Search

Die Vielseitigkeit von Papierprodukten gründet sich darauf, dass bei der Herstellung eine große Variation an Rohstoffen und polymeren Additiven verwendet wird. Additive auf Stärkebasis spie-len dabei als Trockenverfestiger und Retentionsmittel eine wichtige Rolle. Durch die Verringerung des Frischwasserverbrauchs und die ansteigende Verwendung von Altpapierfaserstoffen im Papierherstellungsprozess reichern sich Störstoffe im Prozesswasser an und das häufige Recyceln führt zu einer Verschlechterung des Festigkeitspotentials der Faserstoffe. Der Einsatz kationischer Stärke muss daher auf die verwendeten Rohstoffe, die Wasserqualität und die Prozessführung abgestimmt werden, um die angestrebten Papierfestigkeiten zu erreichen. Die vorliegende Arbeit beschäftigt sich mit den wechselseitigen Beeinflussungen von kationischen Stärkederivaten und synthetischen Polykationen bei der Adsorption an Faserstoffen. Un-tersuchungen bezüglich der Wechselwirkungen zwischen kationischen Stärken und anionischen Störstoffen sind ebenfalls Gegenstand der Arbeit. Der Einfluss von Stärkeparametern (Stärkeart, DS-Wert und Amylosegehalt), der Konstitution des synthetischen Polykations, von Prozesspara-metern (Adsorptionszeit und Dosierreihenfolge) sowie von Faserstoffart und Elektrolytgehalt des Prozesswassers wurden untersucht. Es wurde festgestellt, dass die Adsorption von kationischen Stärken an Füllstoffen trotz erhöhtem Elektrolytgehalt im Wasser anstieg. Synthetische Polykationen hatten einen negativen Einfluss auf die Stärkeadsorption und auf die Papierfestigkeit. Je höher die Ladungsdichte des synthetischen Polykations war, desto niedriger waren die adsorbierten Stärkemengen. Die Dosierreihenfolge der Additive beeinflusste die Stärkeadsorption ebenfalls signifikant. Die Zugabe der Stärke vor den synthetischen Polykationen reduzierte den negativen Einfluss auf die Stärkeadsorption und Papierfestigkeit. Beim Vergleich des Adsorptionsverhaltens der verwendeten Stärken wurde deutlich, dass mit Kartoffelstärke (DS=0.065) höhere Adsorptionsmengen erreicht wurden als mit allen anderen kationischen Stärken. Dieses Verhalten war unabhängig vom synthetischen Polykation, vom Faserstoff und von der Wasserqualität zu beobachten. Eine Korrelation zwischen adsorbierter Stärkemenge und resultierender Papierfestigkeit konnte nur begrenzt hergestellt werden. Die Zugabe von synthetischen Polykationen hatte jedoch einen signifikanten Einfluss auf die Füllstoffretention, den Formationsindex und die Entwässerung. Mittels Transmissionsmessungen, Partikelgrößenanalytik und mikroskopischen Aufnahmen wurde die Polyelektrolytkomplexbildung sowie die Aggregation zu makroskopischen Flocken infolge der Wechselwirkungen zwischen kationischen Stärken und anionischen Modellstörstoffen untersucht. Die Entwicklung der Trübung war zeitabhängig und wurde signifikant vom anwesenden Störstoff beeinflusst. Der Trübungswert der Lösung korrelierte mit der Größe, Menge und Ladung der gebildeten Flocken. Der maximale Trübungswert wurde bei neutralen Polyelektrolytkomplexen erreicht. Die Anwesenheit von anionischen Störstoffen steigerte den Aschegehalt und die Festigkeiten von Laborblättern. Die Praxisrelevanz der ermittelten Zusammenhänge konnte an ausgewählten Dosierempfehlungen im Technikumsversuch größtenteils bestätigt werden., The versatility of paper products is due to the usage of various raw materials and polymeric addi-tives. Additives based on modified starches play an important rule as a dry strength or retention aid. The decrease of fresh water wastage and the increasing usage of recycled paper in the paper production cause trash compound concentration and every recycling step results in a degradation of paper strength. The dosage of cationic starch has to be fine tuned relating to the used fiber, the water quality and the production process in order to achieve the desired paper properties. This work deals with the interaction between cationic starches and synthetic polycations regard-ing to their adsorption behaviour on cellulosic fibers. Investigations about the interaction be-tween cationic starches and anionic trash compounds are also included. The influences of starch parameters (starch origin, degree of substitution and amylose content), the constitution of syn-thetic polycation, the process parameters (adsorption time and dosage order), the fiber origin and water quality were also investigated. It has been found out, that the adsorbed amounts of cationic starch onto fillers increased alt-hough the amount of electrolytes in the water rose. Synthetic polycations had a negative influ-ence on the starch adsorption and the paper strength. The higher cationic charge of the synthetic polycation the less starch adsorption was found. The dosage order also impacted the starch adsorption significantly. The application of cationic starch before the synthetic polycation re-duced the negative influence on the starch adsorption and paper strength. Comparing all the used starches it has been found out, that cationic potato starch (DS=0.065) was less influenced by synthetic polycations than all other cationic starches. This dependency was discovered independ-ent to the used synthetic polycation, the fiber type and the water quality. A Correlation between adsorbed starch amount and resulting paper strength could not be estab-lished in all experiments. The application of synthetic polycation had a significant influence on the filler retention, the formation of the paper and the drainage rate. With transmission measurements, particle analysis and microscopic viewing it was possible to characterize the PEC and floc formation because of the interaction of cationic starches and anionic trash compounds. The development of the turbidity in solution was time dependent and was controlled by the trash compound. The value of turbidity correlated with the size, the amount and the charge of the flocs. The maximum of turbidity was achieved with neutral polyelectrolyte complexes. The attendance of anionic trash compounds increased the filler retention and paper strength of laboratory sheets. The relevancy for practice of the results was tested and mostly confirmed on a pilot plant paper machine.

The current state of knowledge in the field of synthesis and properties of polyglycerols and polyglycerol fatty acid esters is presented. Alternatives for the analytical characterization of these families by means of physico-chemical methods, with special reference to chromatography and spectroscopy, are described. Furthermore, the use of polyglycerol fatty acid esters as food additives is considered from the view-points of the physiology of nutrition and of processing technology.

The node-and-spacer approach is widely employed in crystal engineering to construct coordination polymers. It consists of self-assembly processes involving mononuclear cationic species and exo-dentate ligands. We enlarged this strategy using preformed homo- and heterometallic complexes as nodes. The presence of two or more metal ions within a node leads to novel network topologies, as well as to new properties, arising from the intra- and internode interactions. This paper reviews some representative examples of coordination polymers obtained in our laboratory and constructed from: i) binuclear alkoxo-bridged complexes; ii) heterometallic 3d-3d' and 3d-4f complexes.

Biomedical microsystems attain to contact with environments like blood, ephitHelium and saline solutions therefore they need an encapsulation. Parylene seems to be a suitable polymer to cover the implants and protect them against moisture and aggressive environment. This paper describes the characterisation of Parylene C coatings and its possibilities to protect implants. Beside the encapsulation of biomedical microsystems the manufacturing of fexible electrodes and the cytotoxicity behavior of RIE etched Parylene layers was investigated.

In the present paper a technique is demonstrated wherein the closure of the pancreatic remnant following left pancreatectomy with absorbable staples was performed. The good results with minimal complications recommend this method.

The author in his present paper reports a program of comparative materials testing of which the purpose was to assess the value of positive pressure polymerization of thermosets. This particular program required polymerization temperature measurements. K-value determinations, and cone indentation hardness tests to be made on samples of plastic material polymerized under positive liquid or steam pressure and in cuvets, respectively, the conditions of polymerization being those which are used in actual practice. The results obtained indicated a favorable influence of positive liquid pressure polymerization on the final hardness of the plastic material.

The traditional theories of senile cataract formation have one common denominator. Nearly all the agents and factors heretofore ascribed as causes of cataract formation have some element involving a potent crosslinking agent. The factors considered in this paper include endocrine and metabolic factors, involutional and hereditary influences, nutritional deficiencies, osmotic changes, ionizing radiation, ultraviolet light, altered capsular permeability, and the cumulative effects of subliminal exposure to noxae. Throughout life, the human lens is exposed to the influence of numerous potent crosslinking agents and it now appears that the cumulative actions of crosslinkage is the chief cause of senile cataracts. If this theory proves to be correct, it will offer some hope that cataract formation can be retarded by agents which counteract crosslinkage or by avoidance of excessive exposure to crosslinking agents.

This paper describes a method of measuring the porosity, shape, distribution and formation of cavities in acrylic cement. We distinguish between big spherical cavities greater than 60 mu and small cavities less than 60 mu which form a variable "basic porosity" with a large number, but a minor volume of bubbles. The bubbles are formed in two different ways. The first is through introduction of air bubbles in the mixing phase by stirring the cement before the working time. These bubbles expand little by temperature rise. The second method of formation is through neoformation of bubbles by evaporation of the monomer at about 100 degrees C. This neoformation of porosity expands the cement. The rise of volume through the neoformation and expansion of bubbles is able to compensate the shrinking of cement due to the polymerization. This effect, however, cannot be currently controlled. Cement strength is influenced by the degree of porosity.

Cold polymerizates "Kallocryl K" and "Palacos" were characterized by means of physico-chemical methods of examination. The residual monomer content of the polymerizates, which is of major toxicological interest, was also determined quantitatively. It was possible to show that the residual monomer content decreases exponentially as a function of the duration of polymerization. "Palacos" polymerizates had much higher residual monomer contents than "Kallocryl K" polymerizates when the same time of polymerization was used. Also discussed in this paper are possible methods of reducing the residual monomer content prior to implantation of the plastic materials.