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

Dangling-End Double Networks: Tapping Hidden Toughness in Highly Swollen Thermoplastic Elastomer Hydrogels

This report introduces a unique method of significantly improving toughness in highly swollen block copolymer-based thermoplastic elastomer (TPE) hydrogels by converting an intrinsically large population of dangling chain ends into a mechanically active second network. In one form, the TPE hydrogels developed by our group are based on swelling of a vitrified melt-blend of two amphiphilic block copolymer species, sphere-forming polystyrene-poly­(ethylene oxide) (SO-H) diblock and triblock (SOS) copolymers. Here, the PEO midblock in the SOS triblock copolymer serves to tether adjacent PS spherical aggregates, producing hydrogel networks that are incredibly elastic and mechanically robust, preserving their shape even at the very high intrinsic swelling ratios produced at low SOS concentrations (e.g, 37 g of H₂O/(g of polymer) at 3.3 mol % SOS). In this report, we advance the utility of this framework by exploiting the hundreds of dangling PEO chain ends per spherical aggregate to form a second, mechanically active network. The approach is based on a stepwise installation of two tethering SOS triblock copolymer populations. The first is present directly during <i>melt-state</i> self-assembly of the original diblock/triblock copolymer blend and inherently determines the equilibrium swelling ratio of resulting hydrogel. The second population is then introduced <i>postswelling</i>, by simply coupling the dangling SO diblock copolymer chain ends under conditions largely free of the mechanical stress osmotically imposed on the primary network. Notably, this action simply shifts the ratio of diblock and triblock copolymer without compromising the thermoplasticity of the network. Here, we use the facile water-based coupling of PEO-terminal azide and alkyne groups to demonstrate the scale of toughness enhancements possible through conversion of dangling ends into a second network. The dangling-end double networks produced exhibit remarkable improvements in tensile properties (tensile modulus, toughness, strain at break, and stress at break), including a 58-fold increase in mean toughness (to 361 kJ/m³) and a 19-fold increase in mean stress to break (to 169 kPa) in highly swollen samples containing up to 95% (g/g) water. Importantly, these improvements could be realized without altering water content, shape, small-strain dynamic shear, and unconfined compressive properties of the original TPE hydrogels

Interaction between PEO–PPO–PEO Copolymers and a Hexapeptide in Aqueous Solutions

Interaction between PEO–PPO–PEO copolymers and a hexapeptide, growth hormone releasing peptide-6 (GHRP-6), was investigated by NMR to study the potential use of the copolymers in peptide drug delivery. ¹H NMR and nuclear Overhauser effect spectroscopy (NOESY) measurements determined that PO methyl protons interacted with methyl protons of the Ala moiety, aromatic protons of the Trp moiety, and some of the Phe aromatic protons. The Lys moiety and part of the Phe moiety entered the hydrophilic EO environment via hydrogen bonding. PEO–PPO–PEO copolymers and the peptide formed a complex in 1:1 stoichiometry. Binding constants between copolymers and GHRP-6 were determined, and it was indicated that the copolymers containing more EO and PO units will lead to greater affinity with the peptide. Isothermal titration calorimetry (ITC) measurements confirmed the results of NMR experiments. This study indicates that PEO–PPO–PEO copolymers have great potential in delivering peptide drugs

Two new <i>ent</i>-atisanes from the root of <i>Euphorbia fischeriana</i> Steud.

<div><p>Two new <i>ent</i>-atisanes <i>ent</i>-1β,3β,16β,17-tetrahydroxyatisane (<b>1</b>), <i>ent</i>-1β,3α,16β,17-tetrahydroxyatisane (<b>2</b>) together with 11 known diterpenes were isolated from the anti-tumour activity fraction of <i>Euphorbia fischeriana</i> Steud. The compounds were identified by detailed spectroscopic analysis, including extensive 2D-NMR experiments. X-ray analysis was applied to determine the structure of compound <b>2</b>. All 13 compounds were screened for cytotoxicity <i>in vitro</i> against human tumour MCF-7, HepG-2 and SGC-7901 cell lines. Compounds <b>1</b> and <b>2</b> showed the inhibitory effects against MCF-7 with IC₅₀ levels of 23.21 and 15.42 μM; simultaneously, compounds <b>4</b>, <b>6</b>, <b>8</b> and <b>11</b> also had definite inhibitory effect against different cell lines.</p></div

Magnetic Flocculant for High Efficiency Harvesting of Microalgal Cells

Magnetic flocculant was synthesized for the highly efficient recovery of microalgal cells. The highest flocculation was achieved using the magnetic flocculant synthesized with iron oxide and 0.1 mg/mL cationic polyacrylamide (CPAM). This resulted in a recovery efficiency of more than 95% within 10 min using a dosage of 25 mg/L for <i>Botryococcus braunii</i> and 120 mg/L for <i>Chlorella ellipsoidea</i>. For both species, the adsorption isotherm data fit the Freundlich model better than the Langmuir model, indicating that the adsorption process was a heterogeneous multilayer. The maximum adsorption capacity was 114.8 and 21.4 mg dry cells/mg-particles at pH 7 for <i>B. braunii</i> and <i>C. ellipsoidea</i>, respectively. The primary flocculation mechanism was bridging, which was assisted by the electrostatic interactions between the microalgal cells and the magnetic flocculant under acidic conditions. These results provide new opportunities and challenges for understanding and improving the harvesting of microalgae using magnetic separation

Initial Reduction of CO₂ on Pd‑, Ru‑, and Cu-Doped CeO₂(111) Surfaces: Effects of Surface Modification on Catalytic Activity and Selectivity

Surface modification by metal doping is an effective treatment technique for improving surface properties for CO₂ reduction. Herein, the effects of doped Pd, Ru, and Cu on the adsorption, activation, and reduction selectivity of CO₂ on CeO₂(111) were investigated by periodic density functional theory. The doped metals distorted the configuration of a perfect CeO₂(111) by weakening the adjacent Ce–O bond strength, and Pd doping was beneficial for generating a highly active O vacancy. The analyses of adsorption energy, charge density difference, and density of states confirmed that the doped metals were conducive for enhancing CO₂ adsorption, especially for Cu/CeO₂(111). The initial reductive dissociation CO₂ → CO* + O* on metal-doped CeO₂(111) followed the sequence of Cu- > perfect > Pd- > Ru-doped CeO₂(111); the reductive hydrogenation CO₂ + H → COOH* followed the sequence of Cu- > perfect > Ru- > Pd-doped CeO₂(111), in which the most competitive route on Cu/CeO₂(111) was exothermic by 0.52 eV with an energy barrier of 0.16 eV; the reductive hydrogenation CO₂ + H → HCOO* followed the sequence of Ru- > perfect > Pd-doped CeO₂(111). Energy barrier decomposition analyses were performed to identify the governing factors of bond activation and scission along the initial CO₂ reduction routes. Results of this study provided deep insights into the effect of surface modification on the initial reduction mechanisms of CO₂ on metal-doped CeO₂(111) surfaces

Methanol Oxidation on Pt₃Sn(111) for Direct Methanol Fuel Cells: Methanol Decomposition

PtSn alloy, which is a potential material for use in direct methanol fuel cells, can efficiently promote methanol oxidation and alleviate the CO poisoning problem. Herein, methanol decomposition on Pt₃Sn­(111) was systematically investigated using periodic density functional theory and microkinetic modeling. The geometries and energies of all of the involved species were analyzed, and the decomposition network was mapped out to elaborate the reaction mechanisms. Our results indicated that methanol and formaldehyde were weakly adsorbed, and the other derivatives (CH_<i>x</i>OH_<i>y</i>, <i>x</i> = 1–3, <i>y</i> = 0–1) were strongly adsorbed and preferred decomposition rather than desorption on Pt₃Sn­(111). The competitive methanol decomposition started with the initial O–H bond scission followed by successive C–H bond scissions, (i.e., CH₃OH → CH₃O → CH₂O → CHO → CO). The Brønsted–Evans–Polanyi relations and energy barrier decomposition analyses identified the C–H and O–H bond scissions as being more competitive than the C–O bond scission. Microkinetic modeling confirmed that the vast majority of the intermediates and products from methanol decomposition would escape from the Pt₃Sn­(111) surface at a relatively low temperature, and the coverage of the CO residue decreased with an increase in the temperature and decrease in partial methanol pressure

Additional file 1 of Comparison of intestinal flora between patients with chronic and advanced Schistosoma japonicum infection

Additional file 1: Fig. S1. Shannon curve showed that all samples were saturated

Photocatalytic Tandem Radical Cyclization Enables Expeditious Total Synthesis of Epoxyhinokiol Analogues for Anticancer Activity Evaluation

A photocatalytic radical cascade with an unusual endo-trig cyclization was developed, which enables the efficient assembly of divergent tricyclic diterpenoid frameworks. The first total synthesis of abietane 10-epi-epoxyhinoliol was thus achieved in six steps by a subsequent reductive coupling of i-PrBr under photoredox/nickel dual catalysis. Inhibitory tests of chiral 10-epi-epoxyhinoliol and its analogues in 4T1 cancer cells demonstrated the critical role of the C12 hydroxyl group, leading to a discovery of the simplified analogue with better activity

Architecting a Mesoporous N‑Doped Graphitic Carbon Framework Encapsulating CoTe₂ as an Efficient Oxygen Evolution Electrocatalyst

To improve the efficiency of cobalt-based catalysts for water electrolysis, tremendous efforts have been dedicated to tuning the composition, morphology, size, and structure of the materials. We report here a facile preparation of orthorhombic CoTe₂ nanocrystals embedded in an N-doped graphitic carbon matrix to form a 3D architecture with a size of ∼500 nm and abundant mesopores of ∼4 nm for the oxygen evolution reaction (OER). The hybrid electrocatalyst delivers a small overpotential of 300 mV at 10 mA cm^–2, which is much lower than that for pristine CoTe₂ powder. After cycling for 2000 cycles or driving continual OER for 20 h, only a slight loss is observed. The mesoporous 3D architecture and the strong interaction between N-doped graphitic carbon and CoTe₂ are responsible for the enhancement of the electrocatalytic performance