S. M. Lomakin

Fire-retardant additives for polymeric materials. I. Char formation from silica gel-potassium carbonate

Silica gel combined with potassium carbonate is an effective fire retardant for a wide variety of common polymers (at mass fraction of only 10% total additive) such as polypropylene, nylon, polymethylmethacrylate, poly(vinyl alcohol), cellulose, and to a lesser extent polystyrene and styrene-acrylonitrile. The peak heat release rate is reduced by up to 68% without significantly increasing the smoke or carbon monoxide levels during the combustion.

Structural-dynamic characteristics of matrices based on ultrathin poly(3-hydroxybutyrate) fibers prepared via electrospinning

Structural-dynamic analysis based on combined thermophysical and molecular mobility measurements via spin-probe ESR spectroscopy has been applied to films and fibrous matrixes based on poly(3-hydroxybutyrate). The dynamic behaviors of partially crystalline samples during deformation under conditions of electrospinning and cold rolling have been compared. The comparative results of the complex investigation of films and ultrathin fibers in the poly(3-hydroxybutyrate) matrix have shown that the electromechanical action leads to additional crystallization of the crystalline regions, spherulites, and lamellas in the polymer. The changes in the crystalline phase of the polymer are accompanied by an increase in the packing density of macromolecules in the intercrystalline space. With the use of the spin-probe ESR method, the effect of water and the oxidant ozone on the morphology of the amorphous phase of poly(3-hydroxybutyrate) ultrathin fibers has been determined. The measurements of the dynamics of spin-probe rotation in samples before and after cold rolling have shown that the additional orientation of poly(3-hydroxybutyrate) spherulites in a mechanical field results in stabilization of amorphous regions more resistant to the aggressive effects of ozone.

Thermal degradation and combustion of a polypropylene nanocomposite based on organically modified layered aluminosilicate

The specific features of thermal degradation and combustion of polypropylene nanocomposites based on organically modified layered aluminosilicate were studied. On the basis of thermogravimetric analysis data, a kinetic model that takes into account the diffusive character of the thermal degradation process for the PP nanocomposite was proposed. The basic flammability parameters of the nanocomposite were determined with the use of a cone calorimeter. The influence of diffusion constraints in the charred nanocomposite layer on the maximum heat release rate as a principal parameter of flammability was considered.

Nonwoven blend composites based on poly(3-hydroxybutyrate)–chitosan ultrathin fibers prepared via electrospinning

With the use of scanning electron microscopy, differential scanning calorimetry, and electron paramagnetic resonance, the structural–dynamic analysis of ultrathin fibrous matrixes based on poly(3-hydroxybutyrate) and blend composites of this polymer with chitosan is performed. It is shown that the addition of a small amount of chitosan causes change in the morphologies of the matrixes and leads to a marked increase in their melting enthalpies. It is found that the studied fibers contain amorphous regions with various morphologies. The dynamics of the spin probe TEMPO in these regions is investigated, and its change under the influence of increased temperature, an aqueous medium, and ozone is examined. The mechanism controlling the effects of chitosan, temperature, and an oxidative aggressive medium on the structuring of fibers is advanced.

Preparation and characteristics of composites based on polypropylene and ultradispersed calcium carbonate

Feasibility studies directed at the parallel increase in the elastic modulus and impact toughness of polypropylene via introduction of ultradispersed CaCO3 particles with sizes of 100 (Socal U1S2) and 60 nm (Socal 312V) have been performed. The effects of the content and sizes of CaCO3 particles and the nature of a surfactant on the character of distribution of particles, the thermophysical characteristics of the polymer matrix, and the mechanical characteristics and heat resistance of the nanocomposites are analyzed. Microscopic studies reveal that nanoparticles show a tendency toward structuring. DSC studies have proved the nucleating action of ultrafine particles during the crystallization of PP. For the composites containing 15 vol % of Socal 312V CaCO3 nanoparticles, the increase in the tensile elastic modulus achieves its maximum; depending on the nature of the surfactant, the reinforcing effect increases by 70-40%. As compared to the initial PP, the presence of ultrafine particles in the composites prevents a decrease in the storage modulus of PP with increasing temperature from 0 to 50°C; as a result, the reinforcing effect increases from 30-40% at temperatures below the glass transition temperature to 40–75% at 50°C. For the nanocomposites with U1S2 in the presence of Triton X-100 or fluorinated alcohol telomer, the impact toughness increases over the entire filler content interval; when the filler concentration is 15 vol %, the impact toughness of nanocomposites is higher than that of the initial PP by factors of 3 and 4.5, respectively. It has been found that nanocomposites containing 5 vol % CaCO3 nanoparticles show the effect of thermal stabilization, which comes up to about 50°C.

Structural dynamic properties of nonwoven composite mixtures based on ultrafine tissues of poly(3-hydroxybutyrate) with chitosan

The structural dynamic parameters of ultrafine fibrous matrices of poly-3-hydroxybutyrate (PHB) and composite mixtures of PHB with chitosan were studied by differential scanning calorimetry, EPR spectroscopy, and scanning electron microscopy. The melting enthalpy of PHB fibers considerably increased when a small amount of chitosan was added. Amorphous regions with diverse morphology were found in the fibers under study. The dynamics of the TEMPO spin probe in these regions and its change in the fibers under the action of temperature, aqueous medium, and ozone was determined. The mechanism responsible for the effect of chitosan, temperature, and aggressive oxidating medium on the structure of ultrafine PHB fibers was suggested.

Role of Structural Stresses in the Thermodestruction of Supercoiled Cellulose Macromolecules after Nitration

Thermogravimetry is used to study the thermodestruction of nitrocellulose (NC) with various nitrogen contents at various heating rates. At high degrees of nitration and high heating rates of the sample, the reaction occurs in an explosion mode with a threshold of its weight loss depending on the temperature. To explain this behavior, it is assumed that the nitration of cellulose gives rise to structural stresses, which weaken the covalent bonds in it by ∼37 kJ/mol (at a nitrogen content of ∼13%). This process apparently involves two different mechanisms of weight loss during heating: (a) conventional thermal destruction of NC macromolecules through the rupture of covalent bonds (with k0 = 1013 s−1, E = 150.2 kJ/mol, and n = 1) at heating rates of up to 10 K/min and nitrogen content in NC of up to 9%; (b) Zhurkov’s thermofluctuational mechanism of the destruction of strained macromolecules, characterized by a sharp (threshold) dependence of the weight loss on the heating rate, which is operative at heating rates above ∼4 K/min and high (>13%) nitrogen contents and at 20 K/min and a low (∼9%) nitrogen content. Under conditions of rapid heating, ∼10–20 K/min, the work done by stressed states to overcome the potential barrier to the rupture of covalent bonds causes an increase in the decomposition rate by a factor of 2000. The observed threshold pattern of weight loss during the thermodestruction of NC explains the long-known critical dependence of the properties of NC used to manufacture propellants on small changes in the nitrogen content.

Oxygen-induced free-radical reactions in phenylone nitrated by nitroxide dioxide

The conversion of phenylone polymer (poly-m-phenylene isophthalamide) at 293 K under the action of a nitrogen dioxide−oxygen gaseous mixture and nitrogen dioxide and oxygen individually is studied by the ESR method. In the first case, aryliminooxyl and arylacylaminoxyl free radicals are recorded, whereas in the second, diarylaminoxyl and phenoxy free radicals. The presence of phenolic and phenyl benzoate polymeric products in nitrated phenylone is detected by IR spectroscopy. The mechanisms of reactions occurring in both the oxidation modes are considered.