I. Chodák - Academia.edu (original) (raw)

Papers by I. Chodák

Journal of Applied Polymer Science, 1999

The fracture toughness of the interface, G a , of the self-healed joints of poly(ethylene) (PE) w... more The fracture toughness of the interface, G a , of the self-healed joints of poly(ethylene) (PE) was measured using the wedge method. Samples of PE modified by mixing with three additives (branched low-molecular weight PE, a graphite filler, and polypropylene oil) were investigated. The development of the strength of partially healed joints formed by several hours of contact at a welding temperature of 105°C can be represented in all cases by the linear dependence of the G a parameter on the square root of time, in accordance with the diffusion mechanism of the interface formation. The presence of the additive in samples was found to enhance the fracture toughness of a joint for a given welding time. In the graphite composites, an induction period of welding was observed. In contrast, an instant nonzero strength occurred in joints of PE with PP oil samples. The results confirmed that the concept of the chain entanglement control of fracture toughness developed originally for the glassy polymers is well transferable to the semicrystalline PE. However, additional mechanisms due to the crystallization of PE upon cooling are also effective in the development of the joint strength. These mechanisms denoted as cocrystallization, transcrystallization, local crystallization, mechanical interlocking, etc., are substantially affected by the concentration of additives.

Macromolecular Symposia, 2001

ABSTRACT The stability of electrical and mechanical properties of two kinds of polymer composites... more ABSTRACT The stability of electrical and mechanical properties of two kinds of polymer composites - polyethylene/carbon black and polyethylene/carbon black modified by polypyrrole - was investigated during slow cycle heating and cooling. Conductivity in composites was measured in heating/cooling cycles in the temperature range from 16°C to 125°C. It was found that the thermal treatment resulted in the conductivity changes and the mechanical properties of treated composites have also been influenced. The effect was explained by increased crystallinity in the polymer matrix of thermally treated composites.

Synthetic Metals, 1999

The method of chemically initiated oxidative modification of polypropylene particles in suspensio... more The method of chemically initiated oxidative modification of polypropylene particles in suspension by pyrrole was used for preparation of conductive polypropylenelpolypyrrole composites. Their properties were compared with either polypropylene/polypyrrole composites prepared by melt mixing of virgin polypropylene with chemically synthesized polypyrrole or with polypropylene/carbon black composites prepared also by melt mixing. The composites were characterized by elemental analysis and by mechanical testing. The influence of the processing conditions on the properties of composites is shown. The antistatic properties of prepared composites were demonstrated.

Journal of Applied Polymer Science, 2009

Conducting composites were prepared by melt mixing of ethylene-propylene-diene terpolymer (EPDM) ... more Conducting composites were prepared by melt mixing of ethylene-propylene-diene terpolymer (EPDM) or styrene-butadiene rubber (SBR) and 35 wt % of carbon black (CB). Stability of electrical properties of rubber/CB composites during cyclic thermal treatment was examined and electrical conductivity was measured in situ. Significant increase of the conductivity was observed already after the first heating-cooling cycle to 85 C for both composites. The increase of conductivity of EPDM/35% CB and SBR/35% CB composites continued when cyclic heating-cooling was extended to 105 C and 125 C. This effect can be explained by reorganization of conducting paths during the thermal treatment to the more conducting network. EPDM/35% CB and SBR/35% CB composites exhibited very good stability of electrical conductivity during storage at ambient conditions. The electrical conductivity of fresh prepared EPDM/35% CB composite was 1.7 Â 10 À2 S cm À1 , and slightly lower conductivity value 1.1 Â 10 À2 S cm À1 was measured for SBR/35% CB. The values did not significantly change after three years storage.

Synthetic Metals, 2002

Electrical conductivity and elongation at break of polyurethane (PU) filled with two different gr... more Electrical conductivity and elongation at break of polyurethane (PU) filled with two different grades of graphite, Ag-coated basalt particles and fibres were investigated in this paper. Percolation concentrations were determined to be as follows: 21 or 22 vol.% for PU/graphite composites, 29 vol.% for both PU/Ag-coated particles and PU/Ag-coated fibres composites. It was found that the steepest increase in electrical conductivity and the more pronounced decrease in elongation at break occurs at the same filler concentration range for all investigated systems. A good correlation between phenomenological model, introduced in [J. Mater. Sci. Lett. 18 (1999) 1457], and experimental data for all investigated systems was also observed. #

Polymer Degradation and Stability, 2006

It was shown that controlled degradation of poly-[(R)-3-hydroxybutyrate] (PHB) can be achieved by... more It was shown that controlled degradation of poly-[(R)-3-hydroxybutyrate] (PHB) can be achieved by alcoholysis with two types of alcohol in the presence of a catalyst. PHB oligomers terminated with free hydroxyl groups were prepared in this way. Molecular weight of the prepared samples was studied with three methods: SEC analysis with polystyrene calibration, SEC analysis using universal calibration, and viscometry. The data lead to the conclusion that SEC analysis using polystyrene calibration is a suitable method for monitoring degradation. The degradation proceeds by random chain scission and the molecular weight was decreased by almost two orders of magnitude depending on the alcoholysis conditions. The crystallinity and melting temperature, T m , of PHB after alcoholysis, investigated by differential scanning calorimetry (DSC) show the independence of crystallinity on molecular weight and a decrease in T m with decreased molecular weight. Time dependence of mechanical properties of selected samples (mechanical ageing) reveals that mechanical properties change with time for degraded samples in a similar way as for the parent polymer.

Journal of Applied Polymer Science, 1986

ABSTRACT Crosslinking of polypropylene was investigated when initiated by thermal decomposition o... more ABSTRACT Crosslinking of polypropylene was investigated when initiated by thermal decomposition of organic peroxides. p-Benzoquinone was found to be an effective coagent of crosslinking. The efficiency of benzoquinone is about 5 times higher than that of polyfunctional monomers. Almost complete crosslinking of polypropylene can be reached at proper conditions.

European Polymer Journal, 1995

The kinetics of isothermal crystallization of low density polyethylene (LDPE) crosslinked and fil... more The kinetics of isothermal crystallization of low density polyethylene (LDPE) crosslinked and filled with low surface area silica was investigated by DSC method. The crosslinking initiated by thermal decomposition of peroxide leads to overall retardation of crystallization. The filling of LDPE with low surface area silica leads to the increasing nucleation. The isothermal crystallization of crosslinked and filled LDPE is affected by nucleation, retardation and formation of preordered structure, all effects acting simultaneously making overall dependences sometimes rather complicated.

Journal of Materials Science Letters, 1999

Isotactic polypropylene (iPP), as one of the most frequently processed polymers, possesses excell... more Isotactic polypropylene (iPP), as one of the most frequently processed polymers, possesses excellent physico-mechanical properties. The low value of iPP free surface energy (near 30 mJ · m −2 ) and its low hydrophilicity and wettability are a major drawback, however, because some components must often be lacquered or glued to fulfill application demands . To overcome these difficulties, various treatments have been suggested, consisting of introducing some polar groups on the polymer macromolecules to increase the free surface energy of iPP. The bulk properties of the polymer are not affected, because the modification of iPP leads to the creation of only a very thin modified surface layer having a thickness of 1-10 µm. Achieving satisfactory adhesion properties of iPP, however, requires an effective modification that can satisfactorily promote bondability. The enhancement of adhesive properties of iPP can be supported via many methods of surface modification .

Chemicke Listy

Poly(imide-siloxane) (PIS) block copolymers have been studied with respect to their structure and... more Poly(imide-siloxane) (PIS) block copolymers have been studied with respect to their structure and surface properties relationship. The relatively small amount of siloxane in PIS block copolymer, 10-20 wt.%, increased significantly the contact angle of water due to the surface hydrophobization of the copolymer. The significant decrease of the surface energy of the PIS copolymer due to growth of the siloxane content was observed. The polar component of surface energy shows an intense decrease, whereas its dispersive component increases. The study of the morphology of PIS copolymers characterized by The X-ray Photoelectron Spectroscopy (XPS) analysis showed an excessive increase of Si on the polymeric surface. Scanning electron microscopy (SEM) shows a growth of the surface roughness by increase of the content of siloxane.