Impact of particle morphology on structure,crystallization kinetics,and properties of PCL composites with TiO<Subscript>2</Subscript>-based particles

Crystallization kinetics of polycaprolactone (PCL) filled with TiO₂-based particles (TiX) was shown to depend on the TiX particle type and concentration, which were associated with a slight polymer matrix degradation. The partially degraded, shorter, and more mobile polymer chains increased the overall crystallization rate at the initial stage of crystallization, while at the later stages, the non-nucleating TiX particles acted as a sterical hindrance, slowing down the crystallization process. The PCL/TiX composites were prepared by melt-mixing and contained 2.5 and 5 wt% of the filler. The investigated TiX particles included isometric anatase microparticles (mTiO₂) and titanate nanotubes with high-aspect ratio (TiNT). Light and electron microscopy showed very homogeneous dispersion of the mTiO₂ particles in the PCL matrix, while the TiNT formed large agglomerates. In situ polarized light microscopy displayed faster isothermal crystallization of all PCL/TiX composites, but the micrographs indicated that the TiX particles did not act as nucleation centres. Isothermal DSC experiments, evaluated in terms of Avrami theory, confirmed the PLM results and showed that the overall rate of isothermal crystallization increased in the following order: PCL <PCL/TiNT <PCL/mTiO₂. Non-isothermal DSC and rheological measurements revealed the correlation between the crystallization rate and the polymer matrix degradation—the well-dispersed mTiO₂ particles with high specific surface caused the highest PCL degradation and, consequently, the earliest start of non-isothermal crystallization as well as the fastest isothermal crystallization. Microindentation hardness measurements confirmed that the partial degradation of the polymer matrix did not have a significant impact on the mechanical performance of PCL/mTiO₂ composites.     

The impact of drying and steaming processes on surface color changes of tension and normal beech wood

Abstract

Beech wood has a high frequency of defects such as red heartwood, reaction wood (tension wood). For the experimental measurements four logs without visible defects like red heartwood, which can noticeably affects the measurements' results were qualified. The drying medium temperature in the first phase of the process before the moisture content of the specimens fell below the FSP was maintained at 45?°C. Then, the temperature was gradually increased to the maximum value 65?°C. The results showed that different initial wood moisture content does not affect to final value of tension and normal wood. The colorimetric parameter L* was much higher for tension wood. After steaming, there were greater differences in the colorimetric parameters, respectively, a* and b*. After drying the difference of all colorimetric parameters between tension and normal wood was significantly less. The color changes were only noticed in the surface layers of specimens. Differences were small, and thus, the impact of the tension wood on the color changes was not confirmed. However, since the lightness of tension wood plays a key role for its visual detection, it may be adequate to only measure the lightness parameter (L*).     

Analysis of the strain and hardness in self-cured and light-cured self-adhesive resin based cement

The study showed an application of the 3?D Digital Image Correlation Method (3?D-DIC) for detection of von Mises strain in samples of the self-etch, self-adhesive resin based cement (RBC). The aim was to determine and compare strain in the self-cured and light-cured Maxcem Elite, furthermore to investigate the hardness of these two cement-types. The experiment was carried out using two groups of Maxcem Elite (Kerr, Orange, CA, USA) samples; each tested group includes five (ø5?×?2?mm sized) samples, for both self-curing and light-curing mode. All samples were prepared by filling teflon ring-type molds. In addition, Vickers micro-hardness was measured for all samples. Maxcem Elite showed similar maximum strain values from 10% to 12% for both groups. Besides the maximum strain value, the 3?D-DIC method also enabled monitoring the change of strain field even after the recommended polymerization time. This method has shown that the polymerization shrinkage continues even after 10?min which disagreed with manufacturer’s suggestion. Group II showed maximum strain values of 12% in the peripheral zone after 10?min, in the last Stage (Stage 60). Statistically significant difference was not found in the overall strain between self- and light-cured Maxcem Elite neither peripherally (p?=?0.118) nor centrally (p?=?0.879). However, statistical significance was found in strain regarding central and peripheral zone in both, self-cured (p?=?0.020) and light-cured (p?=?0.002) Maxcem Elite. The mean von Mises strain values in the periphery of the samples (Section 0) were significantly higher compared to strain values in the center of the samples (for Section 1 and 2). The last stage (Stage 60) of the light-cured Maxcem Elite polymerization showed significantly higher values of von Mises strain compared to initial stage (Stage 0). Higher values of micro-hardness were noticed on the surfaces directly exposed to LED lamp after performing measurements of micro-hardness on light-cured samples.     

High temperature monoclinic-to-tetragonal phase transition in magnesium doped lanthanum ortho-niobate

Magnesium doped lanthanum ortho-niobate (La_0.98Mg_0.02NbO₄) was prepared by the molten salt synthesis method. X-ray diffraction and dilatometry methods were used to study high temperature behavior of the ceramic material. Special attention was paid to the phase transition between the monoclinic and tetragonal phases. The values of spontaneous strain on the basis of unit cell parameter, obtained by Rietveld refinement, have been calculated as well as Landau order parameter. The thermal expansion coefficient (TEC) of La_0.98Mg_0.02NbO₄ was determined to be 12×10^?6 1/K and 8×10^?6 1/K below and above 500 °C, respectively.     

The Effect of Long-Lasting Swimming on Rats Skeletal Muscles Energy Metabolism after Nine Days of Dexamethasone Treatment

This study investigates the effect of Dexamethasone (Dex) treatment on blood and skeletal muscle metabolites level and skeletal muscle activity of enzymes related to energy metabolism after long-duration swimming. To evaluate whether Dex treatment, swimming, and combining these factors act on analyzed data, rats were randomly divided into four groups: saline treatment non-exercise and exercise and Dex treatment non-exercised and exercised. Animals in both exercised groups underwent long-lasting swimming. The concentration of lipids metabolites, glucose, and lactate were measured in skeletal muscles and blood according to standard colorimetric and fluorimetric methods. Also, activities of enzymes related to aerobic and anaerobic metabolism were measured in skeletal muscles. The results indicated that Dex treatment induced body mass loss and increased lipid metabolites in the rats’ blood but did not alter these changes in skeletal muscles. Interestingly, prolonged swimming applied after 9 days of Dex treatment significantly intensified changes induced by Dex; however, there was no difference in skeletal muscle enzymatic activities. This study shows for the first time the cumulative effect of exercise and Dex on selected elements of lipid metabolism, which seems to be essential for the patient’s health due to the common use of glucocorticoids like Dex.     

The Periplasmic Oxidoreductase DsbA Is Required for Virulence of the Phytopathogen Dickeya solani

In bacteria, the DsbA oxidoreductase is a crucial factor responsible for the introduction of disulfide bonds to extracytoplasmic proteins, which include important virulence factors. A lack of proper disulfide bonds frequently leads to instability and/or loss of protein function; therefore, improper disulfide bonding may lead to avirulent phenotypes. The importance of the DsbA function in phytopathogens has not been extensively studied yet. Dickeya solani is a bacterium from the Soft Rot Pectobacteriaceae family which is responsible for very high economic losses mainly in potato. In this work, we constructed a D. solani dsbA mutant and demonstrated that a lack of DsbA caused a loss of virulence. The mutant bacteria showed lower activities of secreted virulence determinants and were unable to develop disease symptoms in a potato plant. The SWATH-MS-based proteomic analysis revealed that the dsbA mutation led to multifaceted effects in the D. solani cells, including not only lower levels of secreted virulence factors, but also the induction of stress responses. Finally, the outer membrane barrier seemed to be disturbed by the mutation. Our results clearly demonstrate that the function played by the DsbA oxidoreductase is crucial for D. solani virulence, and a lack of DsbA significantly disturbs cellular physiology.     

Viscoelastic properties of poly(ε‐caprolactone)/clay nanocomposites in solid and in melt state

Viscoelastic properties in solid and in melt state of poly(ε‐caprolactone), PCL, nanocomposites with organomodified clays (Cloisite30B and Cloisite15A) are thoroughly investigated. Although WAXD is insensitive to the difference in the nanocomposites structure, the melt rheology reveals pronounced differences between the two series. Melt yield stress values, obtained from fittings by the Carreau–Yasuda model, are used as a measure of partial exfoliation of the clay. Temperature dependence of the shift factors, used for time–temperature superposition of the modulus curves, yields similar values of the flow activation energies for all the samples. Temperature dependences of the dynamic modulus and loss factor of solid nanocomposites were correlated to the structural differences deduced from the melt rheology. The increase in the storage modulus is compared to the theoretical predictions from the Halpin–Tsai model. The effective aspect ratio obtained from this comparison agrees reasonably with the value estimated from the melt rheology. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42896.     

Poly(hydroxybutyrate‐co‐hydroxyvalerate)/titanium dioxide nanocomposites: A degradation study

Nanocomposites, based on a poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) matrix and titanium dioxide (TiO₂) nanoparticles and fabricated with a solvent‐casting technique, were characterized with differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. The content of TiO₂ nanoparticles varied between 0.5 and 10 wt %. Degradation studies, including hydrolytic degradation in a strong base medium (1N NaOH) and degradation under ultraviolet light at 365 nm, were performed. It was confirmed that the inorganic filler had no great influence on thermal properties such as the melting and crystallization temperatures. Improved degradation temperatures were also confirmed with the increase in the filler content. Degradation observations confirmed significant increases in hydrolytic erosion with the filler content increasing in comparison with the degradation of a pure PHBV film. Also, the photocatalytic activity of the inorganic filler TiO₂ in all investigated composites [irradiated at λ = 365 nm and immersed in a liquid medium (H₂O)] was evaluated. The degraded samples were analyzed with Fourier transform infrared spectroscopy, which confirmed their increased crystallinity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009