Low-temperature combustion of energetic materials in filled polymer systems

In systems filled by inert additives, combustion of cellulose nitrate (CN) proceeds in a flameless low-temperature regime with a low linear burning rate. At a standard temperature, the exponent in the low of CN combustion in ballasted mixtures with inert additives in the pressure range of 0.1 to 10 MPa is several times lower than that of pure cellulose nitrate and amounts to 0.23. The qualitative and quantitative composition of gaseous products of flameless CN conversion is found. It is noted that this composition approximately corresponds to data available in the literature for the products of thermal decomposition of cellulose nitrate at comparatively low temperatures. Based on this fact and on a weak dependence of the CN burning rate on pressure in ballasted systems, the process under these conditions is assumed to be controlled by conversion of the energetic component predominantly in the condensed phase. In the case of a composite consisting of cellulose nitrate, silicon carbide, and polymer binder, for samples 10–25 mm in diameter, armoring exerts practically no effect on combustion parameters. Combustion of the same mixture with smaller diameters of non-armored samples is unstable. The presence of a liner establishes a clearly expressed critical combustion diameter in the examined systems. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 98–102, May–June, 2007.     

Gas absorption with photochemical reaction

Gas-liquid reactions can be activated by high energy radiations (photons). When gas absorption is accompanied by pseudo-first order reaction further enhancement in the specific rate of absorption can be realised for situations where either the reactive species in the liquid phase is activated or the dissolved solute gas is activated.     

Gas absorption with wetted-wick column

The newly designed wetted-wick column was constructed by using fiber glass and wire mesh and studied to investigate its feasibility as an alternative to the conventional packed tower in gas purification processes. Absorption of carbon dioxide in water for physical absorption and in aqueous mono-ethanolamine (MEA) solution for chemical absorption were employed for this investigation. A comparison with the packed tower, based on overall mass transfer coefficients (K_OGa) and height of transfer units (HTU_OG) at the same range of operating conditions, feed gas compositions, and gas retention time was made. High mass transfer coefficients (K_OGa) and low heights of transfer unit (HTU_OG) were obtained for the wetted-wick column. The high efficiency of mass transfer was caused by a number of factors: the separate passage of liquid and gas flow, an increased wetting surface, a longer period of residence time of the liquid and gas stream, and an increased interfacial area. The present study shows that the wetted-wick column is a highly recommendable device as an alternative to the packed tower in gas purification processes, either for physical gas absorption or for chemical gas absorption.     

PTC effect of polymer blends filled with carbon black

Low-density polyethylene/ethylene-propylene-diene terpolymer (LDPE/EPDM) blends and LDPE/ethylene-ethyl acrylate (EEA) blends were chosen as objects of study. Their positive temperature coefficient (PTC) phenomena and their distinctive aspects were described. The explanations were given from the structural characteristics of the blends. © 1994 John Wiley & Sons, Inc.     

Gas absorption with autocatalytic reaction

The film theory has been employed to investigate gas absorption accompanied by an autocatalytic chemical reaction of the form A + ? → ? + ?. This reaction has been taken to be the simplest analogue of the autocatalytic features of chain reactions encountered in the industrially important gas-liquid oxidation and chlorination reactions. Numerical solutions have been obtained using standard library subroutines for integrating systems of first order equations, having transformed the two describing second order non-linear differential equations into suitable first order initial value form. Predictions of the Enhancement Factor show that it can be very considerably larger than that for the ‘equivalent’ first order reaction. This is due to the accumulation of radicals within the mass transfer film. An asymptotically exact empirical approximation for the Enhancement Factor is also presented. The ‘degree of conversion’ of the absorbed gas across the mass transfer film is shown to be more sensitive to the kinetic and diffusional parameters than is the case for a first order reaction.     

Linear viscoelasticity of polymer melts filled with nano-sized fillers

The linear dynamic rheology of polymer melts filled with nano-sized fillers is investigated in relation to a proposed two phase model. A common principle is disclosed for nanofilled polymers exhibiting either fluid- or solid-like behaviors with increasing filler volume fraction. The bulky polymer phase far away from the filler inclusions in the nanocomposites behaves the same as in the unfilled case while its contribution to the composite modulus is enlarged due to strain amplification effect. The filler forms aggregates together with polymer chains absorbed on the filler surface, which is termed as the “filler phase” in the proposed model. The dynamics of the “filler phase” slow down with increasing filler concentration. The applicability of the proposed two phase model is discussed in relation to the well-known structural inhomogeneity of nanofilled polymers as well as the strain amplification and the filler clustering effects.     

Lithium polymer batteries using the highly porous membrane filled with solvent-free polymer electrolyte

Solid polymer electrolyte supported by a microporous membrane was prepared and characterized. The polymer electrolyte was prepared by penetrating the highly conductive solvent-free polymer electrolyte based on poly(oligo [oxyethylene] oxyterephthaloyl) into the pores of the highly porous membrane. The electrochemical characteristics of the solid polymer electrolytes are presented, and we discuss the possibility of them as an electrolyte material for lithium polymer batteries.     

Synthesis and properties of oil absorption resins filled with polybutadiene

Polybutadiene (PB) is used to fill an oil absorption resin as a physical crosslinker to construct a kind of 3‐dimensional network with a high degree crosslinking and low crosslink density. A series of acrylic resin particles with various compositions are prepared by suspension polymerization, using benzoyl peroxide (BPO) as an initiator and ethylene glycol dimethacrylate (EGDMA) as a chemical crosslinker. The effects of the polymerization temperature, initiator concentration, monomer feed ratio, and chemical and physical crosslinker concentrations on the oil absorbency and gel fraction (degree of crosslinking) are studied. The recipe and operation conditions are optimized as follows: a mass ratio of 3:1 for styrene (St)/dodecyl methacrylate or St/butyl acrylate, 0.5 wt % BPO, and 80°C for 7–8 h. The effect of the physical crosslinker (PB) concentration is complex. The oil absorbency increases with increasing PB at lower EGDMA concentrations. However, under this same condition, particles cannot be formed if the PB concentration is higher than a certain value. By contrast, there is an optimum PB concentration when the EGDMA concentration is higher. The oil absorption speed is also investigated. The presence of PB can speed up absorption. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3309–3314, 2003     

Plasticity structural analysis of polymer nanocomposites filled with carbon nanotubes

A structural analysis of an increasing plasticity effect for polymer nanocomposites filled with carbon nanotubes was carried out. It was shown that this effect was due to densely packed interfacial layer formation on an atomic scale on the smooth nanotube surfaces, which resulted in changes in the polymer molecular matrix and structural characteristics. A prediction of the nanocomposite properties as a function of nanotube contents was obtained. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Percolation conductivity of polymer composites filled with dispersed conductive filler

This paper deals with the conductivity of binary polymer composites filled with an electronically conductive material. A “dynamic cluster model” is offered to describe the conductivity of such polymer composites in the highly filled region, i.e. above the percolation threshold. The model is based on the following assumptions:

• 1 a modification of the basic statistical percolation equation, i.e. σ (φ−φ_c)^t, where t = 1.6 to 1.9, should be applied for all systems in the highly filled region, although application is limited to the range φ = φ_c + Δφ, Δφ ⟹ 0 in the strict statistical percolation approach;
• 2 the most important modifications with respect to the basic equation of the statistical percolation theory are
  • (a) the use of a constant t_eff, including a constant part t₁ (resembling “t” in the basic statistical percolation approach) and a variable part t₂ (depending on the filler concentration φ of the specific mixture) and
  • (b) the definition of φ_c as the filler concentration where a perfect three-dimensional network of the conductive phase has been established. This idea has been adopted from the bond-percolation approach of Aharoni;
• 3 the resulting equation should include parameters of specific polymer composites.

The generalized equation σ = f(φ) is used to calculate the maximum possible conductivity of a certain mixture as well as the dependence of σ on the filler content.     

填充聚合物的流变行为探讨

对炭黑、无机物质、纤维填充聚合物的流变行为分别进行了讨论。初步探讨了影响填充聚合物流变性能的因素,并概括了其流变特性和粘弹性质。     

Uniaxial compaction behavior of filled polymer powders

A simple method is described to obtain rheological data on filled polymeric materials in the form of powders. The powder is compacted in a cylindrical chamber by a plunger driven by the cross-head in an Instron testing machine and the load-displacement curve is recorded. Further information is obtained by compressing the powder to a fixed load and measuring the load decay with time (stress-relaxation). The tests are illustrated by application to “monocomponent toner” powders used in dry copying or nonimpact printing processes. It is shown that compaction and stress-relaxation data are able to differentiate between different toners and facilitate the prediction of their relative performances in terms of pressure fusing. A mechanical spring-dashpot-slider model is effective in describing the rheological behavior of these powders and its dependence on the loading of a hard filler (magnetic pigment). The latter affects the “slider” yield stress in the model but has no influence on the relaxation times.     

The elastic modulus of filled polymer composites

The elastic modulus of polyepichlorohydrin (PECH) filled with glass beads and wollastonite was studied. It was found that the elastic modulus of the composites depends not only on the volume fraction of the fillers but also on their size. Percolation theory was used to explain the experimental results. © 1993 John Wiley & Sons, Inc.     

Preparation of zeolite filled glassy polymer membranes

The incorporation of zeolite particles in the micrometer range into polymeric matrices was investigated as a way to improve the gas separation properties of the polymer materials used in the form of membranes. The adhesion between the polymer phase and the external surface of the particles appeared to be a major problem in the preparation of such membranes when the polymer is in the glassy state at room temperature. Various methods were investigated to improve the internal membrane structure, that is, surface modification of the zeolite external surface, preparation above the glass-transition temperature, and heat treatment. Improved structures were obtained as observed by scanning electron microscopy, but the influence on the gas separation properties was not in agreement with the observed structural improvements. © 1994 John Wiley & Sons, Inc.     

Extrusion of highly filled flexible polymer sheet

Highly-filled polymer systems include color masterbatches, feedstocks for powder injection molding, and rigid sheets with high levels of flame retardants, but they have not been explored for flexible sheet. This work investigated the (a) selecting a polymer matrix with enough melt strength and flexibility to form a stable sheet with high filler loading, (b) the maximum achievable filler loading for the sheet, and (c) optimizing the process of extruding a highly-filled flexible polymer system. Extrusion grade low-density polyethylene (LDPE) provided sufficient flexibility and permitted a maximum filler loading of 36 vol% (~78 wt%). Good dispersion of the nanoparticle filler, however, required two passes through multiple screw extruders and a small reduction in the viscosity of the LDPE. Sheet with thickness of 415 μm, surface roughness of <1 μm, and sufficient flexibility was extruded continuously at a rate of 10 m/min., but it required a more traditional coat hanger manifold to prevent filler hang up in the sheet die. The filler particles were distributed uniformly through the core and skin of the sheet, giving the sheet good mechanical properties.     

Rheological behavior of highly filled polymer melts

The rheological behavior of highly filled polymer melts has been examined. At concentrations near the maximum packing fraction, strain-dependent behavior was observed at strains as low as 1 percent. Selected surface treatments were shown to reduce particle agglomeration. This produced composite melts with lower viscosities and higher maximum loadings. While η* – ω plots provide information on the shear strength of the interparticle network, G′ – ω plots show evidence of phase separation.     

Morphology and rheology of immiscible polymer blends filled with silica nanoparticles

The effect of silica nanoparticles on the morphology and the rheological properties of an immiscible polymer blend (polypropylene/polystyrene, PP/PS 70/30) was investigated. Two types of pyrogenic nanosilica were used: a hydrophilic silica with a specific surface area of 200 m²/g and a hydrophobic silica having a specific surface area of 150 m²/g. First, a significant reduction in the PS droplet volume radius, from 3.25 to nearly 1 μm for filled blends with 3 wt% silica, was observed. More interestingly, image analysis of the micrographs proved that the hydrophilic silica tends to confine in the PS phase whereas hydrophobic one was located in the PP phase and at the PP/PS interface (interphase thickness ≈ 100-200 nm). Furthermore, a migration of hydrophilic silica from PP phase toward PS domains was observed.An analysis of the rheological experimental data was based on the framework of the Palierne model, extended to filled immiscible blends. Due to the partition of silica particles in the two phases and its influence on the viscosity ratio, limited cases have been investigated. The rheological data obtained with the hydrophobic silica were more difficult to model since the existence of a thick interphase cannot be taken into account by the model. Finally, the hypothesis that hydrophilic silica is homogeneously dispersed in PS droplets and that hydrophobic silica is dispersed in PP matrix was much closer to the actual situation. It can be then concluded that stabilization mechanism of PP/PS blend by hydrophilic silica is the reduction in the interfacial tension whereas hydrophobic silica acts as a rigid layer preventing the coalescence of PS droplets.