Continuously cooling cotton fiber and its preparation method

Abstract

This application provides a continuously cooling cotton fiber and its preparation method, belonging to the field of functional textile processing technology. The preparation method of the continuously cooling cotton fiber includes: firstly, dissolving an initiator and a monomer with boron-nitrogen functional groups in a solvent and stirring until homogeneous to obtain a mixed solution; then immersing cotton fibers in the mixed solution, allowing them to react fully, followed by washing and drying to obtain the continuously cooling cotton fiber. This application introduces boron-nitrogen functional groups with high thermal conductivity through chemical grafting, which are covalently bonded to the surface of the cotton fiber, thereby obtaining a continuously cooling cotton fiber. The continuously cooling cotton fiber obtained by this invention has a long-lasting cooling function and good wash resistance, expanding the function and application of cotton fibers.

Description

Technical Field

[0001] This invention relates to the field of functional textile processing technology, specifically to a continuous cooling cotton fiber and its preparation method. Background Technology

[0002] Cooling textiles are textiles that, upon contact with the skin, cause rapid heat loss and a sudden drop in temperature, thus creating a cooling sensation. As people's living standards improve, their demands for the comfort of textiles are also increasing. In the hot summer, consumers want clothing and bedding that provide a cool and comfortable experience, leading to the development of cooling textiles to meet this need for coolness in high-temperature environments.

[0003] Cotton fiber is a natural cellulose fiber with a relatively compact structure. Compared to some synthetic fibers that inherently possess high thermal conductivity (such as metal fibers or certain functional polyester fibers), cotton fiber has a lower thermal conductivity. This means that heat is conducted more slowly in cotton fabrics, making it difficult to transfer heat from the skin's surface as quickly as highly thermally conductive fibers, thus making it less likely to produce a cooling sensation. Traditional methods of modifying cotton fabrics mostly involve finishing techniques, encapsulating cooling substances (such as menthol and xylitol) in microcapsules, and then attaching these microcapsules to the surface of the cotton fibers using adhesives. During wear, due to friction and other factors, the microcapsules gradually rupture, releasing the cooling substances. After the menthol microcapsules rupture, the menthol evaporates on the skin's surface, carrying away heat and providing a cooling sensation, much like applying a cooling balm to the skin. Alternatively, mineral powders with excellent thermal conductivity (such as jade powder and mica) can be added.

[0004] In the prior art, patent CN119102035A discloses a xylitol cellulose facial mask fabric, its preparation method, and its application. The xylitol cellulose facial mask fabric includes a cotton yarn layer with a mesh structure. Both sides of the cotton yarn layer are provided with xylitol cellulose fiber layers, and the fibers of the cotton yarn layer and the xylitol cellulose fiber layers are interwoven and entangled. By selecting a combination of cotton yarn and xylitol cellulose fibers, and by specifically defining the structure of the cotton yarn layer and limiting the interwoven nature of the fibers, the resulting xylitol cellulose facial mask fabric exhibits excellent breathability, a cooling sensation, and a soothing effect. However, the cooling sensation obtained through post-treatment modification is unsustainable and has poor washability. Patent CN118704154A discloses a jade-like cooling and UV-resistant functional fabric and its preparation method. The method involves blending cotton, spandex, and linen fibers to form a first blended yarn, and then blending modal and modified polyester fibers to form a second blended yarn. The first and second blended yarns are woven at a weight ratio of 4:3 using a circular knitting machine to obtain a knitted fabric. This knitted fabric is then impregnated and improved. Finally, the impregnated and improved fabric is heat-set at 120°C for 2-3 seconds to obtain the jade-like cooling and UV-resistant functional fabric. The modified polyester fiber and the impregnated and improved fabric in this invention work synergistically to improve the cooling sensation and further enhance the washability and stability of the product. However, blended fabrics introduce other chemical fibers, making them unsuitable for industries requiring pure cotton fabrics. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a continuous cooling cotton fiber and its preparation method, aiming to solve the problem that existing cooling fabrics use finishing technology or introduce chemical fibers, resulting in poor water resistance and unsuitability for special scenarios.

[0006] In a first aspect, this application provides a continuously cooling cotton fiber and a method for preparing the same, comprising the following steps:

[0007] S1. Dissolve the initiator and the monomer with boron-nitrogen functional groups in DMF solution, stir until homogeneous, and obtain a mixed solution;

[0008] S2. Soak cotton fibers in the mixed solution, allow them to react fully, filter, wash, and dry to obtain cotton fibers with a continuous cooling sensation.

[0009] In the technical solution of this application embodiment, boron-nitrogen functional groups with high thermal conductivity are introduced through chemical grafting. These functional groups are covalently bonded to the surface of cotton fibers, utilizing their excellent in-plane thermal conductivity to construct thermally conductive channels at the molecular level of the cotton fibers. This allows heat to be transferred more quickly between fibers, resulting in a continuous cooling sensation. The grafted boron-nitrogen functional groups also affect the crystallization behavior of the cotton fibers, promoting increased crystallinity. Increased crystallinity typically leads to a more regular arrangement of the molecular chains in the cotton fibers, resulting in weaker phonon scattering, which is beneficial for heat transfer. This method enables faster heat transfer within and between fibers, thereby enhancing the overall cooling sensation of the cotton fabric.

[0010] In some embodiments, in step S1, the initiator is benzoyl oxide; and in the mixed solution, the concentration of benzoyl oxide is 0.4–0.6 mol / L.

[0011] In this embodiment, the initiator generates free radicals under heating conditions. These free radicals attack the hydroxyl groups on the cotton fiber molecular chain and also generate active free radicals in the boron-nitrogen monomers, creating conditions for the grafting of boron-nitrogen functional groups onto the cotton fiber.

[0012] In some embodiments, in step S1, the monomer with boron-nitrogen functional groups is a boron-nitrogen heterocyclic compound; and in the mixed solution, the concentration of the boron-nitrogen heterocyclic compound is 0.4–0.6 mol / L.

[0013] In this embodiment, by introducing boron-nitrogen functional groups and utilizing their excellent in-plane thermal conductivity, a thermally conductive channel is constructed at the molecular level of cotton fibers, enabling heat to be transferred more quickly within the fibers and between fibers, thereby obtaining cotton fibers with a continuous cooling sensation.

[0014] In some embodiments, the reaction temperature in step S2 is 75–85°C.

[0015] In this embodiment, the initiator can be excited to generate free radicals at a certain temperature. If the temperature is too high, the reaction rate may be too fast, which may make the grafting reaction difficult to control to some extent. Excessive temperature may also cause the reactants to decompose or side reactions to occur, resulting in a decrease in grafting efficiency. Furthermore, the products of the side reactions may affect the purity and performance of the final product.

[0016] In some embodiments, the reaction time in step S2 is 1.5 to 2.5 hours.

[0017] In this embodiment, if the grafting reaction time is too long, the reaction may continue even after reaching equilibrium. In this case, further extending the time will not help improve the grafting rate; instead, it will waste time and energy.

[0018] In some embodiments, in step S2, the cotton fiber accounts for 95-105 g / L of the mass volume fraction of the mixed solution.

[0019] In this embodiment, a certain amount of cotton fiber reacts with the mixed solution to ensure a full reaction and a higher grafting rate of boron-nitrogen functional groups.

[0020] In some embodiments, in step S1, the solvent is a DMF solution.

[0021] In this embodiment, DMF, as a solvent, can cause cotton fibers to swell. During the grafting of boron and nitrogen functional groups, the swollen cotton fibers allow the grafting reagent to enter the fiber interior more easily and come into contact with more reaction sites, thereby improving the grafting efficiency.

[0022] In some embodiments, the drying temperature in step S2 is 55-65°C.

[0023] In this embodiment, drying is performed at a specific temperature without damaging the grafting effect.

[0024] In some embodiments, the grafting rate of boron-nitrogen functional groups in the continuously cooling cotton fiber is 33-37%.

[0025] In this embodiment, the higher grafting rate greatly improves the thermal conductivity of the cotton fibers, thereby enhancing their cooling sensation.

[0026] In some embodiments, the thermal conductivity of the cotton fabric woven from the continuously cooling cotton fiber is 0.14 to 0.20 W / (m·K).

[0027] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0029] Figure 1 This is a schematic diagram of the chemical reaction formula for grafting boron-nitrogen heterocyclic compounds onto cotton fibers in Example 1. Detailed Implementation

[0030] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terms “comprising” and “having” and any variations thereof as used herein are for the purpose of describing particular embodiments only and are not intended to limit this application.

[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0033] To address the issues of poor washability and unsuitability for specific applications in existing cooling fabrics that rely on finishing techniques or the introduction of chemical fibers, this application provides a continuous cooling cotton fiber and its preparation method. Through chemical grafting, high thermal conductivity boron-nitrogen functional groups are introduced into cotton fibers and covalently bonded to the fiber surface. Utilizing the excellent in-plane thermal conductivity of these boron-nitrogen functional groups, thermal channels are constructed at the molecular level of the cotton fibers, allowing for faster heat transfer between fibers and thus achieving a continuous cooling sensation. The grafted boron-nitrogen functional groups also influence the crystallization behavior of the cotton fibers, increasing their crystallinity. Increased crystallinity typically results in a more regular molecular chain arrangement and weaker phonon scattering, which is beneficial for heat transfer. It's like opening a new "highway" on the previously "blocked" heat conduction pathways of the cotton fibers, allowing for faster heat transfer within the fibers and between fibers, thereby enhancing the overall cooling sensation of the cotton fabric. This continuous cooling cotton fiber offers long-lasting cooling performance and good washability, expanding the functionality and applications of cotton fibers.

[0034] On the one hand, this application provides a method for preparing a continuously cooling cotton fiber, comprising the following steps:

[0035] S1. Dissolve the initiator and the monomer with boron-nitrogen functional groups in a solvent, stir until homogeneous, and obtain a mixed solution;

[0036] S2. Soak cotton fibers in the mixed solution, allow them to react fully, wash with water, and dry to obtain cotton fibers with a continuous cooling sensation.

[0037] In the technical solution of this application embodiment, boron-nitrogen functional groups with high thermal conductivity are introduced through chemical grafting. These functional groups are covalently bonded to the surface of cotton fibers, utilizing their excellent in-plane thermal conductivity to construct thermally conductive channels at the molecular level of the cotton fibers. This allows heat to be transferred more quickly between fibers, resulting in cotton fibers with a continuous cooling sensation. The grafted boron-nitrogen functional groups also affect the crystallization behavior of the cotton fibers, promoting increased crystallinity. Increased crystallinity typically leads to a more regular arrangement of the molecular chains in the cotton fibers, resulting in relatively weaker phonon scattering, which is beneficial for heat transfer. This method enables heat to be transferred more quickly within the fibers and between fibers, thereby enhancing the overall cooling sensation of the cotton fabric.

[0038] Furthermore, in some embodiments, in step S1, the initiator is benzoyl oxide; and in the mixed solution, the concentration of benzoyl oxide is 0.4–0.6 mol / L.

[0039] In the technical solution of this application embodiment, the initiator generates free radicals under heating conditions. These free radicals attack the hydroxyl groups on the cotton fiber molecular chain, and at the same time, they cause the boron nitrogen monomers to generate active free radicals, creating conditions for the grafting of boron nitrogen functional groups onto the cotton fiber.

[0040] Furthermore, in some embodiments, in step S1, the monomer with boron-nitrogen functional groups is a boron-nitrogen heterocyclic compound; and in the mixed solution, the concentration of the boron-nitrogen heterocyclic compound is 0.4–0.6 mol / L.

[0041] In the technical solution of this application embodiment, by introducing boron-nitrogen functional groups and utilizing their excellent in-plane thermal conductivity, a thermally conductive channel is constructed at the molecular level of cotton fibers, enabling heat to be transferred more quickly between fibers. Grafting boron-nitrogen functional groups also affects the crystallization behavior of cotton fibers, promoting increased crystallinity. Increased crystallinity usually makes the molecular chains of cotton fibers more regularly arranged, and the scattering of phonons is relatively weak, which is beneficial to heat transfer.

[0042] Furthermore, in some embodiments, the reaction temperature in step S2 is 75–85°C.

[0043] In the technical solution of this application embodiment, the initiator can be excited to generate free radicals at a certain temperature. If the temperature is too high, the reaction rate may be too fast, which to some extent will make the grafting reaction difficult to control. The excessively high temperature will also cause the reactants to decompose or side reactions to occur, resulting in a decrease in grafting efficiency. Furthermore, the products of the side reactions will affect the purity and performance of the final product.

[0044] Furthermore, in some embodiments, the reaction time in step S2 is 1.5 to 2.5 hours.

[0045] In the technical solution of this application embodiment, if the grafting reaction time is too long, the reaction may continue even after reaching equilibrium. In this case, further extending the time will not help improve the grafting rate, but will instead waste time and energy.

[0046] Furthermore, in some embodiments, in step S2, the cotton fiber accounts for 95-105 g / L of the mass volume fraction of the mixed solution.

[0047] In the technical solution of this application embodiment, a certain amount of cotton fiber reacts with the mixed solution to ensure a full reaction, thereby increasing the grafting rate of boron and nitrogen functional groups.

[0048] Furthermore, in some embodiments, in step S1, the solvent is a DMF solution.

[0049] In the technical solution of this application embodiment, DMF as a solvent can cause cotton fibers to swell. During the grafting of boron and nitrogen functional groups, the swollen cotton fibers allow the grafting reagent to enter the fiber interior more easily and come into contact with more reaction sites, thereby improving the grafting efficiency.

[0050] Furthermore, in some embodiments, the drying temperature in step S2 is 55–65°C.

[0051] In the technical solution of this application embodiment, drying is performed at a specific temperature without damaging the grafting effect.

[0052] Secondly, embodiments of this application provide a continuously cooling cotton fiber, which is prepared by the method of any one of claims 1 to 8, wherein the grafting rate of boron and nitrogen functional groups of the continuously cooling cotton fiber is 33% to 37%.

[0053] In the technical solution of this application embodiment, the higher grafting rate greatly improves the thermal conductivity of cotton fibers, thereby improving their cooling sensation.

[0054] Furthermore, in some embodiments, the thermal conductivity of the cotton fabric woven from the continuously cooling cotton fibers is 0.14–0.20 W / (m·K).

[0055] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0056] Example 1

[0057] This embodiment provides a method for preparing a continuously cooling cotton fiber, which specifically includes the following steps:

[0058] (1) Dissolve 0.5 mol / L benzoyl oxide and 0.5 mol / L 1,2-boron-azocyclohexane in DMF solution and stir until homogeneous to obtain 1 L of mixed solution.

[0059] (2) Weigh 100g of cotton fiber, soak it in the mixed solution, stir it evenly, react it at a reaction temperature of 80℃ for 2 hours, then filter it, wash it with water, and then dry it in an oven at 60℃ to obtain cotton fiber with a continuous cooling sensation.

[0060] In this embodiment, the chemical reaction formula for grafting boron-nitrogen heterocyclic compounds onto cotton fibers is as follows: Figure 1 As shown.

[0061] Depend on Figure 1 As can be seen, the boron-nitrogen double bond in the 1,2-boron-nitrogen heterocycle opens and copolymerizes with the hydroxyl groups in the cotton fiber, causing the boron-nitrogen functional groups to be grafted onto the cotton fiber.

[0062] Infrared spectroscopy was performed on the continuous cooling cotton fiber prepared in Example 1, and the grafting rate of boron-nitrogen functional groups was found to be 35%.

[0063] Examples 2-3 and Comparative Examples 1-2

[0064] Examples 2-3 and Comparative Examples 1-2 each provide a method for preparing a continuously cooling cotton fiber. The difference from Example 1 is that the concentration of benzoyl oxide is different. The specific concentration is shown in Table 1. The other steps are roughly the same as in Example 1, and will not be repeated here.

[0065] Table 1 shows the concentrations of benzoyl oxide in Examples 2-3 and Comparative Examples 1-2.

[0066] Examples / Comparative Examples Example 2 Example 3 Comparative Example 1 Comparative Example 2 Dosage / mol / L 0.4 0.6 0.3 0.7

[0067] The grafting rate of boron-nitrogen functional groups was obtained by infrared spectroscopy testing of the continuous cooling cotton fibers prepared in Examples 2-3 and Comparative Examples 1-2, as shown in Table 2.

[0068] Table 2 shows the grafting rates of boron-nitrogen functional groups in Examples 2-3 and Comparative Examples 1-2.

[0069] Examples / Comparative Examples Example 2 Example 3 Comparative Example 1 Comparative Example 2 Grafting rate / % 28.8 30.9 18.5 20.6

[0070] As shown in Table 3, the grafting effect of the continuously cooling cotton fibers prepared in Examples 2-3 was better; the grafting effect of the continuously cooling cotton fibers prepared in Comparative Examples 1-2 was poor. This is because when the concentration of benzoyl oxidase catalyst is low, the number of active centers is limited. In the grafting reaction, a lower catalyst concentration results in fewer free radicals generated, and these free radicals can only initiate a limited grafting reaction, thus resulting in a lower grafting rate. However, when the catalyst concentration is too high, it leads to over-initiation. Too many active centers cause self-polymerization reactions between grafting monomers instead of effectively grafting them onto the cotton fibers, thereby reducing the grafting rate.

[0071] Examples 4-5 and Comparative Examples 3-4

[0072] Examples 4-5 and Comparative Examples 3-4 respectively provide a method for preparing a continuous cooling cotton fiber. The difference between Example 1 and Example 2 is that the grafting reaction temperature is different, as shown in Table 3. The other steps are roughly the same as in Example 1 and will not be repeated here.

[0073] Table 3 shows the grafting reaction temperatures in Examples 4-5 and Comparative Examples 3-4.

[0074] Examples / Comparative Examples Example 4 Example 5 Comparative Example 3 Comparative Example 4 Temperature / °C 75 85 70 90

[0075] The grafting rate of boron-nitrogen functional groups was obtained by infrared spectroscopy testing of the continuous cooling cotton fibers prepared in Examples 4-5 and Comparative Examples 3-4, as shown in Table 4.

[0076] Table 4 shows the grafting rates of boron-nitrogen functional groups in Examples 4-5 and Comparative Examples 3-4.

[0077] Examples / Comparative Examples Example 4 Example 5 Comparative Example 3 Comparative Example 4 Grafting rate / % 33 37 26.7 26.6

[0078] As shown in Table 4, the grafting rate of the continuously cooling cotton fibers prepared in Examples 4-5 was better, while the grafting rate of the continuously cooling cotton fibers prepared in Comparative Examples 3-4 was not very good. This indicates that when the concentration of the initiator benzoyl oxide was 0.4-0.6 mol / L and the reaction temperature was 75-85℃, the boron-nitrogen functional groups could achieve a higher grafting rate. This is because at lower temperatures, the molecular motion, monomer diffusion rate, and chemical bond formation rate in the reaction system are relatively slow. Consequently, the generation of free radicals, monomer diffusion, and chemical bond formation are slower and insufficient, thus reducing the grafting rate. When the temperature is too high, some adverse effects occur. On the one hand, the initiator may decompose too quickly, generating too many free radicals. These free radicals may undergo mutual termination reactions, leading to a decrease in the concentration of free radicals that can effectively initiate the grafting reaction. On the other hand, excessively high temperatures can cause the molecular chains of the fiber to break, reducing the active sites available for grafting, and also causing the already grafted parts to fall off, thus leading to a decrease in the grafting rate.

[0079] The thermal conductivity of the continuously cooling cotton fibers obtained in Examples 1-5 and Comparative Examples 1-4 was tested and compared with that of ungrafted cotton fibers. The test results are shown in Table 5.

[0080] Table 5. Thermal conductivity of the sustained-cool cotton fibers obtained from Examples 1-5, Comparative Examples 1-4, and ungrafted cotton fibers.

[0081]

[0082] As can be seen from Table 5, the thermal conductivity of the continuous cooling cotton fibers obtained in Examples 1 to 5 is significantly improved compared with the ungrafted cotton fibers; the thermal conductivity of the continuous cooling cotton fibers obtained in Comparative Examples 1 to 4 is also improved compared with the ungrafted cotton fibers, but the best effect is not achieved.

[0083] In summary, this application provides a continuously cooling cotton fiber and its preparation method. By chemically grafting boron-nitrogen functional groups with high thermal conductivity, these groups are covalently bonded to the surface of the cotton fiber. Utilizing the excellent in-plane thermal conductivity of these boron-nitrogen functional groups, thermal channels are constructed at the molecular level of the cotton fiber, allowing for faster heat transfer between fibers, thus achieving a continuously cooling cotton fiber. The grafted boron-nitrogen functional groups also affect the crystallization behavior of the cotton fiber, promoting increased crystallinity. Increased crystallinity typically results in a more regular molecular chain arrangement and relatively weaker phonon scattering, which is beneficial for heat transfer. It's like opening a new "highway" on the previously "blocked" heat conduction pathways of the cotton fiber, allowing for faster heat transfer within the fiber and between fibers, thereby enhancing the overall cooling sensation of the cotton fabric. This continuously cooling cotton fiber exhibits long-lasting cooling properties and good washability, expanding the functions and applications of cotton fibers.

[0084] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a continuously cooling cotton fiber, characterized in that, Includes the following steps: S1. Dissolve the initiator and the monomer with boron-nitrogen functional groups in a solvent, stir until homogeneous, and obtain a mixed solution; S2. Soak cotton fibers in the mixed solution, allow them to react fully, wash with water, and dry to obtain cotton fibers with a continuous cooling sensation. The initiator is benzoyl peroxide; the concentration of benzoyl peroxide in the mixed solution is 0.4~0.6 mol / L. The monomer with boron-nitrogen functional groups is a boron-nitrogen heterocyclic compound; the concentration of the boron-nitrogen heterocyclic compound in the mixed solution is 0.4~0.6 mol / L.

2. The method for preparing continuously cooling cotton fiber according to claim 1, characterized in that, In step S2, the reaction temperature is 75~85℃.

3. The method for preparing continuously cooling cotton fiber according to claim 1, characterized in that, In step S2, the reaction time is 1.5 to 2.5 hours.

4. The method for preparing continuously cooling cotton fiber according to claim 1, characterized in that, In step S2, the cotton fiber accounts for 95~105 g / L of the mass volume fraction of the mixed solution.

5. The method for preparing continuously cooling cotton fiber according to claim 1, characterized in that, In step S1, the solvent is a DMF solution.

6. The method for preparing continuously cooling cotton fiber according to claim 1, characterized in that, In step S2, the drying temperature is 55~65℃.

7. A type of cotton fiber with a continuous cooling sensation, characterized in that, The continuously cooling cotton fiber is prepared by the preparation method of any one of claims 1 to 6, wherein the grafting rate of boron and nitrogen functional groups of the continuously cooling cotton fiber is 33-37%.

8. The continuously cooling cotton fiber according to claim 7, characterized in that, The thermal conductivity of the continuously cooling cotton fiber is 0.14~0.20 W / (m·℃).

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