Hydrolytic degradation of ionically cross-linked polyphosphazene microspheres

The hydrolytic degradation of gel microspheres based on calcium cross-linked phosphazene polyelectrolytes, poly[di(carboxylatophenoxy)phosphazene] (PCPP) and poly[(carboxylatophenoxy) (glycinato)phosphazene] (PCGPP), was investigated. These microspheres are of importance as carriers in protein and cell encapsulation. Both PCPP and PCGPP ionotropic polyphosphazene hydrogels are degradable in an aqueous environment (pH 7.4, 37°C). The degradation rates can be increased by incorporation of hydrolysis sensitive glycinato groups as the pendant structures in the polymer (PCGPP). Hydrolysis of these polymer hydrogels led to low molecular weight (<1,000 Da) products. The erosion and molecular weight profiles varied also according to the molecular weight of the polyphosphazene constituting the gel beads. Another approach to affect the degradation rates consists of coating microspheres with poly-L -lysine. Ionotropic polyphosphazene hydrogels have potential as biodegradable devices for controlled drug delivery systems. © 1994 John Wiley & Sons, Inc.     

Softening and melting mechanisms of polyamides interfering with sliding stability under adhesive conditions

The thermal stability of polymers is a main issue when used as friction elements under dry sliding. Cast polyamide grades processed with either natrium or magnesium catalysors are slid on a small-scale and a large-scale test configuration to reveal the effect of softening or degradation on the sliding stability and to investigate possibilities for extrapolation of friction and wear rates between both testing scales. The combination of softening and afterwards transition into the glassy state is detrimental for the sliding stability of natrium catalysed polyamides, characterised by heavy noise during sliding. A transfer film formed under continuous softening also provides high friction. Melting during initial sliding is necessary for stabilisation in both friction and wear, and eventual softening of a molten film near the end of the test then not deteriorates the sliding stability. Softening of magnesium catalysed polyamides is favourable for the formation of a coherent transfer film resulting in more stable sliding than natrium catalysed polyamides. The differences in softening mechanisms of both polyamide grades is correlated to structural changes investigated by thermal analysis and Raman spectroscopy: the γ crystalline structure prevails in magnesium catalysed samples and the α crystalline structure is predominant in natrium catalysed samples. For internal oil lubricated polyamides, a time dependent degradation of the polyamide bulk deteriorates the supply of internal oil lubricant to the sliding interface, resulting in high friction and wear under overload conditions. As the degradation mechanisms during sliding are strongly correlated to the test set-up, extrapolation is only possible for friction in a limited application range, while wear rates cannot be extrapolated.     

Ignition and Combustion of Dust-Gas Suspensions

The ignition and combustion of dust-gas suspensions are considered. It is shown that the ability of these systems to accumulate heat is determined not only by their kinetic and thermal properties but also by the relation between their reaction surface and the heat-removal surface (f). Experimental information on flame temperatures, ignition delays, and flame propagation over gas suspensions is processed using the parameter f, and the postulate on the stimulating role of the developed reaction surface in activating these processes is validated. It is shown that during overall burning, diffusion combustion of particles occurs only for rather small values of f. The ambiguous effect of the parameter f on the ignition and combustion processes leads to the necessity of optimizing the fuel size distribution and concentration for the effective operation of the power devices. The role of the macroparameters of two-phase flames of refractory metals in the synthesis of combustion nanoproducts is analyzed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 6, pp. 3–14, November–December, 2005.     

Polyelectrolyte swelling of polyamidobenzimidazole

Conclusions An extreme character of the swelling of PABI fibres in DMAc-water mixtures has been detected. The maximum is observed in the region of a 10% water content.The peculiarity in swelling has been explained by the manifestation of a polyelectrolyte nature of the polymer.Translated from Khimicheskie Volokna, No. 5, pp. 34–35, September–October, 1987.     

Methods of controlling curing kinetics in polymer coatings

Traditional methods have limitations for controlling curing of polymers in a coating. The promise of using the method of dielectric spectroscopy for studying the kinetics of curing of the binder in polymer coatings is demonstrated. __________ Translated from Khimicheskie Volokna, No. 1, pp. 59–62, January–February, 2007.     

Carbon Nanofibers: A New Ultrahigh-Strength Material for Chemical Technology

Carbon nanofibers are described as a new ultrahigh-strength material, which is superior to both ordinary carbon fibers and other high-strength materials. The place occupied by nanofibers in the classification of carbon materials is shown, and an analysis is made of the relationship between the structure of a fiber and its useful properties, in particular, the strength and tensile modulus. Studies on the synthesis of nanofibers are reviewed. It is shown that the practically important problem of producing nanofibers of maximum possible length must be solved by controlling the temperature conditions of the reaction. The prospects for introducing nanofibers into the market of high-strength and heat-resistant materials are analyzed. The most likely prospect seems to be the partial replacement of polyacrylonitrile-based fibers by nanofibers, first and foremost, in the fields where the requirements for high strength are particularly stringent due to safety reasons.     

Interrelationship of the baric index for the normal burning velocity of gas—Air mixtures and the kinetics of trimolecular reactions in a flame front

Through numerical simulation of flame propagation through a methane- and hydrogen-air mixture, with consideration given to the transfer and chemical reactions, we have investigated the relationship between the kinetics of trimolecular reactions and the baric index of the normal burning velocity. It has been demonstrated that the lower the constants of the trimolecular reaction rates, the higher the magnitude of the baric index. In the case of methane the baric index, although it grows, it nevertheless remains negative, while in the case of hydrogen this index changes sign.Balashikha. Translated from Fizika Goreniya i Vzryva, No. 2, pp. 46–49, March–April, 1991.     

Relative Energies of 〈011〉 Tilt Boundaries inNiO

The variation of the relative energy of symmetrical 〈011〉 tilt boundaries in nickel oxide was studied as a function of misorientation by measuring the angle of the groove formed following thermal etching of bicrystals. Cusps on the energy curve were observed for high-coincidence angles.     

Morphology and mechanical properties of amine-terminated butadiene-acrylonitrile/epoxy blends

Morphology and mechanical properties of (amine terminated butadiene acrylonitrile rubber/diglycidyl ether of bis-phenol-A epoxy resin) blends of different compositions, cured in wide range of temperatures, are described. Curing at low temperature promoted formation of homogeneous materials with poor fracture resistance. On the contrary, at high temperature tough heterogeneous blends were obtained. Such blends showed phase inversion above 20 percent of rubber. The volume fraction of precipitated phase, determined on SEM micrographs, was higher than the amount of added rubber. A fracture mechanism to account for this is proposed. Extensive voiding and interface damage were observed in the low temperature cured materials. Such phenomena did not contribute to the fracture energy.