Scientific publications

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Title	Year
Characterisation of polyolefins used for Extrusion Coating via non-linear rheological methods 2011, Elke Pachner, Susana Filipe. Characterisation of polyolefins used for Extrusion Coating via non-linear rheological methods TAPPI PLACE Conference 2011 Bregenz, - (-), 2011, - The appropriate characterisation of polymers suitable for extrusion coating is still one of the main challenges faced by polyolefin producers. The understanding of the links between molecular structural properties and end performance requires the development and use of sophisticated analytical methods. Within this work a series of different industrial polypropylene and polyethylene based systems will be analysed with respect to their rheological behaviour under both shear and extensional flows. The molecular structural characterisation of these systems will be done resorting to novel non-linear rheological parameters, which retrieve both a semi-qualitative and semi-quantitative description of the molecular topology. The analysis will include Large Amplitude Oscillatory Shear (LAOS), uniaxial extensional flow and rheotens measurements. It will be shown that, regardless of the technique used, all non-linear rheological parameters are sensitive to both amount and type of long chain branching, in polyethylene as well as polypropylene based materials. printme	2011
New Concepts for Impact Modification of Polypropylene 2011, Markus Gahleitner, Doris Machl, Tung Pham, Christelle Grein, Klaus Bernreitner. New Concepts for Impact Modification of Polypropylene "Frontiers in Polymer Science" Conference 2011 Lyon, - (-), 2011, - Isotactic polypropylene is a polymer which has grown significantly in volume, importance and application range over the last 50 years due to a unique combination of cost efficiency, performance and versatility. For most technically demanding applications, like in the automotive field, for sewage pipes or performance packaging, low-temperature impact properties are a key factor. These are normally achieved by multi-stage copolymerization of propylene with ethylene or higher alpha-olefins, resulting in multiphase impact copolymers. The design of such multiphase systems with crystalline matrix and purely amorphous or crystalline/amorphous (core/shell) impact modifier particles has been refined over many years, but some conflicting requirements could not be met. While normally engineers will try to balance the property profile of these reactor-based polymers further with external elastomers and mineral modifiers, new concepts are required for extreme property requirements. Three concepts will be presented: - the modification of the crystal structure of the iPP matrix by selective nucleation in combination with elastomers and non-nucleating mineral particles - the combination of hydrolytically crosslinkable polyethylenes (copolymers or grafting products with vinyl-alkoxysilanes) with silicate particles to generate core/shell structures - the synthesis of core/shell nanoparticles with silica core and poly(isobutylene) shell using a “grafting from” approach and living polymerization, using these nanoparticles as efficient impact modifiers for polypropylene printme	2011
Effects of EPR Design and Crystallinity on the Shrinkage of RTPOs 2011, Gregory Potter, Georg Grestenberger, Christelle Grein, Cornelia Kock. Effects of EPR Design and Crystallinity on the Shrinkage of RTPOs "Frontiers in Polymer Science" Conference 2011 Lyon, - (-), 2011, - printme	2011
Effects of external donors and hydrogen concentration on oligomer formation and chain end distribution in propylene polymerization with Ziegler-Natta catalysts 2010, Torvald Vestberg, Peter Denifl, Matthew Parkinson, Carl-Eric Wilen. Effects of external donors and hydrogen concentration on oligomer formation and chain end distribution in propylene polymerization with Ziegler-Natta catalysts J.Polym.Sci.A:Polym.Chem., 48 (2), 2010, 351-358 The effect of type and concentration of external donor and hydrogen concentration on oligomer formation and chain end distribution were studied. Bulk polymerization of propylene was carried out with two different Ziegler-Natta catalysts at 70 °C, one a novel self-supported catalyst (A) and the other a conventional MgCl2-supported catalyst (B) with triethyl aluminum as cocatalyst. The external donors used were dicyclopentyl dimethoxy silane (DCP) and cyclohexylmethyl dimethoxy silane (CHM). The oligomer amount was shown to be strongly dependent on the molecular weight of the polymer. Catalyst A gave approximately 50 % lower oligomer content than catalyst B due to narrower molecular weight distribution in case of catalyst A. More n-Bu-terminated chain ends were found for catalyst A indicating more frequent 2,1 insertions. Catalyst A also gave more vinylidene-terminated oligomers, suggesting that chain transfer to monomer, responsible for the vinylidene chain ends, was a more important chain termination mechanism for this catalyst, especially at low hydrogen concentration. Low site selectivity, due to low external donor concentration or use of a weak external donor (CHM), was also found to increase formation of vinylidene-terminated oligomers. printme	2010
Strain determination of polymeric materials using digital image correlation 2010, Michael Jerabek, Zoltan Major, Reinhold W. Lang. Strain determination of polymeric materials using digital image correlation Polym.Testing, 29 (3), 2010, 407-416 Application of digital image correlation (DIC) to polymeric materials has been proven to be a powerful tool for non-contact strain measurement. In this paper the limits of accuracy of this optical strain measurement system under different environmental conditions were investigated, and the technique was applied to the characterization of polypropylene (PP) and PP composites (PP-C) in the pre- and post-yield regimes. As regards accuracy, a fine speckle pattern and a light intensity just below overexposure provided best results. While vibrations related to the operation of the test machine were of minor influence in reducing the strain measurement accuracy, more pronounced effects were found for the operation of the temperature chamber. In characterizing the transverse strain behavior of PP-C, DIC results exhibited smaller values compared to transverse strains determined utilizing a mechanical clip-on extensometer. The latter effect is attributed to viscoelastic creep indentation of the extensometer pins, which mechanically interact with the specimen via the clip-on spring forces of the extensometer, into the surface. For the DIC system, it could be shown that it allows for the proper strain determination both in the pre- and post-yield regimes, and in terms of longitudinal and transverse strains as well as in terms of global average and local strains. printme	2010
Comparative Theoretical Study on Homopolymerization of alpha-Olefins by Bis(cyclopentadienyl) Zirconocene and Hafnocene: Elemental Propagation and Termination Reactions between Monomers and Metals 2010, Anniina Laine, Mikko Linnolahti, Tapani Pakkanen, Esa Kokko, John R. Severn, Anneli Pakkanen. Comparative Theoretical Study on Homopolymerization of alpha-Olefins by Bis(cyclopentadienyl) Zirconocene and Hafnocene: Elemental Propagation and Termination Reactions between Monomers and Metals Organometallics, 29 (-), 2010, 1541-1550 A comparative quantum chemical study has been performed to shed light on the fundamental differences between hafnocenes and zirconocenes concerning reactions between the metals and alpha-olefin monomers, namely, ethene, propene, 1-butene, and 1-hexene. Analogous species along the alpha-olefin polymerization pathways were studied for bis(cyclopentadienyl) zirconocene and hafnocene, taking into account the structural variations of the first two monomer insertion steps and of the competitive chain-termination reactions. The results were analyzed as a function of both the metal and the monomer, the metal showing more distinct differences. The most notable difference in the reactions of the zirconocene and hafnocene can be seen in beta-hydrogen transfer to metal, activation energies for which are significantly higher for the hafnocene. printme	2010
On-Line Detection of Polymer Melt Flow Instabilities in a Capillary Rheometer 2010, Humberto Palza, Ingo F.C. Naue, Manfred Wilhelm, Susana Filipe, Alfons Becker, J. Sunder, Axel Goettfert. On-Line Detection of Polymer Melt Flow Instabilities in a Capillary Rheometer KGK, - (10), 2010, 456-461 Polymer melt flow instabilities limit the optimum throughput conditions in the plastic processing industry with high economic and environmental consequences. A new set-up able to measure on-line pressure fluctuations inside a slit-die arising from polymer melt flow instabilities is introduced by using a capillary rheometer. This set-up consists of three high sensitive piezoelectric pressure transducers located inside a slit-die together with the application of advanced mathematical tools to process the acquired time dependent pressure signals. Our novel tool improves the time resolution by a factor of ~10E3 and under optimum conditions pressure fluctuations about 10E-5 bar can be detected. Examples of these pressure oscillations arising from the main melt flow instabilities typically observed during extrusion based processes of commercial polyethylenes are presented. printme	2010
Filler/matrix-debonding and micro-mechanisms of deformation in particulate filled polypropylene composites under tension 2010, Michael Jerabek, Zoltan Major, Karoly Renner, Janos Moczo, Bela Pukanszky, Reinhold W. Lang. Filler/matrix-debonding and micro-mechanisms of deformation in particulate filled polypropylene composites under tension Polym.Test., 51 (-), 2010, 2040-2048 Volume strain measurements of particulate filled polypropylene (PP) composites containing different glass beads and talc as filler were carried out in tension as a function of temperature and strain rate to determine the micro-mechanisms of deformation. While local cavitation mechanisms (micro-voiding, crazing, and micro-cracking) and subsequent debonding of the particles dominated as failure mechanisms at high strain rates and at room temperature, a more significant contribution of local shear yielding was observed with a reduced contribution of cavitational mechanisms at low strain rates or at 80°C. This change in the dominating micro-mechanisms of deformation resulted in smaller volume strains during the tensile loading of the composites than for the respective neat matrix. Moreover, a novel approach is introduced for the detection of debonding using volume strain measurements, which takes into account the dilatational and deviatoric behavior of the neat matrix polymer and the composite. The results are supported by acoustic emission measurements carried out simultaneously on the same specimens. printme	2010
Nucleation of Polyolefins: Theory and Practice 2010, Markus Gahleitner, Christelle Grein, Saeid Kheirandish, Johannes Wolfschwenger. Nucleation of Polyolefins: Theory and Practice PPS26 International Conference, Banff/CA, 04.-08.07.2010, - (-), 2010, - From the physical principles of crystal nucleation in polymers to practical examples of polypropylene nucleation an overview of different aspects will be presented. The overall efficiency of nucleation results from a combination of epitaxy quality and dispersion quality, while for practical purposes also other factors like toxicity, thermal stability, discoloration and price need to be considered. Differences between the two physically distinct classes of nucleating agents for iPP and PE, namely particulate systems with a classical dispersion mechanism and soluble systems with a solution/recrystallization sequence for dispersion will be presented. A brief review of recent developments in the understanding of the complex interaction between nucleation, polymer parameters and processing phenomena will be given, leading to detailed results on mechanical and optical consequences of heterogeneous nucleation. printme	2010
Analysis, Comparison and interpretation of instrumented Charpy and puncture impact test results of brittle to ductile transition behaviour of PP-compounds 2010, Dieter Huber, Zoltan Major, Reinhold W. Lang. Analysis, Comparison and interpretation of instrumented Charpy and puncture impact test results of brittle to ductile transition behaviour of PP-compounds PPS26 International Conference, Banff/CA, 04.-07.07.2010, - (-), 2010, - Different pp-compounds were tested and analysed in order to evaluate different influences on the breaking mechanisms of different material compositions more en detail. Samples were injection moulded and compression moulded for evaluation of the influence of processing conditions. There are different kinds of impacts possible and therefore different methods for determination of the impact behaviour are in use. Two methods were analysed more en detail: Instrumented Charpy test, where the stress state is uniaxial and instrumented puncture impact test, where the stress state is biaxial. The latter becomes more and more important as a biaxial stress state is more relevant for further applications. Instrumented Charpy tests were performed on notched and unnotched specimens. Force- deformation curves at different temperatures and the further analysis of these curves gives an improved insight of the material response. The evaluation of the deformation and energy offers the possibility to interpret this transition regime. An overview of the evaluated transition regimes and the consequences will be given, furthermore different influences as notching, material, test performance and evaluation methods will be discussed more en detail. It could be found that not only the transition temperature but also the behaviour in the transition regime is different and could be used for improved material characterisation. The specimen failure modes were analysed in addition and compared with the evaluated results. Furthermore puncture impact tests were performed with different notch geometries in order to evaluate the influence of an initial defect on the material response in biaxial stress state. printme	2010