Green Polymer-Based Nanocomposites Containing Ceria and Their Use in the Process of Stem Cell Proliferation

A technique of fabrication of bacterial cellulose-based films with CeO2 nanofiller has been developed. The structural and morphological characteristics of the materials have been studied, their thermal and mechanical properties in dry and swollen states having been determined. The preparation methodology gives way to obtaining composites with the uniform distribution of nanoparticles. The catalytic effect of ceria regarding thermal oxidative destruction of cellulose was confirmed by TGA and DTA methods. An increase in CeO2 content leads to a rise in the elastic modulus (1.27-fold rise caused by the introduction of 5 wt.% of the nanofiller into polymer) and strength of the films. This effect is explained by the formation of additional links between polymer macro-chains via the nanoparticles’ surface. The materials fabricated are characterized by a limited swellability in water. Swelling causes a 20-30-fold drop in the stiffness of the material, the mechanical properties of the films in a swollen state remaining germane to their practical use. The application of the composite films in cell engineering as substrates for the stem cells proliferation has been studied. The increase in CeO2 content in the films enhanced the proliferative activity of embryonic mouse stem cells. The cells cultured on the scaffold containing 5 wt.% of ceria demonstrated increased cell survival and migration activity. Analysis of gene expression confirmed the improved cultivation conditions on CeO2-containing scaffolds.

INVESTIGATION OF THE INFLUENCE OF THE THERMAL REGIME OF FDM PRINTING ON THE STRUCTURING AND WARPING OF POLYETHYLENE SAMPLES

The study of the influence of the temperature of polyethylene printing on the dimensional stability of samples obtained by the method of FDM printing has been carried out. It is shown that a change in the temperature of the nozzle from 200 to 260 °C leads to a decrease in the deviation from the plane by a factor of eight. In this case, the tensile strength remains practically unchanged, and the elongation increases by 30 %. It has been established by the methods of rheological and microstructural studies that the observed effect is associated with a change in the structure of polyethylene, which is initiated by an increased temperature of the printer's extruder head. It has been suggested that the likely reason for the change in the structure of polyethylene is a change in the course of the crystallization process due to partial thermal oxidative destruction of the polymer matrix in the extruder head of a 3D printer.

Obtaining and Investigation of the β-Cyclodextrin Inclusion Complex with Vitamin D3 Oil Solution

Background. The research results of fat-soluble vitamin D3 (cholecalciferol) encapsulation with β-cyclodextrin have been presented in this work. The vitamin D3 inclusion complex with β-cyclodextrin was obtained under microwave radiation. The surface morphology of obtained clathrate inclusion complexes was described with the help of a scanning electron microscope. The thermographic measurement results on a differential scanning calorimeter have been presented. The activation energy of the β-cyclodextrin : vitamin D3 clathrate complex thermal oxidative destruction reaction was calculated. The clathrate thermal destruction kinetic parameters were determined. The inclusion complex spectral properties were characterized by IR-Fourier and 1H and 13C NMR spectroscopy. The existence of β-cyclodextrin inclusion complex with vitamin D3 in a 2 : 1 ratio was confirmed by the experimental results. The activation energy of thermal destruction of the inclusion complex of β-cyclodextrin with vitamin D3 was calculated using four different methods.

THE INVESTIGATION ON THERMAL OXIDATIVE DESTRUCTION AND ASSESSMENT OF RUBBER SERVICE PERIOD BASED ON TRIPLE COPOLYMER OF TETRAFLUOROETHYLENE, VINYLIDENE FLUORIDE AND HEXAFLUOROPROPYLENE

By thermogravimetric analysis it was studied the thermal oxidative degradation of rubber based on a triple copolymer of tetrafluoroethylene, vinylidene fluoride, and hexafluoropropylene. It was found that the object is characterized by a sufficiently high heat resistance, which is proven by the rather high temperature of loss of 5% of the initial mass of the sample (412 ° C). The service life of the tested unloaded material in air atmosphere, according to the Arrhenius equation, is 2084, 450 and 107 days at the temperature of 185, 200 and 215 ° C respectively.

Preparation and investigation of properties of metal-containing nanocomposites on the basis of epoxy diane resin

The influence of additions of nanofillers (NF) containing nanoparticles of copper and zinc oxides, stabilized by polymer matrix of high pressure polyethylene, prepared by mechano-chemical method on peculiarities of structure and properties of the metal-containing nanocomposites on the basis of epoxy diane resin (ED-20) by the methods of differential-thermal (DTA) and IR-spectral (IRS) and X-ray diffraction (XRD) has been investigated. It has been shown that an introduction of the metal-containing NF in composition with ED-20 shifts the cold curing reaction temperature from 90 to 75 °C, and hot curing from 125 to 100 °C and favors increase of its thermal stability, which is confirmed by growth of activation energy of thermal-oxidative destruction (Eact) from 210 to 225 kJ/mol. It has been shown that the nanoparticles of copper oxide increase the thermal properties of ED-20 and are the catalysts of curing reaction as evidenced by peak height on curing curve. In this case, the nanoparticles of zinc oxide practically don’t influence on thermal properties of nanocomposites on the basis of ED-20.

CRACKING OF MONOLITHIC POLYCARBONATE SHEETS IN A STRESSED STATE

The accelerated stress cracking of monolithic polycarbonate sheets was investigated. Cracking of polycarbonate organic glasses during operation leading to a drop in impact strength and transparency is their main disadvantage. The main role in the acceleration of the process of cracking is played by the stresses that arise when they are formed and mounted. The aim of this work was to investigate the dependence of the cracking start time on the stress applied to the sheet monolithic polycarbonate. This makes it possible to predict the lifetime of polycarbonate products. The experiments were carried out in air and in contact with an adsorption-active medium (a mixture of toluene and n-propanol). The stresses applied to the samples varied in the range from 25 to 55 MPa. It is shown that the dependence of the cracking start time of a polycarbonate on the applied stress can be described by Zhurkov exponential equation. The coefficients of this equation for the processes of cracking in air and in contact with the adsorption-active liquid are calculated. It is established that the activation energy of the polycarbonate cracking process (129.5 kJ/mol) is close in magnitude to the activation energy of the thermal-oxidative destruction (about 145-155 kJ/mol). In contact with the adsorption-active mixture of toluene (25% mass.) and n-propanol, the activation energy of the cracking is reduced to 98.5 kJ/mol. At the same time, the structural coefficient in the Zhurkov equation ("activation volume") increases from 1.45 to 2.45 nm3. The analysis of the obtained results made it possible to predict the lifetime of monolithic polycarbonate sheets and products made of them at various operating stresses