Measurement of the rheological properties of polymer melts with slit rheometer. II. Blend systems

A slit rheometer described in part I of this series was used for characterizing two blend systems by their viscous and elastic properties in the molten state. The blend systems chosen for study were blends of two high-density polyethylenes having widely different molecular weight distributions and blends of polystyrene and polypropylene which are incompatible in the molten state. The present study shows that blends of two high-density polyethylenes and blends of polystyrene with polypropylene exhibit a minimum in melt viscosity and a maximum and minimum in melt elasticity (in terms of “exit pressure”) at certain blending ratios. These results confirm the author's earlier findings, which were obtained with a capillary rheometer.     

Measurement of the rheological properties of polymer melts with annular rheometer

An annular die has been designed having a very thin gap distance between two coaxial cylinders. The die was then used to measure wall normal stresses along the longitudinal direction of polymer melts flowing through the thin annulus. The materials investigated were high-density polyethylene, low-density polyethylene, polypropylene, and polystyrene. Also investigated were blends of polystyrene and polypropylene, and blends of polystyrene and high-density polyethylene The measurements of wall normal stresses were used to determine the rheological properties of the melts, namely, the melt viscosity from the slope of axial wall normal stress profiles and the melt elasticity from exit pressures. The interpretation of the experimental data was made possible by the fact that the narrow-gap annular die can be considered as a substitute for a thin slit die. It has been found that the results obtained in the present study are consistent with those reported earlier by the author, who at that time used both capillary and slit dies.     

Measurement of the rheological properties of polymer melts with slit rheometer. III. Two-phase systems—high-impact polystyrene and ABS resin

Measurements were made of the rheological properties of commercially available rubber-reinforced two-phase polymer systems. The polymers chosen for study were two high-impact polystyrenes (Union Carbide Corp., TGDB9500 and TGDB2100) and an acrylonitrile–butadiene–styrene (ABS) resin (Monsanto Co., Lustran I240 Natural). For the study, a slit rheometer was used, which was described in part I of this series. The present paper, the third of this series, clearly demonstrates the usefulness of the slit rheometer for characterizing polymer systems of industrial importance by means of their viscous and elastic properties in the molten state.     

Rheological properties of molten polymers. I. Homopolymer systems

Experimental work has been carried out to investigate the influence of molecular weight distribution and long chain branching on both viscous and elastic properties of molten polymers, using a capillary rheometer, as described in a recent paper by Han. The materials used for the study are three high-density polyethylene samples of widely different molecular weight distributions and a low-density polyethylene containing much long-chain branching. For the analysis of the experimental data, and to obtain the information on the melt elasticity, the concept of the exit pressure recently advanced by Han is used. The study shows that the sample containing long-chain branching is much more elastic than the samples containing little or no long-chain branching, and that the broader the molecular weight distribution of the material, the more elastic the material is. These findings are in conformity with those reported in the literature. Also studied were blends of two high-density polyethylenes having widely different molecular weight distributions. The results of the blends systems show a maximum in melt viscosity as well as in elasticity for a certain blending ratio. The results of the present study may be of considerable interest to those who are concerned with modifying the structure of polymer and also with determining optimum processing conditions.     

Measurement of the elastic properties of polymer melts

A method and apparatus for measuring the elastic and other properties of polymers in the melt state is presented. The recoverable strain magnitude and the rate of strain recovery have been measured as a function of: applied shear rate, applied shear magnitude, temperature and molecular weight. The elastic properties indicate that there is an abrupt change or “transition” in the response of polystyrene melts at temperatures well above the glass transition. This abrupt change is found to be molecular weight dependent. The results are interpreted qualitatively in terms of molecular structure and practical processing operations. The possible relationship of this “transition” to T_u, is briefly discussed.     

A comparison of measurements of the viscoelastic properties of polymer melts by means of the Han slit/capillary rheometer and the Weissenberg rheogoniometer

Measurements were taken of the viscoelastic properties of six polymer melts by mean of the Weissenberg rheogoniometer and the Han slit/capillary rheometer. Polymers in vestigated were three high-density polyethylenes of different polydispersity, a low-density polyethylene, a polypropylene, and a polystyrene. The range of shear rates tested was from about 5.0 × 10^?3 to 10 sec^?1 with the Weissenberg rheogoniometer, from about 10 to 10² sec^?1 with the slit rheometer, and from about 10² and 10³ with the capillary rheometer: the temperature of measurement was 200°C. The three different apparatuses give consistent results over almost six decades of shear rates, yielding satisfactory correlations of shear viscosity to shear rate and of normal stress difference to shear rate.     

Effect of composition and processing on rheological properties of multicomponent polymer melts

Polyamide and polyether maleic anhydride were blended with carbon black at various compositions and processing conditions. The compositions were varied from 0/92/8 percent, 23/69/8 percent, 46/46/8 percent, 69/23/8 percent to 92/0/8 percent of polyamide/polyether maleic anhydride/carbon black. The polymer blends were processed by a Banbury roll mill and an extruder under various conditions and were spray dried. The effects of composition and processing conditions on steady state and dynamic viscoelastilc properties were determined. These effects were compared with the thermal and morphological properties of the blends.     

Dynamic rheological behavior of polypropylene melts with pulsatile pressure flow in a dynamic capillary rheometer

A self‐made dynamic capillary rheometer (DCR) was designed to investigate the dynamic viscoelastic characteristic of polypropylene (PP) melt during the pulsatile pressure extrusion. A vibration force field was parallel superposed upon steady shear flow in this DCR by means of a vibration driven piston. During the pulsatile pressure extruding process in DCR, the PP melt displayed apparent viscoelasticity. The experiment results proved the pressure pulsatile extrusion could reduce the viscosity of polymer melts effectively. The phase difference between the shear stress and the shear rate decreased with the superposed vibration. But, at large amplitude conditions, the viscosity has an increasing tendency. This maybe illuminated that large amplitude could be harmful for the vibration‐assistant polymer processing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1834–1838, 2006     

The influence of titanium dioxide on the rheological and extrusion properties of polymer melts

An experimental study of the influence of titanium dioxide (TiO₂) on the rheological and extrusion properties of five polymer melts (two low-density polyethylenes, two high-density polyethylenes, and a polystyrene) has been carried out. Increasing TiO₂ loading increases the shear viscosity η, with the extent of increase being greater at lower shear rates. At moderate and high TiO₂ loadings, the filled melts may possess yield values. Empirical equations relating viscosity to filler loading have been developed. The first normal stress difference was measured for the melts and found to increase with increasing TiO₂ loading. However, the extent of increase was less than found for the viscosity function and interpretation in terms of the theory of viscoelasticity suggests that the characteristic relaxation time of the melts decreases with increasing TiO₂ level. Empirical equations relating the first normal stress difference coefficient to volume fraction of the filler have been developed. Addition of TiO₂ is found to decrease extrudate swell and retard the occurrence of extrudate distortion.     

Measurement of the pressure dependence of viscosity of polymer melts using a back pressure‐regulated capillary rheometer

The effect of pressure on the melt viscosity was experimentally investigated for five polymers: polycarbonate (PC), acrylonitrile‐butadiene‐styrene (ABS), polystyrene (PS), polypropylene (PP), and low‐density polyethylene (LDPE). Measurements were carried out using capillary rheometer modified to allow regulation of back pressure. To enable correction for the entrance pressure drop, two round‐hole dies were used: a 1‐mm diameter die of length 10 mm and an orifice die of the same diameter. For determining the pressure coefficient from the experimental viscosity data, time‐pressure superposition was applied to generate a master curve to which the Carreau‐Yasuda model was fitted. The resulting pressure coefficients revealed that for the polymers studied the order of the degree of the pressure dependence is as follows: PS > ABS > PC > PP > LDPE. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of sodium chloride on rheological properties and cross-linking in melts of polymer blends

The rheological properties and cross-linking processes in melts of PP-CPA and POM-CPA blends containing 0.5, 1, and 2% NaCl of the weight of the polymer from the disperse phase were investigated. It was shown that the viscosity decreases and the elasticity of a melt of the blends increases in the presence of 0.5% salt due to improvement of fibre formation of the polymer in the disperse phase. The salt additives affect the temperature and heat of phase transitions of the components of the blends and have a stabilizing effect on liquid jets of PP or POM in a CPA matrix. Destructive wave perturbation is damped on NaCl crystals and acceleration of crystallization processes promotes solidification and rapid conversion of liquid jets into microfibres. Filter materials ensuring a purification fineness of 0.45 μm were fabricated from PP-CPA-0.5% NaCl and POM-CPA-0.5% NaCl blends. State Academy of Light Industry of Ukraine, Kiev. Translated fromKhimicheskie Volokna, No. 5, pp. 23–26, September–October, 1999.     

Dynamic rheological properties of bromine-terminated polybutadiene melts

The viscous and elastic properties of bromine-terminated polybutadiene were investigated as functions of temperature, molecular weight, and molecular weight distribution. They were found to depend on these variables in a manner similar to other polybutadienes. It was shown that the effect on the viscous properties due to bromine terminal functionality is not as great as for carboxyl and/or hydroxyl terminal functionality. In this study it was shown that the viscosity resultant from the blending of two samples of the same polymer differing in molecular weight is dependent on the polydispersity of the polymers from which the blend is prepared. A form of the Ninomiya and Ferry theory was modified and compared with experiment. As a result of the experiments involving blending, it was shown that the temperature dependency of elasticity is less for polymers exhibiting greater polydispersity.     

转矩流变仪表征熔融聚合物的流变性能

采用温度校正后的转矩流变模型,研究了结晶与非晶聚合物的流变性能,并将流变结果与毛细管流变仪进行对比。结果表明,在非牛顿指数及流动活化能测量方面,转矩流变仪与毛细管流变仪测量结果差异较小;由于黏滞耗散作用,转矩流变仪在进行流变表征时需要进行转矩的温度校正;转子等效半径与几何结构有关,而与物料种类及加工条件无关;转矩流变仪测量的剪切速率范围较窄。     

用于聚合物流变性测量的智能转矩流变仪的研制

介绍了计算机控制的智能聚合物转矩流变仪的系统组成及特点，将其应用到生产设备(如混炼器装置、塑料挤出装置)中测量聚合物流变性能，该仪器具有优良的性能指标、强大的数据文件处理能力、友好的人机界面和操作简单等特点。     

A single-mode rheological model for steady flows of polymer melts

The steady shear viscosity (η_s), the steady first normal stress coefficient (Ψ₁), the steady second normal stress coefficient (Ψ₂), and extensional viscosity (η_e) are four important parameters for polymer melts during polymer processing. In this article, we propose a stress and rate-dependent function to describe creation and destruction of polymer junctions. Moreover, we also introduce a movement expression to describe nonaffine movement of network junctions. Based on network theory, a nonaffine single-mode rheological model is presented for the steady flow of polymeric melts, and the equations of η_s, Ψ₁, Ψ₂, and η_e are derived from the model accordingly. Furthermore the dependences of η_s and η_e on model parameters are discussed for the model. Without a complex statistical simulation, the single-mode model with four parameters yields good quantitative predictions of the steady shear and extensional flows for two low density polyethylene melts reported from previous literature in very wide range of deformation rates. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

流变仪对PVC干混料流变性能的评价

介绍了流变仪对PVC干混料流变性能的评价以及其影响因素,认为通过流变曲线可评价PVC干混料的加工性能,以指导生产。     

New measures of polydispersity from rheological data on polymer melts

The rheological properties of polymer melts depend strongly on the underlying molecular structure: molecular weight distribution, and long chain branching. It is of considerable importance, both fundamental and practical, to relate the molecular architecture to polymer melt rheology. The focus of the present work is in extracting a measure of polydispersity from rheological data. Various polydispersity measures that have been proposed in the literature are critically examined and their limitations are pointed out. New measures of polydispersity are proposed that overcome these limitations. The evaluation of the various polydispersity measures is performed by reference to rheology fundamentals, with model calculations and examples drawn from industrial practice. The issues of eliminating molecular weight and temperature effects in characterizing polydispersity are comprehensively addressed. The presence of small levels of long chain branching in an otherwise linear polymer alters most of these measures of polydispersity dramatically, while no detectable change appears in the molecular weight distribution obtained using a gel permeation chromatograph. It is demonstrated that the polydispersity measures proposed in the present work, and which are extracted from frequency response data in the linear viscoelastic region, can be used reliably to characterize polydispersity in polymer melts. © 1995 John Wiley & Sons, Inc.     

Measurement of dynamic viscoelastic properties of polymer melts and liquids by the modified rheovibron

A new technique is presented which permits the quantitative characterization of the dynamic viscoelastic properties of polymer melts and liquids. A new sample holding system with oscillatory shear platen and modification of the amplifier and oscillating unit made it possible to measure rheological properties of the viscous liquids using the Rheovibron. The dynamic shear modulus, viscosity, and internal friction of acrylic dope, and silicone fluids are obtained by using the new procedure and developed mathematical expressions. This technique will be useful in studies on the rheological properties characterization of polymer melts and liquids in conjunction with process parameters.