Kelly A.M.,Polymer Competence Center Leoben |
Wiesbrock F.,University of Graz
Macromolecular Rapid Communications | Year: 2012
Poly(2-oxazoline)-based networks currently receive great interest due to their versatile properties that can be tailor made by desktop-planned modifications. This feature summarizes strategies for the preparation of these networks, comprising the in situ cross-linking as well as polymer-analogous cross-linking routines such as (reversible) complex formation, physical processes, and covalent bond formation (involving reactions with olefinic species as well as with epoxides, isocyanates, aldehydes, acids, and their derivatives). Reflecting prominent application examples in the biomedic(in)al sector, poly(2-oxazoline)-co-polyester networks are described in a dedicated section. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Frank A.,Polymer Competence Center Leoben |
Pinter G.,University of Leoben
Polymer Testing | Year: 2014
Several tests methods are available for the characterization of the slow crack growth (SCG) resistance of polyethylene (PE) for pipe applications. Unfortunately, due to the increase of the SCG resistance of modern PE pipe grades, these test methods are exceeding practical time frames so that new test methods for accelerated and reliable material ranking are required. The Cyclic CRB Test was proposed as a promising test method for a quick material ranking of PE pipe grades by their SCG resistance, even at ambient temperatures. In this, paper different studies about the Cyclic CRB Test are summarized. On the one hand, the results show the potential for a quick and reliable material ranking at ambient temperatures within only a couple of days, even for modern PE 100-RC grades. On the other hand, results of two Round Robin Tests will be discussed. The presented results demonstrate high reproducibility and reliability of the Cyclic CRB Test in terms of material ranking by SCG resistance. © 2013 Elsevier Ltd. All rights reserved.
Schlogl S.,Polymer Competence Center Leoben |
Trutschel M.-L.,Martin Luther University of Halle Wittenberg |
Chasse W.,Martin Luther University of Halle Wittenberg |
Riess G.,University of Leoben |
Saalwachter K.,Martin Luther University of Halle Wittenberg
Macromolecules | Year: 2014
This Perspective highlights how entanglement effects on rubber elasticity can be unveiled by a combination of different macroscopic and microscopic methods, taking advantage of new developments in proton low-field NMR spectroscopy as applied to bulk and swollen rubbers. Specifically, the application of a powerful yet routinely applicable double-quantum method, combined with a back-extrapolation procedure over results measured at different degrees of swelling, allows one to characterize the recently introduced "phantom reference network" state, which only reflects contributions of actual cross-links and topologically trapped entanglements. We further present an assessment of the qualitative yet popular Mooney-Rivlin analysis of mechanical data, where the influence of entanglement contributions on the fitted, purely empirical parameters C1 and C2 is reconsidered in the context of different tube models of rubber elasticity. We also review the impact of entanglements on results of equilibrium swelling experiments and address the validity of the common Flory-Rehner approach, where we stress its qualitative nature and the need to use NMR observables for a correct estimation of the relevant volume fractions. We discuss semiquantitative estimations of the cross-link density from these macroscopic experiments with its microscopic determination by NMR on the example of lowly cross-linked synthetic and natural poly(isoprene) rubber prepared by a novel UV-based curing protocol of dried latex based upon thiol-ene chemistry, which in contrast to previously studied thermally peroxide-cured natural rubber contain only small amounts of short-chain defects. We find that the entanglement effects in these samples can best be described by the Heinrich-Straube tube model with positive scaling exponent ν > 0.3 as well as by the slip-link model of Ball et al./Edwards-Vilgis with a slip parameter η > 0.1. A comparison with literature results demonstrates that these findings are not universal in that the apparent entanglement contribution depends significantly on the sample (in)homogeneity, i.e., of the NMR-determined fraction of inelastic defects and spatial cross-linking inhomogeneities. This means that conclusions on the validity or invalidity of specific tube theories cannot be drawn without careful consideration of the network microstructure. © 2014 American Chemical Society.
Koller M.,University of Graz |
Muhr A.,University of Graz |
Muhr A.,Polymer Competence Center Leoben |
Braunegg G.,ARENA Arbeitsgemeinschaft fur Ressourcenschonende und Nachhaltige Technologien
Algal Research | Year: 2014
As major part of the phytoplankton, microalgae are pivotal for the global food chain. Their exceptional capacity for CO2-fixation illustrates their indispensable significance to sustain earth's ecosystems. Further, they play a still underestimated role in eliminating contaminants from various environments. In addition to ecological benefit, many microalgal species exhibit high nutritional value and, at the same time, generate valued bio-products: Pigments, lipids, bioactive compounds, certain polysaccharides, bio-hydrogen and even biopolyesters with plastic-like properties have the potential for successful market penetration.Three substantial pigment groups, namely chlorophylls, carotenoids, and phycobilins, are essential for light harvesting and CO2 fixation. Those pigments will most likely undergo quick commercial success in "functional food", cosmetics, aquaculture, pharmaceuticals, or food technology.Due to often high contents of polyunsaturated fatty acids essential for human metabolism, microalgal oils can be commercialized as health food and in the pharmaceutical and therapeutic field, creating much higher value than by converting them to biofuel.Finally, algal biomass remaining as residue after product recovery can be used as forage, biogas feedstock or biofertilizer. This utilization is needed for balancing the material- and energy cycles of the entire process. Thus, technology platforms following the principles of bio-refineries shall be established to enable the design of sustainable and economically feasible production of marketable microalgal products. © 2014 Elsevier B.V.
Likozar B.,Polymer Competence Center Leoben |
Likozar B.,University of Ljubljana
Soft Matter | Year: 2011
In order to achieve good morphological, mechanical, structural, and thermal properties of a polymer electrolyte, ionic-liquid-in-polymer electrolytes have been explored. It was found that 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, and 1-butyl-1-methylpyrrolidinium tetrafluoroborate (EMImBF 4, BMImBF 4, and BMPyBF 4), hexafluorophosphate (EMImPF 6, BMImPF 6, and BMPyPF 6), and bis(trifluoromethylsulfonyl)imide (EMImTFSI, BMImTFSI, and BMPyTFSI) in hydroxy-functionalized multi-walled carbon nanotubes (MWCNT-OH) reinforced hydrogenated poly(acrylonitrile-co-1,3-butadiene) (HNBR) produce homogeneous solids. HNBR/MWCNT-OH/ionic liquid solid electrolytes were prepared by melt compounding of the nanotubes in the elastomer, mixing with curing system, curing, and immersion in the ionic liquid. Cross-linked with 12.9 wt% of the curing system (per total composite weight prior to ionic liquid sorption), these HNBR-based electrolytes displayed elastomeric properties and high tensile strength (up to 24 MPa). HNBR/MWCNT-OH/ionic liquid composites had the elongation at break up to 378% (BMPyTFSI) at the room temperature and ionic liquid concentrations up to 18 wt% (BMImTFSI). Thermal analysis showed that the T g of HNBR/MWCNT-OH/ionic liquid systems decreased as a function of increasing ionic liquid content at the constant polymer content in a composite. © 2011 The Royal Society of Chemistry.