Papers by Markus Gahleitner
A new apparatus for measuring high viscosities
Journal of Physics E: Scientific Instruments, 1988
A new viscometer especially designed for the high viscosity region is presented. The magnetovisco... more A new viscometer especially designed for the high viscosity region is presented. The magnetoviscometer uses Stokes' falling sphere principle, where the gravitational force is substituted by a magnetic one. The working principle and set-up of the apparatus are described; some results obtained on technical polymers are given and special features of the magnetoviscometer (such as measurement under pressure and the use of disposable cells) are emphasised.
Polypropylene
Ullmann's Encyclopedia of Industrial Chemistry, 2014
RSC Adv., 2014
The optical properties of polypropylene (PP) were modified by nine different sorbitol type clarif... more The optical properties of polypropylene (PP) were modified by nine different sorbitol type clarifiers available commercially or synthesized in the study. The solubility of the clarifiers in PP was estimated by thermodynamic model calculations. The results showed that the solubility of these additives in PP is small, a few 1000 ppm at most. Solubility is determined by the chemical structure of the sorbitol, and the heat of fusion of the latter changes solubility by at least one order of magnitude. Solubility can be estimated reasonably by the Flory-Huggins lattice theory. The morphology of most sorbitols transforms at a temperature much below their melting point upon heating. This transformation, which is accompanied by crystal perfection, seems to influence melting and solubility. A fibrillar structure forms upon the cooling of molten sorbitols, but the diameter of the fibrils is much larger than those forming in the polymer melt. The nucleating effect of the clarifier depends on solubility, but also on processing conditions. Nucleus density is related to the amount of dissolved clarifier. A close correlation was found between the Flory-Huggins interaction parameter of sorbitols and the smallest achievable haze, which can be explained by the effect of solubility and nucleus density.
Rheologica Acta, 1987
Streaming of a non-Newtonian fluid around a sphere is of special importance not only for measurin... more Streaming of a non-Newtonian fluid around a sphere is of special importance not only for measuring viscosities with falling spheres, but also for many problems connected with polymer processing. Using the mentioned measuring principle, attention has to be paid to the following points: The sphere is moving in a fluid (melt) of finite extension which requires the application of wall and perhaps end corrections. These are possibly not the same for Newtonian and non-Newtonian fluids. To calculate the viscosity with the help of Stokes law the steady-state velocity is necessary, and it is essential, how long it takes the sphere to reach it. To compare our results with other data, an average shear rate has to be calculated, since there is no uniform shear rate around the sphere. Velocities being very low in our experiments result in very small Reynolds numbers (Re < 10-3), which allows the application of Stokes law practically without corrections. The experiments were performed at zero shear and in the transition region above. It turned out, that it is usually not possible to extrapolate from shear-dependent viscosity data to zero-shear viscosity.
Rheologica Acta, 1996
To obtain the time dependent viscosity function over a wide experimental window, data from two di... more To obtain the time dependent viscosity function over a wide experimental window, data from two different measuring instruments and methods were combined. The instruments involved were a conventional dynamic rheometer and the magnetoviscometer (MVM), a novel apparatus specially designed for measuring at low shear rates. For most of the investigated materials the MVM-data allow an expansion of the known time-range to higher values, thus giving additional infor-marion about the longest relaxation times in the systems, which in turn correspond to the high-molecular tail of the molar mass distribution. Especially in the long time range where it is difficult to get good dynamical data the experimental error of the MVM-data is very small.
Polymer Testing, 1999
Based on information available in the literature and new investigations, the ageing behaviour of ... more Based on information available in the literature and new investigations, the ageing behaviour of polypropylene at room temperature and in annealing was studied. Two effects have to be discerned: changes in the amorphous and/or mesomorphic regions of the material at room temperature, which lead to an increase in density and modulus in connection with embrittlement on the one hand, and relaxation-and recrystallization-processes at higher temperatures, which positively influence heat deflection temperature and impact strength alongside with modulus and density on the other hand. Use of elevated temperatures to accelerate ageing for the determination of long-term properties is therefore not possible in the case of polypropylene.
Polymer Engineering & Science, 2006
Polypropylene homopolymers and ethylene/propylene‐random‐copolymers formulated with and without a... more Polypropylene homopolymers and ethylene/propylene‐random‐copolymers formulated with and without anti‐blocking additives were extruded to cast films with an industrial scale extruder equipped with a soft box, a specific air knife that expels a higher volume of air at lower velocity. The films were analyzed as to their optical properties haze and clarity. A comprehensive topographical characterization was performed using atomic force microscopy (AFM) and confocal microscopy. To obtain morphological information on a nanometer scale AFM phase imaging, micro‐thermal analysis and small angle X‐ray scattering (SAXS) were done. A significant effect of additives and processing conditions on the film topography and the optical properties was revealed. The films without anti‐blocking and antacid aids showed the best optical properties and lowest vertical roughness fluctuations. In contrast, the addition of anti‐blocking and antacid aids reduced the optical properties associated with an increas...
Polymer Degradation and Stability, 1999
A series of experiments was carried out to develop an additive package for HDPE blown films. The ... more A series of experiments was carried out to develop an additive package for HDPE blown films. The evaluation of the results yielded interesting correlations relating the colour of the polymer to its chain structure and to the properties of the films. Additional experiments proved that all reactions are related to each other. The discolouration of the polymer could be described by simple first order reaction kinetics and a linear correlation was found between stability and a quantity calculated from the kinetic model. The reaction of the vinyl functionality of the polymer seems to be related to the changes in its rheological properties. In spite of the good general correlations found, some details remained unexplained and need further investigation.
Monatshefte für Chemie - Chemical Monthly, 2006
Polypropylene homopolymer and ethylene=propylene-random-copolymer cast films formulated with slip... more Polypropylene homopolymer and ethylene=propylene-random-copolymer cast films formulated with slip, anti-blocking, and acid scavenger aids were analyzed as to material structure and optical properties. The structural and topographical characterization was done by atomic force microscopy and by spectroscopic methods. Optical properties were determined using a hazemeter and an UV=VIS=NIR spectrophotometer. As to the effect of additives it was established that slip and antiblocking aids migrate to and accumulate on the surface, resulting in increased surface roughness and larger scattering identities close to the surface. Acid scavenger additives were shown to contribute to less significant slip aid domains and hence to lower haze. In general, films without additives showed much better optical properties. The separation of haze into its bulk and surface components revealed that the total haze is dominated by surface haze.
Journal of Non-Newtonian Fluid Mechanics, 1988
Empirical and theoretically based numerical interconversions between viscoelastic material functi... more Empirical and theoretically based numerical interconversions between viscoelastic material functions are used to compare results of two different measuring techniques for polymer melts. The methods compared are the magnetoviscometer and a dynamic-mechanical apparatus. For the case of two technical polystyrenes results are given which show the possibility of determining the zero shear viscosity and, using an empirical conversion, more of the flow curve from results of the magnetoviscometer. In general, the results of both techniques are in good accordance.
Post-Crystallization and Physical Aging of Polypropylene: Material and Processing Effects
Journal of Macromolecular Science, Part B, 2002
The application properties of plastic products are significantly influenced by the structural cha... more The application properties of plastic products are significantly influenced by the structural changes after conversion, resulting from a combination of post-crystallization and physical aging for semicrystalline materials. For three different types of polypropylene—homopolymer, ethylene/propylene random- and heterophasic copolymer—and two types of conversion—injection molding and cast film extrusion—the aging processes were studied extensively. The temperature level of the aging process plays a decisive role in determining the effects; atleast two important transitions can be identified with increasing temperature. Apart from that, the nature of the polymer and the type and conditions of conversion are also important. The cumulative effects of crystallization behavior of the polymer and cooling history determine the crystallinity and superstructure of the formed article, which in turn determines the aging behavior.
Journal of Applied Polymer Science, 2013
ABSTRACTFive polypropylene (PP) homopolymers were selected and their molecular structure was thor... more ABSTRACTFive polypropylene (PP) homopolymers were selected and their molecular structure was thoroughly characterized to determine the effect of molecular architecture on their annealing behavior and on the ultimate stiffness achieved by heat treatment. Molecular mass and its distribution were characterized by rheological measurements, while chain regularity was determined by differential scanning calorimetry (DSC) using stepwise isothermal segregation technique (SIST). The samples were annealed in two different ways. Tensile bars were treated in an oven at 165 °C for increasing times to determine changes in stiffness. Various defects (microcracks and voids) developed during the annealing of tensile specimens that did not allow the reliable determination of modulus by direct measurement. On the other hand, the second approach, the annealing of small samples in a DSC cell clearly showed the changes occurring in crystalline structure and also the effect of nucleation and molecular arc...
European Polymer Journal, 2009
The effect and efficiency of three nucleating agents, a sorbitol based clarifier, a traditional h... more The effect and efficiency of three nucleating agents, a sorbitol based clarifier, a traditional heterogeneous nucleating agent and poly(vinylcyclohexane) (PVCH) was studied in polypropylene (iPP) homopolymer. The nucleating agents were added to iPP in different amounts; PVCH in 0-200 ppm, while the other two in 0-2000 ppm. Optical and mechanical properties were determined on injection molded plates or bars, respectively. Nucleation efficiency was studied by thermal analysis, while structure was characterized by polarized light (PLM), scanning electron (SEM) and atomic force microscopy (AFM). Nucleus density was calculated using the method of Lamberti, which is based on the kinetic theory of the crystallization developed by Lauritzen and Hoffmann. The results proved that the nucleating agents modify properties in different ways and extent. PVCH is very efficient already at small concentrations and increases the stiffness of iPP considerably more than the other two compounds. On the other hand, the clarifier and the traditional nucleating agent induce better optical properties even at smaller efficiency. The structure developing in the presence of the three nucleating agents is also different. The clarifier forms a network in iPP and induces the formation of a microcrystalline structure according to the former literature data. Microspherulitic structure develops in the presence of the heterogeneous nucleating agent studied, while relatively large supermolecular units form in iPP nucleated by PVCH even under the conditions of injection molding. The calculation of nucleus density by existing models and the comparison of the results to optical properties proved that haze is determined by the size of the supermolecular units of the polymer and this latter depends on nucleus density.
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Papers by Markus Gahleitner