Characterization of the Orientation Parameters Around Crack Tips in Unfilled and Nanofilled Poly(propylene) Using in-situ Synchrotron Small and Wide Angle Scanning Scattering Techniques

The fracturing behavior of polymers and polymeric composites is of great interest in the scientific and application community. Especially in the case of silicate-layered nanocomposites the influence of fillers on the fracturing behavior is still fairly unclear. Fractures of semicrystalline polymers are accompanied by various processes of which shearing and cavitations are the most common ones. Nanocomposite deformation due to the delamination of fillers seems to be the most practical way leading to fractures with relatively low strains. With the method of scanning small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD) it is possible to combine information on the structural details with the position on the sample, with the actual position resolution of the investigation being defined by the size of the X-ray beam used to scan the sample. By means of the application of synchrotron radiation it is nowadays possible to adjust the actual beam size to the dimensions of the region of interest, which is why it is an adequate tool for studying the deformation region near a crack tip. In a native polypropylene sample, the fracturing process was accompanied by shear yielding as well as lamellae fragmentation and reorienting. In the highly deformed material near the crack tip fibrillated material could be found. However, in the polymeric nanocomposites (PNC) shearing, lamellae fragmentation, and fibrillation were hindered by the filler due to which the material did not have so much freedom to dissipate energy and fractures occurred much earlier. In this paper the comparison of a PNC and its native polymer is to provide an overview of the different deformation mechanism and the structural details around the crack tip.     

Anticircular high performance thin-layer chromatography

The principal analytical details for the third of three possible modes in high performance thin-layer chromatography are given, namely the anticircular mode. Separation is achieved by allowing the mobile phase to enter the plate layer on a precise outer circle line, from where it flows towards the centre with nearly constant speed. This technique is theoretically and practically the fastest of all three possible in HPTLC. It permits maximum sample capacity with a minimum of time, layer and mobile phase consumption. It is therefore the most economical HPTLC technique. A new carrier-free mobile phase transfer principle is used. The conditions for qualitative and quantitative analysis are good: repeatability, reproducibility and accuracy of routine TLC analyses are superior to those achieved by the classical trough technique. The specially narrow spot-path in anticircular HPTLC facilitates automated quantitation. Compared with the linear and circular modes, the anticircular mode shows better separation and significantly increased sensitivity at higher Rf-values. The drawback, however, is that the separation power (expressed by the separation number) is lower compared with the other two modes.     

Low-temperature plasma surface modification of textiles made from natural fibers and advanced technologies

Processes that occur in natural fibers during glow-discharge plasma treatment are considered. A study of the plasma etching kinetics, capillarity changes, the fiber surface (using electron microscopy and attenuated total multiple internal reflection IR spectroscopy), and the principal mechanical and other properties demonstrated that modification and degradation affect the fiber surface layers. It is evident that the surface membranes of flax and wool fiber cells are damaged. Important reaction pathways are processes involving the transformations of free radicals. Plasma treatment of gray linen fabric leads to degradation and modification of impurities, thereby opening an opportunity for accelerating the laborious bleaching process and making it environmentally more benign. The enhancement of the sorption-diffusion properties by plasma treatment makes it possible to intensify the dyeing and printing processes.     

Mechanism of dissolution of sparingly soluble electrolytes

Recent constant composition dissolution studies of sparingly soluble calcium phosphates have revealed an interesting and unusual behavior in that the rates decreased, eventually resulting in effective suppression, even though the solutions remained undersaturated. Contrary to traditional theories of dissolution, these experimental results indicated the importance of not only the particle size on the dissolution rate but also the participation of critical phenomena. In these theories, it is assumed that when the dissolution reactions are initiated, they continue spontaneously until all solid phase has disappeared. In terms of these mechanisms, there are no critical phenomena in the dissolution mechanism. Although the crystal size decreases during dissolution, when the reaction is controlled by polypitting (formation and growth of pits), the edge free energy increases at the very first stage due to the creation of pits and dissolution steps. The constant composition experimental results demonstrate the development of surface roughness as the dissolution steps are formed, implying an increase of the total edge length during the reactions. In an exactly analogous mechanism to crystal growth, the participation of critical conditions involving dissolution steps is a possibility. In contrast to crystal growth, dissolution is a process of size reduction and, when the particle size is sufficiently reduced, critical phenomena become important so that the influence of size must be taken into consideration. This paper proposes such a model for dissolution reactions, and although these unusual phenomena probably apply to all mineral phases, they are more evident for sparingly soluble electrolytes in which the critical conditions are attained much more readily.     

A tensile testing machine for a scanning electron microscope; Its structure,properties and applications

This work introduces a micro tensile testing machine built in to an ISI 40 SEM scanning electron microscope. With additional accessories (an anticontamination system and a Robinson detector), the machine is suitable for studying non-conductive materials, such as polymers, plastics and non-metallic composites, without coating, during tension or compression.With regard to its properties, the micro tensile testing machine developed in this context can structurally be compared in all aspects to normal mechanical universal tensile testing machines. The difference is that in this case, in addition to the conventional information (force, deformation), a continuing picture of the surface of test materials can be recorded from the area where the most interesting changes are happening. With the micro tensile testing machine it has been possible to retain all movements of the specimen stage, which enables the efficient observation of the specimen in a scanning electron microscope.The examples of applications presented in this paper show that the tensile machine is suitable and useful in studies of plastics and plastic-based composites in a very wide area.     

The rapid determination of cadmium, lead, copper and zinc in whole blood by atomic absorption spectrometry with electrothermal atomization. Improvements in precision with a peak-shape monitoring device

The Varian AA6 atomic absorption instrument with a CRA Model 63 in combination with a peak-shape monitoring system makes it possible to avoid losses of volatile elements during the ashing stage. Lead, cadmium, copper and zinc can be measured with sufficient precision even when only simple sample dilution is applied. Time is saved as laborious extraction procedures and frequent blank firings can be omitted. Zinc is measured above the oven so that 10–20 times lower dilutions with consequent gain in precision are possible.     

Simulation of a movement of dispersed particles in view of a second gas circulation in a cyclone

The gas flow in the cyclone was simulated in view of a constant component of a gas velocity directed from periphery to center of a cyclone. An influence of this component of the gas velocity makes it possible a judgment that with an increase in a value of the radial flowing off the particle velocity can shift and achieve outside wall of a vortex body. Its occurrence was not observed earlier and its forecast was difficult since the radial flowing off was directed to other side. As shown from computations at certain intensity of the second circulation such a critical size of the particles occurs that the particles transfer from suspension to rapid movement toward the outside wall of the vortex chamber.     

Solid state reactions in Al based composites made by mechanofusion

Mixtures of aluminium and other metal powders were milled in a Hosokawa AM-15F mechanofusion system in order to produce composite materials with coated or layered microstructure. These composites were then annealed or used in plasma spraying experiments. The intermetallic phases produced in the consecutive steps of the treatment were investigated by different methods.In the case of the Al-Ni powder system the presence of intermetallic phases confirmed that phase forming solid state reactions start during the first, mechanofusion step. After milling the powder mixture in the Hosokawa equipment, crystalline Al₃Ni could be detected by TEM. A second intermetallic phase, Al₃Ni₂ was also observed after a heat treatment at 750 K. In Al-Cu-Fe and Al-Cu-Co powder composites, produced by milling, binary and ternary phases could be found only after plasma spraying. That means that in these cases the thermodynamic and kinetic requirements of the reactions could not be fulfilled by this mild milling. Nevertheless, the considerably large specific surface of the metal-metal interfaces, formed during the milling process in the ternary composites, makes it possible to produce multi-phase coatings from these composites. It means that only two technological steps are required (milling — plasma spraying). All of the other known technologies consist of three steps: alloy preparation — milling — plasma spraying or alloy preparation —atomisation — plasma spraying.Similarities and differences between the reactions taking place in thin films and thin and/or small milled particles are discussed.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Radiation synthesis of telomers at a constant tetrafluoroethylene concentration in acetone

Radiation-initiated polymerization of tetrafluoroethylene (TFE) in acetone has been carried out in a specially designed reactor, which makes it possible to maintain a constant concentration of the monomer in a solution during synthesis. The features of the telomerization process at different initial concentrations (pressures) of TFE have been studied. Concentrated solutions of telomers have been obtained. The carrying out of the process at different pressures in the reactor makes it possible to obtain telomers differing in molecular mass and thermal resistance.     

Explorative data analysis of two-dimensional electrophoresis gels

Methods for classification of two-dimensional (2-DE) electrophoresis gels based on multivariate data analysis are demonstrated. Two-dimensional gels of ten wheat varieties are analyzed and it is demonstrated how to classify the wheat varieties in two qualities and a method for initial screening of gels is presented. First, an approach is demonstrated in which no prior knowledge of the separated proteins is used. Alignment of the gels followed by a simple transformation of data makes it possible to analyze the gels in an automated explorative manner by principal component analysis, to determine if the gels should be further analyzed. A more detailed approach is done by analyzing spot volume lists by principal components analysis and partial least square regression. The use of spot volume data offers a mean to investigate the spot pattern and link the classified protein patterns to distinct spots on the gels for further investigation. The explorative approach in analysis of 2-D gels makes it possible, in a fast and convenient way, to screen many gels in order to determine the protein patterns that form clusters and could be selected for further examination.     

PVA/PEG/Mg(OH)_2复合材料体系的非等温结晶行为

采用熔融共混法,以聚乙二醇(PEG)为增塑剂、Mg(OH)2为稳定剂制备了聚乙烯醇(PVA)/PEG/Mg(OH)2复合材料。利用差示扫描量热仪(DSC)考察了PVA/PEG/Mg(OH)2复合体系中PVA的非等温结晶行为。结果表明:在熔融过程中PEG与PVA大分子形成的分子间氢键,破坏了PVA分子内或分子间的氢键,改善了PVA的热塑性能,使研究其熔融结晶行为成为可能。     

Properties of ultrahighly filled composites based on polymers and ground rubber

The stress-strain and strength properties of ultrahighly filled composites based on thermoplastic polymers and ground rubber wastes are studied. The content of the elastic filler is higher than 70 wt%. As is shown, introduction of minor amounts of the plastic polymer, which serves as the binder for the filler particles, makes it possible to improve the strength properties of ultrahighly filled composites and to prepare materials of a desired thickness. A correlation between the stress-strain properties of the plastic polymer-rubber systems and the effective viscosity of the matrix polymer is established. When a polymer with homogeneous deformation and good adhesion to the elastic filler is used as the matrix, the resultant composites are characterized by properties close to those of vulcanized rubbers. A new method is proposed for processing of ground rubber wastes and preparation of materials that are similar to hard rubbers.     

Quantitative determination of interfacial adhesion in composites with strong bonding

An approach was proposed for the quantitative determination of adhesion strength in composites, in which adhesion is created by other mechanisms than secondary interactions. The approach is based upon a model, which gives debonding stress as a function of interfacial adhesion. Debonding stress was determined by acoustic emission experiments. The mechanism of deformation was checked by SEM experiments and the approach was verified on composites with known interfacial adhesion. The results showed that the use of functionalized polymer in PP/CaCO₃ composites resulted in adhesion strength one order of magnitude larger than without the coupling agent. The application of various surface modification techniques in PP/glass bead composites yielded different adhesion values covering a range of about one order of magnitude. The quantitative determination of interfacial adhesion makes possible the design and optimization of most surface modification techniques in particulate filled and short fiber reinforced composites.     

Kinetic parameters from thermogravimetric study of used rubber granulates–polyurethane composites

From the TG data of rubber granulates, different polyurethane and composites it can be seen that the thermal decomposition for the rubber granulate and all of the composites start above 520 K. Two major mass losses for the rubber granulates and majority of the composites were observed and thermal decomposition is essentially complete by ~820 K. The changes of activation energies of lower and higher temperature decomposition, calculated according to the different equations were observed for a priori assumed first-order reaction for devolatilisation. Differences between determined and calculated results could suggest a possible reaction between polyurethane agents and rubber granulate during the composites formations.     

Improving piezoelectric performance of lead-free polymer composites with high aspect ratio BaTiO3 nanowires

Flexible and lead-free piezoelectric nanocomposites were synthesized with BaTiO₃ nanowires (filler) and poly(vinylidene fluoride) (PVDF) (matrix), and the piezoelectric performances of the composites were systematically studied by varying the aspect ratio (AR) and volume fraction of the nanowire and poling time. BaTiO₃ nanowires with AR of 18 were synthesized and incorporated into PVDF to improve the piezoelectric performance of the composites. It was found that high AR significantly increased the dielectric constant up to 64, which is over 800% improvement compared to those from the composites containing spheroid shape BaTiO₃ nanoparticles. In addition, the dielectric constant and piezoelectric coefficient were also enhanced by increasing the concentration of BaTiO₃ nanowires. The piezoelectric coefficient with 50-vol% BaTiO₃ nanowires embedded in PVDF displayed 61 pC/N, which is much higher than nanocomposites with spheroid shape BaTiO₃ nanoparticles as well as comparable to, if not better, other nanoparticle-filled polymer composites. Our results suggest that it is possible to fabricate nanocomposites with proper mechanical and piezoelectric properties by utilizing proper AR fillers.     

Mixtures of organocobalt chelates as initiators of emulsion polymerization of styrene

The emulsion polymerization of styrene has been investigated in the presence of the mixture of alkylcobalt(III) chelates with a tridentate Schiff base containing linear or branched alkyl ligands and characterized by different decomposition constants. The addition of as low as 10 wt % of the complex with the isopropyl ligand to the mixture has been shown to decrease the induction period by a factor of 5 compared with the ethylcobalt complex. The optimal mass ratio between organic cobalt complexes containing isopropyl and ethyl ligands is 1: 3. It has been established that the use of a pair of initiators containing alkyl ligands of different structures, with one of them (more active) efficiently initiating the polymerization at the initial stage and the other (with a lower decomposition rate constant) providing the presence of free radicals in the reaction zone until complete conversion of the monomer, makes it possible to carry out the process to high conversions (>99%) within the optimal period.     

Effect of structural parameters of Ni-ScSZ cermet components on the SOFC anodes characteristics

The effect of the degree of dispersion and the ratio of initial components of metalloceramic composites based on Ni and Sc₂O₃-stabilized ZrO₂ (Ni/ScSZ) on the kinetics of sintering, conductivity, and polarization resistance of the corresponding anodes in solid-oxide fuel cells (SOFC) is studied. The composites are prepared from nano- and submicrosized powders of NiO and ScSZ (10.5 mol % Sc₂O₃) containing particles with the average size of 0.02–0.33 μm. Anode composites of three types differing in the ratio of initial components (NiO-ScSZ) with different degrees of dispersion: micro-micro, nano-micro, and nano-nano are studied. Due to the ratio of particle sizes, the anodic composites of the nano-nano type demonstrate the preferential electronic conduction (the percolation threshold) starting from the Ni content of about 35 vol %, in contrast to the other two types of anodic composites for which this threshold is achieved at 30 vol %. The lowest polarization resistance is typical of anode composites with the Ni content of about 40 vol %. The use of one or both components in the nanosized state makes it possible to decrease the anodic polarization up to two times. It is demonstrated that an active cermet anode for SOFC can be fabricated in the form of a planar three-layer structure Ni/ScSZ-ScSZ-Ni/ScSZ prepared from nanosized powders by the tape casting technique and cosintering.     

Statistical Modeling of Unidirectional Fibrous Structures

Some textiles such as slivers, rovings, yarns, and highly oriented polymer fibers as well as the reinforcing structure of unidirectional composites have a kind of unidirectional or quasi-unidirectional fibrous structures. The statistical properties of their structure and strength can be modeled by using idealized fiber bundles as model elements. In this study the tensile test process of unidirectional short fiber structures is modeled for different damage types using the instantaneous fracture model and special idealized fiber bundles for gradual damages such as fiber breakage and fiber slippage. Constant fiber length and exponential fiber length distribution as extreme cases of the Erlang distributions were used for analysis. In case of exponential fiber length distribution and constant fiber breaking strain simple analytical relationships between the mean tensile strength and the fiber length were derived and compared to those for constant fiber length and written in a general form which is valid for all the damage modes discussed. The convex linear combination of the solutions for exponential fiber length distribution and constant fiber length was proposed to use for cases when the variation coefficient of the fiber length is between 0 and 1. The practical applicability of the results was demonstrated by identifying the relationship between the mean tensile strength and the average molecule mass of polypropylene fibers that made it possible to estimate the critical molecule mass and the tensile strength of the molecules without further measurements.     

A critical study of some methods used to investigate atom formation processes in GFAAS

Proposed methods that yield information about mechanisms of atom formation, utilize the shapes of analytical signals that lie either under the rising or under the constant part of the temperature curve. We have evaluated both types of methods by use of a versatile data acquisition system, by which temperature and corresponding absorbance values were simultaneously sampled and stored. The stored data were subsequently used for calculations referring to arbitrary parts of the analytical signal, thus permitting accurate evaluations.Results obtained from “constant temperature methods” were found to be influenced by factors like sample amount, type of graphite surface and inner gas flow-rate. Meaningful results were only obtained for sample amounts larger than those used during normal working conditions.Results obtained from “rising temperature methods” were in rough agreement with each other. However, they all showed large standard deviations, indicating that several mechanisms are acting during atom formation. This makes it difficult to extract useful information from energy values obtained with these methods.     

Viscoelastic Drag of Particles Settling in Wormlike Micellar Solutions of Varying Surfactant Concentration

Wormlike micellar octadecyl trimethyl ammonium chloride (OTAC) solution is a self-assembled fracturing fluid used to carry proppants into fractures in oil recovery. Slow settling velocity of proppant is desirably resulted from the viscoelastic drag with low viscosity of fracturing fluids for fracturing work. Steel spheres, as a substitute for proppants, fall into three semi-dilute OTAC solutions. The steady rheology demonstrates that OTAC solutions are divided into shear-thickening and shear-thinning regimes by the critical shear rate. The applied steel spheres always lie in the shear-thickening regime of the 2.8 wt% OTAC solution with aggregated micelles as their characteristic shear rates are less than the critical shear rate of the solution. Strong shear-thickening viscous drag results in lower settling velocity of steel spheres. Most of the applied steel spheres, on the other hand, lie in the shear-thinning regime of the 4 wt% OTAC solution with orientated micelles. Although the latter solution has small dissipation coefficient, high Weissenberg number, and consequently high elastic effect, the shear-thinning viscosity results in higher settling velocity of steel spheres.