Scientific publications

Irreversible deformation of isotactic polypropylene in the pre-yield regime

2011, D. Tscharnuter, Michael Jerabek, Zoltan Major, Gernot Pinter.

Irreversible deformation of isotactic polypropylene in the pre-yield regime
European Polymer Journal, 47 (-), 2011, 989-996

In the modeling of the mechanical response of a polymer over a large strain range, the nonlinear viscoelastic and viscoplastic behavior must be considered. For many polymers, nonlinear behavior is observed at low loads, e.g. by a stress-dependence of the creep compliance for stresses above 2 MPa in case of the polypropylene used in this study. Additionally, plastic deformation has been observed at strains below the yield point for several polymers. In this study, the irreversible deformation by cavitation and shear yielding of polypropylene are characterized in the pre-yield regime in uniaxial tensile tests using digital image correlation. The recovery of strain after unloading at a prescribed strain level is measured and used to identify the evolution of the plastic strain during uniaxial tension. An experimental technique for simultaneous determination of the true stress–true strain curve and the degree of stress whitening, which relates to the amount of cavitation, is introduced and the initiation of cavitation is compared to the plastic deformation detected in strain recovery at various temperatures.

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Borstar® PE – Expanding the possibilities

2011, Michel Daumerie, Markus Gahleitner.

Borstar® PE – Expanding the possibilities
Maack PPPE Conference 2011, - (-), 2011, -

The Borstar® PE process has the capability for producing HDPE and LLDPE in a wide range of density and molecular weight resulting from a unique loop/gas phase process technology, using propane as diluent for reaching the liquid state in the first reactor. This is not only the first proprietary polymerization technology developed by Borealis, but also an extremely flexible and efficient process which has been upgraded and expanded since starting up the first plant in Porvoo, Finland in 1995. This presentation will outline the product range of the Borstar® PE process by presenting some of the most recent developments: - Borshape™ high -olefin terpolymers offer opportunities for innovative packaging films with less material, greater efficiency and improved environmental and lifecycle performance. High toughness and very high stiffness allow faster line speeds and downgauging of up to 30%. - Borlite™ LLDPEs set new standards in the performance of Machine Direction Orientation (MDO) films. It offers step-change downgauging, high impact strength, high puncture resistance, and good tear resistance in machine direction, in addition to lower operational costs and reductions in energy and CO2 emissions. - Bormed™ HDPE grades combine highest purity with excellent processability and perform well in bottles and ampoules as well as syringes and catheters. - Borsafe™ pipe grades set new standards in long-term performance of pressure pipes and are also the safest choice in case of earthquakes. - BorPEX™ for PEX-c pipes crosslinked by irradiation with electron beams has a significantly improved chlorine resistance is the material of choice for extreme requirements. And polyolefins have certainly not reached their theoretical performance limit yet. Through continued research on the structure-property relations governing the application performance of PP and PE, researchers in academia and industry contribute to a continuous expansion of the application range.

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Sterilization of propylene/ethylene random copolymers: Annealing effects on crystalline structure and transparency as influenced by polymer structure and nucleation

2011, Markus Gahleitner, Christelle Grein, Rebecca Blell, Johannes Wolfschwenger, Thomas Koch, Elisabeth Ingolic.

Sterilization of propylene/ethylene random copolymers: Annealing effects on crystalline structure and transparency as influenced by polymer structure and nucleation
eXPRESS Polymer Letters, 5 (9), 2011, 788–798

An extensive investigation of three different series of isotactic ethylene/propylene (EP) random copolymers was performed to understand the factors influencing the change in optical properties in the steam sterilization of extrusion cast films from such materials. Different analytical methods (differential scanning calorimetry (DSC), X-ray diffraction and electron microscopy) were employed to elucidate structural changes determining film optics, and in addition to the polymer structure parameters also nucleation and processing effects were studied. The findings clearly show that a combination of homogeneously randomized comonomer distribution and nucleation can partly inhibit lamellar thickening in sterilization, thus preserving high transparency even after a heat treatment. In detail, attention has to be paid to the combined effects of primary and secondary post-crystallization, which both are affected by the chain regularity.

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Design of experiment - versatile tool for structure-property relationship investigations

2011, Andrey Buryak.

Design of experiment - versatile tool for structure-property relationship investigations
EPF European Polymer Congress 2011 Granada, Spain, - (-), 2011, -

A series of bimodal polyethylene resins consisting of high and low molecular weight fractions was produced in a multistage polymerization process using Ziegler-Natta catalyst. Four polymer design parameters were varied: 1st component melt flow rate, final melt flow rate, final resin density and the split between the two fractions. Tensile and impact (V-notched Charpy) properties of the produced resins were measured on specimens prepared from compression moulded plates and correlated to the polymer design parameters. The results show that design of experiment is a very convenient and versatile tool for systematic investigation of structure-property relationships in complex polymer systems. In a single series of experiments, the influence of several polymer design parameters on the properties of interest can be evaluated while minimizing the number of experiments and improving the efficiency of research work.

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Morphology development of polypropylene elastomer blends - From mixing to injection molding

2011, Velichko Hristov, Tung Pham.

Morphology development of polypropylene elastomer blends - From mixing to injection molding
GAK Gummi, Fasern, Kunststoffe, 9 (64), 2011, 559-563

Model compounds of a polypropylene homopolymer with high and low molecular weight ethylene-octene copolymers (EOC) were melt blended. The blends were compounded at different processing conditions altering the shear rate, specific energy input, and residence time in the extruder. The morphology of the samples taken at different locations along the screw channel and from injection moulded tensile specimens was studied by SEM. It was found that the morphology evolution depends largely upon the processing conditions, time spent in mixing and formulation. Elastomer particle coalescence and break up phenomena compete with each other in defining the final blend morphology and properties of the blends.

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