Stephan Laske
University of Leoben
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Featured researches published by Stephan Laske.
Waste Management | 2015
Petr Stloukal; Silvie Pekařová; Alena Kalendova; Hannelore Mattausch; Stephan Laske; Clemens Holzer; L. Chitu; Sabine Bodner; Guenther A. Maier; Miroslav Šlouf; Marek Koutny
The degradation mechanism and kinetics of polylactic acid (PLA) nanocomposite films, containing various commercially available native or organo-modified montmorillonites (MMT) prepared by melt blending, were studied under composting conditions in thermophilic phase of process and during abiotic hydrolysis and compared to the pure polymer. Described first order kinetic models were applied on the data from individual experiments by using non-linear regression procedures to calculate parameters characterizing aerobic composting and abiotic hydrolysis, such as carbon mineralization, hydrolysis rate constants and the length of lag phase. The study showed that the addition of nanoclay enhanced the biodegradation of PLA nanocomposites under composting conditions, when compared with pure PLA, particularly by shortening the lag phase at the beginning of the process. Whereas the lag phase of pure PLA was observed within 27days, the onset of CO2 evolution for PLA with native MMT was detected after just 20days, and from 13 to 16days for PLA with organo-modified MMT. Similarly, the hydrolysis rate constants determined tended to be higher for PLA with organo-modified MMT, particularly for the sample PLA-10A with fastest degradation, in comparison with pure PLA. The acceleration of chain scission in PLA with nanoclays was confirmed by determining the resultant rate constants for the hydrolytical chain scission. The critical molecular weight for the hydrolysis of PLA was observed to be higher than the critical molecular weight for onset of PLA mineralization, suggesting that PLA chains must be further shortened so as to be assimilated by microorganisms. In conclusion, MMT fillers do not represent an obstacle to acceptance of the investigated materials in composting facilities.
Journal of Cellular Plastics | 2016
Bernd Geissler; Michael Feuchter; Stephan Laske; Michael Fasching; Clemens Holzer; Günter R. Langecker
In this study, different strategies to improve the mechanical properties of physically foamed high-density polylactic acid sheets were examined to produce polylactic acid foam sheets with tailor-made mechanical properties. The first part was the determination of the effect of different blowing agents (CO2 and N2) on the foam morphology. The second part of the study was the modification of the formulation. For this purpose, both a linear and a branching chain extender and a thermoplastic elastomer were used to improve the elongational properties (tensile modulus and strain at break) of the polylactic acid foam sheets. Additionally, the effect of the addition of cellulose fibers on the foam morphology and the mechanical properties was investigated. All experiments were carried out on a laboratory flat-film line. This extrusion line consists of a 30-mm single-screw extruder attached with a 250-mm flat sheet die. The results show a strong influence of the material formulation on the mechanical properties of the high-density foam sheets. Both the mechanical properties and foam morphology could be improved by the right material formulation. The addition of the thermoplastic elastomer leads to a better foam morphology and also to a reduced brittleness of the foam sheets. Furthermore, it could be demonstrated that cellulose fiber can be used as a nucleating agent for polylactic acid but causes a further decrease in the strain at break.
PROCEEDINGS OF PPS-29: The 29th International Conference of the Polymer Processing Society - Conference Papers | 2014
Hannelore Mattausch; Stephan Laske; Kristin Cirar; Helmut Flachberger; Clemens Holzer
Perlite is an oversaturated, volcanic, glassy rock, which has chemically bound water from 2 to 5 wt%. Upon heating, perlite can be expanded up to 20 times of its original volume. Important applications are in the field of building industry, in refrigeration engineering or the pharmaceutical industry. As mineral filler in polymers, expanded perlite can increase the thermal conductivity, the viscosity and the mechanical properties of polypropylene composites. But there are still many challenges that must be analyzed to reach the full potential of those composites. This research work focuses on the morphology of expanded perlite/polypropylene (PP) compounds and the interactions between filler and polymer. To achieve good performance a homogenous dispersion of the filler in the polymer matrix is needed because the enhancement of the material correlates strongly with the morphology of the composite. Therefore it is necessary to characterize the microstructure of these materials in order to establish adequate s...
Archive | 2018
Alena Kalendova; Jiri Smotek; Petr Stloukal; Milan Kracalik; Miroslav Šlouf; Stephan Laske
This paper deals with the evaluation of gas transport properties of bionanocomposites based on polylactic acid 2003D (PLA). Montmorillonite based fillers, Cloisite® 10A, 20A, 30B and natural Cloisite® Na+, were incorporated into PLA polymer films. PLA/clay mixtures were produced by twin screw extruder ZSK-25. Further testing sheets were prepared from PLA/clay mixtures by Brabender Plasti-Corder equipped by flat die. The prepared composites were evaluated for water absorption, permeability of gases and water vapors. Further material morphology was assessed using X-ray diffraction as well as transmission electron microscopy. The best results achieved compositions with PLA/Cloisite10A and Cloisite 30B.This paper deals with the evaluation of gas transport properties of bionanocomposites based on polylactic acid 2003D (PLA). Montmorillonite based fillers, Cloisite® 10A, 20A, 30B and natural Cloisite® Na+, were incorporated into PLA polymer films. PLA/clay mixtures were produced by twin screw extruder ZSK-25. Further testing sheets were prepared from PLA/clay mixtures by Brabender Plasti-Corder equipped by flat die. The prepared composites were evaluated for water absorption, permeability of gases and water vapors. Further material morphology was assessed using X-ray diffraction as well as transmission electron microscopy. The best results achieved compositions with PLA/Cloisite10A and Cloisite 30B.
International Polymer Processing | 2017
Abdelhamid Mostafa; Gernot Pacher; Thomas Lucyshyn; Clemens Holzer; Elke Krischey; Helmut Flachberger; Bertram Fritz; Stephan Laske
Abstract In the current study, an assessment of the melt-compounding approach upon the behavior of blast furnace slag (BFS) filled polypropylene (PP) is reported. Two melt-compounding technologies are compared in terms of thermodynamic considerations as well as final behavior of the produced compounds. For this comparison, three PP-BFS formulations are introduced, where non-treated BFS is melt-mixed with PP via (1) internal lab mixer (IM) and (2) co-rotating twin-screw compounder (TSC). PP-BFS compounds from both processes are formed into plates via compression molding, characterized and tested for rheological, thermal and mechanical behavior. Processing parameters were evaluated for both processes such as specific shear work, residence time and shear rates. In addition, the rheological, thermal and mechanical behavior of comparable compounds are evaluated. The calculated specific shear work values for IM and TSC are 0.15 and 0.1 kW · h · kg−1. Calculated residence time for TSC is 55 s. Regarding the rheological behavior, it was found that melt mixing via both technologies did not show major differences in complex viscosity or storage- and loss moduli values. DSC findings show that crystallization and melting temperatures of IM- and TSC formulations are comparable. Decreased strain values are noticed for TSC compounds, while tensile modulus is found to be independent of process variation.
PROCEEDINGS OF PPS-30: The 30th International Conference of the Polymer Processing Society – Conference Papers | 2015
Hannelore Mattausch; Stephan Laske; Dieter Hohenwarter; Clemens Holzer
In many polyolefin applications, such as electrical cables or automotive applications, the fire protection is a very important task. Unfortunately flame-retardant polymeric materials are often halogenated and form toxic substances in case of fire, which explains the general requirement to reduce the halogen content to zero. Non-halogenated, state-of-the-art flame retardants must be incorporated into the polymer in very high grades (> 40 wt%) leading to massive decrease in mechanical properties and/or processability. In this research work halogen-free flame-retardant polypropylene (PP) /expandable graphite (EG) were filled with minerals fillers such as layered silicates (MMT), magnesium hydroxide (MgOH), zeolite (Z) and expanded perlite (EP) in order to enhance the flame-retardant effect. The rheological, mechanical and thermal properties of these materials were investigated to gain more fundamental knowledge about synergistic combinations of flame-retardants and other additives. The rheological properties were characterized with a rotational rheometer with plate-plate setup. The EG/EP/PP compound exhibited the highest increase in viscosity (∼ 37 %). As representative value for the mechanical properties the Young’s modulus was chosen. The final Young’s modulus values of the twofold systems gained higher values than the single ones. Thermo gravimetric analysis (TGA) was utilized to investigate the material with respect to volatile substances and combustion behavior. All materials decomposed in one-step degradation. The EG filled compounds showed a significant increase in sample weight due to the expansion of EG. The combustion behavior of these materials was characterized by cone calorimeter tests. Especially combinations of expandable graphite with mineral fillers exhibit a reduction of the peak heat release rate during cone calorimeter measurements of up to 87% compared to pure PP.In many polyolefin applications, such as electrical cables or automotive applications, the fire protection is a very important task. Unfortunately flame-retardant polymeric materials are often halogenated and form toxic substances in case of fire, which explains the general requirement to reduce the halogen content to zero. Non-halogenated, state-of-the-art flame retardants must be incorporated into the polymer in very high grades (> 40 wt%) leading to massive decrease in mechanical properties and/or processability. In this research work halogen-free flame-retardant polypropylene (PP) /expandable graphite (EG) were filled with minerals fillers such as layered silicates (MMT), magnesium hydroxide (MgOH), zeolite (Z) and expanded perlite (EP) in order to enhance the flame-retardant effect. The rheological, mechanical and thermal properties of these materials were investigated to gain more fundamental knowledge about synergistic combinations of flame-retardants and other additives. The rheological properties...
Journal of Materials Science: Materials in Medicine | 2014
Stefan Haubenwallner; Matthias Katschnig; Ulrike Fasching; Silke Patz; Christa Trattnig; Natascha Andraschek; Gerda Grünbacher; Markus Absenger; Stephan Laske; Clemens Holzer; Werner Balika; Manuela Wagner; Ute Schäfer
The polymeric niche encountered by cells during primary culturing can affect cell fate. However, most cell types are primarily propagated on polystyrene (PS). A cell type specific screening for optimal primary culture polymers particularly for regenerative approaches seems inevitable. The effect of physical and chemical properties of treated (corona, oxygen/nitrogen plasma) and untreated cyclic olefin polymer (COP), polymethymethacrylate (PMMA), PP, PLA, PS, PC on neuronal stem cell characteristics was analyzed. Our comprehensive approach revealed plasma treated COP and PMMA as optimal polymers for primary neuronal stem cell culturing and propagation. An increase in the number of NT2/D1 cells with pronounced adhesion, metabolic activities and augmented expression of neural precursor markers was associated to the plasma treatment of surfaces of COP and PMMA with nitrogen or oxygen, respectively. A shift towards large cell sizes at stable surface area/volume ratios that might promote the observed increase in metabolic activities and distinct modulations in F-actin arrangements seem to be primarily mediated by the plasma treatment of surfaces. These results indicate that the polymeric niche has a distinct impact on various cell characteristics. The selection of distinct polymers and the controlled design of an optimized polymer microenvironment might thereby be an effective tool to promote essential cell characteristics for subsequent approaches.
Cellular Polymers | 2014
Bernd Geissler; Michael Feuchter; Stephan Laske; Matthias Walluch; Clemens Holzer; Günter R. Langecker
In this study, different strategies to improve the mechanical properties of physically foamed high density polylactic acid (PLA) sheets were examined to produce PLA foam sheets with tailor-made mechanical properties. The first part was the determination of the influence of the blending of PLA with polybutylene succinate (PBS) on the properties of the high density foam sheets. Additionally, the influence of the PBS on the rheological properties was investigated with a cone plate rheometer. The second part was to manufacture multilayer films with a physically foamed middle layer and highly filled skin layers. The foamed sheets were characterized in terms of mean cell size, cell density, density and surface roughness. The experiments were carried out on lab scale multi-layer extrusion line.
NOVEL TRENDS IN RHEOLOGY IV | 2011
Milan Kracalik; Stephan Laske; Clemens Holzer
Morphological characterization in polymer nanocomposites is usually performed using X‐ray scattering and microscopic techniques, while the enhancement of processing and mechanical properties is commonly investigated by rotational as well as capillary rheometry and tensile testing. However, all of these techniques are time consuming and require expensive scientific equipment. A fast and efficient way of estimating the level of reinforcement in polymer nanocomposites can be performed by melt extensional rheology, because it is possible to correlate the level of melt strength with mechanical properties, which reflect both the 3D network formed by the clay platelets/polymer chains as well as final molecular structure in the filled system. The physical network made of silicate filler and polymer matrix has been evaluated by X‐ray diffraction and transmission electron microscopy. Extensional rheometry and tensile testing have been used to measure efficiency of the compatibilizer amount in a polypropylene‐nanocl...
Polymer Testing | 2015
Petr Stloukal; Alena Kalendova; Hannelore Mattausch; Stephan Laske; Clemens Holzer; Marek Koutny