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1.
J. Lyngaae-Jrgensen 《应用聚合物科学杂志》1976,20(9):2497-2509
PVC melts are predicted to be homogeneous with single molecules as the stable flow units (monomolecular melts) at corresponding values of high temperatures and/or high shear stresses. Under these conditions, it is found that the zero shear viscosity in simple shearing flow of rigid compounds depends on the average molecular weight by weight to the 3.5 power for molecular weights between 24,000 and 100,000. All data measured under conditions where monomolecular melts are predicted fall on a master curve of reduced viscosity versus reduced shear rate when a relaxation time proportional to η0/c2T is used. It is, therefore, concluded that monomolecular melts of PVC compounds follow the same structure–viscosity relations as found for other linear melts in viscometric flow. 相似文献
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Isothermal melt spinning experiments have been conducted using two polyethylene melts of low density (LDPE) and high density
(HDPE) to produce steady state spinline profiles. The data revealed the threadline extensional viscosity exhibiting a contrasting
picture : extension thickening behavior for LDPE and extension thinning one for HDPE. A White-Metzner model having a strain
rate-dependent relaxation time was then found to be able to simulate this dichotomy in melt spinning fairly well: the fluids
whose relaxation times have smaller strain rate-dependence can fit LDPE data with extension thickening extensional viscosity
whereas the fluids whose relaxation times have larger strain rate-dependence can fit HDPE data with extension thinning extensional
viscosity. This dichotomous nature of viscoelastic fluids is also believed to be able to explain other similar contrasting
phenomena exhibited by polymer melts, such as vortex/no vortex in entry flows, cohesive/ductile fracture modes in extension,
and more/less stable draw resonance than Newtonian fluids. 相似文献
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Low-density polyethylene (LDPE) melts show anomalous rheological behavior; their viscoelastic properties vary with their shearing histories although their molecular structural parameters do not change. Capillary flow and die swell behavior were dependent not only on the experimental conditions such as temperature or shear stress but also on the processing index (PI), which was introduced in a preceding article in order to quantify the anomalous rheological behavior of LDPE melts. In addition, it was found that the flow activation energy at constant shear stress also varied with the shearing histories. The experimental findings are discussed in terms of the rheological flow units of LDPE melts. 相似文献
6.
E. Menefee 《应用聚合物科学杂志》1972,16(9):2215-2238
Relaxation times in polydisperse polymers were calculated on the basis of more realistic viscosity mixing rules than have previously been used. These relaxation times and mixing rules are in turn used to calculate viscoelastic functions such as stress relaxation following sudden straining or steady shearing. Inversion of these functions provides an accurate way to estimate the molecular weight distribution. This method is useful for insoluble or otherwise intractable polymers. 相似文献
7.
Yu. S. Lipatov V. F. Shumsky A. N. Gorbatenko Yu. N. Panov L. S. Bolotnikova 《应用聚合物科学杂志》1981,26(2):499-508
Viscoelastic properties of polymer blend melts of polystyrene–polycarbonate were investigated in a wide range of temperatures, frequencies, and compositions. It was established that the more essential changes in viscoelastic characteristics took place at small concentrations of one of the components and at low frequencies, probably because of a putting down of the slow relaxation processes. The marked decrease in the viscosity of the melts takes place in the region of phase separation due to thermodynamic incompatibility of the components and is in a good correlation with the appearance of excess free volume in the system. 相似文献
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A major objective in polymer rheology is to predict a fluid's response to a general deformation from molecular information. A method has been developed which allows one to predict the viscoelastic properties of polymer melts from a limited amount of rheological and molecular data for the polymer. The input parameters are: (a) zero-shear viscosity; (b) molecular weight distribution; (c) temperature and density; and (d) constants relating Graessley's relaxation time to the Rouse relaxation time. The technique then “simulates” a discrete relaxation spectrum using G′ and G″ data from the Rouse theory and finally requires that a continuum model of polymer viscoelasticity be fit to shear viscosity data predicted by Graessley's theory. Examples of the utility of the procedure are given to illustrate the role of molecular weight and weight distribution in determining rheological behavior. 相似文献
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A new and simple instrument for measurement of elongational flow response of polymer melts in constant uniaxial extension rate experiments is described. Quantitative stress development data are presented for a series of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), and poly(methyl methacrylate) (PMMA) melts. For small elongation rate E, linear viscoelastic behavior was observed; while for large E, LDPE and PS showed exponential stress growth, while HDPE and PP showed only linear stress growth. Stress relaxation experiments were carried out for several of the same melts in the instrument. Elongation to break and mechanisms of filament failure were studied. HDPE and PP have a tendency to neck and exhibit ductile failure, while at high E, LDPE and PS seem to show cohesive fracture. The elongational flow stress response data were compared to predictions of nonlinear viscoelastic fluid theory, specifically the Bogue-White formulation. The qualitative differences in responses of the melts studied were explained in terms of different dependences of the effective relaxation times on deformation rate and, more specifically, on values of the a parameter in the theory. 相似文献
10.
涤纶长丝生产喷丝板的选择 总被引:5,自引:1,他引:5
论述了高聚物熔体在喷丝孔区的流变性及粘弹行为。具体分析了喷丝孔直径与剪切速率及喷丝头拉伸倍数之间的关系,提出了喷丝孔直径的选择依据。 相似文献
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In this article, under shearing vibration and pressure vibration, the rheological behavior of HDPE, ABS, and PS melts and the mechanical properties of molded parts are studied. The experimental results show that, under the vibration condition, the apparent viscosity of the polymer melt decreases with an increasing of the vibration frequency and amplitude applied. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1587–1592, 2002 相似文献
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The equibiaxial elongational viscosity of six commercially available polymer melts is measured using a novel technique known as continuous lubricated squeezing flow. This technique is a modification of simple lubricated squeezing flow. The systems were chosen in order to investigate the dependence of equibiaxial elongational viscosity on molecular structure. Three of the melts are polyethylene with long chain branching, two are polyethylene with short chain branching, and one is polyisobutylene with linear chains. Each polymer was subjected to strain rates ranging from 0.003 to 0.1 s?1 and compared to the linear viscoelastic prediction so that the degree of strain hardening could be determined. For a modestly branched polymer, comparison of rheological behavior in both uniaxial and equibiaxial deformations was possible. POLYM. ENG. SCI., 55:1012–1017, 2015. © 2014 Society of Plastics Engineers 相似文献
13.
Chang Dae Han 《应用聚合物科学杂志》1974,18(3):821-829
An experimental study was carried out to investigate the viscoelastic behavior of calcium carbonate-filled polypropylene melts, using the Han slit rheometer. In the analysis of the experimental data, the pressure gradient was used to determine the wall shear stress, and the exit pressure to determine the elasticity of the filled polymers. The study shows that the materials studied follow a power law in viscous behavior over the range of shear rates investigated and that the viscosity increases and elasticity decreases as filler concentration is increased. Also investigated was the effect of temperature on the viscoelastic properties of filled polypropylene melts. 相似文献
14.
Gwo‐Geng Lin Hsi‐Hsin Shih Ping‐Chang Chai Shio‐Jin Hsu 《Polymer Engineering and Science》2002,42(11):2213-2221
Metallocene‐catalyzed, low‐density and linear low‐density polyethylenes with similar melt indexes were used to investigate how side‐chain structures influence the elongation viscosity and viscoelastic properties. The viscoelastic properties were determined with a rotation rheometer, while the elongation viscosities were acquired by using isothermal fiber spinning. The Phan‐Thien‐Tanner (PTT) model was also used to understand how the side‐chain structure affects the elongation behavior. Experimental results demonstrate that the log G′ vs. log G″ plot can qualitatively describe the effects of the side chain branch on the rheological properties of polyethylene melts. According to the results determined by the PTT model, low‐density polyethylene (LDPE) has low elongation viscosities at high strain rates. This low elongation viscosity can be attributed to the fact that LDPE has high shear thinning behavior. The long‐chain branching tends to increase entanglements, thereby enhancing the storage modulus, elongation viscosity and shear‐thinning behaviors. Uniform side‐chain distribution lowers the entanglements, which results in a low storage modulus, elongation viscosity and shear‐thinning behavior. 相似文献
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Rheologic behavior of the common Ryton-type poly(phenylene sulfide) (PPS) and Fortron PPS has been studied using a capillary rheometer. The effects of shearing rate, shearing stress, and temperature on the apparent viscosities of PPS are discussed. The non-Newtonian index and the activation energy of the viscous flow were obtained. The results show that the apparent viscosity of the Ryton PPS decreased obviously with increase of shearing rate or shearing stress, and with increase of the temperature, the apparent viscosity is not considerably decreased. On the contrary, the apparent viscosity of the Fortron PPS is more sensitive to temperature than to shearing rate and shearing stress. © 1995 John Wiley & Sons, Inc. 相似文献
16.
Yongsok Seo 《应用聚合物科学杂志》2003,88(2):510-515
In order to describe the transient stress growth for polymer melts, the empirical model proposed by Seo for the viscosity of steady‐state flow is combined with a phenomenological viscoelastic model of a differential type (the White–Metzner model) along the lines proposed by Souvaliotis and Beris. The relaxation time is taken as a function of the invariant of the stress tensor (hence that of the configuration tensor) rather than that of the rate of the deformation tensor. Numerical results show a good correlation with experimental data. The model predictions approach steady‐state values at long times after the startup. The nonlinear form of the model correlates very well with the experimental data over many decades of the deformation rate, both in shearing and elongational deformations. The proposed model is a simple one that can also describe the overshoot in the transient stress growth. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 510–515, 2003 相似文献
17.
David O. Kazmer 《Polymer Engineering and Science》2014,54(12):2824-2838
An investigation was conducted to identify and characterize the relaxation spectrum of polymer melts from transient capillary rheological data. System identification techniques using an iterative prediction‐error minimization (PEM) method were applied to isolate the viscoelastic melt response from the apparatus dynamics. Parameters for linear time invariant (LTI) models of varying complexity were estimated using capillary rheology data across a range of temperatures and shear rates using the principle of time‐temperature superposition. Melt capillary rheology data for polystyrene was found to exhibit viscoleastic behavior. Subsequently, three viscoelastic constitutive models were then implemented and their model coefficients directly fit using optimization techniques. The implemented methods provided useful relaxation behavior from melt capillary rheology data while also explaining much of the residual error in the purely viscous response as traditionally fit to the Cross‐WLF model. POLYM. ENG. SCI., 54:2824–2838, 2014. © 2014 Society of Plastics Engineers 相似文献
18.
P. Cassagnau A. Michel P. Aulagner‐Revenu C. Carrot J. Guillet 《Polymer Engineering and Science》2000,40(4):880-891
The rheological behavior during the bulk polymerization of urethane systems made from diphenyl methane 4,4′ diisocyanate (MDI) and poyether macro diol was studied in connection with the kinetics of the reaction. The linear viscoelastic behavior in the terminal zone has been reasonably predicted using the molecular weight distribution obtained from size exclusion chromatography (SEC) and owing to only a few rheological parameters, namely, the scaling law relating the zero shear viscosity to the average weight molecular weight and the plateau modulus. These parameters were previously determined from oscillatory shear experiments performed on model samples of various molecular weights. The combination of this predictive model together with a reasonable kinetic scheme for such systems, enables to calculate the evolution of the viscoelastic parameters (storage and loss moduli) during bulk polymerization. The overall calculation was shown to give a reasonable depiction of the viscosity function. However, some discrepancies were noted as far as the elasticity of the melt is concerned. This was attributed to an additional relaxation mechanisms in the earliest stage of the polymerization connected to hydrogen bonding. Nevertheless, the procedure remains fundamental for apprehending some aspects of the viscoelastic changes of the material during a reactive processing technique such as extrusion for example. 相似文献
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Amir Saadat Hossein Nazockdast Fatemeh Sepehr Milad Mehranpour 《Polymer Engineering and Science》2010,50(12):2340-2349
Melt viscoelastic behavior and the die swell of Acrylonitrile‐Butadiene‐Styrene (ABS) and ABS/clay nanocomposites varying in organoclay loading were studied. A pronounced low‐frequency nonterminal behavior exhibited in linear viscoelastic experiments along with an apparent yield stress in transient startup flow tests suggested the existence of a network type, because of interconnection of rubber particles in ABS matrix. From the results of linear and nonlinear viscoelastic measurements, it was found that the incorporation of organoclay can lead to the formation of an additional network formed between organoclay tactoids that caused reduced temperature dependency of linear viscoelastic properties of the nanocomposite samples compared with ABS matrix. The swelling behavior of samples was interpreted using the results of stress relaxation experiments after cessation of steady shear flow. The great reduction in the die swell of nanocomposite samples could be explained in terms of great surface area and anisometric nature of organoclay tactoids and/or platelets, which promote energy consumption and less energy to be stored in chains. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers 相似文献