Zur abhängigkeit der mechanischen eigenschaften von thermoplasten von ihrer thermischen vorgeschichte

K.-H. ILLERS has recently shown that the mechanical properties of PVC foils can be considerably influenced by annealing the material at a temperature some-what below the glass transition. This effect ist due to the fact that, in general, at the glass temperature a relative high hole concentration is frozen in which can be diminished by annealing the polymer glass. The variation of the hole concentration during the annealing process was measured by ILLERS with the aid of a new calorimetric method. The purpose of the investigation presented here was to continue ILLERS' measurements and in particular to complete them with regard to the mechanical properties. For this reason tensile tests in the speed range between 10?3 and 1 cm/s and biaxial impact penetration tests were carried out, using specimens cut from a sheet of PVC without plasticizer and annealed for differently long times. It was found that the position of the brittle-tough transition between times until fracture from 10 to 1000 s, caused by a certain molecular relaxation mechanism, is not influenced perceptibly by the hole concentration. If the time until fracture ist shorter than the transition time, or with other words, if the strain rate is sufficiently high, the extensibility of the specimens does not depend very much on the hole concentration. On the other hand the fracture stress, i. e. the strength of the sheet, distinctly increases in this region if the hole concentration decreases. Above the transition, i. e. at long times or low strain rates, the fracture stress is nearly independent of the hole concentration whereas the extensibility strongly decreases with decreasing hole concentration. This means that the sheet material, when being annealed, is improved (reinforced) in the brittle region and deteriorated (brittled) in the tough region. The above-mentioned experimental results were interpreted qualitatively. Furthermore their technical consequences were pointed out with regard to the investigated material as well as to other thermoplastic materials.     

Die Fettreifbildung von Schokolade in Abhängigkeit von der verfahrenstechnischen Durchführung der Vor- und Erstarrungskristallisation

Dependence of Bloom-Formation in Chocolate from Technical Operation of Pre-Crystallization and Solidification The undesired bloom-formation in chocolate is caused by post-crystallization of cocoa fat during storage. Experiments were carried out systematically in order to reveal, in what manner the bloom-formation is dependent on pre-crystallization and solidification operations. It was found that chocolate is more resistent to bloom-formation, higher the amount of fat that crystallizes out during pre-crystallization. Increased stability of strongly pre-crystallized chocolate with respect to bloom-formation is due to transformation of cocoa fat into a stable crystalline state, already during pre-crystallization and solidification.     

Die Medienabhängigkeit der alkalischen Hydrolyse von Methylmethacrylat-Polymeren

The rate of the alkaline hydrolysis of poly(methylmethacrylate)(PMMA) and copolymers of methylmethacrylate (MMA) and ethyl acrylate increases with increasing dielectric constants of solvents and decreasing capability of solvation of OH^?-ions in aliphatic monofunctional alcohols and aprotic solvents. With respect of the series of alcohols used this dependence yields maximum rates in propanols. The rate of hydrolysis is strongly reduced by higher contents of water. The rate constants of hydrolysis of the ethyl acrylate and MMA units differ by one order of magnitude under the reaction conditions investigated. During hydrolysis suspension copolymers of MMA and ethyl acrylate in ethanol 80°C form homogeneous solutions, highly swollen gels and dispersions under the condition of a low, medium and high content of alkaline hydroxide and water, respectively. The partial hydrolysis offers commercially interesting variants.     

Beeinflussung der Waschintensität (WI) in Abhängigkeit von Chemie und Mechanik

Influence of Chemical and Mechanical Factors on the Intensity of Washing Mutual effects of the two significant chemical and mechanical factors that influence the removal of dirt could be studied by treating the fabric in specific manner using a roller-type washing machine, which was developed in author's institute, and a device for measuring the working force. The tests revealed distinctly that intensity of washing is preferably promoted under the action of a solution of washing agent when fibres within the thread are displaced as widely as possible. When the aforesaid conditions are fulfilled, dirt substances from fabrics are suitably dispersed and suspended, which result in optimum washing action.     

Über die druckabhängigkeit der viskoelastischen und physikalisch-chemischen eigenschaften von polymeren, 8. Die viskosität von polyethylen bis 5000 bar

A new high pressure viscosimeter is described which permits rheological investigations up to 5000 bar and 200°C. The dependence on pressure and shear rate of the apparent viscosity of polyethylene is measured at 130, 155, and 190°C. Newtonian viscosity is calculated according to the method of Spencer and Dillon, its pressure coefficient decreases with pressure; crystallization induced by flow causes the pressure coefficient to increase abnormally. Free volume decreases in quite the same way as the pressure coefficient when pressure raised. From the slope of the log η_s-P_M-curve can be concluded that the pressure coefficient of non-Newtonian flow decreases with increasing pressure and shear rate.     

Die Zusammensetzung tierischer Organ- und Depotfette in Abhängigkeit von der Fütterung II Gas-chromatographische Analyse der Fettsäuren von Kälber- und Rinderfetten

The Composition of Lipids of Animal Organ and Depot Fats in Relation to Feed II: Gas-chromatographic Analysis of Fatty Acids of Calves and Cattle Fats In the milk as well as in the fats of calves and cattle 81 fatty acids were found. The composition of fatty acids of the depot and organ fats of cattle — in winter with stall-feeding and in summer with pasture-feeding — were compared with the winter and summer milk fats. The differences between the fats from the same parts of calves and cattle are discussed.     

Berechnung der relativen Lösungsviskosität in Abhängigkeit vom Umsatz und der zugesetzten Reglermenge bei der Polymerisation von Laurinlactam

FLORY'S model for calculating solution viscosities of polyamide-6 is applied in a simplified manner to the polymerization of laurinlactam. According to this simpified model it is possible to calculate the relative solution viscosity of polyamide-12 for any given (high) conversion and concentration of chain regulators. Experimental data are in good agreement with the calculated results.     

Die Bestimmung der Enzymaktivität von enzymhaltigen Waschmitteln

Determination of Enzyme Activity of Enzyme-Containing Washing Agents Four analytical methods for the determination of the proteolytic activity of detergents and enzymes for use in detergents have been compared. They were the following: 1) Determination of casein hydrolysis products by UV spectrophotometry; 2) Determination of azocasein hydrolysis products by colorimetry; 3) Determination of casein hydrolysis products by UV polarimetry; 4) Titration of casein hydrolysate. The activity of the enzymes can be increased or decreased by components used in detergents. Perborate especially interferes strongly. The polarimetric method is the most accurate and the simplest, but necessitates expensive equipment. The spectrophotometric and colorimetric methods are more accurate and reproducible than the titrimetric method.     

Die viskosität von polymerlösungen in der nähe von oberen und unteren entmischungstemperaturen

The viscosity of liquid mixtures exhibits a characteristic temperature dependence near the consolute point. For polymer solutions this phenomenon is well studied in the case of upper critical solution temperatures, whereas no such measurements exist in the vicinity of lower critical solution temperatures. Viscosity measurements were performed for the system cyclohexane/polystyrene (upper critical solution temperature) and for the system orthotrimethylformiate/diethylether/polystyrene (lower critical solution temperature). For the former system qualitative agreement with. the results of Debye and coworkers was found. The investigations in the vicinity of the lower critical solution temperatures also disclosed that an additional function is superimposed to the normal temperature dependence of the viscosity which leads to an increase in viscosity before demixing sets in. This behaviour can be described by an equation analogous to that used for lower solubility gaps.     

Bestimmung der Temperaturabhängigkeit der Inhibierungsperiode und der Radikalbildungskonstante von AIBN bei der Polymerisation von Methylmethacrylat

The dependence on temperature of the specific reaction rate quotient of the inhibition period has been determined as by dilatometric measurement of the inhibition period caused by dissolved oxygen, and by the initial rate of the methyl methacrylata polymerisation, using azoisobutyronitrile (AIBN) aa initiator. In the examined concentration range the initial polymerisation rate and the reciprocal of the inhibition period are strictly proportional to the root of the initiator concentration, the yield of free initiator radicals is thus independent of the initiator concentration. It is, therefore, possible to determine the radical forming constant k_R of AIBN represented by the equation The fraction of the radicals recombining in the cage can be determined from k_R and the decomposition constant k_z; at 60°C for example it amounts to 24%. This value corresponds very well to the value obtained by the gas-chromatographic investigation of the recombination products by VOGT and DULOG.     

Prinzipien der Herstellung und Stabilität von Emulsionen

Principles of formation and stability of emulsions. The present state of knowledge concerning the principles of emulsion formation and stability are summarised and new theoretical and experimental results are presented. Also described are the characteristic features of the most common types of machines used for emulsification and the mechanics of droplet disruption in laminar and turbulent flow as well as cavitation. In laminar flow, the minimum droplet size is theoretically determined by the shear stress and regulated by a critical Weber number, provided that the particular emulsifier can rapidly occupy sites on the newly formed interface. If this occupation is inhibited, than only larger droplets can be formed. The upper size limit can be calculated from kinetic considerations. The second part of the paper addresses the fundamentals of emulsion stability and the emulsifier's influence on interactions between dispersed droplets. A way of describing the state of the droplets in an emulsion at rest using a population balance theory is also discussed.     

Inline‐Bestimmung der CO2‐Beladung von wässrigem Diglykolamin in Abhängigkeit von Viskosität und Temperatur

The solvents CO₂ loading is an important factor when evaluating the efficiency of an absorption/desorption process. There is almost no possibility to measure the CO₂ loading inline. Therefore experiments were made to determine a correlation between the CO₂ loading and the solvents viscosity as well as the solvents temperature. The correlation was verified using control tests and values from the literature. An overall maximum relative error under 10 % could be observed. Simultaneously investigations were made to understand if the solvents electrical conductivity and pH value are suitable for a similar correlation.     

Substituentenabhängigkeit der Photoleitung von Arylaminen

Dependence on the Substituents of the Photoconduction from Arylamines Aromatic amines are often used as charge transporting agents in electrophotographic two-layer-systems. Structure-property-relations of this substance class are discussed on the basis of homogeneously sensitized polycarbonat-layers containing derivatives of anilines. Substituent variation of the actinic compounds has a significant influence on the electrophotographic sensitivity. Correlations between Hammett substituents constants and electrophotographic sensitivity are useful for the preselection of arylamin structures. Dibenzylamino groups lie out of these correlations and induce an unexpected high photoconductivity. This fact was investigated by cyclovoltammetric measurements of 22 various dibenzylanilines. Low half-peakpotentials and reversible one-electron oxidation steps of dibenzylanilines are necessary for outstanding photoconductor properties.     

Die Ausnutzung von Gesamtfettsäuren und Calcium von gesunden Säuglingen im 1. Lebensvierteljahr in Abhängigkeit vom Fettsäuren-Gehalt und von der Fettsäuren-Zusammensetzung in Milchmischungen

Utilization of Mixed Fatty Acids and Calcium by Healthy Sucklings in the First Quarter Year of Their Life in Relation to the Fatty Acid Content and the Fatty Acid Composition of the Milk Mixtures The daily utilization of calcium and mixed fatty acids by 43 healthy sucklings from 4^th till 90^th day of their life is reported. The sucklings received the usual cow milk mixtures with different fat contents and varying fatty acid compositions. It is shown that the calcium utilization by the new-borns and young sucklings is, even on feeding with mother's milk, lower than in the later infant age. Furthermore, a statistically proved relationship is shown to exist between the level of fat content as well as the fatty acid spectrum of the feed and the calcium utilization.