Pokročilé polymerní materiály a kompozit

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Photocatalytic Microplastics "On-The-fly" Degradation via Motile Quantum Materials-Based Microrobots
(Wiley-VCH, 2023-05-16) Jančík Procházková, Anna; Jašek, Vojtěch; Figalla, Silvestr; Pumera, Martin
Nano/micro-plastics pollution is an emerging global concern. A variety of biodegradable polymers have been synthesized to enhance the degradation of plastic materials and thereby avoid their accumulation in the environment. However, even biodegradable polymers can accumulate in environments under specific conditions and present a potential hazard. Here, antimony sulfide-based microrobots decorated with magnetite nanoparticles are designed for microplastics degradation. The propulsion of microrobots is enabled by two independent orthogonal physical modes via magnetic field and via light irradiation. Due to phoretic interactions, the microrobots exhibit affinity toward poly(3-hydroxybutyrate) (PHB) and poly(lactic acid) (PLA) microplastics, which enables subsequent transport of the microplastics in a transversal rotating magnetic field. The photocatalytic activity of Sb2S3 quantum material provides microrobots with the ability to degrade the microplastics under UV light irradiation in the "on-the-fly" regime without the need for any fuel. This proof-of-concept work shows efficient capture, transport, and photocatalytic degradation of microplastics and paves the way toward their elimination, especially in water environments.
Biaxial porosity gradient and cell size adjustment improve energy absorption in rigid and flexible 3D-printed reentrant honeycomb auxetic structures
(Elsevier, 2024-06-01) Štaffová, Martina; Ondreáš, František; Žídek, Jan; Jančář, Josef; Lepcio, Petr
This paper compares different uniaxial and biaxial graded designs of auxetic reentrant honeycomb structures to enhance their mechanical properties, especially the specific energy absorption under compressive load. The lattice structures were 3D printed using the vat photopolymerization masked-stereolithography technique from two different materials - tough (OR) and flexible (FR). The results were evaluated from a material and structural point of view, investigating the effect of porosity, cell number, size, graded design, and fracture mode. The universally best energy-absorbing performance was found in a biaxially graded structure with a center-wise location of the highest local porosity. Depending on the used resin, its energy absorption capacity was up to 2-3 times enhanced compared to a reference uniform-porosity auxetic design. The presented data constitutes a fundamental understanding of auxetic structures and identifies practical approaches for tuning the auxetic structures' performance regarding their mechanical response. Finally, this study demonstrates the potential of shape versatility offered by 3D printing and other additive manufacturing techniques.
The centrifugal spinning of vitamin doped natural gum fibers for skin regeneration
(Elsevier, 2022-10-15) Říhová, Martina; Lepcio, Petr; Čičmancová, Veronika; Frumarová, Božena; Hromádko, Luděk; Bureš, Filip; Vojtová, Lucy; Macák, Jan
The study investigates the use of fiber carriers, based on biopolymeric gums as potential candidates for cosmetic and dermatological applications, in particular for skin regeneration. Gum arabic (GA), xanthan gum (XA), and gum karaya (GK) were used as the main gum materials for the fibers, which were prepared by centrifugal spinning from an aqueous solution. These solutions of different mass gum ratios were blended with poly (ethylene oxide) (PEO) for better spinnability. Finally, vitamins E and C were added to selected solutions of gums. The resulting fibers were extensively investigated. The morphology and structure of all fibers were investigated by scanning electron microscopy and Fourier transformed infrared spectroscopy. Most importantly, they were characterized by the release of vitamin E loaded in the fibers using UV-VIS spectroscopy. The presentation will show that the newly prepared fibers from GA and PEO represent a very promising material for cosmetic and dermatologic applications.
Dynamic Responsive Formation of Nanostructured Fibers in a Hydrogel Network: A Molecular Dynamics Study
(Frontiers Media, 2020-02-26) Žídek, Jan; Milchev, Andrey; Jančář, Josef
In an effort to study natural fiber formation, such as, e.g., spider silk, we present a model, which is capable of forming biomimetic fibrillar nanostructure from a hydrogel micellar network. The latter consists of interacting atomic groups which form cores of micelles, and of flexible chains forming the shells of the micelles. Micelles are connected in a compact network by linearly stretched chains. The structural elements of the network can be transformed during deformation from micellar into fibrillary type and their evolution is found to depend significantly on strain rate. Our model suggests a set of conditions suitable for the formation of nanostructured fibrillar network. It demonstrates that a fibrillar structure is only formed upon sufficiently fast stretching while, in contrast, the micellar gel structure is preserved, if the material is pulled slowly. We illustrate this key aspect by a minimalistic model of only four chains as part of the whole network, which provides a detailed view on the mechanism of fibril formation. We conclude that such a simplified structure has similar functionality and is probably responsible for the formation of nano-structured molecular fibrils in natural materials.
Printability, Mechanical and Thermal Properties of Poly(3-Hydroxybutyrate)-Poly(Lactic Acid)-Plasticizer Blends for Three-Dimensional (3D) Printing
(MDPI, 2020-10-23) Kontárová, Soňa; Přikryl, Radek; Odehnalová, Veronika; Menčík, Přemysl; Horálek, Matyáš; Figalla, Silvestr; Plavec, Roderik; Feranc, Jozef; Sadílek, Jiří; Pospíšilová, Aneta
This paper investigates the effect of plasticizer structure on especially the printability and mechanical and thermal properties of poly(3-hydroxybutyrate)-poly(lactic acid)-plasticizer biodegradable blends. Three plasticizers, acetyl tris(2-ethylhexyl) citrate, tris(2-ethylhexyl) citrate, and poly(ethylene glycol)bis(2-ethylhexanoate), were first checked whether they were miscible with poly(3-hydroxybutyrate)-poly(lactic acid) (PHB-PLA) blends using a kneading machine. PHB-PLA-plasticizer blends of 60-25-15 (wt.%) were then prepared using a corotating meshing twin-screw extruder, and a single screw extruder was used for filament preparation for further three-dimensional (3D) fused deposition modeling (FDM) printing. These innovative eco-friendly PHB-PLA-plasticizer blends were created with a majority of PHB, and therefore, poor mechanical properties and thermal properties of neat PHB-PLA blends were improved by adding appropriate plasticizer. The plasticizer also influences the printability of blends, which was investigated, based on our new specific printability tests developed for the optimization of printing conditions (especially printing temperature). Three-dimensional printed test samples were used for heat deflection temperature measurements and Charpy and tensile-impact tests. Plasticizer migration was also investigated. The macrostructure of 3D printed samples was observed using an optical microscope to check the printing quality and printing conditions. Tensile tests of 3D printed samples (dogbones), as well as extruded filaments, showed that measured elongation at break raised, from 21% for non-plasticized PHB-PLA reference blends to 84% for some plasticized blends in the form of filaments and from 10% (reference) to 32% for plasticized blends in the form of printed dogbones. Measurements of thermal properties (using modulated differential scanning calorimetry and oscillation rheometry) also confirmed the plasticizing effect on blends. The thermal and mechanical properties of PHB-PLA blends were improved by the addition of appropriate plasticizer. In contrast, the printability of the PHB-PLA reference seems to be slightly better than the printability of the plasticized blends.

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