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Multi-wall carbon nanotube networks prepared from pure MWCNT and their oxidised forms effect of compressive strain on electric resistence
Olejník, R. ; Slobodian, P. ; Říha, Pavel ; Kimmer, D. ; Sáha, P.
Multi-wall carbon nanotube networks were prepared by filtration of CNT aqueous dispersions. CNT dispersions were prepared with the help of surfactant system (sodium dodecyl sulfate with amylalcohol) by ultrasonication. Three types of MWCNT tubes were used. The first were pure CNT delivered by supplier. The others were oxidized CNT oxidized (1. acid solution of KMnO4; 2. the mixture of acids H2SO4 + HNO3). It was found that oxidization significantly changes properties of prepared carbon nanotube networks. There were observed differences in porous structures networks analyzed by SEM microscopy. Moreover, the apparent density of prepared MWCNT networks also changes according to the used CNT. The network electrical resistance is also affected by process of MWCNT oxidation as well as by compressive strain. It was found that the network resistance is sensitive to compressive strain both in the course of strain growth and when loading/unloading cycles are imposed.
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Polyvinyl chloride catheters with repressed migration of plasticizers
Sedláček, T. ; Polášková, M. ; Kašpárková, V. ; Filip, Petr ; Sáha, P.
Impart flexibility and desired softness of polyvinylchloride (PVC) – one of the most widely used polymeric materials for medical device production – is achieved by addition of appropriate amount of plasticizer, usually di(2-ethylhexyl phthalate) (DEHP), into polymer matrix. DEHP is not chemically bonded to PVC and migrates to the surrounding media such as saliva, blood, plasma, or serum resulting in several toxic effects. Migration of DEHP can be significantly suppressed by embedding PVC into another polymer preventing its direct contact with surrounding liquid media. Coextruded TPU-PVC-TPU catheters were prepared with various thicknesses of TPU layers to evaluate its repressing effect on DEHP releasing. Releasing kinetic of DEPH from both three layered catheters and PVC catheters into the acetonitrile was observed in various time intervals and determined using reverse-phase liquid chromatographic technique.
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Polyvinyl chloride filled with bismuth oxychloride powder
Polášková, M. ; Sedláček, T. ; Kharlamov, Alexander ; Pivokonský, Radek ; Saha, P.
Mixing of polymers with radiopaque agents enables the polymers visibility on X-ray images and represents the easiest way to accurately locate the polymeric surgical device during a critical procedure. Medical-grade polyvinyl chloride was compounded with various amounts of bismuth oxychloride, chosen for its unique properties such as high radiopacity, non-toxicity, excellent chemical and physical stability and good dispersibility in the polymeric matrix. Micro-compounder Haake MiniLab II, consisting of a conical co-rotating twin-screw compounder with an integrated backflow channel, was used for melt mixing and simultaneously for rheological measurement. Rheological data received from micro-compounder were supplemented and correlated with the data obtained from Anton Paar rotational rheometer. Structure of prepared composites was studied by scanning electron microscopy, and their thermo-mechanical properties were tested using dynamic mechanical analysis.
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Critical shear values of extruded polymer blends
Filip, Petr ; David, Jiří ; Keyzlarová, L. ; Sáha, P.
The onset of flow instabilities (encountered during extrusion of polymer melts) corresponds to the flow conditions when the critical shear stresses or the critical shear rates are attained. These critical values were experimentally determined for two cases of polymer blends. Consequently there were used the mixture rules of a logarithmic type for desciption of behaviour of critical shear values.
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