Jiřina Hromádková

Effect of layered silicates and reactive compatibilization on structure and properties of melt-drawn HDPE/PA6 microfibrillar composites

Microfibrillar composites (MFCs) of HDPE matrix with PA6 reinforcing fibrils formed in situ by melt drawing were modified by ethylene/glycidyl methacrylate copolymer (PEGMA) and addition of layered silicates using different mixing protocols. The goal was enhancement of adhesion between fibrils and matrix, their reinforcement by clay, and evaluation of the effect of clay on the MFC morphology, especially the fibril dimensions. Improved mechanical properties, including toughness, were found in the case of pre-blending Cloisite 15A (C15) with both polymeric components. Pre-blending of Cloisite C30B (C30) in PA6 is effective at low draw ratios only, whereas simultaneous addition of both clays leads to significant worsening of properties. In many cases, low stiffness increase indicates existence of clay-induced controversial effects which may eliminate reinforcement induced by fibrils and clay. The results indicate that these effects are significantly affected by the extent and course of clay migration between polymer phases during extrusion-mixing and melt drawing. Possible explanation of affecting the properties due to low-modulus interface supported by finite element analysis (FEA) is presented.

Ultrathin sectioning of polymeric materials for low-voltage transmission electron microscopy

The relief in ultrathin sections is interpreted as one of the reasons for the image contrast observed in low-voltage transmission electron microscopy. In order to clarify this, processes taking place in the course of ultrathin sectioning were monitored using a polymeric material composed of hard matrix and soft particles (high-impact polystyrene). Volume changes leading to a surface relief were observed both on cut surfaces and in ultrathin sections.

Phase structure of binary and ternary polycarbonate blends

Abstract Phase structures of binary and ternary blends of polycarbonate (PC) with poly(styrene-co-acrylonitrile) (PSAN), and poly(methyl methacrylate-co-styrene) (PMMAS) were examined by transmission (TEM) and/or scanning transmission electron microscopy (STEM). Osmium or ruthenium tetroxides were applied to ultrathin sections and significant differences in the staining of phases were observed: PC was stained most intensely, while staining of the PSAN- and PMMAS-rich phases was affected by the concentration of the dissolved (partially miscible) PC. The blends within the phase inversion interval contained both PC continuous and PC dispersed phases, which were observed at different places on the sample cross-section. Three-phase structure, found in ultrathin sections of binary blends and confirmed on plasma-etched cut surfaces, is discussed from the point of view of likely artefacts; a possible interpretation considers non-uniform blending in the melt.

Visualisation of the phase structure of selected polycarbonate blends using various preparation techniques

Abstract The importance of knowledge of the phase structure in designing a polymer blend requires that the phase structure must be capable of visualisation. For this purpose several preparation techniques have been developed, varying in laboriousness and in the volume of the output information. Applicability of several visualisation techniques for polycarbonate blends, such as classic ultra-thin sectioning, etching, swelling, volume relaxation and fracturing, is reported and compared. Ultra-thin sectioning, the most reliable method, is the most laborious. The alternative methods, the drawbacks of which consist mainly in lower resolution, are generally less complicated and can provide additional information on the system studied, such as on orientation of particles close to the (cut) surface, some properties of the individual constituents, and also on the interfacial adhesion (fracture surfaces).

The role of lubricants in Reactive compatibilization of polyolefin blends

Reactive compatibilization using liquid polybutadienes and dialkyl peroxides was studied in model low-density polyethylene/polypropylene (4/1) blends and the commingled waste of composition similar to these blends. The influence of three types of lubricants (Ca stearate, stearic acid - Loxiol G20 and paraffin - Loxiol G22) on the structure and toughness of these blends was determined. In spite of the fact that in the waste material, a coarse morphology and poor toughness were found in comparison with the blend of virgin polyolefins, reactive compatibilization has approximately the same effect in both types of the blends as far as the structure parameters and mechanical behaviour are concerned. This effect is enhanced by addition of lubricants, the most efficient being the paraffin in the model blends, probably due to its partial miscibility with LDPE. In the commingled waste, liquid polybutadienes supported on precipitated SiO 2 appear to be quite efficient. No influence of the reactive compatibilization on both the crystal modification and the crystalline content was observed in both types of these blends.

Ultrathin Sectioning Of Polymeric Materials For Low-voltage Transmission Electron Microscopy: Relief On Ultrathin Sections

Ultrathin sectioning, one of the types of specimen preparations for transmission electron microscopy (TEM), has been considered the most perfect sectioning technique leading to the thinnest sections (50–100 nm). Following a study based on a newly developed low-voltage TEM technique, a relief on the ultrathin sections of polymer blends was observed that was ascribed to substantial differences in mechanical properties of the blend constituents.[1] In this study, an analogous relief was observed with a blend, the constituents of which are both hard in cutting. The origin of the surface relief on ultrathin sections of polymer blends was sought using low-voltage scanning TEM and atomic force microscopy. Polycarbonate/styrene-co-acrylonitrile blend was examined as a representative of blends with all components well under T g at room temperature. A distinct surface relief was observed on both ultrathin sections and remaining cut surfaces of the blend for low-temperature and room-temperature cutting. A rougher surface relief was found on the ultrathin sections than on the remaining cut surfaces. The surface relief was assumed to occur in the course of the cutting when extensive shearing occurs. Correspondence of the surface relief with the phase structure proves the influence of different mechanical behavior of individual blend components on the resulting morphology. #Presented in part at the 5th Multinational Congress on Electron Microscopy, Lecce, Italy, 20–25 September 2001.

Multifunctional polypyrrole@maghemite@silver composites: synthesis, physico-chemical characterization and antibacterial properties

Maghemite (γ-Fe2O3) nanoparticles were synthesized by coprecipitation of ferrous and ferric salts with ammonia and oxidation with sodium hypochlorite. Polypyrrole (PPy) was obtained, by the chemical oxidative polymerization of pyrrole in an aqueous solution in the presence of iron oxide nanoparticles. The morphology of PPy was turned from globular to nanofibers by addition of dyes. The resulting PPy@γ-Fe2O3 hybrid composites were characterized by transmission electron microscopy, magnetic and electrical conductivity measurements and energy dispersive X-ray spectroscopy. Both the electrical conductivity and magnetic properties of the PPy@γ-Fe2O3 nanocomposites were controlled by the maghemite content due to the insulating properties of magnetic iron oxide nanoparticles added to the conducting polymer. Antibacterial activity of all materials was defined by determination of minimal inhibitory concentration. Antibacterial properties of native materials were improved by the reduction of silver ions from an aqueous solution to obtain PPy@γ-Fe2O3@silver composites. Due to the antibacterial properties of these composites, especially of those with silver particles, they can be considered for the applications where bacterial contamination can deteriorate the functionality of material.