Designation: D5422 − 09Standard Test Method forMeasurement of Properties of Thermoplastic Materials byScrew-Extrusion Capillary Rheometer1This standard is issued under the fixed designation D5422; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (´) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThis test method uses capillary rheometry to measure the rheological properties of thermoplasticsand thermoplastic compounds. This test method utilizes a screw-extrusion-type capillary rheometer.1. Scope*1.1 This test method covers the use of a screw-extrusion-type capillary rheometer for the measurement of flow proper-ties of thermoplastics and thermoplastic compounds. Themeasured flow properties, which are obtained through labora-tory investigation, may help to describe the material behaviorthat occurs in factory processing.1.2 Since a screw-type capillary rheometer imparts shearenergy to the material during testing, the measurements willusually differ from those obtained with a piston-type capillaryrheometer (see Test Method D3835).1.3 Capillary rheometer measurements for thermoplasticsand thermoplastic compounds are described in Test MethodD3835.1.4 The values stated in SI units are to be regarded asstandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.NOTE 1—There is no known ISO equivalent to this standard.2. Referenced Documents2.1 ASTM Standards:2D618 Practice for Conditioning Plastics for TestingD883 Terminology Relating to PlasticsD1238 Test Method for Melt Flow Rates of Thermoplasticsby Extrusion PlastometerD3835 Test Method for Determination of Properties ofPolymeric Materials by Means of a Capillary RheometerE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 Definitions: (See Terminology D883):3.1.1 apparent shear rate (γ˙a)—shear strain rate (or veloc-ity gradient) of the thermoplastic or thermoplastic compoundextrudate as it passes through the capillary die.3.1.1.1 Discussion—This velocity gradient is not uniformthrough the cross-section of the capillary die. The shear rate iscalculated for the region of highest shear, which is at the wallof the capillary. By selecting a die diameter and controlling thevolume flow per unit time through the die, a specific level ofapparent shear rate is achieved. Alternately, the shear stress(entrance pressure) is controlled, and the apparent shear ratemeasured.3.1.1.2 Discussion—Mathematically, the apparent shear rateat the wall of the capillary for a Newtonian fluid at the capillarywall is given by the following:γ˙a532·Qπ·D3(1)where:γ˙a= apparent shear rate, s−1,Q = quantity of fluid extruded per time, mm3/s,π = 3.142, andD = diameter of the measuring capillary, mm.3.1.2 apparent shear stress (τa)—the measured resistance tothe flow through a capillary die. It may be determined bymeasuring the die entrance pressure for a specific die, thenapplying appropriate geometric factors.3.1.2.1 Discussion—Mathematically, apparent shear stressis given by the following:1This test method is under the jurisdiction ofASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.30 on Thermal Properties(Section D20.30.08).Current edition approved April 1, 2009. Published April 2009. Originallyapproved in 1993. Last previous edition approved in 2003 as D5422 – 03. DOI:10.1520/D5422-09.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at

[email protected] For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1τa5P4·~L/D!(2)where:τa= apparent shear stress, Pa,P = pressure at the entrance of the measuring capillary, Pa,L = length of the measuring capillary, mm, andD = diameter of the measuring capillary, mm.3.1.3 apparent viscosity (ηa)—ratio of apparent shear stressto apparent shear rate, Pa·s.3.1.3.1 Discussion—For an extrusion capillary rheometer,the ratio is usually calculated at a given shear rate. At constanttemperature, the apparent viscosity of most polymers is notconstant, but varies with shear rate. The viscosity is generallyannotated with the shear rate at which the measurement wasmade.3.1.4 capillary rheometer—an instrument in which thermo-plastics or thermoplastic compounds can be forced from areservoir through a capillary die. The temperature, pressureentering the die, and flow rate through the die can be controlledand accurately measured.3.1.5 corrected shear rate (γ˙w)—the actual shear rate at thewall of the capillary die determined by applying the Rabinow-itsch correction for non-Newtonian materials, s−1.3.1.5.1 Discussion—The Rabinowitsch correction math-ematically adjusts the shear-rate values to compensate fornon-Newtonian behavior of the polymer. To obtain correctedshear rate, at least two measurements of apparent shear stressand apparent shear rate are made. This is generally accom-plished by increasing the rate of extrusion (Q) while using thesame measuring capillary.3.1.5.2 Discussion—As a first step, the Bagley correction(as stated in 3.1.6) is made to the shear-stress values. Then,either by algebraic means (if only two measurements aremade), or by a regression method (for a greater number ofpoints), the equation in 3.1.11 is solved for n, using thecorrected shear stress (τw).3.1.5.3 Discussion—The corrected shear rate (γ˙w) is deter-mined by the following:γ˙w5F3n114nG·γ˙a(3)For most thermoplastics and thermoplastic compounds,the magnitude of shear sensitivity (n) will vary, dependingon material composition.3.1.6 corrected shear stress (τW)—the actual shear stress atthe wall of the capillary die, Pa. The corrected shear stress isobtained by applying the Bagley Correction Factor (E)totheapparent shear stress (see 3.1.7.1 and 3.1.7.2). The Bagleycorrection compensates for energy losses at the entrance andexit of the die.3.1.6.1 Discussion—This correction is often applied asthough it were an additional length of capillary. The correctionis often termed “end effect.” Capillary entrance angle andgeometry have great influence on the magnitude of thiscorrection.3.1.6.2 Discussion—The Bagley correction will also removethe influence of any static pressure in the system that does notvary with die length.3.1.6.3 Discussion—Since the magnitude of correction is afunction of shear rate, data for this correction are obtained byusing two or more dies of different length, but of the samediameter (and thus the same apparent shear rate, as calculatedin 3.1.4.2). If the data from these additional dies are compared,either graphically or mathematically, a linear relationship ofextrusion pressure with die geometry is usually obtained in thefollowing form:P 5 c·FLD1EG(4)where:E = the Bagley Correction Factor. (This term is often called“end effect.” It is expressed as the equivalent length ofcapillary necessary to extrapolate the pressure-linevalue on the P versus L/D plot to zero, mm.)c = slope of the line.The Bagley Correction Factor (E) and the slope (c) arefunctions of the thermoplastic compound and the shear rate.Corrected shear stress is therefore as follows:τw5P4·@~L/D!1E#(5)3.1.6.4 Discussion—Each value of corrected shear stressmust be annotated with the shear rate with which it ismeasured.3.1.7 corrected viscosity (η)—the ratio of corrected shearstress to corrected shear rate, Pa·s.3.1.7.1 Discussion—Since both the material properties andthe correction equations are functions of shear rate, it is veryimportant to state the particular value of shear rate at whicheach measurement is made.3.1.7.2 Discussion—Other corrections to measured valuesare often made in rheological research studies to compensatefor the effects of pressure, viscous heating, compressibility,time effects, etc. The terms “true shear stress,” “true shearrate,” and “true viscosity” are often used for the results of suchexhaustive calculations. This test method addresses only thetwo most important corrections, Bagley and Rabinowitsch.3.1.8 die entrance pressure (P)—the pressure in the reser-voir at the die entrance.3.1.9 newtonian fluid—a material for which the measure-ment of viscosity is not changed by changing the shear rate.Simple liquids, such as water, are considered Newtonianwhereas most polymeric materials are not.3.1.10 power-law fluid—a material for which the viscosityvaries with the shear rate in accordance with the followingknown relationship:τa5 K·~γ˙a!n(6)where:τa= apparent shear stress, Pa,γ˙a= apparent shear rate, s−1,K = a material constant, often called “consistency index,”andD5422 − 092n = shear sensitivity, dimensionless.Most non-Newtonian fluids follow this relationship for atleast short ranges of the shear rate variable. The power-lawequation is generally used in its logarithmic form as follows:log~τa!5 log~K!1n~log~γ˙a!!(7)3.1.11 shear sensitivity (n)—a dimensionless materialparameter, also called the “power-law index,” that representsthe magnitude of the shear sensitivity of a polymer. It is equalto 1.00 for Newtonian fluids, and generally less than 0.8 fornon-Newtonian fluids.3.1.11.1 Discussion—Mathematically, the shear sensitivityis given by the following:n 5dlog~τw!dlog~γ˙a!(8)where:d log(τw) = the change in log corrected shear stress overvarying extrusion rates, andd log(γ˙a) = the change in log apparent shear rate overvarying extrusion rates.4. Summary of Test Method4.1 The thermoplastic material is fed into a laboratoryextruder, the barrel of which is equipped with a temperaturecontrol. The output end of the extruder is equipped with acapillary die containing an insert of specified dimensions.Temperatures of the extruder barrel and capillary die arenormally kept constant. (It may be necessary to alter the die-settemperature only to compensate for shear heating of thematerial at different extrusion rates.)4.2 A suitable pressure transducer and temperature-measuring device, such as a thermocouple, are positioned inthe die just before the entrance to the insert.4.3 The rate of material extrusion, or mass throughput (Q)isdetermined by collecting extrudate over a timed interval andthen weighing it. The extrusion rate is controlled by adjustingthe drive speed.4.4 In order to calculate the flow properties of the material,extrusion is performed at a minimum of two different drivespeeds through an insert of specified dimensions (DieA).Then,extrusion is performed again, at the same drive speeds, throughat least one additional die insert of different specified dimen-sions (Die B or Die C).4.5 This procedure allows for the determination of apparentshear rate, apparent shear stress, apparent viscosity, correctedshear stress, corrected shear rate, corrected viscosity, shearsensitivity, and entrance/exit effects.5. Significance and Use5.1 This test method is useful for the characterization ofthermoplastics and thermoplastic compounds, in terms ofviscosity, or resistance to flow.5.2 The data produced by this test method has been founduseful in both quality-control testing and compound develop-ment. However, direct correlation with factory conditions isnot implied.5.3 Flow-performance data permits quality control of in-coming thermoplastics and thermoplastic compounds becausethe flow parameters are sensitive to molecular weight andmolecular-weight distribution. Therefore, this test method maydistinguish differences between lots.5.4 The shear viscosity or flow viscosity of thermoplasticsand thermoplastic compounds will not only be sensitive to theraw-polymer molecular properties, but will also be affected bythe type and amount of filler, additive, plasticizer, or stabilizer,by the type of copolymer blend, and by the addition of othercompounding materials. This test method can serve as aquality-control tool for either incoming materials or for in-house quality-assurance checks on production mixing. This testmethod is useful to the research and development of newproducts in that the rheological behavior of a yet uncharacter-ized thermoplastic or thermoplastic compound can be mea-sured and considered for comparative analysis.6. Interferences and Precautions6.1 Since the flow properties of non-Newtonian materialsare not linear, capillary rheometers should be operated atconditions of flow (temperature, pressure, and rate) similar tothose of selected commercial processes. These processes in-clude mixing, calendering, molding, and extrusion of thermo-plastics and thermoplastic compounds.6.2 Screw-extrusion-type rheometers impart significantamounts of energy to the thermoplastic or thermoplasticcompound before the measurement is made. Interpretation ofthe data for factory operations such as production extrusion,calendering, or injection molding is therefore more straightfor-ward than for compression-molding operations, where factory-work input is quite small.6.3 Increasing the rate of extrusion will induce shearheating, and therefore may alter the temperature of the materialflowing through the capillary die. It is essential to maintain aconstant melt temperature in the die in order to performaccurate viscosity measurements. It may be necessary tocompensate for shear heating by manually adjusting thedie-heater set temperature.6.4 Extruder residence time and shearing actions at aparticular melt temperature will often affect a material’sviscosity. It is recommended that consideration be given to thetemperature and shear-stability characteristics of each thermo-plastic or thermoplastic compound before using this testmethod.7. Apparatus7.1 A schematic diagram of a screw-extrusion capillaryrheometer is shown in Fig. 1. Only those parts essential to themeasurement are depicted. Suitable supports, drivecomponents, and fixtures, such as devices for securing the dieto the barrel are essential, but are not shown.D5422 − 0937.2 The screw-extrusion system controls both the rate ofextrusion and the temperature of the stock at the die entrance.7.2.1 A single-screw-type laboratory extruder having a bar-rel diameter of not greater than 31.7 mm nor less than 19 mmis recommended. The length to diameter (L/D) ratio of thebarrel should not be less than 20:1 nor more than 30:1.7.2.2 Compression of the stock is accomplished by transportaction of the rotating screw. In some extruders, the volumebetween the screw and the wall, occupied by the polymericcompounds, is less at the end of the barrel than at the feedsection. The