M. I. Voronova

Thermal stability of polyvinyl alcohol/nanocrystalline cellulose composites.

Thermal stability of polyvinyl alcohol/cellulose nanocrystals (PVA/CNCs) composites prepared with solution casting technique was studied. The PVA/CNCs composites were characterized by Fourier transform infrared spectrometry, X-ray diffraction, differential scanning calorimeter (DSC) and thermogravimetric (TG) analysis. Due to the presence of CNCs nanoparticles, thermal degradation of the composites occurs at much higher temperatures compared to that of the neat PVA. Thermal stability of the PVA/CNCs composites is maximally enhanced with CNCs content of 8-12 wt%. Some thermal degradation products of the PVA/CNCs composites were identified by mass spectrometric analysis. TG measurements with synchronous recording of mass spectra revealed that the thermal degradation of both CNCs and PVA in the composites with CNCs content of 8-12 wt% occurs simultaneously at a much higher temperature than that of CNCs or the neat PVA. However, with increasing CNCs content more than 12 wt% the thermal stability of the composites decreases. In this case, the degradation of CNCs comes first followed by the degradation of PVA.

Nanocrystalline cellulose with various contents of sulfate groups.

Properties of films derived from aqueous nanocrystalline cellulose dispersions by water evaporation depend on concentration of sulfate groups. Namely type of thermodestruction and surface morphology change as a function of contents of sulfate groups. Surface roughness increases and water adsorption enhances with increasing sulfate groups content particularly at high relative pressure.

Polymorphism of 4-tert-butylcalix[4]arene upon formation of n-hexane and acetonitrile complexes and thermal desolvation

Simultaneous analysis of X-ray powder diffraction patterns and DSC traces for 4-tert-butylcalix[4]arene-n-hexane and 4-tert-butylcalix[4]arene-acetonitrile compounds as functions of thermal history allows us to reveal the complex relationship between guest-free polymorphic products and desolvation of 4-tert-butylcalix[4]arene inclusion compounds.

Complexation of solvents and conformational equilibria in solutions of the simplest calix[4]arenes.

Structure optimization and calculation of electronic adsorption spectra of 25,26,27,28-tetrahydroxycalix[4]arene and 25,27-dimethoxy-26,28-dihydroxycalix[4]arene conformers have been performed by density-functional theory using hybrid B3LYP functional in cc-p VTZ and cc-p VDZ basis sets in Gaussian 09 package. Analysis of experimental UV-Vis spectra of solutions of 25,26,27,28-tetrahydroxycalix[4]arene, 4-tert-butylcalix[4]arene and 25,27-dimethoxy-26,28-dihydroxycalix[4]arene in various solvents has been carried out. It was shown that the ratio of absorption maxima at characteristic wavelengths at ca. 274 and 283 nm may be used to assess the extent of calix[4]arene/solvent interactions. The conclusion is drawn that spectral characteristics of calix[4]arenes are strongly affected by acid-base interactions.

Adsorption of phenol and toluene from the gas phase and aqueous solutions on cellulose

Adsorption of toluene and phenol from the gas phase and aqueous solutions on various celluloses was studied.

Interaction of water-DMSO mixtures with cellulose

The character of the interaction of cellulose with water-dimethyl sulfoxide mixtures is investigated. It is shown that, in the concentration range 0 < xD < 0.28, cellulose predominantly sorbs water; in this case, in the presence of small amounts of DMSO (xD ∼ 0.1), the sorption is higher than that for pure water. It is established that the formation of hydrogen bonds between hydroxyl groups of cellulose and oxygen atoms in DMSO molecules is most probable at xD > 0.6, where large clusters dominate over hydrophobic dimers.

Polyethylene oxide films reinforced by cellulose nanocrystals: Microstructure-properties relationship

Composite films of polyethylene oxide/cellulose nanocrystals (PEO/CNCs) comprising up to 75wt.% CNCs were obtained via solution casting. For the first time, investigations of the PEO/CNCs composite films over a wide composition range were carried out. Morphology, crystalline structure, thermal stability and the resulting reinforcing effect on the PEO matrix were studied. Polarizing optical microscopy (POM), scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric (TG) analysis, Fourier transform infrared spectroscopy (FTIR), and tensile testing were used to examine the properties of the composites. The revealed extreme dependences of the composite properties refer to the CNCs content of 15-35wt.%. This composition range is characterized by destruction of PEO spherulites and appearance of a pronounced PEO fibrillar structure.

The Adsorption of Aqueous—Organic Mixture Components on Cellulose

The isotherms of composition changes were obtained for the cellulose—water—dimethylsulfoxide and cellulose—water—acetonitrile systems. The isotherms of sorption of aqueous—organic mixture components on cellulose were calculated. The heat effects of wetting of cellulose with water—dimethylsulfoxide and water — acetonitrile solutions were measured. The special features of sorption of the components on cellulose were shown to be related to the character of cluster formation in the binary systems under consideration.

The thermochemical characteristics of solution of phenol and benzoic acid in water-dimethylsulfoxide and water-acetonitrile mixtures

The solution of phenol and benzoic acid in water-dimethylsulfoxide (DMSO) and water-acetonitrile (AN) mixtures was studied. As distinct from benzoic acid, the thermodynamic characteristics of solution of phenol sharply change at concentrations corresponding to a change in the character of cluster formation in water-DMSO and water-AN mixtures. Differences in the solvation of phenol and benzoic acid are explained by different mechanisms of the interaction of the solutes with clusters existing in binary mixtures.

Polymorphic conversions of 4-tert-butylcalix[4]arene upon the formation and thermal destruction of a complex with n-hexane

Complex polymorphic conversions of 4-tert-butylcalix[4]arene upon the formation and thermal destruction of a complex with n-hexane were revealed by combined analysis of powder X-ray pictures and data obtained by differential scanning calorimetry.