Removal of the Basic and Diazo Dyes from Aqueous Solution by the Frustules of Halamphora cf. salinicola (Bacillariophyta).

Industrial wastes with hazardous dyes serve as a major source of water pollution, which is considered to have an enormous impact on public health. In this study, an eco-friendly adsorbent, the porous siliceous frustules extracted from the diatom species Halamphora cf. salinicola, grown under laboratory conditions, has been identified. The porous architecture and negative surface charge under a pH of 7, provided by the various functional groups via Si-O, N-H, and O-H on these surfaces, revealed by SEM, the N2 adsorption/desorption isotherm, Zeta-potential measurement, and ATR-FTIR, respectively, made the frustules an efficient mean of removal of the diazo and basic dyes from the aqueous solutions, 74.9%, 94.02%, and 99.81% against Congo Red (CR), Crystal Violet (CV), and Malachite Green (MG), respectively. The maximum adsorption capacities were calculated from isotherms, as follows: 13.04 mg g-1, 41.97 mg g-1, and 33.19 mg g-1 against CR, CV, and MG, respectively. Kinetic and isotherm models showed a higher correlation to Pore diffusion and Sips models for CR, and Pseudo-Second Order and Freundlich models for CV and MG. Therefore, the cleaned frustules of the thermal spring-originated diatom strain Halamphora cf. salinicola could be used as a novel adsorbent of a biological origin against anionic and basic dyes.

Study on Biogenic Spindle-Shaped Iron-Oxide Nanoparticles by Pseudostaurosira trainorii in Field of Laser Desorption/Ionization Applications.

Nanostructures-assisted laser desorption/ionization mass spectrometry (NALDI-MS) is gaining attention for the analysis of a wide range of molecules. In this present investigation, Pseudostaurosira trainorii mediated biosynthesized iron-oxide nanoparticles (IONPs) have been utilized as nanostructures assisting ionization and desorption for laser desorption/ionization mass spectrometry (LDI-MS). The chain forming diatom, P. trainorii showed efficiency in the production of IONPs against 0.01 M Fe+3 (pH 2) aqueous solution at the intracellular and extracellular level. The whole biomass and external media turned dark orange in color after 3 days of reaction with Fe3+ solution. Scanning electron microscopic (SEM) images illustrated that the surface of Fe3+ exposed frustules of P. trainorii were entirely covered by synthesized nanostructures contrasting with the natural surface ornamentation of control cells. The IONPs loaded frustules also exhibited catalytic properties by decolorizing yellow colored nitrophenol after 3 h of reaction. Transmission electron microscopic (TEM) images confirmed that the produced particles are spindle-shaped with ~50-70 nm length and ~10-30 nm width. The biogenic IONPs were utilized as an inorganic matrix in LDI-MS and showed high sensitivity towards small molecules as glucose, alanine and triacylglycerols at nano- and picomolar level per spot, respectively. The presented biocompatible technique offers new perspectives in nanobiotechnology for the production of spindle-shaped IONPs that can be applied in future for the preparation of NALDI plates.

Synthesis, Physicochemical Characterization, and Antibacterial Performance of Silver-Lactoferrin Complexes.

Antibiotic-resistant bacteria pose one of the major threats to human health worldwide. The issue is fundamental in the case of chronic wound treatment. One of the latest trends to overcome the problem is the search for new antibacterial agents based on silver. Thus, the aim of this research was to synthesize the silver-lactoferrin complex as a new generation of substances for the treatment of infected wounds. Moreover, one of the tasks was to investigate the formation mechanisms of the respective complexes and the influence of different synthesis conditions on the features of final product. The batch-sorption study was performed by applying the Langmuir and Freundlich isotherm models for the process description. Characterization of the complexes was carried out by spectroscopy, spectrometry, and separation techniques, as well as with electron microscopy. Additionally, the biological properties of the complex were evaluated, i.e., the antibacterial activity against selected bacteria and the impact on L929 cell-line viability. The results indicate the formation of a heterogeneous silver-lactoferrin complex that comprises silver nanoparticles. The complex has higher antibacterial strength than both native bovine lactoferrin and Ag+, while being comparable to silver toxicity.

Consideration of a new approach to clarify the mechanism formation of AgNPs, AgNCl and AgNPs@AgNCl synthesized by biological method.

The biological methods are considered as environmental-eco-friendly methods for the silver nanocomposites mediation and are widely used in this context. However, the biological methods go along with the relevant limitations, for instance simultaneous synthesis of silver chlorides (AgNCl) type during the AgNPs mediation process. Therefore, the present research is coming to summarize several aspects in this context. Firstly, to present the possible promotion of the sustainable development using bioactive source (e.g. milk) as a source of two different available and new lactobacillus strains (Lactobacillus curvatus and Lactobacillus fermentum). Secondly, to show the ability of the respective isolates to be involved in mediation of various biosilver nanocomposites ((Bio)NCs) synthesis. Moreover, at this stage, for the first time, two (Bio)NCs mediation methods, called "direct method" and "modified method", have been developed, thus three types (AgNPs, AgNCl and AgNP@AgNCl) of nanocomposites mediated by two different Lactobacillus isolates take place. The interdisciplinary approach included using several spectroscopic, microscopic, spectrometric and thermogravimetric methods demonstrated that all six synthesized nanoparticles (three AgNPs, AgNCl and AgNP@AgNCl types from each source) consist of complex structure including both metallic silver core as well as organic surface deposits. The spectrometric technique allowed to identification of the organics branching surface, naturally secreted by the used Lactobacillus isolates during the inoculation step, suggesting the presence of amino-acids sequences which are direct connected with the reduction of silver ion to metal silver, and subsequently with the formation of coated (Bio)NCs and nucleation process. Moreover, based on the obtained results, the mediation mechanism of each (Bio)NCs has been proposed, suggesting that the formation of AgNPs, AgNCl and AgNP@AgNCl types occurs in different manners with faster synthesis firstly of AgNCl, then of the AgNPs type. No differences between the (Bio)NCs synthesized by two different Lactobacillus isolates have been noticed indicating no discrepancies between metabolites secreted by the respective sources.

Research on Explosive Hardening of Titanium Grade 2.

In this investigation, three different explosive materials have been used to improve the properties of titanium grade 2: ammonal, emulsion explosives, and plastic-bonded explosives. In order to establish the influence of explosive hardening on the properties of the treated alloys, tests were conducted, including microhardness testing, microstructure analysis, and tensile and corrosion tests. It has been found that it is possible to achieve a 40% increase in tensile strength using a plastic explosive (PBX) as an explosive material. On the other hand, the impact of the shock wave slightly decreased the corrosion resistance of titanium grade 2. The change in corrosion rate is less than 0.1µm/year, which does not significantly affect the overall corrosion resistance of the material. The reduction in corrosion resistance is probably due to the surface geometry changes as a result of explosive treatment.

Comprehensive study upon physicochemical properties of bio-ZnO NCs.

In this study, for the first time, the comparison of commercially available chemical ZnO NCs and bio-ZnO NCs produced extracellularly by two different probiotic isolates (Latilactobacillus curvatus MEVP1 [OM736187] and Limosilactobacillus fermentum MEVP2 [OM736188]) were performed. All types of ZnO formulations were characterized by comprehensive interdisciplinary approach including various instrumental techniques in order to obtain nanocomposites with suitable properties for further applications, i.e. biomedical. Based on the X- ray diffraction analysis results, all tested nanoparticles exhibited the wurtzite structure with an average crystalline size distribution of 21.1 nm (CHEM_ZnO NCs), 13.2 nm (1C_ZnO NCs) and 12.9 nm (4a_ZnO NCs). The microscopy approach with use of broad range of detectors (SE, BF, HAADF) revealed the core-shell structure of bio-ZnO NCs, compared to the chemical one. The nanoparticles core of 1C and 4a_ZnO NCs are coated by the specific organic deposit coming from the metabolites produced by two probiotic strains, L. fermentum and L. curvatus. Vibrational infrared spectroscopy, photoluminescence (PL) and mass spectrometry (LDI-TOF-MS) have been used to monitor the ZnO NCs surface chemistry and allowed for better description of bio-NCs organic coating composition (amino acids residues). The characterized ZnO formulations were then assessed for their photocatalytic properties against methylene blue (MB). Both types of bio-ZnO NCs exhibited good photocatalytic activity, however, the effect of CHEM_ZnO NCs was more potent than bio-ZnO NCs. Finally, the colloidal stability of the tested nanoparticles were investigated based on the zeta potential (ZP) and hydrodynamic diameter measurements in dependence of the nanocomposites concentration and investigation time. During the biosynthesis of nano-ZnO, the increment of pH from 5.7 to around 8 were observed which suggested possible contribution of zinc aquacomplexes and carboxyl-rich compounds resulted in conversion of zinc tetrahydroxy ion complex to ZnO NCs. Overall results in present study suggest that used accessible source such us probiotic strains, L. fermentum and L. curvatus, for extracellular bio-ZnO NCs synthesis are of high interest. What is important, no significant differences between organic deposit (e.g. metabolites) produced by tested strains were noticed-both of them allowed to form the nanoparticles with natural origin coating. In comparison to chemical ZnO NCs, those synthetized via microbiological route are promising material with further biological potential once have shown high stability during 7 days.

A Comprehensive Study of a Novel Explosively Hardened Pure Titanium Alloy for Medical Applications.

Pure titanium is gaining increasing interest due to its potential use in dental and orthopedic applications. Due to its relatively weak mechanical parameters, a limited number of components manufactured from pure titanium are available on the market. In order to improve the mechanical parameters of pure titanium, manufacturers use alloys containing cytotoxic vanadium and aluminum. This paper presents unique explosive hardening technology that can be used to strengthen pure titanium parameters. The analysis confirms that explosive induced α-ω martensitic transformation and crystallographic anisotropy occurred due to the explosive pressure. The mechanical properties related to residual stresses are very nonuniform. The corrosion properties of the explosive hardened pure titanium test do not change significantly compared to nonhardened titanium. The biocompatibility of all the analyzed samples was confirmed in several tests. The morphology of bone cells does not depend on the titanium surface phase composition and crystallographic orientation.

A novel effective bio-originated methylene blue adsorbent: the porous biosilica from three marine diatom strains of Nanofrustulum spp. (Bacillariophyta).

In the present paper, for the first time the ability of the porous biosilica originated from three marine diatom strains of 'Nanofrustulum spp.' viz. N. wachnickianum (SZCZCH193), N. shiloi (SZCZM1342), N. cf. shiloi (SZCZP1809), to eliminate MB from aqueous solutions was investigated. The highest biomass was achieved under silicate enrichment for N. wachnickianum and N. shiloi (0.98 g L-1 DW and 0.93 g L-1 DW respectively), and under 15 °C for N. cf. shiloi (2.2 g L-1 DW). The siliceous skeletons of the strains were purified with hydrogen peroxide and characterized by SEM, EDS, the N2 adsorption/desorption, XRD, TGA, and ATR-FTIR. The porous biosilica (20 mg DW) obtained from the strains i.e. SZCZCH193, SZCZM1342, SZCZP1809, showed efficiency in 77.6%, 96.8%, and 98.1% of 14 mg L-1 MB removal under pH 7 for 180 min, and the maximum adsorption capacity was calculated as 8.39, 19.02, and 15.17 mg g-1, respectively. Additionally, it was possible to increase the MB removal efficiency in alkaline (pH = 11) conditions up to 99.08% for SZCZP1809 after 120 min. Modelling revealed that the adsorption of MB follows Pseudo-first order, Bangham's pore diffusion and Sips isotherm models.

Study on Symmetry and Asymmetry Rolling of AA2519-T62 Alloy at Room-Temperature and Cryogenic Conditions.

The aim of this investigation was to identify the effect of rolling at room temperature and under cryogenic conditions on selected properties and the microstructure of the AA2519-T62 aluminum alloy. The rolling processes were conducted with different variants of asymmetry (1.0-symmetry rolling; 1.2, 1.4 and 1.6). The investigation of the obtained samples involves microhardness distribution, microstrains, and microstructure observations using light and transmission electron microscopes. Both rolling at room temperature and under cryogenic conditions increased the micro-hardness of AA2519-T62 by at least 10%. The highest reported increase (25%) was obtained for the sample rolled at room temperature in the symmetry rolling process. The samples rolled under cryogenic conditions are characterized by a lower increase in microhardness than samples rolled at room temperature and by significantly lower values of microstrains. The application of rolling with the asymmetry ratio remaining within the range of 1.2-16 only slightly affected the microhardness values of the samples rolled at room temperature and under cryogenic conditions with respect to conventional symmetrical rolling.

Cytotoxicity and Antibacterial Activity of Mineral Trioxide Aggregate Cement with Radiopacity Introduced by ZrO2.

The article presents the results of in vitro studies on cytotoxicity and antibacterial activity of new MTA-type cements, developed on the basis of the sintered tricalcium silicate enriched with ZnO, along with an agent introducing the radiopacity in the form of ZrO2. The new materials have been developed to ensure that their physical and chemical properties are suited for endodontic applications. The cements were evaluated via characterisation of setting time, compressive strength, as well as translucency on X-ray images, and bioactivity in the simulated body fluid (SBF). The µCT was used to test the influence of the ZrO2 grains in the powder component on the microstructure of the produced cement. Then, the cytotoxic action of the cements was evaluated by applying a reference L-929 cell line. The conditions of the culture upon contact with the tested materials or with extracts from the cements were assessed using image analysis or an MTT colorimetric assay. Two strains of streptococci, Streptococcus mutans and Streptococcus sanguinis, were used to study the antibacterial activity of the tested cements with ZrO2 acting as the agent introducing the radiopacity. The new cements are characterised by appropriate properties as far as retrograde root canal filling is concerned.

Diatom Mediated Production of Fluorescent Flower Shaped Silver-Silica Nanohybrid.

Fabrication of flower-like nanostructures are gaining attention because of their high surface/volume ratio and extensive adsorption capacity. In the present investigation, flower-shaped, autofluorescent silver-silica (Ag-SiO2) hybrid nanoparticles have been fabricated exploiting diatoms as a source of nanosilica. Two different species of Gedaniella including G. flavovirens and G. mutabilis showed their efficacy in synthesizing fluorescent Ag-SiO2 nanoflowers (NFs) and nanospheres (NSs) against 9 mM silver nitrate solution, respectively. The biogenic nanoconjugate (Ag-SiO2) was characterized by Uv-vis spectroscopy, energy dispersive X-ray spectroscopy (EDS), scanning (SEM) and transmission (TEM) electron microscopy. Production of Ag-SiO2 hybrid nanoparticle was confirmed by observing both Ag and Si signals from a single nanoparticle in an EDS study. The broad and single absorption band at ~420 nm in Uv-vis spectroscopy confirmed proper miscibility and production of hybrid nanoparticles. The Ag-SiO2 nanohybrids revealed autofluorescent property under the blue light region (excitation ~450-490 nm). SEM images of particles synthesized by G. flavovirens revealed the production of microscopic flower shaped Ag-SiO2 particles with several layers of petals. A TEM study confirmed that the synthesized Ag-SiO2 NFs are variable in size with 100-500 nm in diameter. Decolorization of methylene blue after exposure to Ag-SiO2 particles confirmed catalytic activity of synthesized nanostructures. This eco-friendly method provides a new dimension in nanobiotechnology for biogenesis of such hierarchical nanostructure in a cost-effective way.

Viscoelastic Polyurethane Foams for Use as Auxiliary Materials in Orthopedics.

One of the essential factors in prostheses is their fitting. To assemble a prosthesis with the residual limb, so-called liners are used. Liners used currently are criticized by users for their lack of comfort, causing excessive sweating and skin irritation. The objective of the work was to develop viscoelastic polyurethane foams for use in limb prostheses. As part of the work, foams were produced with different isocyanate indexes (0.6-0.9) and water content (1, 2 and 3 php). The produced foams were characterized by scanning electron microscopy, computer microtomography, infrared spectroscopy, thermogravimetry and differential scanning calorimetry. Measurements also included apparent density, recovery time, rebound elasticity, permanent deformation, compressive stress value and sweat absorption. The results were discussed in the context of modifying the foam recipe. The performance properties of the foams, such as recovery time, hardness, resilience and sweat absorption, indicate that foams that will be suitable for prosthetic applications are foams with a water content of 2 php produced with an isocyanate index of 0.8 and 0.9.

Reducing Efficiency of Fucoxanthin in Diatom Mediated Biofabrication of Gold Nanoparticles.

In the present investigation, fucoxanthin-one of the major pigments in diatoms-has been extracted from Nanofrustulum shiloi SZCZM1342, and its reducing efficiency in the biogenesis of gold nanoparticles (GNPs) was checked. Fucoxanthin extracted from golden-brown cells of N. shiloi was compared to the healthy, growing biomass of N. shiloi and standard fucoxanthin after separate exposure to 25 mg L-1 aqueous hydrogen tetrachloroaurate solutions at room temperature. Isolated and standard fucoxanthin were found to be able to reduce gold ions within 12 h whereas, the whole biomass turned pink in color after 72 h of reaction. The synthesized particles were characterized by UV-vis spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). UV-vis spectroscopy of purple-colored suspensions showed the absorption band at approximately 520-545 nm, indicating a strong positive signal for GNP synthesis. The SEM study revealed the deposition of GNPs on siliceous frustules of metal-treated diatom cells. The TEM analysis confirmed the GNPs synthesized by whole biomass are triangular, spherical and hexagonal in nature, whereas the particles produced by extracted and standard fucoxanthin are all spherical in nature. This study demonstrates the involvement of fucoxanthin in the reduction of gold ions and subsequent production of gold nanospheres.

Vegetable Fillers and Rapeseed Oil-Based Polyol as Natural Raw Materials for the Production of Rigid Polyurethane Foams.

The reported study concerns the introduction of renewable raw materials into the formulation of rigid polyurethane foams in the quest for the sustainable development of polymer composites. In this study, rigid polyurethane foam composites were prepared using 75 wt.% of rapeseed oil-based polyol and 15 parts per hundred parts of polyol (php) of natural fillers such as chokeberry pomace, raspberry seeds, as well as hazelnut and walnut shells. The influence of the used raw materials on the foaming process, structure, and properties of foams was investigated using a FOAMAT analyzer and a wide selection of characterization techniques. The introduction of renewable raw materials limited reactivity of the system, which reduced maximum temperature of the foaming process. Moreover, foams prepared using renewable raw materials were characterized by a more regular cell structure, a higher share of closed cells, lower apparent density, lower compressive strength and glass transition temperature, low friability (<2%), low water absorption (<1%), high dimensional stability (<±0.5%) and increased thermal stability. The proper selection and preparation of the renewable raw materials and the rational development of the polyurethane recipe composition allow for the preparation of environmentally-friendly foam products with beneficial application properties considering the demands of the circular economy in the synthesis of rigid foams.

A New Method of Diatomaceous Earth Fractionation-A Bio-Raw Material Source for Epoxy-Based Composites.

The authors of this paper use an original method of diatomaceous earth fractionation, which allows for obtaining a filler with a specific particle size distribution. The method makes it possible to separate small, disintegrated and broken diatom frustules from those which maintained their original form in diatomaceous earth. The study covers a range of tests conducted to prove that such a separated diatomic fraction (3-30 µm) shows features different from the base diatomite (from 1 to above 40 µm) used as an epoxy resin filler. We have examined the mechanical properties of a series of diatomite/resin composites, considering the weight fraction of diatoms and the parameters of the composite production process. The studied composites of Epidian 601 epoxy resin cross-linked with amine-based curing agent Z-1 contained 0 to 70% vol. of diatoms or diatomaceous earth. Samples were produced by being casted into silicone molds in vacuum degassing conditions and, alternatively, without degassing. The results have shown that the size and morphology of the filler based on diatomaceous earth affects mechanical and rheological properties of systems based on epoxy resin. Elongation at rupture and flexural stress at rupture were both raised by up to 35%, and impact strength by up to 25%.

Al2O3/ZrO2 Materials as an Environmentally Friendly Solution for Linear Infrastructure Applications.

The present work deals with the evaluation of the effect of ZrO2 on the structure and selected properties of shapes obtained using the centrifugal slip casting method. The samples were made of alumina and zirconia. The applied technology made it possible to produce tubes with a high density reaching 99-100% after sintering. Very good bonding was obtained at the Al2O3/ZrO2 interphase boundaries with no discernible delamination or cracks, which was confirmed by STEM observations. In the case of Al2O3/ZrO2 composites containing 5 vol.% and 10 vol.% ZrO2, the presence of equiaxial ZrO2 grains with an average size of 0.25 µm was observed, which are distributed along the grain boundaries of Al2O3. At the same time, the composites exhibited a very high hardness of 22-23 GPa. Moreover, the environmental influences accompanying the sintering process were quantified. The impacts were determined using the life cycle analysis method, in the phase related to the extraction and processing of raw materials and the process of producing Al2O3/ZrO2 composites. The results obtained show that the production of 1 kg of sintered composite results in greenhouse gas emissions of 2.24-2.9 kg CO2 eq. which is comparable to the amount of emissions accompanying the production of 1 kg of Polyvinyl Chloride (PVC), Polypropylene (PP), or hot-rolled steel products.

Polyurethane Composite Foams Synthesized Using Bio-Polyols and Cellulose Filler.

Rigid polyurethane foams were obtained using two types of renewable raw materials: bio-polyols and a cellulose filler (ARBOCEL® P 4000 X, JRS Rettenmaier, Rosenberg, Germany). A polyurethane system containing 40 wt.% of rapeseed oil-based polyols was modified with the cellulose filler in amounts of 1, 2, and 3 php (per hundred polyols). The cellulose was incorporated into the polyol premix as filler dispersion in a petrochemical polyol made using calenders. The cellulose filler was examined in terms of the degree of crystallinity using the powder X-ray diffraction PXRD -and the presence of bonds by means of the fourier transform infrared spectroscopy FT-IR. It was found that the addition of the cellulose filler increased the number of cells in the foams in both cross-sections-parallel and perpendicular to the direction of the foam growth-while reducing the sizes of those cells. Additionally, the foams had closed cell contents of more than 90% and initial thermal conductivity coefficients of 24.8 mW/m∙K. The insulation materials were dimensionally stable, especially at temperatures close to 0 °C, which qualifies them for use as insulation at low temperatures.

Methodological Aspects of Obtaining and Characterizing Composites Based on Biogenic Diatomaceous Silica and Epoxy Resins.

Diatomaceous earth are sediments of unicellular algal skeletons with a well-defined hierarchical structure. Despite many tests conducted on systems using diatomaceous earth and epoxy resins, we can find many differences in the methods of acquisition and characteristics of the composite, which may considerably affect the results. In our study, we have conducted tests to verify the impact of the method of obtaining samples and the degassing of the composite on its mechanical properties and standard deviation. The samples were cast in glass moulds and silicone moulds and then subjected to testing for their mechanical and functional properties, imaging with the use of an optical microscope and a scanning electron microscope. The tests have shown that, for samples cast in glass moulds, there is no heterogeneity within the area of the tested sample, as in the case of samples cast in silicone moulds. Silicone moulds allow for quite effective self-degassing of the resin due to the large area-to-mass ratio, and the small remaining air vesicles have a limited effect on the mechanical properties of the samples. The filler used also played a significant role. For systems containing base and rinsed diatomite, it is clear that the degassing of mixtures increases the tensile strength. For treated diatomite, the elongation at break grew along with increasing filler concentration, while for base diatomite, the improvement was observed for flexural strength and impact strength. A non-modified epoxy resin shows a tensile strength at 19.91 MPa (silicone mould cast). At the same time, the degassed, glass mould-cast systems containing 12% of base and rinsed diatoms showed a tensile strength of 27.4 MPa and 44.7 MPa, respectively. We have also observed that the higher the filler concentration, the higher were the tensile strength values, which for the rinsed diatoms reached over 55.1 MPa and for the base diatoms were maximum of 43.8 MPa. The tests, therefore, constitute a set of guidelines and recommendations for testing with the use of fillers showing an extended inner structure.

Composites of Open-Cell Viscoelastic Foams with Blackcurrant Pomace.

Taking into account the circular economy guidelines and results of life cycle analyses of various materials, it was proposed to use a blackcurrant pomace filler in the production process of viscoelastic polyurethane (PUR) foams intended for application as mattresses, pillows, or elements for orthopedics. Open-cell viscoelastic PUR foams containing 10-60 per hundred polyols (php) blackcurrant pomace were prepared. It was found that after introducing the filler to the PUR foam formulation, the speed of the first stage of the foaming process significantly decreases, the maximum temperature achieved during the synthesis drops (by 30 °C for the foam containing 40 php of filler compared to unfilled foam), and the maximum pressure achieved during the synthesis of foam containing 20 php is reduced by approximately 57% compared to the foam without filler. The growth time of the foams increases with increasing the amount of introduced filler; for the foam containing 60 php, the time is extended even by about 24%. The effect of the filler on the physical, morphological, mechanical, and functional performances of PUR foam composites has been analyzed. The use of 60 php as the filler reduced the hardness of the foams by approximately 30% and increased their comfort factor from 3 to 5.

Viscoelastic Polyurethane Foams with Reduced Flammability and Cytotoxicity.

Consistent and proper use of respiratory protective devices (RPD) is one of the essential actions that can be taken to reduce the risk of exposure to airborne hazards, i.e., biological and nonbiological aerosols, vapours, and gases. Proper fit of the facepiece and comfort properties of RPDs play a crucial role in effective protection and acceptance of RPDs by workers. The objective of the present paper was to develop viscoelastic polyurethane foams for use in RPD seals characterised by proper elasticity, allowing for the enhancement of the device fit to the face and the capability of removing moisture from the skin in order to improve the comfort of RPD use. Moreover, it was pivotal to ensure the non-flammability of the foams, as well as a simultaneous reduction in their cytotoxicity. The obtained foams were characterised using scanning electron microscopy, infrared spectroscopy, thermogravimetry, and differential scanning calorimetry. Measurements also involved gel fraction, apparent density, compression set, rebound resilience, wettability, flammability, and cytotoxicity. The results are discussed in the context of the impact of modifications to the foam formulation (i.e., flame-retardant type and content) on the desired foam properties. The test results set directions for future works aimed to develop viscoelastic polyurethane foams that could be applied in the design of respiratory protective devices.