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Lach R.,Martin Luther University of Halle Wittenberg | Hutar P.,Academy of Sciences of the Czech Republic | Vesely P.,Martin Luther University of Halle Wittenberg | Vesely P.,Brno University of Technology | And 4 more authors.
Key Engineering Materials | Year: 2011

The microstructure as well as the local mechanical and fracture behaviour of welded joints in plastic pipes made form polyethylene and material zones outside of the welded joints have been analysed using recording microhardness testing, laser extensometry and crack resistance curve tests. In has been found that the mechanical basic properties and damage kinetics are clearly depending on the welding parameters and additional notching. © (2011) Trans Tech Publications, Switzerland.


Nezbedova E.,Polymer Institute Brno | Hutar P.,Academy of Sciences of the Czech Republic | Zouhar M.,Brno University of Technology | Knesl Z.,Academy of Sciences of the Czech Republic | And 2 more authors.
Polymer Testing | Year: 2013

The failure mode termed long time brittle failure (due to slow crack growth - SCG) limits the lifetime of plastic pipes. There are now two main accelerated tests (PENT and FNCT) that enable us to estimate the lifetime of HDPE used in plastics pipes. For unimodal grades, the time to failure corresponding to these accelerated tests is about ten hours, for bimodal grade PE 100 it is roughly a thousand hours and for the new PE 100 RC grade is greater than 1 year. For the HDPE pipes grade with higher resistance against SCG, some modification or, alternatively, new tests should be developed that make it possible even for these materials to obtain the results required in a relatively short time. In this contribution we focus mainly on the PENT test and the possibility of the utilization of a structural analysis as well as a numerical approach for prediction of the lifetime of a new generation of PE grades. © 2012 Elsevier Ltd. All rights reserved.


Rybnikar F.,Tomas Bata University in Zlin | Kaszonyiova M.,Tomas Bata University in Zlin | Cermak R.,Tomas Bata University in Zlin | Habrova V.,Polymer Institute Brno | Obadal M.,Borealis
Journal of Applied Polymer Science | Year: 2013

This study focuses on the structure, morphology, and properties of linear polyethylene (PE) profiles manufactured by continuous extrusion. High level of chain orientation was achieved using specific flow and processing conditions. An extrusion die with semihyperbolic convergency was used to generate high percentage of elongational flow and chain extension. Simultaneously, high extrusion pressure and relatively low melt temperature led to flow-induced crystallization of PE extended chains. The structure of PE tapes consists of crystal aggregates with different level of orientation and crystallinity. © 2012 Wiley Periodicals, Inc.


Smolna K.,Institute of Chemical Technology Prague | Gregor T.,University of West Bohemia | Buran Z.,Polymer Institute Brno | Kosek J.,University of West Bohemia
Macromolecular Materials and Engineering | Year: 2016

This paper reconstructs the principle of rubber incorporation in high impact poly(propylene) (hiPP) particles. The detailed information about the pores and rubber distribution inside and on the surface of hiPP particles is obtained by micro-computed tomography and atomic force microscopy. The strong effect of homopolymer origin on hiPP particle morphology and rubber distribution is demonstrated. To obtain the most homogeneous rubber distribution, the low homopolymer porosity is required. The initial particle porosity has a negligible effect on the thickness of the rubber layer on the particle surface at the medium rubber content. The rubber forms not only along the iPP primary particles and directly or close to the pores but also on or close to the particle surface rather than it flows there. The evidence for these claims is based on the systematic investigation in dependence on EPR content, homopolymer particle porosity (prepared by different catalysts) and antistatic agent deactivating catalyst close to particle surface. Based on the systematical mapping of hiPP morphology by micro-CT and atomic force microscopy, the new concept of rubber incorporation in high impact poly(propylene) particles is introduced. The rubber formation directly on or close to the particle surface is confirmed for the first time here. The effect of homopolymer porosity, rubber content, and antistatic additives on the rubber distribution is discussed. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


Androsch R.,Martin Luther University of Halle Wittenberg | Monami A.,Merseburg University of Applied Sciences | Kucera J.,Polymer Institute Brno
Journal of Crystal Growth | Year: 2014

The effect of addition of 0.1 wt% phosphate-ester based alpha-phase nucleating agent on the crystallization of a random propylene-based copolymer with 3.9 mol% ethylene has been investigated by fast scanning chip calorimetry (FSC). Main purpose of the work was the evaluation of the effect of the nucleating agent on the bimodal temperature dependence of the crystallization rate of propylene-based polymers caused by a change of the nucleation mechanism from heterogeneous to homogeneous nucleation on lowering the temperature to below about 60°C. Presence of the nucleation agent in the copolymer of the present study accelerates crystallization only in the high-temperature range of predominant heterogeneous nucleation, but does not affect the crystallization rate in the low-temperature range of homogeneous nucleation. The observed decrease of the minimum crystallization half-time due to the addition of the nucleation agent, from 0.2 s in case of the unmodified copolymer to 0.04 s in case of the copolymer containing the nucleating agent, is paralleled by an increase of the critical cooling rate required to inhibit crystallization on continuous cooling to below the glass transition temperature from 102 to 103 K s-1. The study is completed by an analysis of the effect of addition of the nucleation agent on the spherulitic superstructure. © 2014 Elsevier B.V. All rights reserved.


Hutar P.,Academy of Sciences of the Czech Republic | Nahlik L.,Academy of Sciences of the Czech Republic | Sestakova L.,Academy of Sciences of the Czech Republic | Sevcik M.,Academy of Sciences of the Czech Republic | And 2 more authors.
Composite Structures | Year: 2010

The influence of a cracked protective layer on the integrity of composite multi-layer pipes is analyzed in this paper. The multi-layer pipe is modeled as a particular case of a bi-material body consisting of two different homogeneous materials. The problem is studied under assumptions corresponding to small scale yielding conditions and ideal adhesion between protective and main layers is assumed. The case of a crack with its tip at the interface between protective and main layers is analyzed in detail and the influence of the material composition on the corresponding critical pressure for a brittle-like failure is discussed. An approximate approach based on estimation of crack mouth opening displacement for thin protective layers is suggested. The results have been applied to study the scratch resistance of multi-layered plastic pipes. © 2009 Elsevier Ltd. All rights reserved.


Hutar P.,Academy of Sciences of the Czech Republic | Sevcik M.,Academy of Sciences of the Czech Republic | Frank A.,Polymer Competence Center Leoben | Nahlik L.,Academy of Sciences of the Czech Republic | And 2 more authors.
Engineering Fracture Mechanics | Year: 2013

This paper presents a quick methodology to assess the lifetime of an internally and externally pressurized polymer pipe using linear elastic fracture mechanics. The non-homogenous distribution of residual stress induced by production technology is incorporated into the numerical model of the cracked pipe. The stress intensity factor of the axially oriented crack growing from the inner surface through the pipe wall is estimated and combined with experimentally determined creep crack growth kinetics used for lifetime assessment. Major parameters affecting the pipe's lifetime are identified and discussed. A simplified equation for estimation of the stress intensity factor value, removing the need for complicated finite element simulation, is then proposed. The combination of the creep crack growth tests and the approach presented can be a very powerful tool for reliable lifetime estimation of plastic pipes. © 2013 Elsevier Ltd.


Hutar P.,Academy of Sciences of the Czech Republic | Sevcik M.,Academy of Sciences of the Czech Republic | Nahlik L.,Academy of Sciences of the Czech Republic | Frank A.,Polymer Competence Center Leoben | And 2 more authors.
Key Engineering Materials | Year: 2014

In this paper a methodology for assessment of residual stress effects on crack behaviour in the polymer pipe is developed. For simplicity's sake, a linear distribution of residual stresses across the pipe wall is assumed. Linear elastic fracture mechanics is used for the fracture mechanics analysis of the cracked pipe. An approximate relation for the stress intensity factor estimation for a crack in a polymer pipe, with residual stress taken into account is suggested and discussed. The methodology presented can be helpful for a rapid lifetime estimation of polyolefin pipelines. © (2014) Trans Tech Publications.


Patent
Polymer Institute Brno | Date: 2010-12-27

The method of preparation of nucleated semi-crystalline polyolefin via coordination polymerization, wherein the nucleating agent is dosed in form of the suspension or the solution in a non-polar hydrocarbon solvent or in concentrated organoaluminum as part of the catalyst system for -olefin polymerization.


Tochacek J.,Brno University of Technology | Vratnickova Z.,Polymer Institute Brno
Polymer Testing | Year: 2014

Correlation of accelerated ageing data with that of outdoor exposure was carried out based on the comparison of total UV radiation energy (TUVR) needed for degradation of the PP - homopolymer, random copolymer (TOT C2 = 3.2 wt.%) and impact copolymer (TOT C2 = 5.4 wt.%) compression moulded 0.5 mm films. Films were stabilized with 1000 ppm butylated hydroxytoluene (BHT), no UV stabilizer was used. Accelerated ageing was realized in a Q-Sun Xe-1 exposure chamber using a filtered xenon light source and a dry cycle. Weathering was carried out at Brno exposure site, representing the typical mid-European climate. Accelerated ageing was carried out at temperatures of 40, 50, 60 and 70 °C. In accelerated ageing, both the onset of carbonyl index (CI) increase and the point of reaching the same relative increase in CI as due to weathering were used as measures of polymer degradation. For induction periods attained at different temperatures, TUVR energies were calculated accordingly and compared to that of 6 months outdoor exposure. It was found that if TUVR of both types of ageing is to be directly compared, accelerated ageing should be carried out at temperatures of 32-36 °C. Under such conditions, the same amount of TUVR energy induces the same extent of polymer deterioration in both types of ageing and may, therefore, be used for a reliable service life-time prediction. © 2014 Elsevier Ltd. All rights reserved.

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