Development of heat-generating polyester fiber harnessing catalytic ceramic powder combined with heat-generating super microorganisms

Abstract

One of the major purposes of fiber is to protect the body from hazardous environments and keep the body temperature at its normal level. To enhance thermal insulation, specially processed fibers have been produced to form air pockets, or various types of heat storage materials are mixed with polymer fiber filament yarns. In addition to thermal insulation, heat-generating fibers have recently been developed. In terms of heat-generating mechanism, there are two methods: the chemical method in which heat is generated through reaction with sweat, and physical method, which converts kinetic energy into thermal energy through the continuous expansion and contraction of fibers. Unlike these heat-generating methods, a brand-new fiber that generates heat using microorganisms was developed. Heat-generating polyester yarn was successfully produced by combining heat-generating microorganisms and ceramic powder together. New fabrics made with this yarn showed superior thermal properties compared to other specially developed fabrics for good thermal insulation. In addition to this, since ceramic powder is embedded in yarns, the heat-generating function of fiber was found to operate normally despite tens of washing. This process may open up a new possibility for the development of functional textiles.

Keywords

Performance materials properties protective and other high-performance clothing systems management of systems product and systems engineering

With the development of nylon in the 1930s, the era of synthetic fiber began. Because of its mass production, it has rapidly substituted natural fiber, which has been used for thousands of years. Since then, a variety of synthetic fibers have been developed. Today, the trend is moving toward adding new functions to the previously developed synthetic fiber. It is not difficult to find functional clothes made of these fibers on the market. In particular, heat-generating fibers have drawn great attention lately.

Conventional heat-generating fibers just keep the body warm through the enhancement of thermal insulation. For this purpose a hollow fiber has been applied and it was found that the air trap retains warm air and enhances insulation effects. Even though the fiber is wet, it stays excellent in terms of thermal insulation and ventilation. In addition, it stays dry all the time due to the air trap, and the fiber is soft and light. Compared to cotton and other insulating materials, it is faster by 20 % and 50 %, respectively, in terms of drying speed according to the manufacturer.¹ However, there is a limit in keeping warm, since this kind of fiber has a thermal insulation effect only, without generating heat.

Recently, new fibers that have thermal storage functions, obtained by mixing thermal storage materials with fibers, have also been developed. In terms of thermal storage materials, the following materials have been used: oxide-based materials with good light reflection such as alumina, carbide-based materials with high heat capacity such as ZrC or SiC, photo-catalyst functional materials such as TiO₂, and other organic compounds.²

Regarding the combining of these materials with fibers, there are two methods: mixing into the inside of yarn during the in-process of fiber spinning, and attachment on the surface by post-processing. In the former method, ceramic powders are combined with polymer resin, and yarn is melt-spun. Since ceramic powders are distributed in the fiber, the effect is semi-permanent with excellent wash and friction resistance. In the post-processing method, thermal storage materials are mixed with binder or dispersant and coated or laminated on the fiber. From the technical aspect, it is easier than the melt-spinning. However, it has less wash resistance. The functions may disappear after more than 10 times of washing.³

However, even in fibers utilizing heat storage materials, they just retain the heat without a thermal source, so that they are passive in terms of heat generation. To overcome this barrier, genuine heat-generating fibers, which absorb moisture from the body, have been developed. With the introduction of hydrophilic functional groups to the surface of acrylate fiber, fiber was converted into having a good hydrophilic property. As a result, moisture absorption is enhanced, and moisture is reacted with the compounds mixed with the fiber to generate heat of absorption.⁴ A critical disadvantage of this fiber is that when there is no more moisture available from the body, the fiber cools down quickly.

There are other products that generate heat by a physical method instead of the chemical method described above. If a wearer takes a walk or engages in jogging, the fiber stretches and contracts on and on, and kinetic energy is converted into thermal energy.⁵ In this case, if there is no movement, there would be no heat generated.

All of the commercially available heat-generating fibers have disadvantages, and they are not only complex in terms of the production process, but are also expensive. To overcome those disadvantages within a simple production process at a price that is competitive, a brand-new heat-generating fiber was developed by mixing of ceramic powder combined with heat-generating microorganisms with polyester fiber. The heat-generating microorganisms have been recently found, and their heat-generating mechanism is under investigation. According to a test, the polyester fiber combined with this ceramic powder showed an excellent performance in terms of heat generation. It appears that the thermal storage effect of ceramic powder has generated synergy effects along with the heat-generating microorganisms.

Characterization of ceramic powder combined with microorganisms

Production of ceramic powder

After collecting and analyzing natural clay mineral resources, which radiate far infrared rays, those with superior properties have been chosen. Figure 1 reveals the radiation characteristics of far infrared rays of the material. The emissivity between 5 and 20 µm of the wavelength at 40 ℃ was 0.927, with excellent emission power, 3.74 × 10²W/m²µm. Figures 1(a) and (b) show the spectral emissivity and spectral emissive power, respectively.

Figure 1.

Far infrared spectral emissivity (a) and spectral emissive power (b) obtained from the raw powder.

After crushing the raw materials into 320 mesh powder, it was ground again using a zirconia bead mill. After grinding, a deironizing process was applied with a magnetic field to remove iron components. Then it was heated at 820 ℃ for 20 hours to remove any possible organic substances and neutralize cold properties. At the end of heating, it was mixed with water in the weight ratio 1 : 1 and 0.01 % in weight of organic substances, extracted from plants known as Indian poke, was added. The mixture was kept at room temperature for 90 days. After the fermentation, it was dried at 180 ℃; the final average particle size was measured to be ∼0.636 µm, as shown in Figure 2. Figure 3 shows the scanning electron microscopy of powders produced by this process. More detailed production processes are described in the patent.⁶

Figure 2.

Result of particle size distribution measurement. Average diameter of the powder is 0.636 µm and 50 % volume size is 0.486 µm.

Figure 3.

Scanning electron microscopy images of ceramic powder combined with microorganisms after fermentation. The scale bar in the white line is 1 µm for (a), and for (b) and (c) it is 100 nm.

According to the result of chemical composition analysis of powder, it is a compound of various oxides that have silicon dioxide and aluminum oxide as major components. It has been confirmed that it is free from any hazardous substances such as heavy metals. Table 1 shows the results of the analysis obtained with inductively coupled plasma (ICP). The powder is officially listed as “Quantum Energy® radiating material” in the “International Cosmetic Ingredient Dictionary and Handbook” published by the Personal Care Product Council (PCPC).⁷

Table 1.

Analysis of composition of powders obtained after heating and fermentation

Content	1st analysis	2nd analysis
SiO₂	61.3%	67.7%
Al₂O₃	12.6%	11.4%
Fe₂O₃	2.67%	2.1%
CaO	4.92%	2.1%
MgO	0.97%	1.2%
K₂O	2.53%	3.08%
Na₂O	1.77%	2.22%
Others	2.24%	3.2%
Ignition loss	11.0%	9.1%
Total	100%	100%

Heat-generating characteristics

The powder that has been produced through this process reveals some unique properties. Among them, a heat-generating function has been confirmed. In particular, heat generation was stronger when temperature was lower. At present, the heat-generating mechanism of ceramic powder, which is high enough to melt ice at below zero, is unknown in detail, but they has been confirmed in phenomena. A test has been performed as follows.

On a square-shaped piece of ice of about 25 cm side length and 2 cm in thickness, a circular hollow concave space of 22 cm in diameter and 1.3 cm in depth was formed in the middle. Then, it was kept in a constant temperature chamber at −12 ℃. After things are ready, 10 g of ceramic powder was sprayed in the middle of the ice, and while keeping it at the same temperature, whether or not the ice melted was examined every 24 hours. Surprisingly, ice melted over time, and the color of ceramic powder changed by absorbing water. Figure 4 shows the change of color in ceramic powder after absorbing the water. As the ice melted more, the percentage of ceramic powder whose color changed increased over time. Even after the ceramic powder absorbed the water, it stayed unfrozen, which means that ice is still melting even at below zero because of the heat generated by the ceramic powder itself. The same result was obtained at −5 ℃ as well. The ice melting was clearer at −5 ℃ than at −12 ℃.

Figure 4.

Melting of ice over time by heat generated by microorganisms combined with ceramic powder dispersed on the ice. (a) Change of color in ceramic powder by absorbing the melted water at −5℃ after 24 hours, 48 hours and 72 hours, respectively, from the left. If the photo is enlarged, the melted parts can be seen more vividly. (b) Change of color in ceramic powder by absorbing the melted water at −12℃ after 24 hours, 48 hours and 72 hours, respectively, from the left. If the melted part on the edge of the ice is enlarged, the change of color can be seen more vividly.

Note that the ceramic powder was manufactured from the clay minerals composed of oxides, and there are no chemically reactive components. Since any ceramic powder cannot generate heat without causing an exothermic chemical reaction, it appears that this heat-generating function was created by the energy metabolism of microorganisms combined with ceramic powder. A systematic study on the energy source of heat-generating microorganisms and the mechanism is ongoing.

Thermal properties

Ever since the heat-generating phenomenon was confirmed, the thermal properties of ceramic powder have been assessed in plural aspects. Firstly, according to measurement by heating up to the melting point with a differential scanning calorimeter, no particular phase transition temperature was observed. However, absorption of heat continued until the melting point. Figure 5 reveals the results of thermal analysis. According to the figure, weight decreased by 12.40 % at 1300 ℃ while absorbing heat continuously. The melting point appeared to be 1117.3 ℃.

Figure 5.

Result of analysis of thermal properties of ceramic powder using differential scanning calorimeter (DSC) and thermo gravimetric (TG) measurement. It was measured under a nitrogen gas atmosphere with a heating rate of 20℃/min for the temperature range from room temperature to 1300℃.

The specific heat of the ceramic powder was measured to be 0.75 J/g ℃ at 25 ℃. This value is quite low, about one fifth of SiO₂, a key component of the ceramic powder combined with microorganisms. It seems that this kind of low specific heat is caused by heat-generating properties as well. Based on these results, it has been confirmed that the ceramic powder combined with microorganisms has very unique thermal properties without a particular crystalline structure.

Characteristics of fiber harnessing ceramic powder

Fabrication of fiber harnessing ceramic powder

Combining the ceramic powder that has been obtained through this process with polymer fiber is another problem. To extract fiber in a smooth manner without break-off, ceramic powder should have good dispersion and adhering property with polyester polymer. Zeta potential was measured to assess the dispersion property of ceramic powder, and it was −37.4 mV without any extra treatment. This value was good enough to have a good dispersion of particles in melt spun fiber. As a next step, to increase bonding between the powder and polyester, the surface of the powder was coated with ethylene glycol. The ethylene glycol-coated powder was mixed with polybutylene terephthalate (PBT) chip in a 1 : 10 ratio. This master chip was mixed with polyethylene terephthalate (PET) chip, again in a 1 : 10 ratio evenly, and then melt-spin was carried out. By this gradual mixing process, it was possible for the ceramic powder to be distributed in the polyester fiber evenly. It has been confirmed that ceramic powder was dispersed in the polyester fiber uniformly and its weight ratio was about 1–2 %, depending on the mixing ratio. Details of processing procedure and conditions are described in the patent.⁸

Figure 6 shows the cross-section of polyester fiber that contains ceramic powder and the results of energy dispersive X-ray (EDX) analysis. It can be found that ceramic powder was evenly dispersed and a silicon peak was detected in the EDX analysis. Note that the cross-sectional shape of the fiber is the same with general fibers. In other words, no special forming process was applied to induce a capillary action.

Figure 6.

Cross-section of polyester fiber that contains ceramic powder and results of energy dispersive X-ray analysis are shown. In (a), white dots indicate the ceramic powders embedded in the yarn. The white scale bar is 10 µm. Energy dispersive X-ray analysis has been carried out for the cross-section of the yarn, and the result obtained from the area inside of box 1 of (b) is shown in (c). From (d), it is clear that the silicon peak from the ceramic powder is the strongest one compared with the carbon and oxygen peaks, which are from the fiber composition. Similar results were obtained for other areas marked by boxes 2 and 3.

Heat-generating characteristics

The biggest problem in using microorganisms for industrial purposes is that most of them cannot undergo the high process temperature. For example, the temperature for the fiber-spinning process is as hot as over 300 ℃, and the dyeing process is carried out at over 180 ℃. Therefore, common microorganisms cannot survive these manufacturing processes. At present, methanopyrus kandleri, a kind of thermophilic microorganism, is known to survive at up to 122 ℃.⁹

To find out whether the microorganisms can undergo the high temperature, ceramic powder was heated again at 1000 ℃ for 10 hours and sterilized with autoclave at 121 ℃ for 15 minutes twice just before the culture experiment to avoid any possible contamination during the transportation. Then, a culture test using yeast extract minimal medium as well as tryptic soy broth was performed. They were cultured at 32 ℃ for 24–30 hours under aerobic and anaerobic conditions. There was no cultivation of microorganisms under the anaerobic condition. However, over 50 different species of environmentally harmless microorganisms were observed under the aerobic condition. They were identified by 16 S rRNA genome analysis and most of them are Staphylococcus and Bacillus microorganisms.¹⁰ Besides this, other kinds of microorganism were observed also and identification is undergoing. Right now, whether or not the microorganism itself is a new kind of extremophile with an excellent heat resistance, or it is the ceramic powder that makes it possible to survive high temperature is under investigation. We named it as a super microorganism for the time being.

The heat-generating function of the microorganism was saved even after the high temperature melt spinning process due to its excellent heat-resistant property. According to a comparison of infrared image photographs taken at room temperature, as shown in Figure 7, the temperature of the ceramic powder combined fiber was higher than that of plain polyester fiber by 2–3 ℃. Just as confirmed in the ice melting test, a higher temperature was observed even without a separate energy source. Even though the amount of ceramic powder mixed in was as little as 1 %, the heat-generating function observed in the ceramic powder was still maintained in the fiber as well. In this test, it has been indirectly confirmed that the heat-generating functions of microorganisms still work in the fiber.

Figure 7.

Infrared image photographs of plain polyester fiber (a) and polyester fiber combined with ceramic powder (b).

To observe the effect of heat generation while the ambient temperature is changed, fabrics made with plain polyester fiber and ceramic powder combined fiber were folded in three layers, and a thermocouple was inserted between them. Once the temperature reaches an equilibrium level after maintaining it for 30 minutes in a constant temperature chamber being kept at 50 ℃, the temperature of the chamber was lowered to 10 ℃. As shown in Figure 8, the cooling speed of the fabric made with ceramic powder combined fiber was slower than that of the fabric made with plain polyester fiber. The cooling speed of the ceramic powder combined fabric was calculated to be −2.75 ℃/min, while that of the control fabric was −3.17 ℃/min for the first 10 minutes after the cooling was started. Even after the temperature reached 10 ℃, the temperature of the ceramic powder combined fabric was still higher by 0.79 ℃ compared to the control when the measurement was taken after 1.5 hours. There is a possibility that the cooling speed was lower for the fabric made with ceramic powder combined fiber because of the thermal storage effect of ceramic powder. However, it appears that the heat-generating properties of ceramic powder have more influence on the temperature change from the result that the fabric temperature was being kept higher even after it reached the equilibrium temperature, 10 ℃.

Figure 8.

Change of fabric temperature by change of the ambient temperature of chamber. Blue line (#1), red line (#2) and light green line (#3) are the temperature of the control fabric, ceramic powder combined fabric and chamber atmosphere, respectively.

The heat generation by microorganisms can be confirmed in the differential scanning calorimeter analysis also. The ceramic powder combined fiber was lower than plain polyester fiber in terms of the heat of fusion by 6.6 % in the first heating and by 11.6 % in the second heating, as shown in Figure 9(c). It appears that the heat of fusion decreased because of the heat-generating effect of ceramic powder. Also the heat of solidification in the first cooling of the ceramic powder combined fiber was lower by 4.7 % than that of plain polyester fiber. Figures 9 (a) and (b) were obtained during the first heating and the first cooling, respectively.

Figure 9.

Differential scanning calorimetry analysis on ceramic powder combined polyester fiber, 75 denier-72 filament draw textured yarn (75/72 DTY). It was measured under the nitrogen gas atmosphere with a heating and cooling rate of 20 ℃/min for the temperature range from room temperature to 300 ℃. Heating and cooling curves are shown in (a) and (b), respectively. Melting point and solidification temperature, heat of fusion and solidification are summarized in (c).

Thermal insulation

As described above, the ceramic powder combined fiber has heat-generating properties and hence it is expected that it would have superior clothing thermal insulation. Thermal insulation performance of fabric was measured using a hot plate chamber being kept at 20 ℃ and 60 % relative humidity. The electrical power required to keep the hot plate surface temperature at 36.5 ℃ was measured and the thermal insulation was calculated from these data. As shown in Table 2, the clothing thermal insulation property of the fabric made with ceramic powder combined fiber is superior to any other synthetic fabric specially processed for good clothing thermal insulation. It is estimated that the excellent insulation property of the fiber was achieved by the synergetic effect of heat generation by microorganisms and thermal storage of ceramic powder.

Table 2.

Measurement of clothing thermal insulation of ceramic powder combined padding fabric and other padding fabrics. Test data were obtained according to the KS K 0466:2007.^a

Product	Composition	Weight (g/m²)	Clothing insulation (clo^b)
Product 1	Polyester 100%	166.7	3.59
Product 2	Polyester 100%	180.0	3.06
Ceramic powder combined fiber	Ceramic powder combined polyester 60% + Plain polyester 40%	165.0	3.70

KS K 0466:2007; Korean Industrial Standard, “Test method for thermal transmittance of textile fabrics”. The measurement process in this standard is quite similar with ASTM D 1518, “Standard test method for thermal resistance of batting systems using a hot plate.”

clo = 0.155 K·m²/W, a unit of thermal resistance defined as the insulation required to keep a resting man in equilibrium with environment at 21℃ in a normally ventilated room.

Sweat-absorbing and fast-drying properties

The conventional fast-drying fibers were mostly designed to wick away moisture from the skin through capillary action and increased evaporation with a particular shaping process, such as a narrow groove or honeycomb-patterned micro-pore.¹¹ In the case of a ceramic powder combined fiber, however, heat is internally generated and sweat can be easily evaporated even without having the capillary phenomenon because of the heat generated by the microorganism. As a result, it is expected that the sweat-absorbing and fast-drying functions are superior compared to specially designed fast-drying fabrics. Table 3 shows the result of the moisture management capability test of fabric in accordance with AATCC 195-2009.¹² According to this standard, the drying performance of fabric is related to the area of liquid moisture spreading as far as the wetting pattern is circular. As shown in this table, the maximum wetted radius, which indicates the spreading area, is so large that the highest fifth grade was observed. The overall moisture management capability ranked in the fourth grade. This result was obtained with the addition of heat-generating ceramic powder only without a special particular shaping process, such as making a narrow groove on the surface of the fiber. According to the fabric classification by moisture management properties, it belongs to the highest level, “Liquid moisture management fabric.”

Table 3.

Results of moisture management property test on the fabric made with ceramic powder combined fiber. The fabric was made with 75D/72 F DTY fiber. For the measurement, 0.22 cc of water was applied onto the fabric as specified in the AATCC 195-2009 standard

Index		Ceramic powder combined fabric		Other product for comparison
Index		Average	Grade	Average	Grade
Wetting time (s)	Surface/back	8.700/6.075	3.5/3.5	3.562/3.806	4.5/4.5
Absorption rate (%/s)	Surface/back	49.310/82.939	3.5/4.0	38.419/52.174	3.0/4.0
Maximum wetted radius (mm)	Surface/back	23.0/24.0	5.0/5.0	18.0/17.0	4.0/3.5
Spreading speed (m/s)	Surface/back	2.783/2.789	3.5/3.5	3.227/2.976	4.0/3.5
Accumulative one-way transport index (R)		202.356	4.0	169.226	3.5
Overall moisture management capability (OMMC)		0.623	4.0	0.525	3.5

Discussion

With the successful melt-spinning of ceramic powder combined with heat-generating microorganisms in polyester fiber, it has been possible to make brand-new synthetic fabrics that have semi-permanent heat-generating functions. At present, the identification and heat-generating mechanism of the microorganism are under investigation through a separate study. Based on the results of preliminary studies so far, it is speculated that the microorganism is a kind of very small extreme microorganism that has a very high heat resistance capability or a living substance known as microzyma.¹³ Also it seems that the heat-generation by the microorganism is a result of energy metabolism.

According to the measurement result of zeta potential of ceramic powder combined with microorganisms, –37.74 mV, it appears that dispersing properties would be very good without having an additional surface treatment process. Because of this superior dispersing property, melt-spinning was easily performed without a problem of clogging of the nozzle. As a result, it has been possible to obtain fibers in which ceramic particles are evenly distributed.

Surprisingly, the heat-generating performance of ceramic powder combined with microorganisms continued even after a fiber was manufactured. Considering the fact that the melt-spinning temperature reaches up to 300 ℃, this kind of result was unexpected. Assuming that the heat-generating property is originated from the microorganism, two possibilities could be estimated as follows. Firstly, the high melt-spinning temperature can be endured due to the superior thermal endurance property of the microorganism. Secondly, ceramic powder has the function of protecting the microorganism from the high temperature. Regarding these possibilities, an additional study needs to be performed.

To understand the detail of these mechanisms, it is necessary to study further the super microorganism and ceramic powder; however, it is confirmed by this work that there is a possibility of utilizing the microorganism for development of new functional and environmentally friendly textiles. In this study, a biological method that uses the heat probably generated by the metabolism of the microorganism was applied for development of a heat-generating fiber as a new approach besides the conventional chemical or physical method. In the case of a chemical method, it is not environment-friendly since it may not be recyclable. In the case of a physical method, the manufacturing process is complicated, and only a limited amount of heat is generated. In a biological method, on the contrary, a heat-generating fiber can be manufactured through the conventional processes without an additional particular process, which could enhance price competitiveness. Because no hazardous chemicals are used, in addition, it is environment-friendly. Since heat is probably generated by the energy metabolism of microorganisms combined with ceramic powder, moreover, the heat-generating performance would be semi-permanent. Because ceramic powders are evenly embedded in a fiber instead of being coated on the surface, the fiber is excellent in terms of wash, dyeing and friction resistance. It showed a good performance even after 50 times of washing. Because this process can be easily applied to natural fibers as well, it is able to develop heat-generating natural fibers also.

Conclusion

A new concept of heat-generating fibers in a brand-new biological process instead of using conventional methods has been developed. This new fiber is advantageous in various aspects, such as price competitiveness, environmental friendliness, and supply of raw materials. Since the heat generated by the energy metabolism of super microorganisms is used, the function of the fiber is semi-permanent. In addition to this, since ceramic powder is embedded in polyester fiber during the melt-spinning process simultaneously, the fiber is superior in terms of wash and friction resistance. With heat-generating properties, in addition, it has excellent thermal insulation and sweat-absorbing and fast-drying performances without applying additional treatment.

Furthermore, the new fiber showed good results in mechanical properties, deodorization and antimicrobial performance, as well as in heat-generating performance. It appears that these diverse functions have occurred because of the energetic function of the microorganism. In-depth study is necessary to understand the mechanism clearly.

Footnotes

Funding

This research work was supported by Quantum Energy Co. Ltd, under a contract between KRISS and Quantum energy Co, Ltd.

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