Adhesive properties of binary mixtures of some ethylene copolymers

It is shown using the example of polyolefin thermoplasts that the value of adhesion strength is determined by the mechanical properties of a composition.     

Mechanics of polymer nanocomposites modified with fulleroid nanofillers

Polymer nacomposites based on thermosetting (epoxy resins) and thermoplastic (PA-12) polymer matrices with fulleroid and carbon modifiers are synthesized through in situ polymerization, and the mechanical properties are investigated. The introduction of fulleroid modifiers has almost no effect on the mechanical properties of thermosetting formulations; however, in the case of thermoplastic formulations, Young’s modulus and tensile strength increase by 30–40% after introduction of 0.02–0.06 wt % fulleroid modifiers.     

Polymer nanocomposites based on polyamide 6 modified with fulleroid fillers

Polymer nanocomposites based on polyamide and fulleroid modifiers are synthesized through in situ polymerization, and their mechanical and electric properties are studied. After introduction of 0.001–0.1 wt % fulleroid modifiers, Young’s modulus and the strength of thermoplastic composites increases by 15–20%, practically independently of the amount of filler. This circumstance is due to the fact that the introduction of fulleroid fillers causes selective crystallization of polyamide 6 only in the α form. The introduction of fullerene fillers considerably improves the tribological characteristics of polymer nanocomposites, thereby decreasing the friction coefficient by a factor of 2. The electric properties of nanocomposites are studied also.     

Modification of epoxy adhesives by hydroxyurethane components on the basis of renewable raw materials

A new class of modifiers for epoxy-amine adhesive and sealant compositions is proposed—carbonated epoxidized vegetable oils. Results of synthesis of the new modifier and properties of hybrid adhesive compositions using it are presented. Physical-mechanical properties were found to improve as a result of the introduction of hydroxyurethane components into the modified compositions.     

A fundamental study of the effects of modifiers in supercritical fluid chromatography

The effects of organic modifiers on retention and peak shape in packed-column supercritical fluid chromatography were studied. The adsorption behavior of different modifiers was investigated on stationary phases consisting of hydrocarbon monolayers chemically bonded on silica. Adsorption isotherms for several modifiers were recorded using breakthrough measurements. The results were compared with those obtained by a simple method based on the injection of different sample sizes. Modifiers were selected to reflect various types of interactions with the silica support. Isotherms were found to be approximately Langmuirean. Experiments were performed to elucidate the influence of adsorbed molecules on the retention of selected test solutes. The introduction of a solvent modifier can lead to a substantial change in the mobile phase density, the effect of which is comparable with that of an increase in the density of pure carbon dioxide. Our results confirm that the effects of low concentrations of modifiers (between 0 and 2 percent) in packed-column SFC are largely due to deactivation of residual silanol groups on the silica support. The accessibility of the active sites was found to depend strongly on the size and structure of the modifier molecules. The decrease of retention due to the addition of low concentrations of modifiers could be described accurately by a model derived from Langmuir adsorption behavior. Some semi-quantitative rules for the selection of modifiers and the required concentrations for optimum deactivation of the support are discussed.     

Effects of organic modifiers on solute retention and electrokinetic migrations in micellar electrokinetic capillary chromatography.

Influences of seven organic modifiers, including urea, methanol (MeOH), dioxane (DIO), tetrahydrofuran (THF), acetonitrile (ACN), 1-propanol (1-PrOH) and 2-propanol (2-PrOH), on the solute retention and the electrokinetic migrations in micellar electrokinetic capillary chromatography (MEKC) are investigated with sodium dodecyl sulfate (SDS) micelle as pseudostationary phase. It is observed that in the limited concentration ranges used in the MEKC systems the effect of organic modifier concentration on the retention can be described by the equation logk1=logk1w-SC for most binary aqueous-organic buffer, but deviations from this retention equation are observed at ACN and particularly THF as organic modifiers. With parameter S as a measure of the elutropic strength, the elutropic strength of the organic modifiers is found to follow a general order urea 相似文献   

Behavior of thorium,zirconium, and vanadium as chemical modifiers in the determination of arsenic by electrothermal atomization atomic absorption spectrometry

The comparative effect of thorium, zirconium and vanadium used as chemical modifiers in wall and platform atomization of arsenic using two sample introduction modes (aerosol vs. liquid drop) was studied. The effect of proton concentration (as hydrochloric acid and nitric acid) on the behavior of these modifiers was also tested. A beneficial effect on the stabilization of arsenic from all the chemical modifiers was essentially derived in the presence of nitric acid mainly for the aerosol introduction mode. Nonetheless, the highest sensitivity and the best stabilization of arsenic were obtained using zirconium and thorium as a chemical modifier, because pyrolysis temperatures as high as ∼1500°C can be used. The mechanistic action of the chemical modifiers used is also studied, resulting in the formation of a mixture of oxides stabilized at high temperatures.     

Liquid chromatographic enantiomeric resolution of amino acids with β-cyclodextrin bonded phases and derivatization with o-phthalaldehyde

The reaction of amino acids with o-phthalaldehyde (OPA) and 2-mercaptoethanol is evaluated as a precolumn derivatization technique in order to achieve the chiral separation and final fluorimetric detection of l,d-glutamic acid in β-cylodextrin bonded phases. The pertinent chromatographic parameters were determined and the effect of organic modifiers, pH, ionic strength and temperature on retention and resolution were evaluated. The chromatographic method finally developed allowed the optical resolution of OPA-derivatized l- and d-glutamic acid using methanol—1% triethylammonium acetate (pH 7.4) (30 + 70, v/v) as eluent.     

Determination of metal additives and bromine in recycled thermoplasts from electronic waste by TXRF analysis

A new method for analysis of metal additives in recycled thermoplasts from electronic waste was developed, based on dissolving the samples in an organic solvent and subsequent analysis of the corresponding solutions or suspensions by total-reflection X-ray fluorescence spectroscopy (TXRF). The procedure proved to be considerably less time consuming than the conventional digestion of the polymer matrix. Additives containing Ti, Zn, Br, Cd, Sn, Sb, and Pb were analyzed in a hundred randomly selected samples from recycling, which provided an overview of the range of elemental concentrations in thermoplasts utilized for consumer electronics. The results were validated independently by instrumental neutron activation analysis (INAA), subsequent regression analysis confirmed the trueness of the chosen approach.     

Photocrosslinking Probes Proximity of Thymine Modifiers Tethering Excitonically Coupled Dye Aggregates to DNA Holliday Junction

A DNA Holliday junction (HJ) has been used as a versatile scaffold to create a variety of covalently templated molecular dye aggregates exhibiting strong excitonic coupling. In these dye-DNA constructs, one way to attach dyes to DNA is to tether them via single long linkers to thymine modifiers incorporated in the core of the HJ. Here, using photoinduced [2 + 2] cycloaddition (photocrosslinking) between thymines, we investigated the relative positions of squaraine-labeled thymine modifiers in the core of the HJ, and whether the proximity of thymine modifiers correlated with the excitonic coupling strength in squaraine dimers. Photocrosslinking between squaraine-labeled thymine modifiers was carried out in two distinct types of configurations: adjacent dimer and transverse dimer. The outcomes of the reactions in terms of relative photocrosslinking yields were evaluated by denaturing polyacrylamide electrophoresis. We found that for photocrosslinking to occur at a high yield, a synergetic combination of three parameters was necessary: adjacent dimer configuration, strong attractive dye–dye interactions that led to excitonic coupling, and an A-T neighboring base pair. The insight into the proximity of dye-labeled thymines in adjacent and transverse configurations correlated with the strength of excitonic coupling in the corresponding dimers. To demonstrate a utility of photocrosslinking, we created a squaraine tetramer templated by a doubly crosslinked HJ with increased thermal stability. These findings provide guidance for the design of HJ-templated dye aggregates exhibiting strong excitonic coupling for exciton-based applications such as organic optoelectronics and quantum computing.     

Hot-melt adhesives based on polyamides of dimerized fatty acids and adhesive compositions from oligoamidoamines and epoxy resins

The production and the application of hot-melt adhesives and adhesive compositions based on polyamide and the oligoamidoamine derivatives of dimerized fatty acids are studied. The possibility of synthesizing basic polyamide thermoplasts with desired physicochemical properties is shown.     

A study of the properties and microstructure of weld-bonded joints

Two fitting techniques—namely, welding and weld bonding—are considered. The technological regimes and the properties of the obtained welded and weld-bonded joints are presented. The microstructure of the heat-affected zone is studied. It is shown that the introduction of boron nitride as a filler into an adhesive significantly decreases the roughness of the heat-affected zone, which proves that a decrease in its looseness has taken place and leads to an increase in the strength of a joint.     

Determination of metal additives and bromine in recycled thermoplasts from electronic waste by TXRF analysis

A new method for analysis of metal additives in recycled thermoplasts from electronic waste was developed, based on dissolving the samples in an organic solvent and subsequent analysis of the corresponding solutions or suspensions by total-reflection X-ray fluorescence spectroscopy (TXRF). The procedure proved to be considerably less time consuming than the conventional digestion of the polymer matrix. Additives containing Ti, Zn, Br, Cd, Sn, Sb, and Pb were analyzed in a hundred randomly selected samples from recycling, which provided an overview of the range of elemental concentrations in thermoplasts utilized for consumer electronics. The results were validated independently by instrumental neutron activation analysis (INAA), subsequent regression analysis confirmed the trueness of the chosen approach. Received: 7 February 2000 / Revised: 25 February 2000 / Accepted: 1 March 2000     

A chemometric investigation of the selectivity of multisolvent mobile phase systems in RP-HPLC

Summary The selectivity of multisolvent mobile phase systems consisting of water, methanol, acetonitrile and tetrahydrofuran was studied when the solvent strength decreases at a constant ratio of the modifiers. From the retention measurements of six benzene derivatives on an octylsilica column at eleven different mobile phase compositions the relation between the logarithm of the capacity factor of each solute and the mobile phase composition was modeled by a quadratic equation. From the models the capacity factors of the solutes were predicted for 3 binary, 3 ternary and 7 quaternary mobile phase systems when the fraction of water decreases and the ratio of the organic modifiers is kept constant for the tenary and quaternary solvent systems. The selectivity factors, alpha, of five pairs of solutes were calculated from the capacity factors and plotted against the solvent strength of the mobile phase systems. The selectivity remained not constant, but varied with the solvent strength: if the water fraction of a multi-solvent system is changed at a constant ratio of the modifiers, not only the solvent strength, but also the selectivity changes. The consequence of this result for optimization strategies is discussed.     

Chiral resolution of some environmental pollutants by capillary electrophoresis

The chiral resolution of the environmental pollutants by capillary electrophoresis is reviewed. Various aspects of the chiral resolution such as chiral selectors, optimization of capillary electrophoresis conditions including composition of the background electrolyte (BGE), pH of the BGE, ionic strength of the BGE, structures and types of the chiral selectors, applied voltage, temperature, structures of the chiral pollutants, use of organic modifiers and other parameters are presented. Furthermore, detection, sample treatment, validation of the methods, and the chiral recognition mechanisms, have been discussed.     

The Effect of Oligoethers Based on Secondary Polyethylene Terephthalate and Oligopropylene Diol on the Properties of Novolac Compounds

The ability to apply PL oligoethers comprising secondary polyethylene terephthalate and oligopropylene diol for efficient modification of novolac oligomers is considered. The influence of modifiers on the properties of novolac C is studied. It is shown that the use of PL polymers as modifiers provides an increase in strength of foam materials of novolac phenol–formaldehyde oligomers by three to five times.     

Rheology behavior of nematic side-chain polymers in blends with thermoplasts

Peculiarities of the rheological behavior of blends composed of thermoplasts and side-chain nematic polymers have been studied. The strong role of interface interactions associated with the polymer chemical structure on the effect of rheology is shown. The influence of the nematic ordering is shown to be effective in the mechanical characteristics of blend extrudates whereas the rheology effect does not depend on the liquid crystal ordering.     

Polymer Nanocomposites Containing Fullerene C60 Nanofillers

Summary: The effect of fulleroids (fullerene C₆₀, mixture of C₆₀/C₇₀ and fulleroids soot which used for fullerenes production) and carbon fillers (carbon black, graphite) on mechanical properties of polymer nanocomposites based on reactoplasts (epoxy resins) and thermoplasts (polyamide-12) was investigated. The nanocomposites were prepared by in situ polymerization. It was found that additives of these fillers did not influenced on the properties of reactoplasts. Therefore, the tensile modulus and tensile strength of thermoplast based polymer nanocomposites are improved by about 30-40% with loading of 0.02-0.08 fulleroids materials. Best results were obtained for a mixture of C₆₀/C₇₀.     

Symmetry in the design of NMR multiple-pulse sequences

The symmetry principles of NMR pulse-sequence design are summarized. The discussion is guided by an analogy with tiling schemes in the decorative arts. The symmetry operations for NMR pulse sequences are discussed in terms of excitation field modifiers and temporal modifiers. The quantum operators which describe the effect of these modifiers on the excitation field spin Hamiltonian are provided. The symmetry transformations of spin propagators, and the different types of pulse-sequence elements are discussed. The common types of symmetry expansion are treated using the propagator transformations and the Euler angles for the excitation field propagators. The selection rules associated with symmetrical pulse sequences are discussed using average Hamiltonian theory.     

Effect of carbon nanoparticles of different shapes on mechanical properties of aromatic polyimide-based composite films

Nanocomposite films based on thermally stable polypyromellitimide are prepared via the introduction of cylindrical and laminar carbon nanoparticles—nanofibers and nanocones/disks—into the prepolymer solution. An increase in the filler concentration increases the elastic modulus and yield stress of the material. Moreover, in composites filled with nanofibers, both characteristics increase much less intensely than those of films containing nanocones/disks. Rigidity increases in composites filled with nanofibers when their concentration is below ～7 vol %. A further increase in concentration is accompanied by the aggregation of nanofibers. The introduction of the nanoparticles of both types into the polymer matrix stabilizes the behavior of the material under prolonged mechanical loading: both the creep strain and the relaxation intensity decline with an increase in the filler concentration. The introduction of nanocones/disks into the polyimide matrix results in a more pronounced stabilization of creep characteristics of films than that in the case of nanofibers.