Petr Saha

Prehydrolyzed Cellulose as Reinforcing Filler for Thermoplastics

Abstract This paper presents the results of an experimental study of the mechanical properties of composites consisting of prehydrolyzed cellulose and thermoplastic matrices. The main feature of prehydrolyzed cellulose fibres is a high degree of brittleness, permitting the fibres to be finely comminuted in the shear field of normal compounding and processing machinery. Such an effect can be anticipated to improve the homogeneity and the mechanical parameters of the moulded samples. In the present work, this has been demonstrated with PP, HDPE and PS containing varying amounts of prehydrolyzed cellulose of different origin (bleached pulps). The tests were done on injection moulded samples. The compounding method (Buss-Kneader vs. twin-screw extruder) had only minor influence on the results. Theoretical assessment of the modulus values using the Tsai–Halpin equation gave somewhat lower values than those recorded on experimental samples. This was interpreted in terms of the disintegration of the cellulose co...

The effect of dielectric properties on the electrorheology of suspensions of silica particles coated with polyaniline

The flow behaviour of silicone-oil suspensions of five types of silica particles coated with a polyaniline base in a DC electric field has been linked to their dielectric properties. The relaxation frequencies corresponding to the position of the dielectric-loss maxima in the frequency spectra identify the interfacial polarization of suspension particles as a controlling factor for a strong electrorheological effect. The yield stresses of suspensions under the influence of electric field and critical shear rates, at which the chains of polarized particles were broken by shear forces, is correlated with the difference between the limit values of dielectric constants above and below the relaxation frequency. The analysis of particle dipole coefficient β showed that particle polarizability is the main factor affecting rigidity of the electrorheological structure. In contrast with this, particle shape and size, controlling the field-off suspension viscosity, become unimportant after the electric field has been applied. The plots of the relative viscosity of studied suspensions vs. Mason number characterizing the relation between shear and polarization forces have been discussed. While the results obtained at different shear rates and field strengths were reduced to a single dependence, for various particle suspensions these dependences differed.

Rheological properties of magnetorheological suspensions based on core–shell structured polyaniline-coated carbonyl iron particles

The sedimentation caused by the high density of suspended particles used in magnetorheological fluids is a significant obstacle for their wider application. In the present paper, core–shell structured carbonyl iron–polyaniline particles in silicone oil were used as a magnetorheological suspension with enhanced dispersion stability. Bare carbonyl iron particles were suspended in silicone oil to create model magnetorheological suspensions of different loading. For a magnetorheological suspension of polyaniline-coated particles the results show a decrease in the base viscosity. Moreover, the polyaniline coating has a negligible influence on the MR properties under an external magnetic field B. The change in the viscoelastic properties of magnetorheological suspensions in the small-strain oscillatory shear flow as a function of the strain amplitude, the frequency and the magnetic flux density was also investigated.

Electrical conductivity of carbon fibres/polyester resin composites in the percolation threshold region

Abstract The electrical conductivity of composites of a polyester resin filled with short carbon fibres has been investigated with a special attention to the properties in the percolation threshold region. A very low percolation threshold (0.7–0.8 vol% of the filler) was confirmed. In contrast to S-shaped curves calculated according to the percolation theory of composites of globular particles, the experimental conductivity vs. fibre content dependence, after a steep increase in the percolation region, increased almost linearly. This atypical behaviour was explained by a different mechanism of formation of fibrous and globular conducting structures above the percolation threshold. An increase in scatter of conductivity values observed at percolation threshold as a consequence of great fluctuation of fibre arrangement manifested itself also in the conductivity–temperature dependences.

Electrorheological properties of suspensions of hollow globular titanium oxide/polypyrrole particles

Hollow globular clusters of titanium oxide (TiO2) nanoparticles were synthesized by a simple hydrothermal method. The prepared particles were consequently coated by in situ polymerization of conductive polymer polypyrrole (PPy) to obtain novel core–shell structured particles as a dispersed phase in electrorheological (ER) suspensions. The X-ray diffraction analysis and scanning electron microscopy provided information on particle composition and morphology. It appeared that PPy coating improved the compatibility of dispersed particles with silicone oil which results in higher sedimentation stability compared to that of mere TiO2 particles-based ER suspension. The ER properties were investigated under both steady and oscillatory shears. It was found that TiO2/PPy particles-based suspension showed higher ER activity than that of mere TiO2 hollow globular clusters. These observations were elucidated well in view of their dielectric spectra analysis; a larger dielectric loss enhancement and faster interfacial polarization were responsible for a higher ER activity of core–shell structured TiO2/PPy-based suspensions. Investigation of changes in ER properties of prepared suspensions as a function of particles concentration, viscosity of silicone oil used as a suspension medium, and electric field strength applied was also performed.

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.

Electrorheological activity of polyphenylenediamine suspensions in silicone oil

Electrorheological and dielectric properties of suspensions of polyphenylenediamine isomers in silicone oil have been investigated. The effectiveness of the base forms of polymers was higher than that of their protonated counterparts. The dielectric spectra showed a low rate of polarization which support the idea of mechanism of interfacial particle polarization. The diferences in the low-shear-rate relative apparent viscosity of the systems were explained as a result of different particle dipole coefficients.

On the development and characterisation of crosslinked sodium alginate/gelatine hydrogels.

Sodium alginate (SA) and gelatine (G) based hydrogels with various SA/G ratios, crosslinked with calcium ions (Ca(2+)) and glutaraldehyde (GTA), respectively, were developed. Scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), and dynamic mechanical analysis (DMA) were applied to determine their physicochemical characterization. The swelling studies, conducted in phosphate-buffered saline with a pH ranging from 1 to 11 at 37 °C, were utilized for an evaluation of their absorption ability. FTIR spectra of the Ca(2+) crosslinked SA/G hydrogels revealed a small shift in symmetric stretching carboxyl groups, indicating an ionic binding between the Ca(2+) ions and the SA. Increasing the G content in hydrogels crosslinked with GTA significantly changed the shapes of the amide I and II bands in the FTIR spectra, thus confirming the G-GTA crosslink formation. After crosslinking, a DMA study proved the enhanced viscoelastic properties and improved thermal stability of the prepared samples. The obtained data indicated that Ca(2+) crosslinked hydrogels with a SA/G 50/50 ratio provide a good balance of swelling and viscoelastic properties, making them applicable as a potential nontoxic wound dressing material capable of adequately assuring a moist environment, elasticity and mechanical strength for comfortable wound healing.

Cell Proliferation of HaCaT Keratinocytes on Collagen Films Modified by Argon Plasma Treatment

Argon plasma treatment was used to modify the surface of atelocollagen films using a plasmochemical reactor. To evaluate the effects of the treatment, the untreated and treated samples were characterized by Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM) imaging, and X-ray Photoelectron Spectroscopy (XPS) techniques. Cell growth was carried out by culturing human immortalized keratinocyte (HaCaT) cells and proliferation was measured via MTT assay. It was observed that argon plasma treatment significantly enhanced the extent of cell proliferation, which was ascribed to the favourable role of plasma treatment in inducing surface oxygen-containing entities together with increasing surface roughness. This can be considered as a potentially promising approach for tissue regeneration purposes.

Influence of particle concentration on the electrorheological efficiency of polyaniline suspensions

The dependence of the efficiency of positive electrorheological (ER) phenomenon, expressed as a ratio of the low-shear electroviscosity to the field-off viscosity, on the particle concentration of polyaniline base suspensions in silicone oil has been studied. A simple analysis reveals that the dependence of the efficiency on the volume fraction of suspended particles may have a maximum at which the optimum ER performance of material is expected. Experimental results confirmed this expectation. It is demonstrated that with higher temperature the maximum is shifted to higher particle concentration.