1、Designation: D 5422 03Standard Test Method forMeasurement of Properties of Thermoplastic Materials byScrew-Extrusion Capillary Rheometer1This standard is issued under the fixed designation D 5422; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、 of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThis test method uses capillary rheometry to measure the rheological properties of thermopl
3、asticsand 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 p
4、roperties, 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 p
5、iston-type capillaryrheometer (see Test Method D 3835).1.3 Capillary rheometer measurements for thermoplasticsand thermoplastic compounds are described in Test MethodD 3835.1.4 The values stated in SI units are to be regarded asstandard.1.5 This standard does not purport to address all of thesafety
6、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 1There is currently no equivalent ISO standard.2. Referenced Documents2.1
7、 ASTM Standards:D 618 Practice for Conditioning Plastics for Testing2D 883 Terminology Relating to Plastics2D 1238 Test Method for Flow Rates of Thermoplastics byExtrusion Plastometer2D 3835 Test Method for Determination of Properties ofPolymeric Materials by Means of a Capillary Rheometer3E 691 Pra
8、ctice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method43. Terminology3.1 Definitions (See Terminology D 883) :3.1.1 apparent shear rate (ga)shear strain rate (or veloc-ity gradient) of the thermoplastic or thermoplastic compoundextrudate as it passes through the cap
9、illary die.3.1.1.1 DiscussionThis 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 di
10、e, a specific level ofapparent shear rate may be achieved. Alternately, the shearstress (entrance pressure) may be controlled, and the apparentshear rate measured.3.1.1.2 DiscussionMathematically, the apparent shearrate at the wall of the capillary for a Newtonian fluid at thecapillary wall is given
11、 by the following:ga532 Qp D3(1)where:ga= apparent shear rate, s1,Q = quantity of fluid extruded per time, mm3/s,p = 3.142, andD = diameter of the measuring capillary, mm.3.1.2 apparent shear stress (ta)the measured resistance tothe flow through a capillary die. It may be determined bymeasuring the
12、die entrance pressure for a specific die, thenapplying appropriate geometric factors.3.1.2.1 DiscussionMathematically, apparent shear stressis given by the following:ta5P4L/D!(2)1This test method is under the jurisdiction ofASTM Committee D20 on Plasticsand is the direct responsibility of Subcommitt
13、ee D20.30 on Thermal Properties.Current edition approved April 10, 2003. Published June 2003. Originallyapproved in 1993. Last previous edition approved in 2000 as D 5422 00.2Annual Book of ASTM Standards, Vol 08.01.3Annual Book of ASTM Standards, Vol 08.02.4Annual Book of ASTM Standards, Vol 14.02.
14、1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.where:ta= apparent shear stress, Pa,P = pressure at the entrance of the measuring capillary,Pa,L = length of the measur
15、ing capillary, mm, andD = diameter of the measuring capillary, mm.3.1.3 apparent viscosity (ha)ratio of apparent shear stressto apparent shear rate, Pas.3.1.3.1 DiscussionFor an extrusion capillary rheometer,the ratio is usually calculated at a given shear rate. At constanttemperature, the apparent
16、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 rheometeran instrument in which thermo-plastics or thermoplastic compounds can be forced from areservoir through a capillary
17、 die. The temperature, pressureentering the die, and flow rate through the die can be controlledand accurately measured.3.1.5 corrected shear rate (gw)the actual shear rate at thewall of the capillary die determined by applying the Rabinow-itsch correction for non-Newtonian materials, s1.3.1.5.1 Dis
18、cussionThe 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 th
19、e rate of extrusion (Q) while using thesame measuring capillary.3.1.5.2 DiscussionAs 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
20、), the equation in 3.1.11 is solved for n, using thecorrected shear stress (tw).3.1.5.3 DiscussionThe corrected shear rate (gw) is deter-mined by the following:gw5F3n1 14nG ga(3)For most thermoplastics and thermoplastic compounds, the magni-tude of shear sensitivity (n) will vary, depending on mater
21、ial compo-sition.3.1.6 corrected shear stress (tW)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
22、 the entrance andexit of the die.3.1.6.1 DiscussionThis 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 DiscussionThe Bagle
23、y correction will also re-move the influence of any static pressure in the system thatdoes not vary with die length.3.1.6.3 DiscussionSince 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 samediame
24、ter (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 FLD1 EG(4)where:E = the Bagley C
25、orrection Factor. (This term is oftencalled “end effect.” It is expressed as the equivalentlength of capillary necessary to extrapolate thepressure-line value 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 thermoplast
26、ic compound and the shear rate.Corrected shear stress is therefore as follows:tw5P4L/D! 1 E(5)3.1.6.4 DiscussionEach value of corrected shear stressmust be annotated with the shear rate with which it ismeasured.3.1.7 corrected viscosity (h)the ratio of corrected shearstress to corrected shear rate,
27、Pas.3.1.7.1 DiscussionSince 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 DiscussionOther corrections to measured valuesare often made in rheological resea
28、rch 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 correct
29、ions, Bagley and Rabinowitsch.3.1.8 die entrance pressure (P)the pressure in the reser-voir at the die entrance.3.1.9 newtonian fluida 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 polyme
30、ric materials are not.3.1.10 power-law fluida material for which the viscosityvaries with the shear rate in accordance with the followingknown relationship:ta5 K ga!n(6)where:ta= apparent shear stress, Pa,ga= apparent shear rate, s1,K = a material constant, often called “consistency index,”andn = sh
31、ear 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:D5422032log ta! 5 log K! 1 n log ga! (7)3.1.11 shear sensitivity (n)a dimensionless materi
32、al pa-rameter, also called the “power-law index,” that represents themagnitude of the shear sensitivity of a polymer. It is equal to1.00 for Newtonian fluids, and generally less than 0.8 fornon-Newtonian fluids.3.1.11.1 DiscussionMathematically, the shear sensitivityis given by the following:n 5d lo
33、gtw!d log ga!(8)where:d log (tw) = the change in log corrected shear stress overvarying extrusion rates, andd log (ga) = 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
34、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
35、 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 collectin
36、g extrudate over a timed interval andthen weighing it. Extrusion rate may be 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,ex
37、trusion 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
38、 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 founduse
39、ful 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 andm
40、olecular-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
41、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 usefu
42、l 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
43、 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 rheom
44、eters 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 oper
45、ations, where factory-work input is quite small.6.3 Increasing the rate of extrusion will induce shear heat-ing, 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 vis
46、cosity 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 may often affect a materialsviscosity. It is recommended that consideration be given to thetemp
47、erature 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, driv
48、e compo-nents, and fixtures, such as devices for securing the die to thebarrel are essential, but are not shown.7.2 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 diamet
49、er 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 ratio of the volume in the feed section to thevolume at the end of the screw is referred to as the “compres-sion ratio
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