The Influence of Graphite Filler on the Self-Lubricating Properties of Epoxy Composites.

In this work, epoxy composites filled with flake graphite of various size (less than 10 µm and less than 45 µm) were produced. The aim of the research was to develop a self-lubricating material with favorable tribological properties, i.e., reduced friction coefficient compared to unfilled epoxy resin and limited abrasive wear. The research material was produced using technical epoxy resins based on bisphenol A. The detailed process of composite production was described, and typical technological problems were considered. The addition of graphite led to an increase in dynamic viscosity, which positively limits the phenomenon of sedimentation, but an increase in the filler content also led to an increase in the porosity of the material. A series of tests have shown that the addition of graphite above 5% by weight allows for a reduction in the friction coefficient from 0.6 to 0.4 and significantly reduces the material's tendency to abrasive wear.

Polymer Composites with Carbon Fillers Based on Coal Pitch and Petroleum Pitch Cokes: Structure, Electrical, Thermal, and Mechanical Properties.

The effect of particle size and oxidation degree of new carbon microfillers, based on coal pitch (CP) and petroleum pitch (PET) cokes, on the structure as well as thermal, mechanical, and electrical properties of the composites based on ultrahigh molecular weight polyethylene (UHMWPE) was investigated. The composites studied have a segregated structure of filler particle distribution in the UHMWPE matrix. It was found that composite with smaller CP grain fraction has the highest Young's modulus and electrical conductivity compared to the other composites studied, which can be the result of a large contribution of flake-shaped particles. Additionally, conductivity of this composite turned out to be similar to composites with well-known carbon nanofillers, such as graphene, carbon black, and CNTs. Additionally, the relationship between electrical conductivity and Young's modulus values of composites studied was revealed, which indicates that electrical conductivity is very sensitive to the structure of the filler phase in the polymer matrix. In general, it was established that the properties, especially the electrical conductivity, of the composites studied strongly depends on the size, shape, and oxidative treatment of CP and PET filler particles, and that the CP coke of appropriately small particle sizes and flake shape has significant potential as a conductive filler for polymer composites.

The influence of UV radiation on the properties of GFRP laminates in underwater conditions.

Degradation of polymer composites is a significant problem in many engineering aspects. Due to the interaction of various degradation factors during the exploitation of composites, a synergistic effect of destruction is observed. The article describes the phenomena occurring in glass fiber reinforced polyester laminates under the influence of ultraviolet radiation (UV) in an aquatic environment. The laminates were exposed to UV-A, UV-B and UV-C radiation for 1000 h in free-air and underwater conditions. During the test, the materials were immersed at stable depth of 1 mm and 10 mm, respectively. The three-point bending tests performed on the samples after being exposed to UV showed an increase in the flexural strength of the composites. Simultaneously, degradation of the outer surface layer was observed. The degradation removed the thin resin film from the surface which resulted in a direct exposure of the reinforcing fibers to the environment. The transformations taking place in the deeper layers of the composite increased the mechanical strength due to the additional cross-linking reactions excited by the energy arising from the radiation. Moreover, the formation of polymer structures from free styrene remaining after the technological process and the occurrence of free radical reactions as a result of the cage effect was also observed.

Polymer Nanocomposites Based on Nanosized Substituted Ferrites (NiZn)1-xMnxFe2O4 on the Surface of Carbon Nanotubes for Effective Interaction with High-Frequency EM Radiation.

To create materials that interact effectively with electromagnetic (EM) radiation, new nanosized substituted ferrites (NiZn)1-xMnxFe2O4 (x = 0, 0.5, and 1) anchored on the surface of multi-walled carbon nanotubes (CNTs) have been synthesized. The concentration of CNTs in the (NiZn)1-xMnxFe2O4/CNT system was from 0.05 to 0.07 vol. fractions. The dielectric and magnetic characteristics of both pristine (NiZn)1-xMnxFe2O4 ferrites and (NiZn)1-xMnxFe2O4/CNT composite systems were studied. The introduction of (NiZn)1-xMnxFe2O4/CNT composites into the amorphous epoxy matrix allows to tailor absorbing properties at the high-frequency by effectively shifting the maximum peak values of the absorption and reflection coefficient to a region of lower frequencies (20-30 GHz). The microwave adsorption properties of (NiZn)1-xMnxFe2O4/0.07CNT-ER (x = 0.5) systems showed that the maximum absorption bandwidth with reflection loss below -10 dB is about 11 GHz.

Formation of Three-Dimensional Polysuccinimide Electrospun Fiber Meshes Induced by the Combination of CaCl2 and Humidity.

Even though electrospinning is getting more and more attention, the preparation of 3D nanofibrous meshes is still a big challenge that limits the application of electrospun materials, especially in tissue engineering. To overcome this problem, several solutions are introduced but most of them focus on the postprocessing of the electrospun meshes. This paper presents a straightforward novel method that utilizes the joint effect of the addition of CaCl2 and the relative environmental humidity (RH), which can induce the random 3D formation of polysuccinimide (PSI) electrospun fibers with different such as wrinkled or ribbon-like structures. Although the effect of humidity and inorganic salt additives on the micro and macrostructure of electrospun fibers is known, the connection between the two in this manner has never been presented. To investigate the effect, fibers with different PSI and CaCl2 concentrations at different humidity RH levels are prepared, and their microstructure is visualized with high-resolution scanning electron microscopy (SEM). To reveal the nature of the interaction between the polymer and the CaCl2, Fourier-transformed infrared (FTIR), X-ray diffraction (XRD), and thermogravimetry (TGA) measurements are carried out and 3D nanofibrous structures are obtained.

Comparison of PLLA-PEG and PDLLA-PEG micelles for co-encapsulation of docetaxel and resveratrol.

The interest in combining chemosensitizers with cytostatics in cancer therapy is growing, which causes also a need to develop their delivery systems. Example of the combination with beneficial therapeutic effects is docetaxel (Dtx) and resveratrol (Res). Although poly(lactide)-co-poly(ethylene glycol) (PLA-PEG) micelles have been considered as one of the most promising platforms for drug delivery, their properties may depend on the stereoisomeric form of hydrophobic block. Therefore, the aim of this study was evaluation of the effect of PLA block on co-encapsulation and release rate of Dtx and Res, which has not been studied so far. This article presents a comparison of single- (Dtx or Res) and dual-drug (Dtx and Res) loaded micelles obtained from poly(l,l-lactide)-co-poly(ethylene glycol) (PLLA-PEG) and poly(d,l-lactide)-co-poly(ethylene glycol) (PDLLA-PEG). The analyzes of the micelles have been conducted including morphology, drug(s) encapsulation efficiency, intermolecular interactions, in vitro drug release, and cytotoxicity. Differences in drug loading ability and release profile have been observed between Res and Dtx but also depending on the polymer and number of drugs in micelles (single vs. dual loaded). The PLLA-PEG micelles have a significantly higher Dtx encapsulation capacity than PDLLA-PEG micelles. The highest cytotoxicity was shown for Dtx and Res dual-loaded micelles, regardless of the polymer. The findings may be used for selection of PLA-based drug delivery systems containing Dtx and Res.

Influence of hydrophilic block length on the aggregation properties of polyglycidol-polystyrene-polyglycidol copolymers.

Amphiphilic triblock copolymers, polyglycidol-polystyrene-polyglycidol (PGL-PS-PGL), were synthesised via anionic polymerization starting from the synthesis of a polystyrene macroinitiator with 60 styrene units in the block terminated by ethylene oxide. Poly(ethoxyethyl glycidyl ether) blocks of different lengths were created on both sides of the macroinitiator. By removing the ethoxyethyl blocking groups, PGL-PS-PGL copolymers containing polyglycidol blocks with DP 11, 23, 44 and 63 were received. Their structures were determined by NMR and FTIR. The hydrophilicity of PLG-PS-PGL films was studied upon exposure to water vapour. To perform the copolymers' aggregation in water, the samples were dialysed from DMF into water. The critical concentration of their micellisation (CMC) was determined by measuring the absorbance of the 1,6-diphenylhexa-1,3,5-triene (DPH) probe and the intensity of light scattered by the copolymers' solution as a function of concentration. CMC values increased with increasing the number of hydrophilic glycidol units in the copolymer chain. The sizes of aggregates formed slightly above the critical concentration were measured by dynamic light scattering (DLS), and particles were imaged by cryo-TEM. Cryo-TEM pictures showed the presence of regular micelles in copolymer dispersions. For copolymers with shorter PGL chains aggregated partices were detected. Moreover, cryo-TEM demonstrated that the copolymers with a polyglycidol block of DP = 63 formed regular spherical micelles that formed 2D ordered organisation on the surface. X-ray measurements showed the formation of a partially crystallised PS core in the micelle's interior. The aggregates of all copolymers were stable. Their sizes did not change after one year of storage. The particles did not disassociate even after diluting their dispersions to a concentration 10 times lower than the critical concentration.

Flexible Piezoresistive Polystyrene Composite Sensors Filled with Hollow 3D Graphitic Shells.

The objective of this research was to develop highly effective conductive polymer composite (CPC) materials for flexible piezoresistive sensors, utilizing hollow three-dimensional graphitic shells as a highly conductive particulate component. Polystyrene (PS), a cost-effective and robust polymer widely used in various applications such as household appliances, electronics, automotive parts, packaging, and thermal insulation materials, was chosen as the polymer matrix. The hollow spherical three-dimensional graphitic shells (GS) were synthesized through chemical vapor deposition (CVD) with magnesium oxide (MgO) nanoparticles serving as a support, which was removed post-synthesis and employed as the conductive filler. Commercial multi-walled carbon nanotubes (CNTs) were used as a reference one-dimensional graphene material. The main focus of this study was to investigate the impact of the GS on the piezoresistive response of carbon/polymer composite thin films. The distribution and arrangement of GS and CNTs in the polymer matrix were analyzed using techniques such as X-ray diffraction and scanning electron microscopy, while the electrical, thermal, and mechanical properties of the composites were also evaluated. The results revealed that the PS composite films filled with GS exhibited a more pronounced piezoresistive response as compared to the CNT-based composites, despite their lower mechanical and thermal performance.

Development of Polyhydroxybutyrate-Based Packaging Films and Methods to Their Ultrasonic Welding.

This study developed a technical task associated with the formation of welded joints based on biodegradable polymers and their subsequent physicochemical characterization. The primary objective was to establish the effect of the welding process and modification of natural poly(3-hydroxybutyrate) (PHB) with N,N-dibutylundecenoylamide (DBUA) as a plasticizing agent on the structure and properties of PHB-based biopolymer materials as well as the process and structure of welded joints formation using ultrasonic welding technique. The weldability of biodegradable layers based on PHB and PHB/DBUA mixture was ultrasonically welded and optimized using a standard Branson press-type installation. The effect of the DBUA plasticizer and welding process on the structure of PHB-based biodegradable material was investigated using scanning electron microscopy, X-ray diffraction, FT-IR spectroscopy, differential scanning calorimetry, and thermomechanical analysis. The results confirmed that the DBUA acted as an effective plasticizer of PHB, contributing to lower crystallinity of the PHB/DBUA mixture (63%) in relation to the crystallinity degree of pure PHB film (69%). Ultrasonic welding resulted in an additional increase (approximately 8.5%) in the degree of crystallinity in the PHB/DBUA in relation to the initial PHB/DBUA mixture. The significant shift toward lower temperatures of the crystallization and melting peaks of PHB modified with DBUA were observed using DSC concerning pure PHB. The melt crystallization process of PHB was affected by welding treatment, and a shift toward higher temperature was observed compared with the unwelded PHB/DBUA sample. The butt-welded joints of biodegradable PHB/DBUA materials made using the ultrasonic method tested for tensile strength have damaged the area immediately outside the joining surface.

Laminar Biomaterial Composite of PVA Cryogel with Amnion as Potential Wound Dressing.

Gel dressings, composed of polymers both natural and synthetic, are successfully used in the treatment of burn wounds. They protect the burn wound site against adverse external factors, ensure an adequate level of tissue hydration, have soothing and pain-relieving properties, and also support the healing process and reduce the risk of pathological scars. Another promising material that can be used in the wound-healing process is an amnion membrane. Due to its valuable properties such as protecting the body against bacterial infections and permeability to nutrition, it has found usage in different brands of medicine. In this work, we have combined the beneficial properties of hydrogels and amnion in order to make the laminar dressing that may serve for wound healing. For that purpose, the physically crosslinked cryogel of poly(vinyl alcohol) (PVA) was covered with an amnion membrane. Subsequently, gamma irradiation was performed, leading to the simultaneous internal crosslinking of the hydrogel, its permanent bonding with the amnion, and dressing sterilization. The physicochemical properties of the dressing including gel fraction, swelling, and hardness were studied. Biological tests such as the MTT assay, antimicrobial activity, and histopathological examination confirmed that the obtained material constituted a promising candidate for further, more in-depth studies aiming at wound dressing application.

Bismuth sulfoiodide (BiSI) nanorods: synthesis, characterization, and photodetector application.

The nanorods of bismuth sulfoiodide (BiSI) were synthesized at relatively low temperature (393 K) through a wet chemical method. The crystalline one-dimensional (1D) structure of the BiSI nanorods was confirmed using high resolution transmission microscopy (HRTEM). The morphology and chemical composition of the material were examined by applying scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively. The average diameter of 126(3) nm and length of 1.9(1) µm of the BiSI nanorods were determined. X-ray diffraction (XRD) revealed that prepared material consists of a major orthorhombic BiSI phase (87%) and a minor amount of hexagonal Bi13S18I2 phase (13%) with no presence of other residual phases. The direct energy band gap of 1.67(1)  eV was determined for BiSI film using diffuse reflectance spectroscopy (DRS). Two types of photodetectors were constructed from BiSI nanorods. The first one was traditional photoconductive device based on BiSI film on stiff glass substrate equipped with Au electrodes. An influence of light intensity on photocurrent response to monochromatic light (λ = 488 nm) illumination was studied at a constant bias voltage. The novel flexible photo-chargeable device was the second type of prepared photodetectors. It consisted of BiSI film and gel electrolyte layer sandwiched between polyethylene terephthalate (PET) substrates coated with indium tin oxide (ITO) electrodes. The flexible self-powered BiSI photodetector exhibited open-circuit photovoltage of 68 mV and short-circuit photocurrent density of 0.11 nA/cm2 under light illumination with intensity of 0.127 W/cm2. These results confirmed high potential of BiSI nanorods for use in self-powered photodetectors and photo-chargeable capacitors.

Pyroresistive Properties of Composites Based on HDPE and Carbon Fillers.

Electrothermal processes were studied in pyroresistive composites based on high-density polyethylene (HDPE) containing 8 vol.% carbon black (CB), 8 vol.% carbon fibers (CF), and their mixture 4 vol.% CB + 4 vol.% CF. It is shown that the kinetic heating curves of composites are well described by an exponential dependence with a certain heating rate constant k for each type of composite. After a short heating time, the equilibrium temperature Te is reached in the sample. When the applied voltage exceeds a certain value, the Te value decreases due to the presence of the positive temperature coefficient of resistance (PTC) effect. Due to the PTC effect, the composites exhibit a self-regulating effect relative to the Te. Relations between the applied voltage, electric power, and equilibrium temperature are found, the Te value depends on the applied voltage according to the quadratic law whereas there is a linear relationship between the Te and electric power. A possible application of such pyroresistive composites is resistance welding of plastics using a heating element (HE) made of a pyroresistive material. The use of HDPE-CB composite to create HE for resistance welding is demonstrated and the welded joint of HDPE parts obtained using HE is shown.

Glassy Carbon Open-Celled Foams as a Reinforcement in Polymer Matrix Composites Dedicated for Tribological Applications.

This work presents the results of a tribological examination of polymer matrix composites reinforced with carbon foams with different porosity. The application of open-celled carbon foams allows an easy infiltration process by liquid epoxy resin. At the same time, carbon reinforcement remains its initial structure, which prevents its segregation in polymer matrix. Dry friction tests, conducted under 0.7, 2.1, 3.5 and 5.0 MPa loads, show that higher friction load results in higher mass loss, but it strongly lowers the coefficient of friction (COF). The change in coefficient of friction is related to the size of the pores of the carbon foam. Open-celled foams with pores size below 0.6 mm (40 and 60 ppi), used as a reinforcement in epoxy matrix, allow to obtain COF twice lower than composite reinforced with 20 ppi open-celled foam. This phenomenon occurs due to a change of friction mechanisms. In composites reinforced with open-celled foams, general wear mechanism is related to destruction of carbon components, which results in solid tribofilm formation. The application of novel reinforcement, in the form of open-celled foams with stable distance between carbon components, allows the decrease of COF and the improvement of stability, even under a very high friction load.

Bioresorbable Nonwoven Patches as Taxane Delivery Systems for Prostate Cancer Treatment.

Prostate cancer is the second most common cancer in males. In the case of locally advanced prostate cancer radical prostatectomy is one of the first-line therapy. However, recurrence after resection of the tumor can appear. Drug-eluting bioresorbable implants acting locally in the area of the tumor or the resection margins, that reduce the risk of recurrence would be advantageous. Electrospinning offers many benefits in terms of local delivery so fiber-forming polyesters and polyestercarbonates which are suitable to be drug-loaded were used in the study to obtain CTX or DTX-loaded electrospun patches for local delivery. After a fast verification step, patches based on the blend of poly(glycolide-ε-caprolactone) and poly(lactide-glycolide) as well as patches obtained with poly(lactide-glycolide- ε-caprolactone) were chosen for long-term study. After three months, 60% of the drug was released from (PGCL/PLGA) + CTX and it was selected for final, anticancer activity analysis with the use of PC-3 and DU145 cells to establish its therapeutic potential. CTX-loaded patches reduced cell growth to 53% and 31% respectively, as compared to drug-free patches. Extracts from drug-free patches showed excellent biocompatibility with the PC-3 cell line. Cabazitaxel-loaded bioresorbable patches are a promising drug delivery system for prostate cancer therapy.

Co-Delivery of 8-Hydroxyquinoline Glycoconjugates and Doxorubicin by Supramolecular Hydrogel Based on α-Cyclodextrin and pH-Responsive Micelles for Enhanced Tumor Treatment.

The sustained release of multiple anti-cancer drugs using a single delivery carrier to achieve a synergistic antitumor effect remains challenging in biomaterials and pharmaceutics science. In this study, a supramolecular hydrogel based on the host-guest complexes between pH-responsive micelle derived poly(ethylene glycol) chains and α-cyclodextrin was designed for codelivery of two kinds of anti-cancer agents, hydrophilic 8-hydroxyquinoline glycoconjugate and hydrophobic doxorubicin. The host-guest interactions were characterized using X-ray diffraction and differential scanning calorimetry techniques. The resultant supramolecular hydrogel showed thixotropic properties, which are advantageous to drug delivery systems. In vitro release studies revealed that the supramolecular hydrogel exhibited faster drug release profiles in acidic conditions. The MTT assay demonstrated a synergistic cancer cell proliferation inhibition of DOX/8HQ-Glu mixture. In vitro cytotoxicity studies indicated excellent biocompatibility of the supramolecular hydrogel matrix, whereas the DOX/8HQ-Glu-loaded supramolecular hydrogel showed a sustained inhibition efficacy against cancer cells. The codelivery of hydrophobic anti-cancer drugs and hydrophilic anti-cancer drug glycoconjugates via a pH-responsive supramolecular hydrogel opens up new possibilities for the development of an effective cancer treatment based on the tumor-specific Warburg effect.

Polylactide/Carbon Black Segregated Composites for 3D Printing of Conductive Products.

One of the most important directions in the development of additive manufacturing or three-dimensional (3D) printing technologies is the creation of functional materials, which allow not only prototyping but also the manufacturing of products with functional properties. In this paper, poly-lactide acid (PLA) /carbon black (CB) composites with segregated (ordered) structure have been created. Computer simulation based on the Mamunya geometrical model showed that the CB content within φ = 2.5-5 vol.% in the polylactide matrix leads to the formation of a continuous electrically conductive phase with an increase of electrical conductivity σdc above the percolation threshold. The simulation results were experimentally confirmed by optical microscopy and studies of the electrical conductivity of the composites. It was found that increasing CB content from φ = 1 vol.% to φ = 7 vol.% in the composites causes insignificant (due to the segregated structure) phase changes in the polylactide matrix and improves the thermal properties of composites. Electrically conductive filaments for Fused Deposition 3D Printing (FDM) were developed from PLA/CB composites and then 3D printed. A correlation between the electrical conductivity σdc and the CB content φ for base composites, filaments produced from them, and final 3D samples, has been found. Conductivity varies within σdc = 3.1·10-11 - 10·10-3 S/cm for the filaments and σdc = 3.6·10-11 - 8.1·10-4 S/cm for the final 3D-products.

Evaluation of the impact of pH of the reaction mixture, type of the stirring, and the reagents' concentration in the wet precipitation method on physicochemical properties of hydroxyapatite so as to enhance its biomedical application potential.

Hydroxyapatite (HAp) constitutes a significant inorganic compound which due to its osteoinductivity, osteoconductivity as well as the ability to promote bone growth and regeneration is widely applied in development of biomaterials designed for bone tissue engineering. In this work, various synthesis methodologies of HAp based on the wet precipitation technique were applied, and the impact of pH of the reaction mixture, the concentration of individual reagents as well as the type of stirring applied (mechanical/magnetic) on the properties of final powders was discussed. Spectroscopic methods (Fourier transform infrared, Raman) and X-ray diffraction allowed to verify the synthesis parameters leading to obtaining calcium phosphate with 96% HAp in phase which indicated higher homogeneity of obtained powder (93.4%) than commercial HAp. Powders' morphology was evaluated using microscopic techniques while specific surface area was determined via Brunauer-Emmett-Teller analysis. Particle size distribution, porosity of powders, and stability of HAp suspensions were also characterized. It was proved that synthesis at pH = 11.0 using mechanical stirring resulted in calcium phosphate with a high phase homogeneity and homogeneous pore size distribution (6-20 nm). Moreover, obtained HAp powder showed 71.8% more specific surface area than commercial material-that is, 110 m3 /g for synthetic HAp and 64 m3 /g in the case of commercial powder-which, in turn, is significant in terms of its potential application as carrier of active substances. Thus it was demonstrated that by applying appropriate conditions of HAp synthesis it is possible to obtain powder with properties enhancing its application potential for medical purposes.

The Use of Carbon Fibers Recovered by Pyrolysis from End-of-Life Wind Turbine Blades in Epoxy-Based Composite Panels.

This work is devoted to evaluating the effectiveness of the recovery of carbon fibers from end-of-life wind turbine blades in the pyrolysis process, and the use of those fibers in the production of flat composite panels. The recovery of carbon fibers from wind turbine blades uses a pyrolysis process at 500-600 °C in a non-oxidizing atmosphere, in such a way that makes it possible to preserve the shape and dimensions of the fibers. Using recycled carbon fibers, flat CFRP sheets with epoxy resin matrix were produced by pressing. Seven different series of samples were tested, which differed in fiber length, fiber orientation, and pressure holding time. The results obtained on the recycled fibers were compared to the original carbon fibers, cut to corresponding lengths. Additionally, one of the series was reinforced with a biaxial fabric. The most favorable pressing parameters are empirically found to be pre-pressing 2 MPa (10 min), and further pressing at a pressure of 7 MPa until the resin completely cross-linked (about 120 min). A number of tests were carried out to demonstrate the usefulness of pyrolytic fibers, including tensile strength of carbon fibers, bending strength, SEM observations, FT-IR, and Raman spectroscopy. The tests carried out on the carbon fibers show that the pyrolysis process used leaves about 2% of the matrix on the surface of the fiber, and the tensile strength of the fibers drops by about 20% compared to the new carbon fibers. The research results show that the use of the recycled carbon fibers in the production of flat composite plates is reliable, and their mechanical properties do not differ significantly from plates made of corresponding original carbon fibers. Composite panels with the pyrolytic fibers (274 MPa) show up to a 35% higher flexural strength than similarly produced panels with the original new carbon fibers (203 MPa), which means that the panels can be used in the production of elements for footbridges, bridges, pipelines, or structural elements of buildings and roofing.

Nematic-to-Isotropic Phase Transition in Poly(L-Lactide) with Addition of Cyclodextrin during Abiotic Degradation Study.

Poly(L-lactide) is capable of self-assembly into a nematic mesophase under the influence of temperature and mechanical stresses. Therefore, subsequent poly(L-lactide) films were obtained and characterized, showing nematic liquid crystal properties both before and after degradation. Herein, we present that, by introducing ß-cyclodextrin into the polymer matrix, it is possible to obtain a chiral nematic mesophase during pressing, regardless of temperature and time. The obtained poly(L-lactide) films exhibiting liquid crystal properties were subjected to degradation tests and the influence of degradation on these properties was determined. Thermotropic phase behavior was investigated using polarized optical microscopy, X-ray diffraction, and differential scanning calorimetry. The degradation process demonstrated an influence on the liquid crystal properties of pressed polymer films. The colored planar texture of the chiral nematic mesophase, which was not observed prior to degradation in films without the addition of ß-cyclodextrin, appeared after incubation in water as a result of the entrapment of degradation products in the polymer matrix. These unusual tailor-made properties, obtained in liquid crystals in (bio)degradable polymers using a simple method, demonstrate the potential for advanced photonic applications.

Effect of Magnesium Powder Application on the Microstructure and Properties of Rods Extruded by the Forward-Backward Rotating Die Extrusion Method.

The effects of severe plastic deformation (SPD) with a forward-backward rotating die (KOBO extrusion) on pure magnesium, in the form of cold-compacted powder, sintered powder, or cast ingots as reference, were examined. This method is known to reinforce metals, but the role of the initial form of magnesium applied in the fabrication of metal-based rods, as well as related phenomena, has not been characterized until now. The problem is important in the potential processing of commercial metal powders, the recycling of metal shavings, and the fabrication of metal matrix composites with discontinuous reinforcing phases. In the presented experiments, rods of 8 mm in diameter and 400 mm in length were obtained, and the structural effects induced by KOBO that occurred on a macro- and microscale on the surface and cross sections were characterized. Changes in the size and orientation of α-Mg crystallites were determined by XRD. The porosity, hardness, tensile strength, and compressive strength were measured, and the mechanisms of decohesion dependent on starting metal form were analyzed. After KOBO extrusion, significant differences were observed in the microstructure and properties between the materials derived from cold-compacted powder, sintered powder, and reference cast magnesium. Due to the application of KOBO, apart from α-Mg grain refinement, the MgO derived from the initial powder's surface was refined to fine regular particles surrounded by magnesium. Their bands curved in the perpendicular plane and were oriented with the extrusion direction of the formed network, which augmented some mechanical properties and changed the decohesion mechanism. The conducted experiments revealed that before extrusion by KOBO, the magnesium powder required sintering under pressure.