Structure Analysis of PVC Nanocomposites

In this paper poly(vinyl chloride)/clay nanocomposites were prepared by melt intercalation using a single screw extruder. Problems with thermal stability of these nanocomposites during compounding were largely eliminated by pre-treatment of the organoclay with plasticizer (dioctyl phthalate), which created a barrier between polymer and quaternary amine. These nanocomposite materials were analyzed with respect to their morphology. The intercalation, exfoliation, nano-phase dispersion and orientation were investigated using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and X-ray diffraction (XRD). Moreover, different types of sample preparation for these techniques were tested as well. It was found that partially intercalated and disordered structure arose in poly (vinyl chloride) composites containing sodium type of montmorillonite, while a fine dispersion of partial to nearly full exfoliation of individual montmorillonite layers in poly (vinyl chloride) matrix was observed when this clay was organically modified. Finally, the influence of different mixing time (in extruder) on nano-phase morphology was surveyed.     

X-ray fluorescence determination of major elements in ferromanganese nodules

In this article, the X-ray fluorescence technique is proposed for the quantitative determination of major elements in ferromanganese nodules and crusts, which is a necessary stage of the oceanic ferromanganese deposits investigation and development. The research was performed using a wavelength-dispersive spectrometer S4 Pioneer (Bruker AXS, Germany). Certified reference materials of ferromanganese nodules, cobalt-bearing ferromanganese crusts and pelagic sediments were dried and prepared by two different techniques: the pressing of powder samples on a boric acid substrate and the homogenization by fusion with lithium tetraborate in an electric furnace at 1050°C. For each sample preparation technique, different forms of calibration curves (linear or quadratic) and methods of matrix effect correction (fundamental parameters or empirical intensities coefficients) were examined. The uncertainty of the proposed technique was assessed by analyzing the certified reference material FeMn-1 and by comparison with the atomic absorption spectrometry, flame photometry and spectrophotometry results. Analysis of both fused beads and pressed pellets provides a quantitative determination of the major elements in the oceanic ferromanganese nodules.     

Separation of f-elements by resins impregnated with amides of pyridine-2,6-dicarboxylic acid

Chemistries of trivalent lanthanides and actinides under aqueous processing conditions are so similar that their satisfying separation is extremely challenging. Preparation of a functionalized solid material by impregnation of a support resin with an organic extraction phase is one of possible routes for novel materials development. The ortho- and para-dialkyl-diaryl-pyridine-2,6-dicarboxyamides were impregnated into two macroporous matrices (PS-DVB and PMA). Influence of the diamide structure, matrix type and conditions for effective extraction chromatography separation of Am(III) from Eu(III) was studied in dynamic conditions. The prepared sorbents exhibited more strong adsorptions of Am(III) to compare with Eu(III). Maximal separation factor (~ 90) was achieved with use of citrate ion as complexing eluent.

     

Reactions of 4-methyl- and 4,6-dimethylresorcinols with (2-ethoxyvinyl)phosphonic dichloride – synthesis of new regioisomeric cage phosphonates

Chemistry of Heterocyclic Compounds - Regioisomeric cage phosphonates have been prepared and isolated for the first time by the reaction of 4-methyl- and 4,6-dimethylresorcinols with...     

Photopolymerization of difunctional cyclopolymerizable monomers with low shrinkage behavior

Cyclopolymerizable monomers (CPM) have been the focus of investigations for over 70 years due to favorably low shrinkage upon polymerization, yet little research dealt with difunctional CPMs, especially in the field of radical photopolymerization. Herein, we synthesized novel difunctional 1,6-diene CPMs based on the isomeric mixture of (2,2,4)/(2,4,4)-trimethylhexane-1,6-diamine as spacer unit, which undergoes cyclopolymerization forming five- or six-membered ring structures in the polymer backbone upon photopolymerization. Different photopolymerizable moieties (allyl-, methacryloyl-, and ester-activated allyl-moieties) were chosen for modification of the spacer unit to investigate their influence on reactivity and shrinkage behavior. The (thermo)mechanical properties of the cured difunctional 1,6-diene CPMs further reveal the effect of reactivity-enhancing electron-withdrawing groups (e.g., ester and carbonyl groups) on the final polymer network. For comparison, similar difunctional monoene compounds were are also synthesized and characterized to illustrate the low shrinkage behavior of the novel difunctional 1,6-diene CPMs.     

Sensitivity of the resonant ultrasound spectroscopy to weak gradients of elastic properties

The applicability of resonant ultrasound spectroscopy on materials with weak spatial gradients in elastic coefficients and density is analyzed. It is shown that such gradients do not affect measurably the resonant spectrum but have a significant impact on the modal shapes. A numerical inverse procedure is proposed to explore the possibility of reconstructing the gradients from experimentally obtained modal shapes. This procedure is tested on synthetic data and applied to determine the gradient of the shear modulus in a continuously graded silicon nitride ceramic material. The results are in a good agreement with the gradient calculated for the examined material theoretically as well as with the results of other experimental methods.     

Liquid chromatography under limiting conditions of desorption 4 separation of blends containing low-solubility polymers

Low solubility polymers, poly(ethylene terephthalate), PET and poly(butylene terephthalate), PBT were mutually separated at ambient temperature with help of a novel method, liquid chromatography under limiting conditions of desorption, LC LCD. The results demonstrate high selectivity of LC LCD, which enabled discrimination of macromolecules of well similar chemical structure, irrespectively of their molar mass. Above poly(terephthalate)s were also readily base-line separated from the aliphatic biodegradable polyesters poly(l-lactic acid) and poly(butylene adipate). The experimentally feasible LC LCD method produces narrow, focused peaks of polymers eluted behind the adsorption promoting barrier of appropriate liquid. This merit of LC LCD enables discrimination and identification of minor macromolecular constituents of multicomponent polymers and facilitates the application of method as an integral part of two-dimensional liquid chromatography for comprehensive molecular characterization of complex polymer systems.     

Hydration of humic and fulvic acids studied by DSC

Qualitative and quantitative aspects of hydration of four humic acids (HA) and three fulvic acids (FA) originating from different sources were investigated. DSC experiments at subambient temperatures were carried out in order to monitor differences in ice behavior originating from freezable water surrounding humic molecules. It was found that kinetic effects play a significant role in hydration processes of both HA and FA. In fact, the hydration took part over 21?days which was detected as a progressive decrease in ice melting enthalpy. Simultaneously, the peak shapes and positions changed indicating structural changes in the physical structure of the humic substances. In case of FA, the dependency of melting enthalpy on water concentration showed a linear trend resembling a complete hydration previously observed for water-soluble hydrophilic polymers. In contrast, the melting enthalpy of some HA increased in a step-like way with increasing water content, suggesting preservation of original hydrophobic scaffold during the hydration. The differences between the rather young FA and the rather old HA lead to the conclusion that water can play a significant role in processes of humification. We assume that separation of hydrophobic and hydrophilic domains and thus increase in nanoscale heterogeneity represents an important physical contribution to the overall humification process. It was also demonstrated that the higher content of oxygen in humic molecules is not the only indicator of higher water holding capacity. Instead the porosity of humic matrix seems to contribute as additional parameter into these processes.     

Uranyl adsorption on solvated edge surfaces of pyrophyllite: a DFT model study

In a computational study we addressed the adsorption of uranyl UO(2)(2+) on solvated (110) and (010) edge surfaces of pyrophyllite, applying a density functional approach to periodic slab models. We explored bidentate adsorption complexes on various partially deprotonated adsorption sites: octahedral Al(O,OH), tetrahedral Si(O,OH), and mixed AlO-SiO. Aluminol sites were determined to be most favorable on the (110) surface of pyrophyllite, while on the (010) surface mixed AlO-SiO sites are preferred. The structural parameters of all low-energy complexes on both surfaces agree rather well with EXAFS results for the structurally similar mineral montmorillonite. We calculate the average U-O distance to surface and aqua ligand oxygen atoms to increase with the increasing coordination number of uranyl whereas EXAFS results indicate the opposite trend. According to our results, several adsorption species, with different coordination numbers on different edge faces, may coexist on clay minerals. This computational finding rationalizes why earlier spectroscopic studies indicated the existence of more than one adsorption species, whereas a single type of adsorption complex was suggested from most EXAFS results.