A. G. Zakharov

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.

The magnetocaloric effect and the heat capacity of aqueous suspensions of porphyrin complexes of rare earth elements according to microcalorimetric data

The magnetocaloric effect (MCE) and heat capacity during the magnetization process of (5,10,15,20-tetraphenylporphyrinato)acetatogadolinium(III), (AcO)GdTPP, and (5,10,15,20-tetraphenylporphyrinato)chlorogadolinium(III) complexes, (Cl)GdTPP, in the form of 6%-aqeous suspensions are determined by the microcalorimetric method in a range of temperatures from 278 to 318 K and magnetic fields from 0 to 1 T. It is found that MCE for all the complexes are positive, i.e., at applying a magnetic field in the adiabatic conditions temperature of a suspension of complex increases. It is established that MCE increases with an increase in magnetic induction at all temperatures and decreases with an increase in temperature at all magnetic fields. It is shown that the substitution of chloride ligand by acetate in (X)GdTPP leads to a significant increas in MCE and its temperature dependence; in the case of (Cl)GdTPP actually MCE does not depend on temperature. Relationships between magnetothermal properties and structure of the complexes are analyzed. The conclusion is argumented that the reason of changes in magnetothermal properties after the replacement of axial ligand in gadolinium complexes and complexes of lanthanides with an unsymmetrically filled f-shell is non-planar geometry of the coordination site and specific electronic properties of the central ion. It is concluded that heat capacity of the complexes slightly increases with an increase in temperature and more noticeably in the case of (AcO)GdTPP; a magnetic component of heat capacity is revealed only in (AcO)GdTPP at temperatures above 298 K, which is connected perhaps with a temperature change in the crystal lattice of the complex and influence of the magnetic properties of gadolinium ion on this change.

Magnetocaloric effect and heat capacity of high-spin manganese complexes in a disperse state

Magnetothermal properties of high-spin chloro(2,3,7,8,12,13,17,18-octaethylporphyrinato)manganese(III), chloro(5,10,15,20-tetraphenylporphyrinato) manganese(III), bromo(5,10,15,20-tetraphenylporphyrinato)manganese(III), and (acetato)(5,10,15,20-tetraphenylporphyrinato)manganese(III) complexes as 6% water suspensions were determined by the microcalorimetric method at 298 K in a magnetic field of 0–1.0 T. It was established that when the magnetic field was applied, the temperature of the systems increases, leading to positive values of the magnetocaloric effect: the higher the magnetic field induction, the higher the values. It is shown that the dependences of the heat capacity of the complexes’ solid particles on the magnetic field induction are of an extreme nature with a heat capacity in the area above 0.6 T less than that in the zero field. The regularities of the dynamics of the numerical values of the change in enthalpy and magnetic entropy of the manganese complexes when a growing magnetic field was applied and the regularities of the influence of the acidoligand in pentacoordinated complexes on their magnetothermal properties were considered.

Fullerene–Naphthalene Interaction on the Water Surface and in the Binary Film

Abstract This work continues the studies on the non‐covalent fullerene–donor interaction that were recently conducted by non‐spectroscopic methods in solution. The Langmuir–Blodgett (LB) technique is engaged as a main experimental tool to exclude interfering solvent effects. Methods to prepare a stable low‐dimensional fullerene–water system and to monitor intermolecular interactions therein are proposed. As a molecular partner of fullerene, β‐benzylnaphthalene (BN) modeling a functional π‐donor is used. No pair C60–BN interactions were found in both C60–BN–H2O and C60–BN systems. Thus, a lack of molecular affinity of fullerene for typical π‐donors is stated not only in solution but in solvent‐free systems as well. For this reason, none of classic non‐covalent interactions can be exploited to control the state of fullerene in solid composites.

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.

Oxidative Delignification of Flax Fiber

Oxidative delignification of flax fiber at 98°C was studied. The intermediate material was produced in moderate yield with high degree of delignification. The optimum conditions of the process were determined.

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.

Interrelation between the crystallinity of polysaccharides and water absorption

The maximum sorption of water and its vapors is calculated using experimental data from calorimetric and effusion studies of flax, wood, and cotton cellulose. X-day diffraction is used to determine the crystallinity of cellulose samples. The equations relating crystallinity (X) with maximum sorption and the enthalpy of interaction between cellulose and water are presented. Experimental results and the literature data on water sorption by chitin, chitosan and other polysaccharides show that our equations for calculating crystallinity are correct.