Characterization of different types of cellulose by dielectric spectroscopy

Various well dried solid celluloses, such as nativecelluloses from different sources, different pulps and regenerated cellulosefibers were compared by dielectric relaxation spectroscopy (DRS) in the lowfrequency (10 mHz to 5 MHz) and low temperature(–130 to 20 °C) range. No significant differences werefound in the polymeric dynamics. In addition, the influence of the watercontenton the -relaxation and the _wet relaxation wasinvestigated for morphologically very different celluloses such as cottonlinters, highly amorphous bead cellulose and lyocell fibers. The lyocell fiberswere investigated in the unmodified form and after modification by a treatmentwith alkali, after mild bleaching and after chemical crosslinking. It was foundthat the water content influences the dielectric dynamics and the intensityparameters differently for these different materials. NaOH-activation usingdifferent lye concentrations also influenced the dielectric dynamics. Finally,opportunities and limitations of DRS as a diagnostic tool are discussed.     

The Existing Methods and Novel Approaches in Mycotoxins’ Detection

Mycotoxins represent a wide range of secondary, naturally occurring and practically unavoidable fungal metabolites. They contaminate various agricultural commodities like cereals, maize, peanuts, fruits, and feed at any stage in pre- or post-harvest conditions. Consumption of mycotoxin-contaminated food and feed can cause acute or chronic toxicity in human and animals. The risk that is posed to public health have prompted the need to develop methods of analysis and detection of mycotoxins in food products. Mycotoxins wide range of structural diversity, high chemical stability, and low concentrations in tested samples require robust, effective, and comprehensible detection methods. This review summarizes current methods, such as chromatographic and immunochemical techniques, as well as novel, alternative approaches like biosensors, electronic noses, or molecularly imprinted polymers that have been successfully applied in detection and identification of various mycotoxins in food commodities. In order to highlight the significance of sampling and sample treatment in the analytical process, these steps have been comprehensively described.     

Contributions to the molecular origin of the dielectric relaxation processes in polysaccharides – the high temperature range

For ionic conducting glasses a concept of correlation of electrical conductivity with dielectric relaxation was developed, which was essential for understanding the relaxation processes found for this substance class. This paper describes on attempt to extend the concept for interpreting the so-called σ-relaxation found in all systems of well dried polysaccharides in the solid state at high temperatures. For various cellulose-based materials, starches and other pure polysaccharides it was found that the activation energies of the dc-conductivity and the dielectric σ-relaxations were well correlated and their values were nearly equal (95–110 kJ/mol) for all substances. The shape and the intensity of this relaxation were nearly independent of temperature for one substance. In cellulose derivatives this process can be only observed, if these have sufficient unsubstituted hydroxyl groups. Highly or persubstituted celluloses show no separable σ-relaxation. Two models are discussed for the interpretation of this relaxation process: the first one assumes a local diffusion process of hydrogen ions between high potential barriers in these disordered systems and the second one a conducting pathway through a badly conducting environment in the material.     

Workflow to Investigate Subtle Differences in Wine Volatile Metabolome Induced by Different Root Systems and Irrigation Regimes

To allow for a broad survey of subtle metabolic shifts in wine caused by rootstock and irrigation, an integrated metabolomics-based workflow followed by quantitation was developed. This workflow was particularly useful when applied to a poorly studied red grape variety cv. Chambourcin. Allowing volatile metabolites that otherwise may have been missed with a targeted analysis to be included, this approach allowed deeper modeling of treatment differences which then could be used to identify important compounds. Wines produced on a per vine basis, over two years, were analyzed using SPME-GC-MS/MS. From the 382 and 221 features that differed significantly among rootstocks in 2017 and 2018, respectively, we tentatively identified 94 compounds by library search and retention index, with 22 confirmed and quantified using authentic standards. Own-rooted Chambourcin differed from other root systems for multiple volatile compounds with fewer differences among grafted vines. For example, the average concentration of β-Damascenone present in own-rooted vines (9.49 µg/L) was significantly lower in other rootstocks (8.59 µg/L), whereas mean Linalool was significantly higher in 1103P rootstock compared to own-rooted. β-Damascenone was higher in regulated deficit irrigation (RDI) than other treatments. The approach outlined not only was shown to be useful for scientific investigation, but also in creating a protocol for analysis that would ensure differences of interest to the industry are not missed.     

Re‐determination of the pseudobinary system Li2O – MoO3

The quasi‐binary phase diagram lithium oxide – molybdenum(VI) oxide was investigated by differential scanning calorimetry and X‐ray diffraction. The four intermediate phases Li₄MoO₅, Li₂MoO₄, Li₄Mo₅O₁₇, and Li₂Mo₄O₁₃ show incongruent melting. The system has one eutectic point at 50.5 mol% MoO₃ and 49.5 mol% LiO_0.5 with a eutectic temperature of 524.6°C. At this point the melt is in equilibrium with Li₂MoO₄ and Li₄Mo₅O₁₇. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bent Carbon Surface Moieties as Active Sites on Carbon Catalysts for Phosgene Synthesis

Active sites in carbon‐catalyzed phosgene synthesis from gaseous CO and Cl₂ have been identified using C₆₀ fullerene as a model catalyst. The carbon atoms distorted from sp² coordination in non‐planar carbon units are concluded to generate active Cl₂. Experiments and density functional theory calculations indicate the formation of a surface‐bound [C₆₀???Cl₂] chlorine species with radical character as key intermediate during phosgene formation. It reacts rapidly with physisorbed CO in a two‐step Eley–Rideal‐type mechanism.     

Complete equilibrium paths for Mises trusses

This paper presents determination of equilibrium paths for Mises trusses with different ratio of height to span. Unsymmetrical deformation modes are considered and the structure is treated as a two DOF system. First, a few special equilibrium configurations are resolved from considerations of free body diagrams. Complete equilibrium paths are determined by solving numerically the governing non-linear equilibrium equations. The stability of possible equilibrium configurations is checked using the second partial derivative test for the total potential energy. The positive definiteness of the appropriate Hessian matrices is checked numerically using the Sylvester criterion.     

Carbon Nanotubes: An Example of Multiscale Development—A Mechanistic View from the Subnanometer to the Meter Scale

We summarize the catalytic synthesis of multiwall carbon nanotubes (MWCNTs). The current understanding of the reaction mechanism is presented, in particular the catalyst design for the CCVD process is analyzed. To complement that, kinetics and reaction engineering aspects are discussed along with the impact of the reaction and reactor operation on the product properties. All these issues are analyzed from the perspective of the industrial synthesis and implications for the application of carbon nanotubes. Carbon‐nanotube technology is a perfect example of multi‐scale development and covers challenges from the nanometer to the meter scale. Problems, methods, and solutions characteristic for different scales will be highlighted. The Co/Mn catalyst is used as reference as one of the first commercially used technologies for the scalable production of multiwall carbon nanotubes.