Stabilität von Dispersionen

Stability of Dispersions The importance of production and application of disperse systems in the industry is steadily growing. On the other site colloidale systems surround us every day (for example foodstuffs, pharmaceutica, and so on). With the knowledge about the mechanism of interaction forces we are able to develope new materials and improve available systems. The stability of such systems is one of the central point of research. One of the well known physical models of colloid stability is given by DLVO‐Theory. With this theory we have a tool to influence the stability of such dispersion systems. In this paper electrokinetic methods are used to investigate interaction forces in disperse systems. The influence of pH‐value, electrolyte concentration, and valency is shown. But, not in all cases the DLVO‐model works satisfactoryly. Some reasons of this behavior will be discussed.     

Basizität von Ketonen

Basicity of Ketones The determination of the protonation ratios of weak organic bases e. g. ketones in strong acidic solutions by means of NMR and UV spectroscopy is described. Different extrapolation procedures which allow to obtain the basicity and solvation parameters are presented and compared. Literature data for aliphatic, cyclic and aromatic ketones as well as diketones are collected and discussed in terms of structural and solvation effects on basicity.     

Funktionalität von Lecithinen

Functionality of lecithins. In industry the functional emulsifying power of soya lecithin has a great technical and commercial importance, while egg lecithin has taken an interesting market niche. The requirements on consistent emulsifying, stabilizing and nutritional properties can be achieved by adjustment of standard qualities and a range of lecithin modifications: Enzymatic hydrolysis, acetylation and hydroxylation give lecithins with increased hydrophilicity and subsequently improved oil-in-water emulsifying properties. Alcohol fractionation, sometimes combined with chromatographic isolation, divides crude lecithin in specific phospholipid fractions, yielding an optimal functionality in specific product applications. Oil free “pure” lecithins in powder and granular form are used because of convenient dosage, neutral taste and enhanced O/W emulsifying performance. Combinations of the processes give a vaste range of tailor made special lecithins with different hydrophilic-lipophilic balance properties in food, feed, pharmaceutical, cosmetic and technical industries.     

Die kristallinität von äthylen-vinylacetat-copolymeren

Copolymers of ethylene and vinyl acetate of different composition were investigated by differential thermal and x-ray analysis in the temperature range of ?80 to 140°C. Compounds with more than 60 weight-% of vinyl acetate are amorphous. In the partially crystalline copolymers with lower contents of vinyl acetate the glass transition temperature is independent of composition and lies below that in amorphous copolymers. The melting points of the partially crystalline compounds increase with ethylene contents and can be described with the aid of a modified FLORY equation. The increase of the degree of crystallinity with ethylene content is demonstrated. The influence of thermal pre-treatment on the melting behaviour is discussed.     

Reststabilität von verarbeitetem Polyvinylchlorid

The residual stability of a PVC-compound, stabilized by a solid stabilizing agent, was measured by degradation experiments in bulk under pure nitrogen at 180°C. Several samples of different processing times were prepared by thermomechanical treatment on an extruder. Investigations of the residual stability showed an increasing tendency after the first runs, and then a decrease in stability. The same experiments were performed with a plasticized PVC-compound. Instead of an increase of the residual stability in the beginning of the thermomechanical treatment, a continuous decrease was observed. The same result was found by application of a liquid stabilizing agent to unplasticized PVC. Thus, maximum initial stability is found in the case of plasticized PVC and with liquid stabilizers in unplasticized PVC. In contrast to this result maximum initial stability of PVC, stabilized by a solid stabilizer, was obtained only after several runs on the extruder. This phenomenon can be attributed to a better homogeneity of the stabilizer and the polymer, which is effected by gelation of the PVC by the thermomechanical treatment on the extruder. If the investigation of the residual stability is measured after each run by degradation in a solution of ethylbenzoate the nonplasticized PVC-compound shows maximum stability at the beginning of the experiment. This result leads to the conclusion that the stability of a PVC-compound does not only depend either on the kind or on the amount of the applied stabilizer. To ensure the optimal efficiency of the utilized amount of stabilizer it is necessary to secure a maximum of homogeneity between stabilizer and polymer from the very beginning. Therefore it is of great importance t o the estimation of the residual stability of a PVC-compound after processing to make sure of maximum homogeneity between stabilizer and polymer.     

Einfluß von Licht und Tocopherolgehalt auf die Oxidationsstabilität von Fettsäuremethylestern

Influence of light and contents of tocopherols on the oxidative stability of fatty acid methyl esters The oxidative stability of different plant oil based fatty acid methyl esters can be estimated by determining the induction period with the active oxygen method. Measuring the volatile and oil soluble acids for a long period preceding the induction period shows that the values are approaching a certain limit. Even if the esters do not differ dramatically in the composition of fatty acids it is a fact that the different production processes influence the amount of tocopherols significantly. The exclusion of light is more crucial than the exclusion of air when storing plant oil based fatty acid esters.     

Partikelform und Porosität von biogenen Pyrolysekoksen

Char particles from pyrolyzed biomass vary in particle size and shape. On average, the particles are more elongated the larger their size. The average size‐specific elongation is almost alike for all investigated samples, i.e. independent from their source material and process. The particle collectives cannot be characterized accurately with classical particle size distributions, which assume spherical particle shape. Accounting for their shape, they can be described more accurately with particle size distributions that are based on an ellipsoid model. The high bulk porosity is mainly attributed to the spaces between particles.     

Automatisches Gerät zur Messung von Erstarrungspunkten

Automatic Device for the Determination of Solidification Point An automatic monitoring device for the determination of solidification point is described. This device is suitable for process control in fatty acid distillation columns. The solidification point must lie between 30° and 80° C. The value obtained correspond to the results provided by the laboratory procedure prescribed in the DGF standard methods.     

Einfluß von zusatzstoffen auf die wärmestabilität von auf PVC basierenden systemen

The instability of systems on PVC basis may be attributed to physical and chemical phenomena. The stability of the system is basically influenced by the oxidation stability of the plasticizers. The volatility loss in plasticizer is only partially due to physical processes. During ageing, oxidation and degradation processes take place to a minor or major degree, or exclusively, depending on the structure of the plasticizer. These processes may be affected in their order of magnitude by the stabilizers and fillers present in the system.