Rheological Characterization of Metalized and Non‐Metalized Ethanol Gel Propellants

The gellation of metalized and non‐metalized ethanol with a methylcellulose gelling agent and its effect on the rheological properties (flow and dynamic study) of these gels is reported herein. The rheological study shows that increasing the shear rate reduces the apparent viscosity for a given yield stress (for a shear rate range of 1 to 12 s⁻¹) for both shear rate ranges (1 to 12 and 1 to 1000 s⁻¹) covered in present experiment. The gellant and metal particle concentrations significantly influence the gel apparent viscosity. Distinct changes in thixotropic behavior were observed, while decreasing the concentration of MC gellant and Al metal particles in the ethanol gels. The dynamic study showed that all of the linear viscoelastic regions (LVE) of the gel samples were independent of strain percentage (1 to 10). The G′ values depended on the frequency and exceeded the G′′ values, which indicated a gel‐like highly structured material. The tanδ values showed that all of the ethanol gels were elastic and weak physical gels with a high degree of cross‐linking.     

Effects of gellant concentration on the burning and flame structure of organic gel propellant droplets

The increasing demand for higher energy density fuels and the ever-increasing concern for their safety have propelled research in the field of gel propellants. For studying the fundamental parameters without the interference of neighbouring droplets, an isolated droplet was chosen to investigate experimentally the combustion process of gel propellants under normal gravity conditions. Phase separation of the gel propellant components leading to bubble nucleation, vapor jetting and microexplosions were found to be the main phenomenon involved during the combustion period. Experiments were comprehensively carried out to study the effect of gellant concentration on the burning rate constant as well as flame structure. The burning rate constant was found to decrease with increase in the gellant concentration. Decrease in the calorific value of the increasing gellant concentrations was proposed as one of the reasons for this variation. The flame exhibited a triple flame structure for all the cases for both radicals as well luminous flames. The horizontal and vertical flame standoff distances were observed to decrease with gellant content. Decrease in the content of the base fuel was proposed as the reason for the same.     

The Online Measurement of Lyocell Fibers and Investigation of Elongational Viscosity of Cellulose N‐methylmorpholine‐N‐oxide Monohydrate Solutions

In this paper, the development of diameter and surface temperature of Lyocell fibers was measured online. The diameter and tensile force on the spin line in the coagulation bath were traced. The velocity, velocity gradient and the tensile stress profiles development of the fibers in the air gap were studied. The apparent elongational viscosity of cellulose N‐methylmorpholine‐N‐oxide monohydrate (NMMO‐MH) solutions was studied by steady‐state melt spinning theory. The decrease of the fiber diameter was mainly taking place near the spinneret, and the decrease of the diameter became more dramatic with increasing taking‐up speed. The surface temperature of the fibers was also dropping faster with increasing taking‐up speed for the heat transfer coefficient increased. The diameter of the Lyocell fibers almost did not change before and after it entered the coagulation bath. The tensile force on the spin line increases with increasing taking‐up speed and coagulation bath length. The velocity and the tensile stress increase slowly near the spinneret, and then accelerate. The apparent elongational viscosity of cellulose NMMO‐MH solutions decreases with increasing temperature at the same elongation rate and decreases with increasing elongation rate at the same temperature. The fiber of the Lyocell process was not really solidified in the air gap and a gel or rubbery state was formed.     

Thermoanalysis and rheological behavior of emulsion copolymers of methyl methacrylate,N‐phenylmaleimide and styrene

Terpolymers of methyl methacrylate (MMA), N‐phenylmaleimide (PMI) and styrene (St) were synthesized by emulsion copolymerization. The thermal stabilities of terpolymers were studied by a programmed thermogravimetric analysis (TGA) technique. Terpolymers show a considerable increase in decomposition temperature with increasing feed content of PMI and St. The glass transition temperatures (T_g) of copolyniers were measured by differential scanning calorimetry (DSC) and torsional braid analysis (TBA). The terpolymer's T_g increases markedly with the increasing PMI feed content, while it decreases with increasing St feed content. The rheological behaviors of copolymers were also studied. The terpolymer's apparent viscosity in melt decreases with increasing feed contents of PMI and St. The terpolymer's flow index n increases with the increasing feed content of PMI. The results also show that the difference value between T_gDSC and T_gTBA ' ΔT_g increases with an increase in the terpolymer's flow index. M?_w and M?_n of copolymers were also determined by gel permeation chromatography (GPC).     

聚丙烯/微胶囊红磷复合材料熔体密度及流动性能研究

采用熔体流动速率仪考察了温度、载荷以及微胶囊红磷含量对聚丙烯/微胶囊红磷(PP/MRP)复合体系熔体密度和流动性能的影响。结果表明:在实验条件下,PP/MRP复合体系熔体密度随温度升高而降低,随载荷的增大而提高,随MRP含量的增加而呈增大的趋势。PP/MRP复合体系熔体的表观剪切应力与剪切速率基本符合幂律方程,熔体为假塑性流体,并且随着温度的升高,熔体黏度降低,假塑性增强;随着MRP含量的增加,熔体的黏度提高,假塑性增强。PP/MRP复合体系熔体的表观剪切黏度对温度的依赖性符合Arrhenius关系。     

In‐line Rheological Behaviors of Gun Propellant Substitute Assisted with Supercritical CO2 in Extrusion Processing

To improve the rheological behaviors of gun propellants, SC‐CO₂ was injected into the gun propellant substitute in extrusion processing. A slit die rheometer was used to investigate the in‐line rheological behaviors of CA solution. A Power model was applied to describe the rheological behaviors of CA/SC‐CO₂ mixtures. The viscosity and pressure of CA solution obviously decrease with the assistance of SC‐CO₂. The viscosity of CA solution reduces by 16.64 % at 55 °C and 10 s⁻¹ with the presence of SC‐CO₂. Increasing the processing temperature makes the viscosity of CA/SC‐CO₂ mixture decrease remarkably, but it weakens the plasticization of SC‐CO₂ to CA. Although the increasing solvent content improves the flow of the CA/SC‐CO₂ mixture, it lowers the strength of CA/SC‐CO₂ mixture, which is not in favor of the quality of product. The investigation of the in‐line rheological behaviors of CA/SC‐CO₂ mixture is fundamental and important for the safe extrusion of gun propellants assisted with SC‐CO₂.     

PBT/海泡石纳米复合材料流变性及形貌特征研究

先对海泡石进行有机化处理,再用PBT对有机化海泡石原位插层(PBTS),将PBTS与PBT熔融共混制备PBT/PBTS插层纳米复合材料。流变测试结果表明:PBT/PBTS插层纳米复合材料为典型的假塑性流动,偏离牛顿流动的程度随PBTS含量的增加而减小,表观黏度和零切黏度随着PBTS含量的增加而减小,PBTS有明显的改善PBT流动性的作用。添加PBTS后的复合材料的黏流活化能明显小于纯PBT,说明复合材料的温敏性降低,流体可以在较宽温度范围内进行成型加工。复合材料的力学性随PBTS含量的增大而增大,达到最大值后有所降低。     

Instability due to Viscosity Stratification Downstream of a Centerline Injector

A common injector geometry upstream of a static mixer is the centerline injector. A flow instability can arise due to viscosity differences between the injected core‐flow and the outer co‐flow. This instability can adversely affect the effectiveness of the mixing operation. An experimental investigation of miscible viscosity‐stratified flow in a circular geometry was performed using Laser Induced Fluorescence (LIF) and Particle Image Velocimetry (PIV). The experimental results for the stable region agree with the analytical results. The unstable region exhibits different modes depending on the viscosity ratio, volume flux ratio, and Reynolds number. The modes include wavy core‐flow with fissures and wavy core‐flow with core breakup. The time‐averaged experiment velocity profiles for the unstable core indicate a broadening of the jet at the centerline, which is consistent with the LIF visualization.     

Effects of compositional variations on CO2 foam under miscible conditions

Foam can mitigate the associated problems with the gas injection by reducing the mobility of the injected gas. The presence of an immiscible oleic phase can adversely affect the foam stability. Nevertheless, under miscible conditions gas and oil mix in different proportions forming a phase with a varying composition at the proximity of the displacement front. Therefore, it is important to understand how the compositional variations of the front affect the foam behavior. In this study through several core‐flood experiments under miscible condition, three different regimes were identified based on the effects of the mixed‐phase composition on CO₂ foam‐flow behavior: In Regime 1 the apparent viscosity of the in‐situ fluid was the highest and increased with increasing x_CO2. In Regime 2 the apparent viscosity increased with decreasing x_CO2. In Regime 3 the apparent viscosity of the fluid remained relatively low and insensitive to the value of x_CO2. © 2017 American Institute of Chemical Engineers AIChE J, 64: 758–764, 2018     

Influence of particle size and fluid fraction on rheological and extrusion properties of crosslinked hyaluronic acid hydrogel dispersions

Crosslinked hyaluronic acid (HA) hydrogels are widely used in gel/HA fluid formulations as a viscosupplement to treat joint diseases; thus, it is important to characterize these hydrogels in terms of their particle size and to investigate the effects of the gel/fluid mixtures on their rheological properties and extrusion force. Hydrogels previously crosslinked with divinyl sulfone were sheared in an Ultra‐Turrax unit to produce particles with mean diameters ranging from 20 to 200 μm. Hydrogels with 75–100 μm mean diameters were also evaluated in dispersions containing a 20–40% mass fraction of HA fluid. The mean diameters were measured by laser light scattering and the rheological behavior was determined by oscillatory and steady measurements in parallel plate geometry. The HA hydrogels exhibited the typical behavior of so‐called weak gels, as analyzed by the storage and loss moduli G′ and G″, respectively. The viscoelasticity, the viscosity, and the extrusion force increased with the hydrogel particle size. The fluid phase dispersions decreased both moduli. At 40% fluid fraction, the gel characteristics were lost and the dispersion behaved as a fluid. Based on these results, the particle size and HA fluid fraction in hydrogel dispersions may be optimized to develop more efficient viscosupplement formulations. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

On-Line Rheological Measurements and Mechanical Properties of Acrylonitrile-Butadiene-styrene/Corn Starch Composite

In this work, rheological and mechanical properties of acrylonitrile–butadiene–styrene/corn starch composites (ABS/starch) were studied. The composites were prepared using a laboratory-scale, single-screw extruder. Rheological properties were determined using the single-screw extruder, apparent shear rate (γ _a ), apparent shear stress (τ _a ), apparent viscosity (η _a ), non-Newtonian index (n), and flow activation energy at a constant shear rate (E _γ) and constant shear stress (E _τ). Mechanical properties in terms of tensile tests were performed using Testometric M350-10KN, stress at break, strain at break, and Young's modulus were determined. Rheological results showed that the composites are pseudo plastic in behavior, and the apparent viscosity of the composites increases with increasing starch content above the additive rule, which indicates a partial compatibility in the composite. It was also found that the flow activation energy of the composite increases with increasing starch content. The mechanical results showed that the strain at break of the composite decreases sharply by the presence of starch, whereas the Young's modulus increases with increasing starch content.     

Orbitally shaken bioreactors—viscosity effects on flow characteristics

Phase‐resolved particle image velocimetry measurements were carried out to assess the flow dynamics occurring in orbitally shaken bioreactors of cylindrical geometry when working fluids of increasing viscosity are considered. Study of the phase‐resolved flow characteristics allowed to built a Re‐Fr map, where four quadrants associated to different flow regimes are identified: in‐phase toroidal vortex (low Fr and high Re), out‐of‐phase precessional vortex (high Fr and high Re), in‐phase single vortex (low Fr and low Re), out‐of‐phase counter‐rotating toroidal vortex (high Fr and low Re). Turbulence levels are found to be significant only in the top right quadrant (high Fr and low Re) and scaling of the turbulent kinetic energy obtained with fluid of varying viscosity is obtained using the ratio of the operating Froude number to the critical Froude number associated to the mean flow transition, . Estimates of the mean flow strain deformation as well as of the flow dissipative scale are provided, while a comparison is made between the flow circulation times obtained for different regimes. © 2014 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 60: 3951–3968, 2014     

Energy Dissipation Rates of Newtonian and Non‐Newtonian Fluids in a Stirred Vessel

Energy dissipation rates of water and glycerol as Newtonian fluids and carboxyl methyl carbonate solution as non‐Newtonian fluid in a stirred vessel are investigated by 2D particle image velocimetry and compared. Mean velocity profiles reflect the Reynolds (Re) number similarity of two flow fields with different rheological properties, but the root mean square velocity profiles differ in rheology at the same Re‐number. Energy dissipation rates are estimated by direct calculation of fluctuating velocity gradients. The varying energy dissipation rates of Newtonian and non‐Newtonian fluids result from the difference in fluid rheology and apparent viscosity distribution which decides largely the flow pattern, circulation intensity, and rate of turbulence generation.     

Shear and elongational flow properties of peroxide‐modified wood/low‐density polyethylene composite melts

Adding fillers to a polymer melt may result in a strain softening behavior in elongational flow in long‐chain branched materials, showing strain‐hardening behavior when compared with unfilled one. To improve the strain‐hardening properties in wood/LDPE composites, the effect of peroxide concentration on both the molecular architecture and molar mass distribution, and the rheological quantities in shear and elongation is studied. Addition of wood flour increases the viscosity according to a logarithmic mixing rule, as expected from the large particle size and the filler fractions used. The peroxide has multiple effects on the molar architecture of the polymer. First, a gel fraction of cross‐linked material is formed, the concentration of gel being dependent of the amount of peroxide used. Second, a higher molar mass component is detected, leading to higher value of M_w and to a broader molar mass distribution. Finally, the degree of long‐chain branching unexpectedly decreases with increasing peroxide content. The changes in molecular architecture are hardly influenced by addition of the wood flour. The peroxide treatment leads to an improved strain‐hardening behavior, detected by elongational viscosity and melt strength measurements. However, the addition of wood flour decreases the amount of strain hardening.POLYM. COMPOS., 33:2084–2094, 2012. © 2012 Society of Plastics Engineers     

Rheological Studies on Virgin and Metallized Unsymmetrical Dimethyl Hydrazine Gelled Systems

Rheological studies on unsymmetrical dimethyl hydrazine-methyl cellulose gelled system have been conducted under varying shear rates in order to establish its flow characteristics. The gel is found to behave as a pseudoplastic thixotrop. The viscosity build-up with respect to time has been traced till apparently a firm gel is set. The viscosity is found to increase with time rapidly in the beginning and minor changes are observed thereafter. The effect of temperature and extent of metal (Al and Mg) loading on apparent viscosity of the gelled system has also been investigated. Both the apparent viscosity and thixotropic character of the virgin gel are found to decrease with increase in temperature. An increase in rate of shear decreases the apparent viscosity significantly. The thixotropic character of the metallized gelled systems is observed to increase with metal content and that they exhibit a shearthinning behaviour too. Power law has been applied to assess the variation of pseudoplastic index n and consistency index K with temperature and metallization. The results reveal that n increases with temperature and decreases with metal loading whereas K shows an opposite trend. The yield value of gelled systems is noted to show decrease with temperature and increase with metal incorporation.     

Rheological and mechanical properties of thermoplastic polyurethane elastomer derived from CO2 copolymer diol

CO₂ copolymer diol‐based thermal polyurethane elastomers (PPC‐TPU) were prepared by the reaction of CO₂ copolymer diol and methylene diphenyl diisocyanate and chain extender (ethylene glycol/1,4‐butanediol/1,6‐hexanediol) (EG/BDO/HG). The rheological and mechanical properties of PPC‐TPU were analyzed. The effects of shear rate, shear temperature, hard segment content, and variety of chain extender on the properties of PPC‐TPU were studied. The results showed that the apparent viscosity (η) of PPC‐TPU decreased with the increasing shear rate (τ), and the non‐Newtonian index (n) was less than 1. PPC‐TPU exhibited a typical character of pseudoplastic non‐Newtonian rheological behavior. The degradation during the processing was obviously inhibited by adding plasticizer and antioxidant. It was also discovered that the apparent viscosity varied with the content of hard segment and chain extender. Under the same temperature (185 °C) and shear rate (50 s^?1), the apparent viscosity increased considerably with the raise of hard segment content, and the apparent viscosity and tensile strength of PPC‐TPU with EG as chain extender was the maximum. It can be seen that with the apparent shear rate increasing, the variation tendency of apparent shear stress levels off, and the nonlinear relationship of τ–γ curve tended to be obvious. PPC‐TPU exhibited a typical character of pseudoplastic non‐Newtonian rheological behavior. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45974.     

ETPE发射药表观黏度的实验研究

利用ARES应变流变仪测试了不同ETPE发射药配方的表观黏度,并对实验结果进行了数学处理,得到ETPE发射药不同配方的表观黏度与剪切应力关系式.结果表明,影响ETPE发射药表观黏度的主要因素是热塑性弹性体ETPE的相对分子质量、固体添加剂RDX的质量分数及其表面特性以及实验温度.用惰性材料处理RDX表面是调节ETPE发...     

Hydrophobically modified poly(sodium 2‐acrylamido‐2‐methylpropanesulfonate): synthesis and viscosity of aqueous solution

BACKGROUND: Hydrophobically modified polyelectrolytes are widely used polymers due to their good water solubility, stretched configuration in water and strong hydrophobic association. The study reported here aimed at researching the double action of hydrophobic association and electrostatic effect of novel hydrophobically modified polyelectrolytes in solution. RESULTS: A series of novel hydrophobically modified polyelectrolytes were synthesized by micellar copolymerization with various feed ratios of sodium 2‐acrylamido‐2‐methylpropanesulfonate, N‐n‐dodecylamine and sodium dodecylsulfonate. Their structure was characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography, and the viscosities of their aqueous and salt solutions were studied. CONCLUSION: The results show that the addition of the hydrophobic comonomer results in a decrease in molecular weight (M_w). The smaller the initial number of hydrophobes in one micelle, the higher is M_w of the resulting copolymer. The viscosity of PAD‐1.73 polyelectrolyte is less sensitive to salt than those of the others. According to the zero shear viscosity and corresponding concentration, the critical cluster‐forming concentration, critical overlap concentration and critical entanglement concentration of these polymer solutions were determined. Moreover, in the dilute regime the viscosity decreases with increasing salinity, while in the semi‐dilute regime the viscosity decreases first and then increases. It is suggested that in dilute and semi‐dilute regimes, hydrophobic intramolecular association and intermolecular association dominate, respectively. Copyright © 2009 Society of Chemical Industry     

尼龙6/环氧树脂共混物流变性能的研究

用毛细管流变仪研究了尼龙6／环氧树脂共混物的流变性能。结果表明,在实验范围内共混物熔体为假塑性流体;随着环氧树脂用量的增加,表观粘度（ηa）增大,非牛顿指数（n）减小,熔体稠度（K）增大,粘流活化能降低。     

Flow behavior of partially crosslinked low-density polyethylene

The viscosity of low-density crosslinked polyethylene was studied as a function of gel content and shear rate (3.75–33 sec^?1). A simple model relating viscosity with gel content is suggested. It is shown that sol viscosity decreases with cross-linking propagation. The rheological parameters of the sol fraction are changed as a result, and it is natural that this effect should be utilized for flow calculations. Experimental data indicate a high degree of interaction between the sol molecules and the gel, and an experimental technique is presented for measuring it. The rheological parameters of crosslinked polyethylene are closely dependent on the gel content, viscosity and pseudoplasticity increasing with the latter.