Preparation of Filtration Sorptive Materials from Nanofibers, Bicofibers, and Textile Adsorbents without Binders Employment

The article deals with the preparation and possibilities of using combined filtration sorption systems usable for the construction of folded filters or respirators. The studied materials are made of several structural layers—a filter membrane made of polymeric nanofibers, an adsorbent containing active carbon or porous silicon dioxide nanofibers, and a supporting or cover nonwoven bicomponent fabric. The layers are connected only by pressure at an elevated temperature without the use of binders, according to utility model PUV 31 375. The result is a compact fabric material of textile character with a high permeability, good mechanical resistance, which effectively catches the submicron particles and the gases of the organic substances. The prepared samples of the filter sorptive material have been evaluated not only from the point of view of morphology and microstructure, but also from the point of view of the capture of pollutants.


Introduction
It is generally known that decreasing the dimensions of basic components of filtration and sorptive materials in barrier layers of filters leads to increasing the efficiency of capture for even gaseous harmful substances [1,2]. The problem, however, is that when the sorbent grain size or the fiber thickness decreases, a rapid increase in the pressure loss occurs when the contaminated air or liquid flows through the barrier layer [3,4].
In the scope of filters that are designed to capture the particles made of fibrous components, this problem is usually solved by enlarging the exposed area of the microfibrous material by folding it into the form of folders [5]. The dimensions of these microfibers, effectively capturing submicron particles of 0.4 µm or greater (F7 to H14 filters), are generally in micrometer units. If we use a polymeric nanofiber (also called submicron) of the thickness of tens to hundreds of nm for the same purpose, we can make filters that capture nanoparticles and viruses, and the pressure loss may not be as significant as for the micron-sized glass fibers. Modern filtration materials made of polymer nanofibers are now commonly manufactured and used in many areas of human activity. They are flexible, stable, and able to form homogeneous filter layers [6][7][8].
For this reason, the formed sorption layer is very breathable with a low pressure loss, high sorption dynamics, and considerable sorption capacity. A certain disadvantage is the small size of the accessible micropores (nm units), which makes it difficult to effectively impregnate them with chemisorbents and, moreover, is of a relatively high price. However, there is also a mesoporous Filtration Activated Carbon (FAC). An advantage of this is the lower influence of moisture on the capture of gaseous pollutants in comparison with other types of adsorbents. The active carbon fiber adsorptive fabrics can be successfully combined with polymeric or inorganic nanofibers [25].
Another interesting sorbent is the porous SiO 2 nanofibers, with a large specific surface (up to 900 m 2 /g) [26]. A surface or spatial formation formed from such porous nanofibers can simultaneously have both separation and sorption properties. Its disadvantage is the considerable current price and the low mechanical resistance. The nanofibrous filter and sorption layers may be provided with a hydrophobic or oleophobic treatment, in order to increase their moisture resistance.
The aim of our research was to apply this knowledge in the development of new filtering sorption materials. We have tried to use newly developed permeable filter membranes, made of polymeric nanofibers, and surface adsorbents, based on powdered, spherical, or fibrous activated carbon or porous SiO 2 nanofibers. For their connection, the adhesive properties of bicomponent fibers without binders' employment can be used.

Materials and Methods
Polymeric nanofibers, active carbon fibers, spherical activated carbon, and porous SiO 2 nanofibers are modern construction materials used in addition to glass fibers and classical adsorbents in the production and development of new filters and filtration equipment [27,28]. The studied materials are made of several structural layers-a filtration membrane made of polymeric nanofibers, an adsorbing fabric containing activated carbon or porous SiO 2 nanofibers, and a carrier cover nonwoven textile from bicofibers. The layers are connected only by pressure in increased temperature without the use of binders, according to utility model PUV 31375. The result is a compact fabric material of a textile character with a high permeability and good mechanical resistance, which effectively catches the submicron particles and vapors of organic substances. The filtration membrane for particle filtration with areal weight of 1-10 g/m 2 has been made by the company PARDAM, Ltd. (Roudnice nad Labem, Czech Republic) from PA-6 and polyvinylidene difluoride (PVDF) polymer nanofibers by centrifugal spinning. To achieve antimicrobial and antifungal properties, these polymeric nanofibers are subsidized by silver nanoparticles. The size of silver nanoparticles moved from 40-60 nm. Its concertation has been stabilized in the amount of 160 ppm/g. In the case of the presented products, silver particles are firmly anchored in a polymeric nanomembrane, so the user's body cannot by contaminated, even if their antibacterial effect is undisputed [29][30][31]. Viscous solutions of PA-6 or PVDF in a suitable organic solvent have been used for spinning. The principle of this technology and the design of the used manufacturing equipment are evident from Figure 1.
The PARDAM PA-6 nanofibers ( Figure 2) are chemically stable, with the exception of acids. Their properties make it possible to use a PA-6 nanofibrous layer, without support material. The typical fiber diameter is 200-500 nm. The weight of the membrane can be 0.5-20 g/m 2 and the air permeability moves in the range of 40 to 500 L/min/dm 2 . The melting point of the PA-6 nanofibers is 220 • C and the softening point is >204 • C. The PA-6 nanomembrane can have antibacterial and photocatalytic properties with doping functionalized particles (Ag, ZnO, TiO 2 , etc.). Hydrophobic, oleophobic, or hydrophilic post treatment with plasma spray is possible. PA-6 nanofibers are possible for using in the environment, because of their biodegradability [32]. The PARDAM PA-6 nanofibers ( Figure 2) are chemically stable, with the exception of acids. Their properties make it possible to use a PA-6 nanofibrous layer, without support material. The typical fiber diameter is 200-500 nm. The weight of the membrane can be 0.5-20 g/m 2 and the air permeability moves in the range of 40 to 500 L/min/dm 2 . The melting point of the PA-6 nanofibers is 220 °C and the softening point is >204 °C. The PA-6 nanomembrane can have antibacterial and photocatalytic properties with doping functionalized particles (Ag, ZnO, TiO2, etc.). Hydrophobic, oleophobic, or hydrophilic post treatment with plasma spray is possible. PA-6 nanofibers are possible for using in the environment, because of their biodegradability [32]. The PVDF nanofibers ( Figure 3) have excellent chemical resistance and flexibility. It is possible to use a PVDF nanofibrous layer without any support material. The membrane has a high permeability with a good filtration efficiency, and the fiber structure is randomly oriented. The typical fiber diameter is 200-500 nm, weight of membrane can be 0.5-15 g/m 2 , and air permeability moves in range of 40 to 500 L/min/dm 2 . The melting point of the PVDF nanofibers is 130 °C. The PVDF nanomembrane can have antibacterial and photocatalytic properties with doping functionalized particles (Ag, ZnO, TiO2, etc.). Their small pore size and high specific surface makes PVDF nanomembranes suitable for hightech applications, like chemically resistant filters, carriers, and separators.  The PARDAM PA-6 nanofibers ( Figure 2) are chemically stable, with the exception of acids. Their properties make it possible to use a PA-6 nanofibrous layer, without support material. The typical fiber diameter is 200-500 nm. The weight of the membrane can be 0.5-20 g/m 2 and the air permeability moves in the range of 40 to 500 L/min/dm 2 . The melting point of the PA-6 nanofibers is 220 °C and the softening point is >204 °C. The PA-6 nanomembrane can have antibacterial and photocatalytic properties with doping functionalized particles (Ag, ZnO, TiO2, etc.). Hydrophobic, oleophobic, or hydrophilic post treatment with plasma spray is possible. PA-6 nanofibers are possible for using in the environment, because of their biodegradability [32]. The PVDF nanofibers ( Figure 3) have excellent chemical resistance and flexibility. It is possible to use a PVDF nanofibrous layer without any support material. The membrane has a high permeability with a good filtration efficiency, and the fiber structure is randomly oriented. The typical fiber diameter is 200-500 nm, weight of membrane can be 0.5-15 g/m 2 , and air permeability moves in range of 40 to 500 L/min/dm 2 . The melting point of the PVDF nanofibers is 130 °C. The PVDF nanomembrane can have antibacterial and photocatalytic properties with doping functionalized particles (Ag, ZnO, TiO2, etc.). Their small pore size and high specific surface makes PVDF nanomembranes suitable for hightech applications, like chemically resistant filters, carriers, and separators. The PVDF nanofibers ( Figure 3) have excellent chemical resistance and flexibility. It is possible to use a PVDF nanofibrous layer without any support material. The membrane has a high permeability with a good filtration efficiency, and the fiber structure is randomly oriented. The typical fiber diameter is 200-500 nm, weight of membrane can be 0.5-15 g/m 2 , and air permeability moves in range of 40 to 500 L/min/dm 2 . The melting point of the PVDF nanofibers is 130 • C. The PVDF nanomembrane can have antibacterial and photocatalytic properties with doping functionalized particles (Ag, ZnO, TiO 2 , etc.). Their small pore size and high specific surface makes PVDF nanomembranes suitable for hightech applications, like chemically resistant filters, carriers, and separators. Several types of constructive materials have been used to form the adsorbent layer. The adsorption fabric based on powdered activated carbon has been made by Fibertex Nonwovens, PLC. The ACC 8092 15 active carbon fiber adsorption textile is produced by Kynol, Ltd. company, (Osaka, Japan) and the adsorption fabric, SARATOGA Pyjama, based on spherical activated carbon is from the Blücher company (Vildbjerg, Denmark). The use of the filtration sorption layer of the porous nanofibers of SiO2, from PARDAM, Ltd., has been also verified. The connection of single constructive layers of one-sided smelting nonwoven fabric of polyester bicofibers, VIGONAIR 1516, with an areal weight of 150 g/m 2 and a 30% share of bicofibers, is made by Fibertex Nonwovens, public limited corporation (PLC), with thermal bonding.
Fibrous NnF CERAM, SiO2 SORBENT (Figure 4), is a stable nanoporous material with a specific surface area 335 m 2 /g and an excellent electrical insulator with an electrical conductivity <10 −18 Sm −1 . This one has a thermal conductivity 1.3 Wm −1 K −1 , high thermal shock resistance with relative index 1.45, and melting point 1 665 °C. A crystal form is amorphous SiO2 with a typical fiber diameter 150-400 nm. A silicon dioxide nanofiberous ceramic membrane is a unique product made from 100% SiO2 nanofibers, without any binders or additives. A mechanically stable membrane with great porosity enables many applications. Nanofibers from Al2O3 (alumina) can also be employed for similar purposes. The appearance of the used adsorptive textile ACC 509215 from activated carbon fiber, from Kynol Ltd., and the example of the permeation of toluene through this material is evident from Figure 5 [33]. The results were taken from the Kynol, Ltd. prospectus, which we received for the material from the manufacturer, and in which these specifications were presented. The basic parameters of the Kynol woven textiles are shown in Table 1. Figure 6 gives basic information about another prospective adsorption carbon textile, ZORFLEX (Tyne and Wear, UK) from the Chemviron Carbon Company (Feluy, Belgium). Its basic information is related to the appearance and sorption properties of another used structural material, SARATOGA Pyjama, and thus, the adsorption textile from Blücher, based on spherical activated carbon, is shown in Figure 7. Several types of constructive materials have been used to form the adsorbent layer. The adsorption fabric based on powdered activated carbon has been made by Fibertex Nonwovens, PLC. The ACC 8092 15 active carbon fiber adsorption textile is produced by Kynol, Ltd. company, (Osaka, Japan) and the adsorption fabric, SARATOGA Pyjama, based on spherical activated carbon is from the Blücher company (Vildbjerg, Denmark). The use of the filtration sorption layer of the porous nanofibers of SiO 2 , from PARDAM, Ltd., has been also verified. The connection of single constructive layers of one-sided smelting nonwoven fabric of polyester bicofibers, VIGONAIR 1516, with an areal weight of 150 g/m 2 and a 30% share of bicofibers, is made by Fibertex Nonwovens, public limited corporation (PLC), with thermal bonding.
Fibrous NnF CERAM, SiO 2 SORBENT (Figure 4), is a stable nanoporous material with a specific surface area 335 m 2 /g and an excellent electrical insulator with an electrical conductivity <10 −18 Sm −1 . This one has a thermal conductivity 1.3 Wm −1 K −1 , high thermal shock resistance with relative index 1.45, and melting point 1 665 • C. A crystal form is amorphous SiO 2 with a typical fiber diameter 150-400 nm. A silicon dioxide nanofiberous ceramic membrane is a unique product made from 100% SiO 2 nanofibers, without any binders or additives. A mechanically stable membrane with great porosity enables many applications. Nanofibers from Al 2 O 3 (alumina) can also be employed for similar purposes. Several types of constructive materials have been used to form the adsorbent layer. The adsorption fabric based on powdered activated carbon has been made by Fibertex Nonwovens, PLC. The ACC 8092 15 active carbon fiber adsorption textile is produced by Kynol, Ltd. company, (Osaka, Japan) and the adsorption fabric, SARATOGA Pyjama, based on spherical activated carbon is from the Blücher company (Vildbjerg, Denmark). The use of the filtration sorption layer of the porous nanofibers of SiO2, from PARDAM, Ltd., has been also verified. The connection of single constructive layers of one-sided smelting nonwoven fabric of polyester bicofibers, VIGONAIR 1516, with an areal weight of 150 g/m 2 and a 30% share of bicofibers, is made by Fibertex Nonwovens, public limited corporation (PLC), with thermal bonding.
Fibrous NnF CERAM, SiO2 SORBENT (Figure 4), is a stable nanoporous material with a specific surface area 335 m 2 /g and an excellent electrical insulator with an electrical conductivity <10 −18 Sm −1 . This one has a thermal conductivity 1.3 Wm −1 K −1 , high thermal shock resistance with relative index 1.45, and melting point 1 665 °C. A crystal form is amorphous SiO2 with a typical fiber diameter 150-400 nm. A silicon dioxide nanofiberous ceramic membrane is a unique product made from 100% SiO2 nanofibers, without any binders or additives. A mechanically stable membrane with great porosity enables many applications. Nanofibers from Al2O3 (alumina) can also be employed for similar purposes. The appearance of the used adsorptive textile ACC 509215 from activated carbon fiber, from Kynol Ltd., and the example of the permeation of toluene through this material is evident from Figure 5 [33]. The results were taken from the Kynol, Ltd. prospectus, which we received for the material from the manufacturer, and in which these specifications were presented. The basic parameters of the Kynol woven textiles are shown in Table 1. Figure 6 gives basic information about another prospective adsorption carbon textile, ZORFLEX (Tyne and Wear, UK) from the Chemviron Carbon Company (Feluy, Belgium). Its basic information is related to the appearance and sorption properties of another used structural material, SARATOGA Pyjama, and thus, the adsorption textile from Blücher, based on spherical activated carbon, is shown in Figure 7. The appearance of the used adsorptive textile ACC 509215 from activated carbon fiber, from Kynol Ltd., and the example of the permeation of toluene through this material is evident from Figure 5 [33]. The results were taken from the Kynol, Ltd. prospectus, which we received for the material from the manufacturer, and in which these specifications were presented. The basic parameters of the Kynol woven textiles are shown in Table 1. Figure 6 gives basic information about another prospective adsorption carbon textile, ZORFLEX (Tyne and Wear, UK) from the Chemviron Carbon Company (Feluy, Belgium). Its basic information is related to the appearance and sorption properties of another used structural material, SARATOGA Pyjama, and thus, the adsorption textile from Blücher, based on spherical activated carbon, is shown in Figure 7.         As a carrier and binder material, thermally nonwoven fabrics with a 30% bicofiber content have been used by Fibertex Nonwovens, PLC, and JILANA, PLC. The thermal bonding technology is based on the heat treatment of the nonwoven fibrous layer, prepared by mixing the mixture of the basic and connective bicofibers. Within hot-air bonding, this layer passes through the hot-air connecting chamber. After melting the binder fibers, solid connections are formed between the fibers to form a flexible and stable nonwoven fabric. A schematic cut of the bicofibers is shown in Figure 8. For the connection and calibration of all construction layers with pressure and temperature, a special laminating device was used, whose principle is evident from the schema on Figures 9 and 10. Figure 9 illustrates a method for preparing the studied samples of the combined filter sorption materials and a particular device used by the PYROTEK company (Blansko, Czech Republic) for this purpose. This device was used to join individual layers of filtration sorptive material from nanofibers, bicofibers, and adsorbing textile at an increased temperature and pressure. The material is pulled between two rubber belts from VITON. The speed of movement, pressure, dimension of the gap, and temperature of heating and cooling can be changed. Attending the single layers connection, consequently binds the attributes of the bicofibers at the increased temperature and pressure. Apart from the nonwoven textile from the bicofibers, the fitting of the nano layers with the struto textile from the bicofibers and adsorption textiles was with successfully verified. The furniture As a carrier and binder material, thermally nonwoven fabrics with a 30% bicofiber content have been used by Fibertex Nonwovens, PLC, and JILANA, PLC. The thermal bonding technology is based on the heat treatment of the nonwoven fibrous layer, prepared by mixing the mixture of the basic and connective bicofibers. Within hot-air bonding, this layer passes through the hot-air connecting chamber. After melting the binder fibers, solid connections are formed between the fibers to form a flexible and stable nonwoven fabric. A schematic cut of the bicofibers is shown in Figure 8. As a carrier and binder material, thermally nonwoven fabrics with a 30% bicofiber content have been used by Fibertex Nonwovens, PLC, and JILANA, PLC. The thermal bonding technology is based on the heat treatment of the nonwoven fibrous layer, prepared by mixing the mixture of the basic and connective bicofibers. Within hot-air bonding, this layer passes through the hot-air connecting chamber. After melting the binder fibers, solid connections are formed between the fibers to form a flexible and stable nonwoven fabric. A schematic cut of the bicofibers is shown in Figure 8. For the connection and calibration of all construction layers with pressure and temperature, a special laminating device was used, whose principle is evident from the schema on Figures 9 and 10. Figure 9 illustrates a method for preparing the studied samples of the combined filter sorption materials and a particular device used by the PYROTEK company (Blansko, Czech Republic) for this purpose. This device was used to join individual layers of filtration sorptive material from nanofibers, bicofibers, and adsorbing textile at an increased temperature and pressure. The material is pulled between two rubber belts from VITON. The speed of movement, pressure, dimension of the gap, and temperature of heating and cooling can be changed. Attending the single layers connection, consequently binds the attributes of the bicofibers at the increased temperature and pressure. Apart from the nonwoven textile from the bicofibers, the fitting of the nano layers with the struto textile from the bicofibers and adsorption textiles was with successfully verified. The furniture For the connection and calibration of all construction layers with pressure and temperature, a special laminating device was used, whose principle is evident from the schema on Figures 9 and 10. Figure 9 illustrates a method for preparing the studied samples of the combined filter sorption materials and a particular device used by the PYROTEK company (Blansko, Czech Republic) for this purpose. This device was used to join individual layers of filtration sorptive material from nanofibers, bicofibers, and adsorbing textile at an increased temperature and pressure. The material is pulled between two rubber belts from VITON. The speed of movement, pressure, dimension of the gap, and temperature of heating and cooling can be changed. Attending the single layers connection, consequently binds the attributes of the bicofibers at the increased temperature and pressure. Apart from the nonwoven textile from the bicofibers, the fitting of the nano layers with the struto textile from the bicofibers and adsorption textiles was with successfully verified. The furniture also facilitates the fitting layers with the help of fuside netting from polyester/polyamide copolymer or fuside powders. also facilitates the fitting layers with the help of fuside netting from polyester/polyamide copolymer or fuside powders.

Results
The prepared sample of the filtration sorptive materials with a filtration membrane from the polymeric PA-6, and the PVDF nanofibers were evaluated from the point of the efficiency of the particle capture within the filtration from an aqueous solution. Selected combinations of used materials are listed in Table 2. The introduced results are the average of at least three values in case of own measurements.

Results
The prepared sample of the filtration sorptive materials with a filtration membrane from the polymeric PA-6, and the PVDF nanofibers were evaluated from the point of the efficiency of the particle capture within the filtration from an aqueous solution. Selected combinations of used materials are listed in Table 2. The introduced results are the average of at least three values in case of own measurements.

Results
The prepared sample of the filtration sorptive materials with a filtration membrane from the polymeric PA-6, and the PVDF nanofibers were evaluated from the point of the efficiency of the particle capture within the filtration from an aqueous solution. Selected combinations of used materials are listed in Table 2. The introduced results are the average of at least three values in case of own measurements.
An example of an evaluation of good (sample No. IV) and poor (sample No. V) particle recovery from the solution is shown in Figure 11.  The selected samples of the filtration sorptive materials were further evaluated for the efficiency of the capture of submicron particles from the gas phase, by SIGMA GROUP, PLC [36,37]. The results of the three selected samples are presented in Table 3. Table 3. Evaluation results of the filtration membrane from PA-6 nanofibers coated on both sides with NT BICO Fibertex nonwoven, weighing 150 g/m 2 after calibration to a thickness of 2 mm. Figure 11. Examples of good and bad quality filtration for samples IV and V; 500 mL of water with 1% of a mixture solution was filtered through filter IV or V. The selected samples of the filtration sorptive materials were further evaluated for the efficiency of the capture of submicron particles from the gas phase, by SIGMA GROUP, PLC [36,37]. The results of the three selected samples are presented in Table 3. Table 3. Evaluation results of the filtration membrane from PA-6 nanofibers coated on both sides with NT BICO Fibertex nonwoven, weighing 150 g/m 2 after calibration to a thickness of 2 mm. For further applications, this material has been combined with an adsorption textile (AT) based on PAC, SAC, and FAC, optionally with a porous SiO 2 adsorption layer. These materials were then used to make folded filters and respirators (Figures 12 and 13). For further applications, this material has been combined with an adsorption textile (AT) based on PAC, SAC, and FAC, optionally with a porous SiO2 adsorption layer. These materials were then used to make folded filters and respirators (Figures 12 and 13).

Figure 12.
Example of folded filters that were made from a nonwoven bicotextile, PA-6 nanofibers filtration membrane, and adsorption textile (AT) sorption layer. The left is a cut of the folds, the middle is a view of the crimp material, and the right is tested filter. Figure 13. Example of respirators that were made with (up) and without (down) an adsorption layer. The left is the top and bottom view of the respirators (with or without valve). The right is a cut through of these respirators, with the view though the construction layer. From the top there is bicotextile, adsorption textile, nanofibers filtration membrane, and bicotextile.
Filter membranes made of polymeric nanofibers were also combined with a 30% part of the bicofibers. The appearance of the used struto textile of JILANA Elastic Universal and the manufactured respirator inserts is shown in Figure 14. For further applications, this material has been combined with an adsorption textile (AT) based on PAC, SAC, and FAC, optionally with a porous SiO2 adsorption layer. These materials were then used to make folded filters and respirators (Figures 12 and 13).

Figure 12.
Example of folded filters that were made from a nonwoven bicotextile, PA-6 nanofibers filtration membrane, and adsorption textile (AT) sorption layer. The left is a cut of the folds, the middle is a view of the crimp material, and the right is tested filter. Figure 13. Example of respirators that were made with (up) and without (down) an adsorption layer. The left is the top and bottom view of the respirators (with or without valve). The right is a cut through of these respirators, with the view though the construction layer. From the top there is bicotextile, adsorption textile, nanofibers filtration membrane, and bicotextile.
Filter membranes made of polymeric nanofibers were also combined with a 30% part of the bicofibers. The appearance of the used struto textile of JILANA Elastic Universal and the manufactured respirator inserts is shown in Figure 14. Filter membranes made of polymeric nanofibers were also combined with a 30% part of the bicofibers. The appearance of the used struto textile of JILANA Elastic Universal and the manufactured respirator inserts is shown in Figure 14. Selected respirators were further evaluated by the State Institute for Nuclear, Chemical, and Biological Protection, from the point of view of the effectiveness of the submicron particle capture on the equipment, PortaCount ® PRO 8038, by the TSI company for the measurement of the respiratory protective factor, depending on the conditions of use, according to the standard methodology. The results of this evaluation are shown in Figure 15.

Principle of Measurement
The PortaCount ® PRO 8038 measures the sum of solid particles, such as the condensation cores, from 20 nm to more than 1 μm. When measured, it switches between sampling concentrations of particles in the surroundings and in the protected area (under the respirator). It can also observe the influence of people and their grimaces on the leakage quality (if required). The result is the so-called Fit factor (Fc), which gives the particle number ratio, around no, to the particle number n, under the respirator in the exhaled air. The measurement results are shown in Table 4. Selected respirators were further evaluated by the State Institute for Nuclear, Chemical, and Biological Protection, from the point of view of the effectiveness of the submicron particle capture on the equipment, PortaCount ® PRO 8038, by the TSI company for the measurement of the respiratory protective factor, depending on the conditions of use, according to the standard methodology. The results of this evaluation are shown in Figure 15. Selected respirators were further evaluated by the State Institute for Nuclear, Chemical, and Biological Protection, from the point of view of the effectiveness of the submicron particle capture on the equipment, PortaCount ® PRO 8038, by the TSI company for the measurement of the respiratory protective factor, depending on the conditions of use, according to the standard methodology. The results of this evaluation are shown in Figure 15.

Principle of Measurement
The PortaCount ® PRO 8038 measures the sum of solid particles, such as the condensation cores, from 20 nm to more than 1 μm. When measured, it switches between sampling concentrations of particles in the surroundings and in the protected area (under the respirator). It can also observe the influence of people and their grimaces on the leakage quality (if required). The result is the so-called Fit factor (Fc), which gives the particle number ratio, around no, to the particle number n, under the respirator in the exhaled air. The measurement results are shown in Table 4.

Principle of Measurement
The PortaCount ® PRO 8038 measures the sum of solid particles, such as the condensation cores, from 20 nm to more than 1 µm. When measured, it switches between sampling concentrations of particles in the surroundings and in the protected area (under the respirator). It can also observe the influence of people and their grimaces on the leakage quality (if required). The result is the so-called Fit factor (F c ), which gives the particle number ratio, around n o , to the particle number n, under the respirator in the exhaled air. The measurement results are shown in Table 4. The appearance and microstructure of the porous NnF CERAM-SiO 2 SORBENT nanofibers are visible in Figure 16. A surface formation with the sorption properties for gaseous pollutants has been prepared by PARDAM, Ltd., using paper-making technology. It is believed that this material will be used as another type of sorption layer in the developed filtration sorptive materials. In addition, the possibility of preparing sorption layers from the powdered form of porous SiO 2 was also verified by the suction from an aqueous slurry or fixation in open polyurethane (PU) foam ( Figure 17). The appearance and microstructure of the porous NnF CERAM-SiO2 SORBENT nanofibers are visible in Figure 16. A surface formation with the sorption properties for gaseous pollutants has been prepared by PARDAM, Ltd., using paper-making technology. It is believed that this material will be used as another type of sorption layer in the developed filtration sorptive materials. In addition, the possibility of preparing sorption layers from the powdered form of porous SiO2 was also verified by the suction from an aqueous slurry or fixation in open polyurethane (PU) foam ( Figure 17).   The appearance and microstructure of the porous NnF CERAM-SiO2 SORBENT nanofibers are visible in Figure 16. A surface formation with the sorption properties for gaseous pollutants has been prepared by PARDAM, Ltd., using paper-making technology. It is believed that this material will be used as another type of sorption layer in the developed filtration sorptive materials. In addition, the possibility of preparing sorption layers from the powdered form of porous SiO2 was also verified by the suction from an aqueous slurry or fixation in open polyurethane (PU) foam ( Figure 17).  The basic parameters of porous SiO 2 nanofibers, comparison of water vapor sorption and desorption with silica gel, and the ability to adsorb selected organic vapors are shown in Figures 18 and 19, and in Table 5. The basic parameters of porous SiO2 nanofibers, comparison of water vapor sorption and desorption with silica gel, and the ability to adsorb selected organic vapors are shown in Figures 18  and 19, and in Table 5.  The basic parameters of porous SiO2 nanofibers, comparison of water vapor sorption and desorption with silica gel, and the ability to adsorb selected organic vapors are shown in Figures 18  and 19, and in Table 5. Figure 18. Comparison of the water adsorption on porous SiO2 nanofibers and on silica gel independence of relative humidity (left) and desorption of water from porous SiO2 nanofibers (right)and silica gel dependent on temperature; and parameters of porous SiO2 nanofibers (down-center).   19. Permeation of vapor: vapors of heptane, acetone, and ethanol with porous SiO 2 nanofibers, prepared by paper-making technology. As a result of the antibacterial and antifungal treatment with silver nanoparticles, the resistance to the long-term exposure of them olds has been tested for the filter membrane made of polymeric nanofibers. Aspergillus niger fungus resistance testing has been carried out in cooperation with the Military High School in Belgrade, according to the European Standard SRPS EN 60068-2-38 [39]. For both of the tested membranes from the PA-6 and PVDF nanofibers, a resistance to Stage 1 has been achieved. It indicates a very good resistance according to the scale below ( Table 6). The appearance of both samples tested after 48 h of exposure is shown in Figure 20. Table 6. Mold resistance assessment according to SRPS EN 60068-2-38 norm.

Grade 0
No growth apparent under a nominal magnification of 50×.

1
Traces of growth plainly visible under the microscope.

2a
Sparse growth visible to the naked eye and/or under the microscope scattered only or localized to a few places covering all together not more than 5% of the test surface.

2b
Growth plainly visible to the naked eye and/or under the microscope, distributed more or less homogenously on many places covering all together not more than 25% of the test surface.

3
Growth plainly visible to the naked eye and covering more than 25% of the test surface. As a result of the antibacterial and antifungal treatment with silver nanoparticles, the resistance to the long-term exposure of them olds has been tested for the filter membrane made of polymeric nanofibers. Aspergillus niger fungus resistance testing has been carried out in cooperation with the Military High School in Belgrade, according to the European Standard SRPS EN 60068-2-38 [39]. For both of the tested membranes from the PA-6 and PVDF nanofibers, a resistance to Stage 1 has been achieved. It indicates a very good resistance according to the scale below ( Table 6). The appearance of both samples tested after 48 h of exposure is shown in Figure 20. Table 6. Mold resistance assessment according to SRPS EN 60068-2-38 norm.

Grade 0
No growth apparent under a nominal magnification of 50×. 1 Traces of growth plainly visible under the microscope.

2a
Sparse growth visible to the naked eye and/or under the microscope scattered only or localized to a few places covering all together not more than 5% of the test surface.

2b
Growth plainly visible to the naked eye and/or under the microscope, distributed more or less homogenously on many places covering all together not more than 25% of the test surface.

3
Growth plainly visible to the naked eye and covering more than 25% of the test surface. Figure 20. The appearance of filtration membranes from PVDF and PA-6 nanofibers after finishing the examination of resistance tomold, after 48 h exposition.

Discussion
During the implementation of the studied filtration sorptive systems, modern construction materials have been used, enabling the combination of both surface and spatial structures to capture both the submicron particles and industrial pollutant vapors. The advantage of this research direction is that most of these materials are commercially available and can be further modified as required. The connection of individual constructive layers without the use of binders, utilizing the good adhesion properties of bicofibers, maintains a high permeability of the product and does not affect the effectiveness of the trapping of pollutants. The obtained results show the practical applicability of the developed filtration sorptive systems in various fields of a human activity, especially in the protection of people against toxic particles, aerosols, molds, and gaseous pollutants.

Conclusions
Based on the results of the recent research of filtration sorptive materials made from nanofibrous membranes with silver nanoparticles, nonwoven, or struto textile from bicofibers, as well as the sorption layers based on the powdered, spherical or fibrous activated carbon, or porous SiO2 nanofibers, it is possible to prepare interesting design materials that are useful in the manufacture of filters, respirators, and similar devices. Centrifugal spinning has been shown to

Discussion
During the implementation of the studied filtration sorptive systems, modern construction materials have been used, enabling the combination of both surface and spatial structures to capture both the submicron particles and industrial pollutant vapors. The advantage of this research direction is that most of these materials are commercially available and can be further modified as required. The connection of individual constructive layers without the use of binders, utilizing the good adhesion properties of bicofibers, maintains a high permeability of the product and does not affect the effectiveness of the trapping of pollutants. The obtained results show the practical applicability of the developed filtration sorptive systems in various fields of a human activity, especially in the protection of people against toxic particles, aerosols, molds, and gaseous pollutants.

Conclusions
Based on the results of the recent research of filtration sorptive materials made from nanofibrous membranes with silver nanoparticles, nonwoven, or struto textile from bicofibers, as well as the sorption layers based on the powdered, spherical or fibrous activated carbon, or porous SiO 2 nanofibers, it is possible to prepare interesting design materials that are useful in the manufacture of filters, respirators, and similar devices. Centrifugal spinning has been shown to produce flexible, compact, and homogeneous filtration membranes with good separation properties for submicron particles. Their overlapping with nonwoven bicofiber textiles enhances their mechanical resistance and improves their further workability. The great advantage of this is that the nanofibrous layer can be applied directly onto the bicofibers textile without the need for a transfer textile. This textile can then be combined not only with bicofiber cover fabrics, but also with other layers with adsorption properties. The elasticity and good mechanical resistance of these combined materials makes it easy to fold or heat-shape without the use of binders, while maintaining the filtration sorptive properties of the initial substrates. The advantage is even the resistance of the polymeric nanofibrous membrane to bacteria and fungi.