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1.
In this study, to measure wall slip velocity of molten polypropylene (PP) by using different length‐to‐diameter (L/D) ratios of capillary dies with fixed diameter, a length‐corrected Mooney technique was proposed. Moreover, the effects of pressure, temperature, and L/D ratio were considered to better represent wall slip mechanism. To verify the feasibility of the length‐corrected Mooney technique, a series of capillary rheological experiments for molten PP were carried out. Meanwhile, the power‐law quantitative equations of slip velocity were established by shear stress. Moreover, the effects of L/D ratio and temperature on rheological properties of PP were investigated. In addition, numerical simulations for slip velocity and rheological properties of PP were performed. Numerical results validated that the length‐corrected Mooney technique, and the power‐law quantitative equations of slip velocity were available. Results showed that wall slip velocity of molten PP decreased with the capillary die's L/D ratio, but increased with the temperature and shear rate. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44589. 相似文献
2.
The nonlinear stress relaxation behavior after a step shear strain of star-shaped SSBR/silica compounds containing 21 vol% filler of various surface areas was measured and simulated using constitutive equations. A styrene-butadiene rubber (SBR) gum and SBR filled with silica having BET surface areas of 55, 135, 160, and 195 m2/g were used. Relaxation modulus behavior of the filled compounds was found to be dependent on surface area. Specifically, stress relaxation tests indicated that an increase in surface area led to increase in values of relaxation moduli in both the linear and nonlinear regimes. The time-dependent relaxation modulus exhibited a plateau at long times of relaxation in compounds containing silica of high surface area. Additionally, good time-strain superpositions were achieved for all samples at intermediate times of relaxation, and the strain-dependent damping function decreased with filler surface area. The constitutive equations proposed by Leonov and Simhambhatla and Leonov, modified to include multimodal relaxation of the particle network, were used to predict the time evolution of the relaxation modulus in the nonlinear regime for all samples. The simulations provided good results for the SBR gum for all tested strain levels. Also, in the compounds filled with silica, both models satisfactorily described the experimental observation in the nonlinear regime at low strain levels. However, at higher strain levels, due to a possible slip effect, the simulations overpredicted measured values of the relaxation moduli, thus leading to only qualitative predictions of the observed behavior. It is also possible that neither model accurately captured the floc rupture kinetics of these complex rubber compounds. 相似文献
3.
Solid composite propellants contain 80–90% of a crystalline oxidizer like ammonium perchlorate and powdery metallic fuel like aluminum with 10 to 15% organic binders like HTPB or CTPB, to bind the solids together and maintain the shape under severe stress and strain environment. Also, the propellant must not crack or become brittle at subzero temperatures. Formulating and processing of the highly filled composite propellants are difficult tasks and need a thorough understanding of rheology, even apart from a knowledge of propellant chemistry, particulate technology, manufacturing methods, and safe handling of explosives and hazardous materials. The flow behavior or rheology of the propellant slurry determines the ingredients and some of the abnormalities of the motor during firing. The propellant viscosity and mechanical properties are determined by the binder system, and the unloading viscosity of the propellant slurry is dependent on the initial viscosity of the binder system, solid loading, particle size, and its distribution, shape, temperature, and pressure. In the present report an attempt is made to study the dependency of viscosity of the HTPB binder system on temperature, plasticizer level (composition), and torque (angular velocity of spindle). The viscosity measurements were made using a Brookfield viscometer model DV III at different plasticizer levels (10–50%), temperatures (30–65°C), and torques (50–100%). The data indicate that the viscosity of HTPB, DOA, and their mixture decreases with increasing temperature and is constant with torque. The Arrhenius equation gives the energy for viscous flow to be ?35 kcal/mol for HTPB. The variation of viscosity with temperature of HTPB/DOA and their mixture follows a mathematical model expressed as where T is the temperature and a1, a2, a3, a4, and a5 are the constants. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1002–1007, 2002 相似文献
4.
The dynamic rheological behaviors at 210, 230, and 250 °C are measured by small amplitude oscillatory shear on a rotational rheometer for a polypropylene(PP)/ ethylene‐propylene‐diene monomer(EPDM) block copolymer/ high density polyethylene (HDPE)/blend. The scanning electron microscope (SEM) photomicrographs show the blend has a droplet/matrix, semi‐co‐continuous, co‐continuous morphology respectively at different weight ratios. The Cole–Cole (G″ vs. G′) data of the blends can be fitted by the simplified Palierne's model only for very narrow weight ratios. A physical scheme is proposed that the dispersed droplets are enclosed by EPDM, thus an equivalent dispersed phase is made up of “expanded” EPDM. With this physical scheme the G″ vs. G′ data of the HDPE‐rich blends at 210 °C can be fitted well by Palierne's model. Also with the physical scheme the G″ vs. G′ data of the PP‐rich blends at three temperatures can be fitted well by G–M's model with G* of interface equals to zero. This means the proposed physical scheme is reasonable. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43709. 相似文献
5.
High viscous polycarbonate melt exhibits some special rheological characters different from generalized Newtonian fluid during squeezing. It is necessary to evaluate whether the typical rheological models are suitable for polycarbonate squeeze. To avoid the difficult of measuring the inner melt rheological behavior directly, this study presents a method of measuring the compressing force applied on the upper disc of the rheometer to reveal the melt rheology indirectly. The finite difference method (FDM) was employed to discretize the governing equations and constitutive equations established on cylinder coordinate system and to simulate the compressing force. The experiments were carried out under four temperatures and three compressing velocities to test the validations of Leonov, Phan‐Thien–Tanner (PTT), eXtended Pom‐Pom (XPP), and Cross Williams‐Landel‐Ferry (Cross‐WLF) models. The experimental results show the unique character of compressing force evolution as ‘steep—steady—steep—steady’ pattern. Comparison between experiments and simulations reveals that both viscoelastic and viscous models can predict the two steady regions correctly, but only viscoelastic models can simulate the steep increase and decrease of the compressing force. Among the evaluated viscoelastic models, XPP is the most suitable to describe polycarbonate melt compression flow. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42279. 相似文献
6.
Ismail Aiad 《应用聚合物科学杂志》2005,98(5):2212-2218
Water‐soluble melamine formaldehyde‐free polycondensate products were prepared. The chemical structure of these polymers was confirmed with different spectroscopic techniques. The effects of these polymers on the rheological properties of the cement pastes were investigated. The rheological parameters (shear stress, yield stress, and plastic viscosity) were calculated with the Bingham model. The minislump of superplasticized cement pastes at different interval times (5, 30, 60, 90, and 120 min) was determined. The results showed that the new superplasticizers increased the fluidity and minislump of the cement pastes and reduced the minislump loss of the cement pastes not only at early ages (30 min) but also at later early ages (120 min). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2212–2218, 2005 相似文献
7.
In this study, the experiments of gas‐assisted extrusion (GAE) for molten polypropylene were carried out under different gas pressures, the different extrudate deformations and sharkskin defects of melt were observed. To ascertain the effects of gas on melt extrusion, non‐isothermal numerical simulation of GAE based on gas/melt two‐phase fluid model was proposed and studied. In the simulations, the melt extruded profile, physical field distributions (velocities, pressure drop, and first normal stress difference) were obtained. Numerical results showed that the deformation degree of melt increased with increasing gas pressure, which was in good agreement with experimental results. It was demonstrated that the influence of gas pressure on the melt extrusion could be well reflected by GAE simulation based on gas/melt two‐phase fluid model rather than simplified‐GAE (SGAE) based on full‐slip wall boundary condition used in the past time. Experimental and numerical results demonstrate that the gas pressure induced first normal stress difference is the main reason of triggering flow behavior changes, extrudate deformations, and sharkskin defects of melt. Therefore, the reasonable controlling of gas pressure is a key in practice of GAE, and the gas layer and its influence should be considered in GAE numerical simulation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42682. 相似文献
8.
Bhaskar Patham 《应用聚合物科学杂志》2013,129(3):983-998
Simulations of evolution of cure‐induced stresses in a viscoelastic thermoset resin are presented. The phenomenology involves evolution of resin modulus with degree of cure and temperature, the development of stresses due to crosslink induced shrinkage, and the viscoelastic relaxation of these stresses. For the simulations, the detailed kinetic and chemo‐thermo‐rheological models for an epoxy‐amine thermoset resin system, described in Eom et al. (Polym. Eng. Sci. 2000, 40, 1281) are employed. The implementation of this model into the simulation is facilitated by multiphysics simulation strategies. The trends in simulated cure‐induced stresses obtained using the full‐fledged viscoelastic model are compared with those obtained from two other equivalent material models, one involving a constant elastic modulus, and the other involving a cure‐dependent (but time‐invariant) elastic modulus. It is observed that the viscoelastic model not only results in lower estimates of cure‐induced stresses, but also provides subtle details of the springback behavior. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
9.
The large amplitude oscillatory shear (LAOS) and steady shear behavior of star-shaped SSBR/silica 60 phr (21 vol%) compounds with various filler surface areas was measured and simulated. An SBR gum and SBR compounds containing four different silicas with surface areas of 55, 135, 160, and 195 m2/g were utilized. Rheological behavior indicated clear correlation with surface area. LAOS tests showed an increase in dynamic moduli, shear stress, and higher order harmonic contributions with surface area. Elastic and viscous Lissajous figures showed significant distortion at intermediate and higher strain amplitudes. Additionally, ratios of third and fifth order stress harmonics to the first stress harmonic (I3/1 and I5/1 , respectively) showed a ''bump'' at intermediate strain amplitudes for the three highest surface area compounds. With regards to steady shear, all materials showed strong shear thinning behavior, and an increase in shear viscosity with surface area. The Cox-Merz rule was shown to be valid for the SBR gum but not for the filled compounds. However, the complex viscosity as a function of shear rate amplitude at various frequencies at high strain amplitudes and the steady shear viscosity as a function of shear rate coincided. This correlation, referred to as the Philippoff approach, has important ramifications for the rubber industry, providing quick data for predicting processing behavior. The Simhambhatla-Leonov model was successfully employed to simulate rheological behavior for the SBR gum and the lowest surface area silica compound, but the model yielded mixed results for the higher surface area silica compounds. 相似文献
10.
Ammonium acrylate was first used as a comonomer to copolymerize with acrylonitrile. The viscosity behavior of dimethyl formamide solutions of acrylonitrile/ammonium acrylate copolymer was studied, and the rheological kinetics of the solutions were studied for comparison. It was shown that the solutions behaved the same as a Newtonian flow as the rotor speed increased beyond 12 rpm. With an increase in temperature, the apparent viscosity of acrylonitrile/ammonium acrylate copolymer solutions showed a trend of decreasing. The changes in the apparent flow‐activation energy of solutions (Eη) calculated by the Arrhenius equation became less prominent along with the changes in the molecular weight of the acrylonitrile/ammonium acrylate copolymers. Eη increased continuously with an increase in copolymer concentration. The viscosity of copolymer solutions decreased continuously as the concentrations of KCl and NaCl increased up to 0.015 mol/L, and then it increased. The Eη showed an obvious trend of decreasing with the addition of alkali salts, and the changes in the Eη containing NaCl were more prominent than those of solutions containing KCl. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2320–2324, 2007 相似文献
11.
对金溪膨润土的流变性进行了系统研究。结果表明:质量分数、剪切力、溶解温度、加热时间、pH值、冻融条件与时间等变化对金溪膨润土的粘度有较大影响。金溪膨润土溶液具有较高的粘度,当矿浆质量分数达到60%时,其粘度为542.8mPa·s,金溪膨润土溶液为"非牛顿流体",加热时间与温度对金溪膨润土粘度影响较大,金溪膨润土溶液在酸性和碱性条件下都较为稳定,冻融处理后金溪膨润土粘度大幅度下降。 相似文献
12.
The reaction kinetics of the postamidation of polyamide 6 in the melt was studied by a new rheological method, and the reaction rate constant was calculated to be about 0.087 kg/mol min at 250°C. To study the effects of the shear flow on a homogeneous polymeric reaction, a more practical technique was used to select the data that responded only to the reaction without the effect of different shear flows. The experimental results showed that the reaction rate constant decreased with an increase in the shear rate. Moreover, the decreases in the rates were different under different shear modes: the reaction rate constant decreased slightly under oscillatory shear but strongly under steady shear. Possible reasons for these phenomena were examined. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3056–3061, 2006 相似文献
13.
Because of their large specific surface area, aqueous‐based pseudolatex systems of ethylcellulose can absorb large amounts of drugs. In addition, the stability of polymeric particles in biological fluids delays the release of the drug as in controlled drug delivery systems. The aim of the present study was to characterize the rheological properties of latex particles as a measure of their colloidal stability. Here, we report the effect of three variables: pH, electrolyte concentration, and temperature. The rheograms clearly show that the polymer suspensions displayed Bingham plastic behavior. Internal structuring of the latex was greatest at acid and natural pH values, particularly at the highest ionic strength. In acid solutions, only temperature appeared to play a fundamental role; both the shear stress corresponding to the onset of nonlinear viscoelasticity and the elastic modulus at all frequencies were higher at 37°C than those at room temperature. This is assumed to be a consequence of deformation of the polymer particles upon heating. The effect of ionic strength was noticeable only at the natural pH (pH ? 6.5). At high concentrations of sodium chloride, the particles aggregated because of the decrease in double layer repulsion, and as a result, the latex became structured and its elastic modulus subsequently increased. Interestingly, when the temperature was increased further, this structure presumably broke, down, at least partially, and the storage modulus was reduced. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 847–851, 2006 相似文献
14.
Graft copolymers of dextran (Dx) and polyacrylamide (PAM) were synthesized through the grafting of PAM chains onto a Dx backbone with a ceric‐ion‐induced solution polymerization technique. By the variation of the amount of the initiator (ceric ammonium nitrate), four different grades of graft copolymers were synthesized. The partial alkaline hydrolysis of Dx‐g‐PAM was carried out in an alkaline medium. Three grades of partially hydrolyzed products were synthesized through the variation of the amount of alkali. These hydrolyzed graft copolymers were characterized with elemental analysis, infrared spectroscopy, neutralization equivalent measurements, a rheological technique, scanning electron microscopy, thermal analysis, viscometry, and X‐ray diffraction. The flocculation efficiency and viscosifying characteristics of the graft copolymers were enhanced upon their alkaline hydrolysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008. 相似文献
15.
Polyaniline (PAni) was synthesized by the miniemulsion polymerization and dispersed in a poly(epichlorohydrine‐co‐ethylene oxide) (ECO) solution. The rheological properties using an R/S Rheometer and the shear‐dependent electrical resistance using a homemade setup were measured. The addition of PAni particles to the ECO solution causes an increase in the shear stress and shear viscosity and the nature of flow changes from a dilatant to a Newtonian fluid. For both the ECO solution and ECO‐PAni mixture, the viscosity at any particular shear rate is higher during the increasing cycle of shear rate compared with the decreasing cycle of shear rate called hysteresis. The ECO‐PAni mixture executes a step‐like viscosity transition over the shear rate region 50–150 s?1, which is known as shear rate‐induced phase transition. The resistance of ECO solution decreases with the increase in shear rate and reversibly increases with the decrease in shear rate, whereas the resistance of ECO‐PAni mixture increases during both the increasing and decreasing cycles of the shear rate. The difference in resistance at zero shear rate before and after the end of shear cycle is termed as electrical set. The ECO solution and ECO‐PAni mixture exhibit 4% and 79% electrical set in terms of decrease and increase of resistance, respectively. The settling process of PAni in the ECO‐PAni mixture is slower compared with the pure ECO in solution. The settling time of PAni in the ECO‐PAni mixture increases with the decrease in shear rate. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
16.
Acrylamide dynamic viscosity has been measured in aqueous solutions. Separate rheological measurements were performed on neat resins devoid of the curing agent over a range of shear rates to yield the initial resin viscosity. The gels were also characterized by sub‐ambient DSC to determine the phase structure as a function of formulation. The dynamic viscosity shows a marked sigmoidal behavior with a plateau viscosity. Mathematical interpretations of the gel time both by sigmoidal and power law models were comparable. The power law model allowed a direct determination of the gel time while the sigmoidal model yielded parameters associated with the initial viscosity, one associated with the plateau viscosity of the gel, and two time constants controlling the sharpness of the transition.
17.
Hydrophobically modified polyacrylamide (HMPAM) is synthesized by a free radical micellar polymerization method with low amounts of anionic long‐chain alkyl, sodium 9‐(and 10)‐acrylamidostearate (NaAAS), which is derived from a renewable resource material, oleic acid. In this progress, the molar ratio of Sodium dodecyl sulfate (SDS) to NaAAS is adjusted, so polymers with different lengths of the hydrophobic blocks (NH = 3 and NH = 6) are obtained. The copolymers are characterized by 1H NMR, and the polymer weight and polydispersity are determined by gel permeation chromatography. The solution behaviors of the copolymers are studied as functions of concentrations, pH, and added electrolytes by steady‐flow and oscillatory experiments. The viscosities of these HMPAMs increase enormously above the critical concentration (c*). The sample with longer hydrophobic blocks exhibits better thickening effect. The rheological behaviors of aqueous solutions of HMPAMs are also investigated at different pH and brine environments. Low pH or the presence of brine promotes the intramolecular associating of hydrophobes for the both copolymers in semidilute solutions. The introduction of ionizable carboxylic group on the long hydrophobic side chain significantly influences the aggregation behaviors of the copolymers, leading to unique solution behaviors of the poly(AAm/NaAAS) copolymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40754. 相似文献
18.
Flow behavior in terms of shear stress and viscosity versus shear rate is investigated for aqueous solutions of Alcoflood polymer materials. Rheostress RS100 is employed for operating, measuring, and analyzing this experimental investigation. Polymer concentration in the range of 100–10,000 ppm was covered. Fitting analysis is carried out for all the examined polymer solutions. Casson and Ostwald‐de‐Waele correlations can be employed for predicting flow behavior, depending upon polymer type. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2896–2904, 2002 相似文献
19.
To evaluate the lowest polymer concentration within a solvent from which there appears beadless nanofibres during the process of electrospinning, is rather complicated. A widely used method is based on a determination of so called entanglement concentration ce and the onsets of beadless nanofibres are characterized by multipliers of ce subjected to used materials. However, a determination of ce as an intersection point of two linear segments (in log–log coordinates specific viscosity vs. concentration) in a semi-dilute region is not applicable for all materials as for instance a solution of poly(ethylene oxide) (PEO) in water does not exhibit 'classical' three linear segments within the dilute and semi-dilute regions determining overlap and entanglement concentrations. For such cases a new approach for the evaluation of an initial concentration from which beadless nanofibres are produced is proposed. This method does not use the terms overlap and entanglement concentrations. The procedure is demonstrated using four PEO solutions differing in molecular weight. The relationship expressing initial concentration in dependence on PEO molecular weight containing no adjustable parameters is proposed. 相似文献
20.
The rheological properties of Egyptian bentonite suspensions in the presence of nonionic polymers were investigated. Two different types of nonionic polymers were studied: poly(ethylene glycol) (molecular weight = 6000 g/mol) and poly(vinyl pyrrolidone) (molecular weight = 40,000 g/mol). The rheological properties (plastic viscosity, apparent viscosity, and yield point) of concentrated clay suspensions (6–8% w/w) at different temperatures after 24 h were determined. As the nonionic polymer concentrations increased, the rheological properties of the bentonite suspensions showed a slight increase, especially at an 8% clay content. The electrical properties (electrophoretic mobility and ζ potential) of Egyptian bentonite in the presence of different nonionic polymers were measured with a ζ meter. The results showed that the ζ potential of this bentonite was higher with 200 mg/L poly (vinyl pyrrolidone) than with 1000 mg/L poly(ethylene glycol). Potential energy profiles for bentonite suspensions for these nonionic polymers were constructed to show that the net energy barrier for bentonite suspensions followed repulsion or attraction between particles. These profiles showed that the potential energy profile of a bentonite suspension with 200 mg/L poly(vinyl pyrrolidone) produced a high repulsion potential energy between clay surfaces; that is, the suspension stability improved. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献