Einfluss der Verarbeitungstechnologie und Werkstoffzusammensetzung auf die Struktur-Eigenschafts-Beziehungen von thermoplastischen Nanoverbundwerkstoffen

Die Einarbeitung von nanoskaligen Füllstoffen zur Steigerung von polymeren Eigenschaftsprofilen ist sehr viel versprechend und stößt daher heutzutage sowohl in der Forschung als auch in der Industrie auf großes Interesse. Bedingt durch ausgeprägte Oberflächen und hohe Anziehungskräfte, liegen Nanopartikel allerdings nicht singulär sondern als Partikelanhäufungen, so genannten Agglomeraten oder Aggregaten, vor. Zur Erzielung der gewünschten Materialverbesserungen gilt es, diese aufzuspalten und homogen in der polymeren Matrix zu verteilen. Bei thermoplastischen Kunststoffen ist die gleichläufige Doppelschneckenextrusion eines der gängigsten Verfahren zur Einarbeitung von Additiven und Füllstoffen. Aus diesem Grund war es Ziel dieser Arbeit, mittels dieses Verfahrens verbesserte Verbundwerkstoffe mit Polyamid 66- und Polyetheretherketon-Matrix, durch Einarbeitung von nanoskaligem Titandioxid (15 und 300 nm), zu generieren. In einem ersten Schritt wurden die verfahrenstechnischen Parameter, wie Drehzahl und Durchsatz, sowie die Prozessführung und damit deren Einfluss auf die Materialeigenschaften beleuchtet. Der spezifische Energieeintrag ist ausschlaggebend zur Deagglomeration der Nanopartikel. Dieser zeigte leichte Abhängigkeiten von der Drehzahl und dem Durchsatz und verursachte bei der Einarbeitung der Partikel keine wesentlichen Unterschiede in der Aufspaltung der Partikel sowie gar keine in den resultierenden mechanischen Eigenschaften. Die Prozessführung wurde unterteilt in Mehrfach- und Einfachextrusion. Die Herstellung eines hochgefüllten Masterbatches, dessen mehrfaches Extrudieren und anschließendes Verdünnen, führte zu einer sehr guten Deagglomeration und stark verbesserten Materialeigenschaften. Mittels Simulation des Extrusionsprozesses konnte festgestellt werden, dass das Vorhandensein von ungeschmolzenem Granulat in der Verfahrenszone zu einer Schmelze/Nanopartikel/ Feststoffreibung führt, die die Ursache für eine sehr gute Aufspaltung der Partikel zu sein scheint. Durch Modifikation des Extrusionsprozesses erreichte die Einfachextrusion annähernd den Grad an Deagglomeration bei Mehrfachextrusion, wobei die Materialien bei letzterem Verfahren die besten Eigenschaftsprofile aufwiesen. In einem zweiten Schritt wurde ein Vergleich der Einflüsse von unterschiedlichen Partikelgrößen und –gehalten auf die polymeren Matrizes vollzogen. Die 15 nm Partikel zeigten signifikant bessere mechanische Ergebnisse auf als die 300 nm Partikel, und die Wirkungsweise des 15 nm Partikels auf Polyetheretherketon war stärker als auf Polyamid 66. Es konnten Steigerungen in Steifigkeit, Festigkeit und Zähigkeit erzielt werden. Rasterelektronenmikroskopische Aufnahmen bestätigten diese Ergebnisse. Eine Berechnung der Plan-Selbstkosten von einem Kilogramm PEEK-Nanoverbundwerkstoff im Vergleich zu einem Kilogramm unverstärktem PEEK verdeutlichte, dass ein Material kreiert wurde, welches deutlich verbesserte Eigenschaften bei gleichem Preis aufweist. Zusammenfassend konnte in dieser Arbeit ein tieferes Verständnis des Extrusionsvorganges zur Herstellung von kostengünstigen und verbesserten Thermoplasten durch das Einbringen von Nanopartikeln gewonnen werden

Using a holistic sustainability framework to support shelter programming in Myanmar

This record includes an extended abstract and MP4 presentation. Presented at the 42nd WEDC International Conference

Curcumin affects gene expression and reactive oxygen species via a PKA dependent mechanism in <i>Dictyostelium discoideum</i>

<div><p>Botanicals are widely used as dietary supplements and for the prevention and treatment of disease. Despite a long history of use, there is generally little evidence supporting the efficacy and safety of these preparations. Curcumin has been used to treat a myriad of human diseases and is widely advertised and marketed for its ability to improve health, but there is no clear understanding how curcumin interacts with cells and affects cell physiology. <i>D</i>. <i>discoideum</i> is a simple eukaryotic lead system that allows both tractable genetic and biochemical studies. The studies reported here show novel effects of curcumin on cell proliferation and physiology, and a pleiotropic effect on gene transcription. Transcriptome analysis showed that the effect is two-phased with an early transient effect on the transcription of approximately 5% of the genome, and demonstrates that cells respond to curcumin through a variety of previously unknown molecular pathways. This is followed by later unique transcriptional changes and a protein kinase A dependent decrease in catalase A and three superoxide dismutase enzymes. Although this results in an increase in reactive oxygen species (ROS; superoxide and H₂O₂), the effects of curcumin on transcription do not appear to be the direct result of oxidation. This study opens the door to future explorations of the effect of curcumin on cell physiology.</p></div

Curcumin reduces catalase A enzyme levels in wild-type cells.

<p>A) Catalase A enzyme specific activity is reduced in curcumin treated cells in a dose dependent manner; B) Reduction in catalase A specific activity is not immediate and takes up to 24 hours to manifest itself, indicating that it is not due to enzyme inhibition; C) Curcumin by itself does not have an effect on the stability of H₂0₂; D) Curcumin by itself does not have a direct effect on the rate of catalase A activity in cell extracts (5 μl of an extract of 2 x 10⁷ cells in 1 ml lysis buffer); and E) Curcumin by itself does not have an effect on the extent of the <i>in vitro</i> catalase A activity (5 μl of an extract of 2 x 10⁷ cells in 1 ml lysis buffer). Error bars represent the standard deviation of the mean. Statistical analyses were carried out using a two-tailed t-test. *p<0.05, **p<0.01, ***p<0.001.</p

Curcumin reduces proliferation and cell viability.

<p>A) Axenically growing AX4 cells were treated with curcumin at the indicated concentrations and cell density was monitored over four days by direct counting with a hemocytometer. B) In separate experiments, viability of curcumin treated cells was assayed by measuring ATP in metabolically active cells using CellTiter-Glo® which measures cell viability. C) Curcumin stability in HL5 growth medium was determined by adding curcumin to medium at the onset of the experiment (0 hours). Flasks were inoculated with cells at time 0, 24 and 48 hours, and each assayed for 72 hours using the CellTiter- Glo® method. Taken together, these results show that curcumin has a lasting inhibitory effect on cell proliferation. Error bars in all figures represent the standard deviation compared to the mean.</p

Heat map of differentially expressed genes following curcumin treatment.

<p><b>A)</b> A differential expression analysis (using baySeq) of the 4 hour samples treated with 0 and 10 μg/ml curcumin (see two red asterisks). The yellow-blue heat map shows the differentially expressed genes at 4 hours. In the heat maps, each row represents the abundance levels of one transcript (scale indicated in the box) and each column represents one condition (time and curcumin concentration). Transcripts that exhibited increased abundance with increased curcumin concentration are clustered above the line (up-regulated), and transcripts that exhibited reduced abundance are clustered below the line (down-regulated). The number of genes in each cluster is indicated. B) Heat map showing differentially expressed genes with at least 3-fold change between 0 and 10 μg/ml curcumin at 4 hours. The above analyses in A) and B) were repeated for 0 and 10 μg/ml samples at 12 hours, C) and D), respectively. E) Heat map showing the expression patterns of the genes that are differentially expressed between untreated and treated (10 μg/ml curcumin) at all time points. Genes that were differentially expressed in the absence of curcumin were subtracted.</p

Curcumin reduces SOD enzyme activity in wild-type cells but not in <i>pkaC</i> null cells.

<p>A) SOD enzyme activity in curcumin treated parental AX4 cells (5 μg/ml and 10 μg/ml) is reduced by nearly half relative to untreated cells. In contrast, there is much less effect on SOD enzyme activity in <i>pkaC</i> null cells treated with curcumin for 24 hours. B) Curcumin has no effect on the rate of generation of superoxide in the assay. P-values are defined in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187562#pone.0187562.g002" target="_blank">Fig 2</a>.</p

The antioxidant NAC affects cells differently than curcumin and does not reverse the oxidant effect of curcumin.

<p>The antioxidant NAC, known to counter the effect of oxidative stress, does not have any effect on cell proliferation of wild-type <i>D</i>. <i>discoideum</i> cells: A) Cell Titer Glo assay and B) direct cell counting. C) NAC did not counter the effect of curcumin on cells treated for 24 hours, indicating that the effect of curcumin on catalase A specific enzyme activity was not directly due to oxidative stress. D) Increased NAC concentrations inhibit cell proliferation at very high concentrations. E) However, these increasing concentrations of NAC still do not counter the effect of cells treated with curcumin for 24 hours. P-values are defined in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187562#pone.0187562.g002" target="_blank">Fig 2</a>.</p

Proposed mechanism of curcumin action.

<p>Curcumin inhibits growth and generates ROS in <i>D</i>. <i>discoideum</i>. Curcumin induced major changes in transcription which included the reduction of catalase A and superoxide dismutase enzyme levels through a PKA mediated pathway. The results of this study suggest that the increase in ROS is not the cause of the decrease in antioxidant enzyme levels, but rather that the decrease in the enzymes results in the increase in ROS levels.</p

Curcumin negatively regulates antioxidant enzyme RNA levels.

<p>Total RNA was prepared from 5×10⁶ axenically growing cells treated with 10 μg/ml curcumin for 24 hours. Transcript levels of the antioxidant enzymes, <i>catA</i>, <i>sodA</i>, <i>sodB</i> and <i>sod2</i> are reduced in cells treated with curcumin. P-values are defined in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187562#pone.0187562.g002" target="_blank">Fig 2</a>.</p