Mechanisch stabile und umweltfreundliche Polymer/Partikel Komposite für den Einsatz als low-fouling Beschichtung im marinen Sektor

In this work, novel ecofriendly and durable marine antifouling coatings on the basis of a two-component thermoset polythiourethane (PTU) have been developed. Mechanical and chemical properties with respect to stoichiometric component-variations were evaluated and long-term immersion experiments were done in the Baltic sea. Enhanced tensile strength and adhesion was obtained by incorporation of 5 wt.% tetrapodal-shaped ZnO (t-ZnO). Contact angle measurements revealed an impact of t-ZnO incorporation on the surface free energy. Preliminary immersion experiments show the reduction of marine fouling as a result of increasing t-ZnO incorporation and based on these results, long-term field experiments were realized. Rresidue-free clean-ability was demonstrated after 12 months. Further, silicone was reinforced by t-ZnO and tensile strengthening as function of increasing filler amount was shown. Immersion experiments demonstrated reduced fouling compared to PTU, but cleaning caused significant damages. Consequently, fouling-release properties of silicones were combined with mechanical features of PTU. The increase in tensile strength of PTU/silicone composites was shown as function of t-ZnO filler content. Surface characteristics demonstrated the formation of silicone microdomains on the surface of the composites embedded into the PTU matrix. The wetting behavior underlined the retention of the silicones surface properties. Immersion results from seawater and subsequent cleaning showed convincing easy-to clean features for all PTU/silicone composites. On the other hand, those samples immersed into freshwater demonstrate self-cleaning properties for composites filled with ZnO particles of arbitrary morphology.In dieser Arbeit wurden neuartige umweltfreundliche maritime Antifoulingbeschichtungen auf Basis des zweikomponentigen Duroplasten Polythiourethane (PTU) entwickelt. Die mechanischen und chemischen Eigenschaften bezüglich stöchiometrischer Komponentenvariationen wurden evaluiert, Langzeitfeldversuche wurden in der Ostsee durchgeführt. Erhöhte Zugfestigkeit sowie Adhäsion konnte durch das Hinzufügen von 5 Gew.% tetrapodalem ZnO (t-ZnO) erreicht werden. Kontaktwinkelmessungen zeigten einen Einfluss der Partikel auf die freie Oberflächenenergie. Vorläufige Immersionstests demonstrierten reduzierten Bewuchs mit zunehmendem Gehalt an t-ZnO, weshalb Langzeitexperimente hinzugenommen wurden. Rückstandsfreie Reinigung der Proben nach 12-monatiger Immersion wurde gezeigt. Weiterhin wurde Silicon mit t-ZnO verstärkt und eine Erhöhung der Zugfestigkeit als Funktion des Partikelgehalts wurde gezeigt. Immersionstests zeigten im Vergleich zu PTU reduzierten Bewuchs, allerdings führten die Reinigungsversuche zu starken Beschädigungen der Oberflächen. Daraus resultierend wurden die fouling-release Eigenschaften von Silikon mit den vorteilhaften mechanischen Eigenschaften von PTU vereint. Die Zunahme der Zugfestigkeit als Funktion des Partikelgehalts wurde aufgezeigt. Charakterisierungen der Oberfläche verdeutlichten in PTU eingebettete Silikondomänen auf den Probenoberflächen. Kontaktwinkelmessungen zeigten, dass die Oberflächeneigenschaften von Silikon in dem Komposit PTU/Silikon vorherrschten. Immersionstests aus der Ostsee und anschließendes Reinigen der Proben zeigte hervorragende easy-to-clean-Eigenschaften für alle PTU/Silikon-Komposite. Zusätzlich zeigten die in Süßwasser eingebrachten Proben Selbstreinigungseigenschaften für mit ZnO gefüllte PTU/Silikon-Komposite

Preventing algae adhesion using lubricant-modified polydimethylsiloxane/polythiourethane nanocomposite

To meet the need for an environmentally friendly fouling-release coating with high mechanical strength and good adhesion to substrates, a four-component nanocomposite was developed by a simple and industrially applicable blending approach. The nanocomposite consists of mechanically stable matrix polythiourethane (PTU), 1 wt% low surface free energy and rubber-like polydimethylsiloxane (PDMS), 1 wt% lubricant silicone oil, and 1 wt% tetrapodal shaped micro-nano ZnO (t-ZnO) filler particles, hereafter named PPZO. The rubber-like PDMS formed microdomains at the PTU/air interface, while silicone oil was distributed between the PDMS microdomains. The tensile strength of PPZO nanocomposite was approximately 63 MPa, two to four hundred times higher than the tensile strength of previously reported oil-modified coatings. The adhesion strength of PPZO to the substrate was 30 times higher than that of pure PDMS. After a five-month dynamic field test, the PPZO surface revealed much less biofouling than the references (AlMg3 and PTU), confirming its long-term biofouling control property. The attached algae on PPZO could easily and completely be removed by gentle brush cleaning. The good biofouling control property of PPZO can be attributed to the increased water repellency (signified by the increased water contact angle) and the surface slippage by silicone oil incorporation

Identification and characterisation of enteroaggregative Escherichia coli subtypes associated with human disease

Enteroaggregative E. coli (EAEC) are a major cause of diarrhoea worldwide. Due to their heterogeneity and carriage in healthy individuals, identification of diagnostic virulence markers for pathogenic strains has been difficult. In this study, we have determined phenotypic and genotypic differences between EAEC strains of sequence types (STs) epidemiologically associated with asymptomatic carriage (ST31) and diarrhoeal disease (ST40). ST40 strains demonstrated significantly enhanced intestinal adherence, biofilm formation, and pro-inflammatory interleukin-8 secretion compared with ST31 isolates. This was independent of whether strains were derived from diarrhoea patients or healthy controls. Whole genome sequencing revealed differences in putative virulence genes encoding aggregative adherence fimbriae, E. coli common pilus, flagellin and EAEC heat-stable enterotoxin 1. Our results indicate that ST40 strains have a higher intrinsic potential of human pathogenesis due to a specific combination of virulence-related factors which promote host cell colonization and inflammation. These findings may contribute to the development of genotypic and/or phenotypic markers for EAEC strains of high virulence

Identification and characterisation of enteroaggregative Escherichia coli subtypes associated with human disease

Enteroaggregative E. coli (EAEC) are a major cause of diarrhoea worldwide. Due to their heterogeneity and carriage in healthy individuals, identification of diagnostic virulence markers for pathogenic strains has been difficult. In this study, we have determined phenotypic and genotypic differences between EAEC strains of sequence types (STs) epidemiologically associated with asymptomatic carriage (ST31) and diarrhoeal disease (ST40). ST40 strains demonstrated significantly enhanced intestinal adherence, biofilm formation, and pro-inflammatory interleukin-8 secretion compared with ST31 isolates. This was independent of whether strains were derived from diarrhoea patients or healthy controls. Whole genome sequencing revealed differences in putative virulence genes encoding aggregative adherence fimbriae, E. coli common pilus, flagellin and EAEC heat-stable enterotoxin 1. Our results indicate that ST40 strains have a higher intrinsic potential of human pathogenesis due to a specific combination of virulence-related factors which promote host cell colonization and inflammation. These findings may contribute to the development of genotypic and/or phenotypic markers for EAEC strains of high virulence

Towards sustainable micro and nano composites from fly ash and natural fibers for multifunctional applications

Manufacturing of petroleum based synthetic materials, exploitation of timber products from forest reserves, improper management of industrial wastes and natural resources greatly persuade the environmental contaminations and global warming. To find viable solutions and reduce such alarming issues, innovative research work on recycling of unutilized materials such as fly ash and natural cellulosic polymers has been reported in this work to develop advanced sustainable hybrid micro/nano composites. In this study, the use of natural cellulosic sisal fibers with fly ash has enhanced the tensile properties and surface finish of composites. Fly ash particulates acted as fillers, additives, as well as surface-finishing medium and sisal fibers as reinforcing elements in achieving glossy finish sustainable composites. The developed composites have been found to be stronger than wood, plastics and have many opportunities for multifunctional applications

Multifunctional Materials: A Case Study of the Effects of Metal Doping on ZnO Tetrapods with Bismuth and Tin Oxides

Hybrid metal oxide nano‐ and microstructures exhibit novel properties, which make them promising candidates for a wide range of applications, including gas sensing. In this work, the characteristics of the hybrid ZnO‐Bi2O3 and ZnO‐Zn2SnO4 tetrapod (T) networks are investigated in detail. The gas sensing studies reveal improved performance of the hybrid networks compared to pure ZnO‐T networks. For the ZnO‐T‐Bi2O3 networks, an enhancement in H2 gas response is obtained, although the observed p‐type sensing behavior is attributed to the formed junctions between the arms of ZnO‐T covered with Bi2O3 and the modulation of the regions where holes accumulate under exposure to H2 gas. In ZnO‐T‐Zn2SnO4 networks, a change in selectivity to CO gas with high response is noted. The devices based on individual ZnO‐T‐Bi2O3 and ZnO‐T‐Zn2SnO4 structures showed an enhanced H2 gas response, which is explained on the basis of interactions (electronic sensitization) between the ZnO‐T arm and Bi2O3 shell layer and single Schottky contact structure, respectively. Density functional theory‐based calculations provide mechanistic insights into the interaction of H2 and CO gas molecules with Bi‐ and Sn‐doped ZnO(0001) surfaces, revealing changes in the Fermi energies, as well as charge transfer between the molecules and surface species, which facilitate gas sensing