摘要:

An instrument modification to a capillary extrusion rheometer is described which permits ready measurement of the viscosity‐shear rate behavior of concentrated polymer solutions, particularly in the generally inaccessible region of high temperatures with volatile solvents. Despite the fundamental rheological and practical commercial importance of defining the viscosity behavior of highly concentrated (e.g., 50–100%) polymer solutions at temperatures well above the solutionTg,few data in this region are available in the literature. This is largely because of the experimental difficulty of making measurements in the concentrated solution region under conditions where significant evaporative solvent losses are likely to occur. Instrumentation and methodology for performing these experiments with relative ease and generally good precision are described, and typical viscosity‐shear rate curves obtained for solutions of polystyrene in ethylbenzene at various concentrations (50–90 wt %) and temperatures (100–225°C) are reported to demonstrate the method.

ISSN:0148-6055    

DOI:10.1122/1.549509

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

The extensional deformation of a viscoelastic droplet suspended in a viscoelastic medium was investigated, both theoretically and experimentally. A theoretical analysis was carried out on the deformation of a droplet suspended in a steady extensional flow field, where both fluids may be represented by the second‐order fluid model. The study took into account the effects of the elasticity, viscosity, and interfacial tension of the fluids concerned. The shape of a deformed droplet is determined by solving the equations of motion for both fluids (droplet phase and medium). A perturbation technique was employed and the iteration method was used to determine the shape of the droplet undergoing extensional deformation. Series solutions of stream function inside and outside the droplet, pressure distribution around the droplet, and the deformation of the droplet were obtained. For the experimental study, a transparent flow channel consisting of a conical section and a straight cylindrical tube was constructed. Along its central axis, the conical section provides extensional flow. Droplets of known volume were injected in the conical section at the centerline of the flow channel, through which a viscoelastic fluid was flowing at a constant flow rate. The deformation patterns of droplets were recorded on both movie and still films as they were traveling along thecenterlineof the conical section. Tracer particles were used to determine the axial velocity profiles. The suspending liquids were aqueous solutions of polyacrylamide at various concentrations (viscoelastic fluids) and corn syrup (Newtonian fluid). For viscoelastic droplets, polyisobutylene dissolved in decalin at various concentrations was used, and for Newtonian droplets, Indopols and benzene were used. It was observed that the droplets, initially spherical, were slightly deformed in the upper section of the cone and greatly elongated at the entrance region of the cylindrical tube. The viscoelastic droplets were less deformable than the Newtonian droplets, and highly viscoelastic media gave rise to large deformations of droplets. The deformability of droplets was analyzed based on the flow conditions and the rheological properties of the fluids concerned. A comparison is made between the theoretically predicted and experimentally observed shapes of droplets in the conical section, only where extension rate is constant.

ISSN:0148-6055    

DOI:10.1122/1.549510

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

The rheological behavior of PVC plastisols that vary in volume fraction of resin from 0.567 to 0.670 was studied. Different particle‐size “cuts” from Tenneco Chemicals, Inc.'s 1730 dispersion‐grade‐poly(vinyl chloride) resin and di‐2‐ethylhexyl phthalate (DOP),n‐butyl benzyl phthalate (BBP), and di‐2‐ethylhexyl adipate (DOA) plasticizers were used to prepare the plastisols. In the range of concentration studied, both shear‐thickening and shear‐thinning behaviors were observed. In all cases discontinuous‐viscosity behavior was observed at a critical shear rate. The shear rate at which this viscosity discontinuity occurred depended strongly on the particle‐size characteristics of the resin and the compatibility of the plasticizer with the resin. This study has led to the following contributions:1. An experimental blending technique was developed that permits the determination of the maximum volume fraction of resin which will produce a fluid plastisol. This maximum volume fraction of resin,φMIX,is related to the particle‐size characteristics of the resin and the compatibility of the plasticizer with the resin.2. The resin content of the plastisols studied was expressed in terms of a reduced volume fraction,φR,that was calculated with the following compositional mixing formula:φR=∑i=1n∑j=1mxiyj (φ/φMIX ij),wherexi=volumefraction of theithliquid phase,yj=volumefraction of thejthsolid phase,φ=totalvolume fraction of resin(s)n=numberof plasticizers,m=numberof resins, andφMIX ij=φMIXof theithplasticizer with thejthresin. Since this expression involved only the determination ofφMIXfor each resin/plasticizer combination,φRcan be easily determined for variations in both the content of resin and the relative amounts of plasticizers and/or resins present in multiple‐component plastisols.3. A correlation was developed that relatesφRto the shear rate,γ̇d,at which the viscosity discontinuity occurs. The correlation equation,log10γ̇d=−9.8568+10.437/φR,was shown to be valid for values ofφRbetween 0.87 and 1.00. The above expression was also found to describe discontinuous‐viscosity behavior published by another investigator who used different resins. This model can be used as an aid in designing plastisols for specific flow properties.

ISSN:0148-6055    

DOI:10.1122/1.549547

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

The time‐dependent flow birefringence was measured on application of a step‐shear strain for an 8% polystyrene solution in chlorinated biphenyl. Measurements were performed with an apparatus of coaxial cylinder type at various shear strains γ ranging from 0.913 to 7.56. The amount of birefringence was in agreement with that evaluated from the shear stress with the use of the stress‐optical law. The extinction angle χ was independent of time and satisfied a relation2 cot 2χ=γ.This result combined with the stress‐optical law indicates that the Lodge‐Meissner relation holds valid for the polystyrene solution, i.e., the first normal stress difference is equal to the shear stress multiplied by the shear strain in the stress relaxation process following an application of step‐shear strain.

ISSN:0148-6055    

DOI:10.1122/1.549511

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

The true shear stress at the wall is discussed. The theoretical result suggests that Bagley's formula holds even if the exit pressure is not negligible in capillary flow of polymer melts. The importance is emphasized of distinguishing the pressure in the axial direction (driving pressure) from that in the radial direction in cases of flow where primary and secondary normal stress differences exist. Accurate experiments were carried out to confirm the theoretical result for two kinds of high‐density polyethylenes. Experimental results indicate that wall pressure, which is normal to the capillary wall, decreases rather rapidly near the entrance and then at a constant rate in the following part, while the driving pressure in the axial direction decreases at a constant rate from the beginning and the shear stress is constant throughout the capillary. We also obtained experimentally the mean normal stress difference, which is the cross‐sectional mean of the primary normal stress difference and half of the secondary normal stress difference. It was shown that the mean normal stress difference decreases gradually untilLc/D=5and remains constant thereafter. The existence of a close correlation between the mean normal stress difference and die swell ratio was found. The primary normal stress difference was obtained from the data of mean normal stress difference and the secondary normal stress difference. The pressure distributionsPzz(r),Prr(r)andPφφ(r)are discussed.

ISSN:0148-6055    

DOI:10.1122/1.549512

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

A Rheometrics mechanical spectrometer was modified to study the elongational properties of polymer melts. A prime concern is that the elongation be uniform so that the microscopic stretch history of fluid elements in the polymer rod will be independent of axial position. By sequential photographic techniques, the conditions under which a constant stretch history is achieved were determined quantitatively in terms of the Weissenberg number,ε̇τm.For Weissenberg numbers much greater than unity, a polymer's response is largely elastic, and uniform stretching is observed. For Weissenberg numbers less than unity, the response of a polymer melt is largely viscous, and uniform stretching is observed only for very small strains. The evaluation of the Weissenberg number for the specific test conditions should serve as a simple guideline for estimating nonuniform deformation conditions.

ISSN:0148-6055    

DOI:10.1122/1.549543

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549550

出版商:The Society of Rheology    

年代:1979

数据来源: AIP