Ivan Chodák

Thermal degradation of plasticized poly(3-hydroxybutyrate) investigated by DSC

The thermal degradation of poly(3-hydroxybutyrate) (PHB) in the presence of two plasticizers (glycerol, glycerol triacetate) was investigated by differential scanning calorimetry (DSC). The thermal degradation was studied as a function of the annealing time, temperature and cooling rate after the thermal treatment. PHB thermal degradation proceeds by the random scission of the polymer chain. The presence of glycerol leads to a significant prodegradative effect on PHB presumably due to the alcoholysis reaction, while glycerol triacetate (triacetine) behaved as an almost inert additive from this point of view. Size exclusion chromatography (SEC) confirmed the results obtained by the DSC method. The data lead to the conclusion that DSC is a suitable method for estimation of PHB thermal degradation.

Analysis of correlation between percolation concentration and elongation at break in filled electroconductive epoxy-based adhesives

Abstract Electrical conductivity and elongation at break of epoxy filled with electroconductive carbon black, graphite or with silver-coated basalt particles or fibres were investigated in this paper. Percolation concentrations were determined to be 14 vol% for epoxy/carbon black composites, 22 vol% for epoxy/graphite composites, 28–29 vol% for both epoxy/silver-coated basalt particles and fibres. The steepest increase in electrical conductivity and the most pronounced decrease in elongation at break occurs at similar filler concentration range for all investigated systems. A good correlation between phenomenological model, introduced in [J. Mater. Sci. Lett. 18 (1998) 1457] and experimental data for all investigated systems was observed.

An in vitro bacterial adhesion assessment of surface-modified medical-grade PVC

Medical-grade polyvinyl chloride was surface modified by a multistep physicochemical approach to improve bacterial adhesion prevention properties. This was fulfilled via surface activation by diffuse coplanar surface barrier discharge plasma followed by radical graft copolymerization of acrylic acid through surface-initiated pathway to render a structured high density brush. Three known antibacterial agents, bronopol, benzalkonium chloride, and chlorhexidine, were then individually coated onto functionalized surface to induce biological properties. Various modern surface probe techniques were employed to explore the effects of the modification steps. In vitro bacterial adhesion and biofilm formation assay was performed. Escherichia coli strain was found to be more susceptible to modifications rather than Staphylococcus aureus as up to 85% reduction in adherence degree of the former was observed upon treating with above antibacterial agents, while only chlorhexidine could retard the adhesion of the latter by 50%. Also, plasma treated and graft copolymerized samples were remarkably effective to diminish the adherence of E. coli.

Electrical and mechanical properties of conducting polymer composites

The method of chemically initiated oxidative modification of polypropylene particles in suspension by pyrrole was used for preparation of conductive polypropylene/polypyrrole 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.

Investigation of the correlation between electrical conductivity and elongation at break in polyurethane-based adhesives

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.

A new route for chitosan immobilization onto polyethylene surface.

Low-density polyethylene (LDPE) belongs to commodity polymer materials applied in biomedical applications due to its favorable mechanical and chemical properties. The main disadvantage of LDPE in biomedical applications is low resistance to bacterial infections. An antibacterial modification of LDPE appears to be a solution to this problem. In this paper, the chitosan and chitosan/pectin multilayer was immobilized via polyacrylic acid (PAA) brushes grafted on the LDPE surface. The grafting was initiated by a low-temperature plasma treatment of the LDPE surface. Surface and adhesive properties of the samples prepared were investigated by surface analysis techniques. An antibacterial effect was confirmed by inhibition zone measurements of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The chitosan treatment of LDPE led to the highest and most clear inhibition zones (35 mm(2) for E. coli and 275 mm(2) for S. aureus).

Thermal lag and its practical consequence in the dynamic mechanical analysis of polymers

The thermal lag associated with the temperature ramping experiment in a dynamic mechanical analysis is demonstrated on carbon black filled vulcanised rubber samples by using a DMTA MkIII from Rheometric Scientific. The importance of achieving thermal equilibrium on the sample before starting the measurement is emphasised. By running a combination of isothermal and ramping steps, the impact of thermal lag on the obtained dynamic mechanical properties can be estimated. For the measurement in tensile mode at a rate of heating of 2°C/min and vertical orientation of the driveshaft motion, the isothermal step applied at the sample glass transition temperature revealed that the temperature equilibration of the sample takes at least 15 min. Consequently, the storage modulus measured during the heating step is overestimated by around two times and the glass transition temperature is shifted to higher values. For the given chamber geometry, the bending mode of measurement exhibits a lower thermal lag than the tensile one. The experimental data indicate that the major factors responsible for thermal lag are heat transfer from the sample environment to the sample surface (which is given by the chamber design), sample position in the chamber and the mutual position of the sample and thermometer Pt-100. Based on the results presented, a recommendation for selecting the experimental conditions is given in order to recognise and minimise the effect of thermal lag on the data obtained by dynamic mechanical analysis.

A Composite LDPE/WOOD Flour Crosslinked by Peroxide

Abstract The properties of a composite consisting of low density polyethylene (LDPE) filled with wood flour were investigated in a broad concentration range of the filler. The adhesion between the matrix and the filler was increased via peroxide-initiated crosslinking. A decrease in both tensile strength and elongation at break and modest increase in Youngs modulus with rising filler content was found for uncrosslinked samples. Crosslinking results in a substantial increase of tensile strength and extreme rise of the Youngs modulus values with an increase of both filler content and peroxide concentration, compared to uncrosslinked composites. A formation of covalent bonds between the filler surface and polymer chains are proposed as the reason for the observed effect of crosslinking. The extraction and swelling data are presented to support this explanation.

Analysis and Characterization of Printed Plasma-Treated Polyvinyl Chloride

Abstract A number of polyvinyl chloride (PVC) applications require a modification of surface properties of the polymer. In the present work, the effects of plasma treatment on the resulting surface, including chemical composition, wettability, and roughness, were assessed using X-ray photoelectron spectroscopy, contact angle measurements, and scanning electron microscopy analysis. A significant alteration regarding the oxygen and carbon content as evidenced by the XPS data was observed after oxygen plasma treatment. Scanning electron microscope images revealed a drastic change of the topography of the treated surface. These changes correspond to improvement in the printability of the treated surface. Therefore, plasma modification in air is demonstrated to be a viable method to improve printability of PVC.

The effect of temperature on peroxide initiated crosslinking of polypropylene

Abstract Crosslinking of polypropylene at 10–220° was investigated. The process was initiated by radicals formed either by thermal or by u.v. decomposition of dicumyl peroxide. It was found that fragmentation of macroradicals is the most important reaction during thermal initiation and the crosslinking efficiency increases with decreasing temperature. For u.v. initiation, several chemical and physical factors are important; the efficiency is highest at 65–80°.