Nowadays, the textile sector strives to develop innovative technologies or to combine different techniques and materials to obtain a new material of different or better properties. Modern solutions appearing in the textile industry are mainly intended to provide the user with the comfort and functionality of the product under specific environmental conditions. To prevent various types of hazards in a hot microclimate environment, specialist clothes are required, particularly protective gloves [1
]. The protective gloves should meet the basic standard [4
]. This standard does not directly apply to the protective properties of gloves, and therefore should not be used as a separate standard, but only in conjunction with the relevant European standards. In the case of protective gloves, in particular gloves protecting against hot factors, it is difficult to reach a compromise between providing adequate protective and functional properties. Usually, a higher level of protection in terms of thermal resistance involves the use of several layers of different materials. These layers significantly reduce the efficiency and ability to manipulate the fingers. Therefore, it is advisable to replace several layers with one textile material with a coating that meets the requirements for protective gloves. Therefore, the basalt fabric was selected for testing. Basalt fibers and products made of them are characterized by a low thermal conductivity, low moisture absorption, and good thermal resistance [5
]. These fibers have high thermal resistance, which enables them can be used in the temperature range from −260 to 800 °C. Due to the non-flammable properties that characterize basalt fibers, the materials made of them are resistant to flames for a very long period of time. In addition, they are resistant to corrosion, UV radiation, and the action of microorganisms. Products made of basalt fibers do not emit toxic products in reaction with the air or water. Basalt fabric is characterized by good thermal and mechanical properties. However, basalt fabrics used without any coating may cause irritation to the skin, respiratory track, and eyes [9
The BAGLO project led by the Lodz University of Technology concerned developing a textile package for protective gloves, the task of which was the protection against hot factors while providing protection against mechanical factors. In order to develop a new type of gloves, the protective fabrics made of basalt fibers were used. These included uncoated basalt fabrics and basalt fabrics, to which aluminum foil has been glued using a special adhesive mean. None of the selected basalt fabrics intended for gloves protecting against the effects of hot factors showed resistance to contact heat for the contact temperature of 250 °C. In the case of heat-resistance tests, the highest (fourth) efficiency level was obtained for all samples of aluminized basalt fabrics. One of the disadvantages of the produced aluminized basalt fabric was the abrasion and cracking of applied coating [1
], which led to a loss of protective properties and durability of gloves. Due to the above-described negative aspects of the conducted research, this work concerns the modification of basalt fabric in a different way (without) gluing the aluminum foil, but by putting chrome or zirconium (IV) oxide directly on the fabric surface.
In order to modify the basalt fabric surface, one of the PVD (physical vapor deposition) processes was applied: magnetron sputtering. It relies on the creation of atoms, atom clusters, or ions in a gas phase by working gas (Argon) ionization in a high voltage potential and them striking the surface of the target. In particular, magnetron sputtering is one of the glow discharge types, with a crossed electric and magnetic field, which allows for electron trapping in a sputtering zone. This is responsible for the higher flying time of electrons and results from the higher amount of sputtering ions in a near-to-target zone. This, in turn, causes the high sputtering rate of the target and faster deposition in comparison to diode sputtering. Magnetron sputtering can be done with the use of metallic targets (i.e., chromium or zirconium) in a case of pure metallic coatings. In order to obtain ceramic phases (nitrides, oxides, or carbides) to the working atmosphere reactive gas (nitrogen, oxygen, or carbon-containing gas, such as for example methane or acetylene) should be introduced. Such a process is called reactive magnetron sputtering (RMS) and is commonly used for the deposition of coatings that improve hardness, corrosion resistance, tribological, or decorative properties as well as other physical properties of products used in various fields of industry. The versatility of magnetron sputtering allows for the constitution of a coating onto a very broad range of shapes and sizes [13
Magnetron sputtering is a technique that allows the improvement of fabric thermal properties. A two-layer coating—aluminum (Al) with silicon dioxide (SiO2
)—and a three-layer coating—silicon dioxide (SiO2
)/aluminum (Al)/silicon dioxide (SiO2
)—were deposited on the aramid fabric surface [14
]. In this way, the radiant resistance of fabric was improved. The thermal and physical properties of nylon fabric subjected to metal sputtering—i.e., aluminum, copper, and nickel—were investigated [15
]. It was found that the sputtering treatment could give significant effects to the heat transfer of nylon without much loss in its shear and bending property, as well as water vapor transmission. The sputtered aluminum fabric was also studied for changes in its heat transfer [16
]. Aluminum was applied onto four textile substrates: nylon, polyester, cotton blend with 50/50 polyester, and shape memory polyurethane. Basic fabrics and fabrics modified with aluminum coating indicated the different thickness and thermal conductivity. The cotton–polyester blend (50/50) showed the lowest heat transfer coefficient.
Conductive paths, antennas, light-emitting diodes, and detector systems are used on the surface of textile materials, mainly used for recording physical and chemical changes in nature. There are many scientific publications on the modification of nonwoven, woven, and knitted fabrics as a result of a physical vapor deposition process intended for the use in textronics. One of the most interesting publications is the study of the resistance of metal coatings used in textronic systems for mechanical deformations [17
]. The work uses a composite Cordura substrate consisting of nylon fibers, which are coated with polyurethane foil. The 99.9% pure silver was deposited on the selected substrate. As a result of the study, it was observed that thin electrically conductive coatings obtained by the process of physical vacuum deposition without protecting their surface against destructive factors showed very good resistance to cyclical mechanical deformations. Besides, the authors stated that such structures can create flexible components that can be used in many areas of textronics and electronics.
The authors are first of all interested in improving the resistance to contact heat at a contact temperature of 250 °C, in order to be able to use the fabric in gloves protecting against the flame and hot factors. Gloves should protect against high temperatures outside, while maintaining a comfortable temperature inside. It is difficult to reach a compromise between providing adequate protective and functional properties.
To improve thermal properties, two different coatings (ceramics and metal) were chosen for the basalt fabric modification, i.e., the zirconium(IV) oxide and chrome coatings. Unmodified and modified basalt fabrics were tested for their thermal and electrical properties to be able to use the fabrics in gloves protecting against the flame and hot factors and damage by an electrostatic discharge. The research was aimed at increasing the contact heat resistance without reducing the radiation heat resistance. The authors also wanted to compare the values of some thermal and electrical parameters obtained for basalt fabric modified with metal and ceramic coatings.
The khaki color of basalt fabric has been changed due to the coating deposition. Instrumental color measurement was used as the method providing an objective data with a sufficient accuracy and repeatability for the color assessment of basalt fabric and basalt fabric modified with the chosen coatings. It is useful in the case of measurements of surface textures [18
], especially the textile material surface [19
]. Using the non-contact digital color imaging system DigiEye, an original method of samples surface analysis was elaborated and presented.
3. Results and Discussion
3.1. Chemical Composition and Thickness of the Coatings
The scanning electron microscope took images of deposited metal and ceramic coatings on the surface of basalt fabric. For the same samples, the spectroscopy of X-ray energy dispersion was carried out as well. Quantitative and color analyses of the content of individual elements on the basalt fabric surface covered with the 20 μm thick chrome coating and the 18 μm zirconium(IV) oxide coating were carried out. The 20 μm chrome coating deposited on the basalt fabric surface showed 98.92% chrome (Cr) content and 0.62% silicon (Si) content. The 18 μm zirconium(IV) oxide coating deposited on the basalt fabric surface showed 68.24% oxygen (O), 25.68% zirconium (Zr), and 3.25% silicon (Si). It may be related to the analysis of a specific piece of fabric.
3.2. Thermal Properties of Fabrics
The results of contact heat resistance tests and radiant heat resistance were analyzed in terms of the requirements for materials used in protective gloves. The results of contact heat resistance measurements for the contact temperatures of 100 and 250 °C for the fabric made of basalt fiber and its modifications with the metal and ceramics are shown in Figure 1
The tests of resistance to contact heat at the contact temperatures of 100 and 250 °C showed a significant difference between the values of contact heat for the basic basalt fabric and its modifications. As shown in Figure 1
, the value of the tested parameter for the fabric made of basalt fibers for the contact temperature of 100 °C is on the level of 10.8 s, while for the contact temperature of 250 °C, it is equal to 4.3 s. The highest resistance to contact heat for both contact temperatures was obtained by the fabric made from basalt fibers modified with zirconium(IV) oxide coatings. For this sample, at the contact temperature of 100 °C, one level of protection efficiency was achieved, while at the contact temperature of 250 °C, it reached the resistance of 5.1 s to contact heat. For the resistance to contact heat for the contact temperature of 100 °C, the result of 15.0 s belongs to the 95% confidence interval of the average value. None of the samples tested reached the first efficiency level for the resistance to contact heat at the contact temperature of 250 °C.
presents the results of thermal radiant resistance measurements for the fabric made of basalt fiber yarns and their modifications.
Based on the test results presented in Figure 2
, it is visible that all the tested fabrics have the first level of efficiency of protection against radiant with the 20 kW/m2
flux density. The highest resistance of the tested parameter was achieved for the modified basalt fabric with chrome. This is due to the silver, shiny color of the sample. None of the tested samples reached the second level of efficiency of protection against thermal radiation, which in our opinion is not satisfactory.
3.3. Comfort Properties of Fabrics
Fabric intended for the production of protective gloves should ensure user comfort. Gloves should protect against high temperatures outside, while maintaining a comfortable temperature inside. Measurements of thermal insulation properties on the Alambeta were performed for the basic (unmodified) fabric made from basalt fibers and for the basalt fabrics modified with chrome and zirconium(IV) oxide coatings. The tested samples of basalt fabric were coated by metal and ceramic only on one side. Since the modified fabrics are not the same from both sides, the right side with coating and left side without coating were tested. The test was carried out under normal climate conditions. Ten measurements were taken for each side of the fabric variant.
Thermal conductivity determines the material′s ability to conduct heat. Under the same conditions, more heat flows through the material, which is characterized by the higher coefficient of thermal conductivity λ
. The thermal conductivity of the given material depends on its structure and porosity. Basalt fabric modified with zirconium(IV) oxide obtained approximately the same values of thermal conductivity as the unmodified basalt fabric (Figure 3
As shown in Figure 3
, the highest value of the tested parameter was obtained for the basalt fabric coated with chrome. The results obtained are related to the thermal conductivity coefficient of selected coatings; for the chrome, it is 93.7 W/(m⋅K), while for the zirconium(IV) oxide, it is 2.0 W/(m⋅K).
Thermal resistance is the ability of a material to resist the flow of heat. The received results are presented in Figure 4
As shown in Figure 4
, the basalt fabric modified with the zirconium(IV) oxide coating showed the highest value of parameter r
; thus, it provides the best barrier against heat penetrating through the material during the test. Besides, with the higher values of thermal resistance, there is observed an increase of the warmth retention of the tested material and its thickness. A value that is slightly lower than that for the modified fabric with zirconium(IV) oxide of the tested parameter concerning the unmodified basalt fabric was obtained for the chrome-modified basalt fabric.
3.4. Electrical Properties of Fabrics
Materials intended for protective gloves are insulation materials. Zirconium(IV) oxide is a dielectric material, but chrome shows a good electrical conductivity. Therefore, the electroconductive properties of coatings applied to the sample surface require assessment. Surface resistance was determined for modified and unmodified basalt fabrics. Surface resistance was equal to 1.9 × 1012 Ω/sq for basalt fabric, 1.0 × 107 Ω/sq for basalt fabric modified with a chrome coating, and 3.0 × 1012 Ω/sq for basalt fabric modified with a zirconium(IV) oxide coating. Measurements were repeated five times, and mean values were calculated.
The surface resistance values of basalt fabric and basalt fabric modified with the zirconium(IV) oxide are comparable. The results place the products in the group of anti-static materials. An increase in the electrical conductivity was noticed in the case of the chrome coating basalt fabric compared to the unmodified basalt fabric. Therefore, it belongs to the group of static dissipative materials and is classified as an anti-static material. Such materials can protect the hands of the user and can prevent electrostatic discharge.
3.5. Surface Color Assessment of Fabrics
Colorimetric measurements of the sample surfaces were made to evaluate the quality of the fabric surface coating. The wavelength region of interest encompassed the electromagnetic energy of wavelengths from approximately 400 nm (violet) to 700 nm (red). Remission curves obtained for the unmodified basalt fabric and basalt fabric modified with the chrome coating and basalt fabric modified with the zirconium(IV) oxide are shown in Figure 5
The results of the remission measurement of samples in the spectrum of 400–700 nm indicate a significant effect of applied coatings on the remission measurement. The smallest value of spectral remission factor R is noticed for the basalt fabric coated with zirconium(IV) oxide. The highest value of factor R is noticed for the basalt fabric coated with the chrome. Therefore, the sample works better in the hot work environment due to a larger stream of reflected light from the tested surface.
The following assumptions have been made. (a) The sample lies on an XY plane in such a way that its center corresponds to the coordinates (0,0); (b) the assumed measuring surface of the sample was divided into 15 squares with length sides of 1 cm (Figure 6
). Each square covers part of the unmodified or modified basalt fabric.
) were assigned to each pair of squares according to Table 3
The colors on DigiEye of two neighboring squares were compared based on the instrumental color measurement. Differences ΔE
that were determined for selected pairs of squares were aimed at assessing the impact of cover on the chosen properties of the basalt fabric. A controlled illumination cabinet with D65 illuminant was chosen. The measurement results are presented in Figure 7
, Figure 8
and Figure 9
in a form of surface 3D plots. The distance-weighted least squares method was used to fit a curve to the data. The received results presented in Figure 7
, Figure 8
and Figure 9
indicate that the sample surfaces are uneven. The unevenness was assessed based on the variation coefficient of the total color difference.
The obtained results show the variation coefficient below 30% (Table 4
). It means that the tested surfaces are uneven, but the values of ΔEav
, and additionally ΔEmax
below 1, indicate that the pairs of colors recognized on the sample surface are not optically distinguished. Moreover, the unmodified basalt fabric is characterized by a 24% variation coefficient of the total color difference.
Unmodified and modified samples were also compared. The total color differences ΔE for pairs of samples were determined. A ΔE value equaling 11.8 was received for the pair of basalt fabric and basalt fabric modified with the zirconium(IV) oxide coating. The lower value of ΔE equal to 7.7 was received for the pair of basalt fabric and basalt fabric modified with the chrome coating. The value of ΔE above 3 is perceived as a significant color deviation.