric after 10 min was higher than that of the regular PET fabric. This phenomenon was assumed to be caused by the heat released from the absorption or accumulation of far-infrared radiation emitted from ZrC in the yarn. According to a previous study [4], far-infrared textiles are effective in retaining heat because the energy absorbed by the far-infrared material contained in the fiber is converted to and emitted as far-infrared rays. In a previous study [3], the emissivity and emissive power of the ZrC-imbedded and regular PET yarns were measured using a Fourier transform infrared (FT-IR) spectrometer with an attached mercury cadmium telewriter (MCT). Table 3 lists the emissive power and emissivity of the ZrC-imbedded and regular PET yarns [3]. The sum of the emissive power of the ZrC-imbedded yarns between 5 and 20 µm of wavelength was 3.65 × 10 2 W/ m 2 , which was larger than that of the regular PET fabric. This was attributed to the ZrC particles imbedded in the yarns. On the other hand, the emissivity of the ZrC-imbedded yarn between 5 and 20 µm was 0.906, which was higher than that of the regular PET specimens; this was also caused by the ZrC particles imbedded in the yarns. The higher emissivity and emissive power of the ZrC-imbedded yarns than the regular PET yarn resulted in a higher surface temperature of the ZrC-imbedded fabric than the regular PET fabric, as shown in Figure 6.
where G is the shear rigidity (N/m) and EB5 is the bias extension under the 5 gf/cm width (%) and T a is the mean ambient temperature.
The bending rigidity (B) was calculated using c, as shown in Eq. (3), which was measured using a FAST-2 measuring device. B1 and B2 are the bending rigidity in the warp and weft directions, respectively.
where B is the bending rigidity (μN·m), c is the bending length (mm), and W is the weight per unit area (g f /m 2 ). The extensibility and compressibility were measured using the FAST-3 and FAST-1 measuring devices, respectively. The extensibility (E20 and E100) was measured at a load of 20 gf/cm and a 100gf/cm width using FAST-3, and the compressibility (ST) was calculated as the difference in thickness of a fabric measured at a pressure of 2 and 100 gf/cm 2 , which is called the surface thickness. Figure 6 presents the light heat emission diagram of the ZrCimbedded fabric and a regular PET fabric specimen as a control fabric. As shown in Figure 6, the temperature rise on the fabric surface of the ZrC-imbedded fabric was observed according to the time lapsed as light is emitted from a 50-cm  ZrC particles in the fabric, when they receive light. According to Lin et al. [6], the fabric with the function of the far-infrared ray absorbs the heat energy from sunlight and then releases it back to the human body in the form of far-infrared radiation, so that it can repeatedly reach the effect of the heat preservation of human body, that is, the ZrC-imbedded fabric can release the heat by far-infrared emission and preserve the heat of the human body. On the other hand, differences in the Clo values (total and torso) of the regular PET fabric between the light on and off states were also observed, which was caused by TiO 2 in the regular PET, that is, TiO 2 emits heat energy by far-infrared radiation from light emission (light on state), even though it is less than that of the ZrC ceramic powder in the yarns, which was obtained by the elemental analysis reported elsewhere [3]. The concentration of Zr and Ti (wt.%) in the ZrC-imbedded yarns and regular PET yarns was 19.29% and 4.43%, respectively [3]. Figure 7 shows the relative mechanical properties of the two types of woven fabric specimens measured using the FAST system. The extensibility (E20 and E100), compressibility (ST), bending rigidity (B1 and B2), and shear rigidity (G) of the ZrC-imbedded woven fabric were plotted as the ratio to those of the regular PET woven fabric. As shown in Figure  7, the compressibility (ST) of the ZrC-imbedded fabric was lower than that of the regular PET fabric. This means that the ZrC-imbedded fabric is less compressible than that of the regular PET fabric, which was assumed to be caused by the nano-sized ZrC powders imbedded in the yarns. The bending

Thermal insulation by thermal manikin test
A quantitative evaluation of the thermal property of the ZrCimbedded fabric was carried out using the thermal manikin experiment. The total Clo value from the 15 positions of the thermal manikin and the Clo value from torso area to which light is emitted were obtained from the ZrC-imbedded and regular fabrics. This assessment was carried out with the light on and off. Table 4 lists the Clo values of the ZrC-imbedded and regular PET fabrics worn by the thermal manikin at 15 positions and the torso position of the thermal manikin. As shown in Table  4, the total Clo value of the ZrC-imbedded fabric exhibited a higher value than the regular PET fabric specimen at the light on state. This means that the effect of the ZrC particles in the ZrC-imbedded fabric to the heat storage and release is superior to that of TiO 2 in the regular PET fabric, which is caused by the higher emissivity and emissive power of the ZrC-imbedded fabric than the regular PET fabric, as listed in Table 3. This finding is consistent with the result of a higher fabric surface temperature of the ZrC-imbedded fabric than the regular PET fabric, as shown in Figure 6. In addition, the Clo values of both the total and torso areas under the light on measuring condition were much higher than those under the light off condition. Moreover, the Clo value of the ZrC-imbedded fabric at the torso area was much higher than that of the regular PET fabric at the light on state. On the other hand, no significant difference in the Clo value between the ZrC-imbedded fabric and regular PET fabric was observed under the light off measuring conditions, as shown in Table 4. This suggests that less heat is released in the light off state than in the light on state, that is, the heat release is caused by the far-infrared rays emitted from the

CONCLUSIONS
The heat storage and release characteristics of ZrC-imbedded woven fabric were examined by light emission and thermal manikin experiments. The results were compared with those of regular PET fabric. The surface temperature of the ZrCimbedded fabric was higher than that of the regular PET fabric, which was caused by the heat released from absorption or accumulation of the far-infrared emitted from ZrC-imbedded in the yarns. This was verified by the higher emissivity and emissive power values of the ZrC-imbedded fabric than those of the regular PET fabric. Furthermore, the Clo values of both the total and torso of the ZrC-imbedded fabric by the thermal manikin experiment were higher than those of the regular PET fabric. In addition, the Clo values of both total and torso areas under the light on measuring conditions were much higher than those under the light off condition, but no significant difference in the Clo value between ZrC-imbedded and regular PET fabric under the light off measuring condition was observed. This means that the heat release is caused by the far-infrared radiation emitted from the ZrC particles imbedded in the yarns as they receive light. On the other hand, the extensibility of the ZrC-imbedded fabric by longitudinal and bias extension was not influenced by the ZrC nanoparticles imbedded in the yarns. Nevertheless, the compressibility in the lateral direction was worse than that of the regular fabric due to the ZrC particles imbedded in the yarns. Therefore, the tactile hand property of the ZrC-imbedded fabric needs to be improved by lowering the bending rigidity and enhancing the compressibility through adjustments of the fabric structural parameters and finishing process factors.

ACKNOWLEDGMENTS
This research was funded by "Development of multi-functional inorganic particle embedded fibers and high comfort sports/ outdoor clothing" project.
rigidities (B1 and B2) of the ZrC-imbedded fabric were slightly higher than those of the regular PET fabric. The ZrC particles imbedded in the yarn were assumed to be protected from the in-plane deformation of the bending of the ZrC-imbedded fabric, which resulted in high bending rigidity. On the other hand, the extensibility (E20) was similar but the extensibility (E100) at 100gf/cm of the ZrC-imbedded fabric was slightly higher than that of the regular fabric. Furthermore, the shear rigidity (G) of the ZrC-imbedded fabric was lower than that of the regular PET fabric, which was assumed to be due to the thinner fabric thickness and less filament numbers in the yarn. This means that the ZrC-imbedded fabric is more extensible in the longitudinal and bias directions than that of the regular PET fabric, even though ZrC nanoparticles were imbedded in the yarns of the ZrC-imbedded fabric, that is, longitudinal and bias extension of the fabric can be changed by the fabric structure such as thickness and weight differently from the bending and compressional deformations, which were influenced by nanoparticles imbedded in the yarns, as mentioned previously. Figure 8 presents SEM images of cross sections of the yarns and fabric of the ZrC-imbedded and regular fabrics. The ZrCimbedded fabric was thinner than that of the regular PET fabric, which caused high extensibility and low compressibility. Moreover, Figure 8(a) shows larger ZrC nanoparticles than those of regular PET (Figure 8c) imbedded in the cross section of the yarn, which also resulted in low compressibility of the ZrCimbedded fabric. Summarizing the tactile hand of ZrC-imbedded fabric from mechanical properties, the extensibility of the ZrCimbedded fabric in the longitudinal and bias extension was not influenced by the ZrC nanoparticles imbedded in the yarns.
On the other hand, the compressibility in the lateral direction was worse than that of the regular fabric because of the ZrC particles in the yarns. Therefore, the tactile hand property of the ZrC-imbedded fabric requires improvement by lowering the bending rigidity and by enhancing the compressibility through adjustments of the fabric structural parameters and finishing process control.