1、Designation: D5422 09D5422 17Standard 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 th
2、e 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 the
3、rmoplasticsand 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 properties ofthermoplastics and thermoplastic compounds. The measured fl
4、ow properties, which are obtained through laboratory investigation,may help to describe the material behavior that occurs in factory processing.1.2 Since a screw-type capillary rheometer imparts shear energy to the material during testing, the measurements will usuallydiffer from those obtained with
5、 a piston-type capillary rheometer (see Test Method D3835).1.3 Capillary rheometer measurements for thermoplastics and thermoplastic compounds are described in Test Method D3835.1.4 The values stated in SI units are to be regarded as standard.1.5 This standard does not purport to address all of the
6、safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.NOTE 1There is no known ISO equivalent to thi
7、s standard. The scope of this standard is mentioned in ISO 11443:2014, PlasticsDetermination ofthe fluidity of plastics using capillary and slit-die rheometers,” Annex C, “Uncertainties in the determination of shear viscosity by capillary extrusion.”1.6 This international standard was developed in a
8、ccordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 AST
9、M Standards:2D618 Practice for Conditioning Plastics for TestingD883 Terminology Relating to PlasticsD1238 Test Method for Melt Flow Rates of Thermoplastics by Extrusion PlastometerD3835 Test Method for Determination of Properties of Polymeric Materials by Means of a Capillary RheometerE691 Practice
10、 for Conducting an Interlaboratory Study to Determine the Precision of a Test Method3. Terminology3.1 Definitions: (See Terminology D883):3.1.1 apparent shear rate (a) )shear strain rate (or velocity gradient) of the thermoplastic or thermoplastic compoundextrudate as it passes through the capillary
11、 die.1 This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.30 on Thermal Properties (SectionD20.30.08).Current edition approved April 1, 2009Dec. 1, 2017. Published April 2009January 2018. Originally approved in 1993. Last
12、 previous edition approved in 20032009 asD5422 03.D5422 09. DOI: 10.1520/D5422-09.10.1520/D5422-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Docu
13、ment Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM r
14、ecommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box
15、 C700, West Conshohocken, PA 19428-2959. United States13.1.1.1 DiscussionThis velocity gradient is not uniform through the cross-section of the capillary die. The shear rate is calculated for the region ofhighest shear, which is at the wall of the capillary. By selecting a die diameter and controlli
16、ng the volume flow per unit timethrough the die, a specific level of apparent shear rate is achieved. Alternately, the shear stress (entrance pressure) is controlled,and the apparent shear rate measured.3.1.1.2 DiscussionMathematically, the apparent shear rate at the wall of the capillary for a Newt
17、onian fluid at the capillary wall is given by thefollowing:a 5 32QpiD 3 (1)where:a = apparent shear rate, s1,Q = quantity of fluid extruded per time, mm3 /s,pi = 3.142, andD = diameter of the measuring capillary, mm.3.1.2 apparent shear stress (a) )the measured resistance to the flow through a capil
18、lary die. It may be determined bymeasuring the die entrance pressure for a specific die, then applying appropriate geometric factors.3.1.2.1 DiscussionMathematically, apparent shear stress is given by the following:a 5 P4L/D! (2)where:a = apparent shear stress, Pa,P = pressure at the entrance of the
19、 measuring capillary, Pa,L = length of the measuring capillary, mm, andD = diameter of the measuring capillary, mm.3.1.3 apparent viscosity (a) )ratio of apparent shear stress to apparent shear rate, Pas.3.1.3.1 DiscussionFor an extrusion capillary rheometer, the ratio is usually calculated at a giv
20、en shear rate. At constant temperature, the apparentviscosity of most polymers is not constant, but varies with shear rate. The viscosity is generally annotated with the shear rate atwhich the measurement was made.3.1.4 capillary rheometeran instrument in which thermoplastics or thermoplastic compou
21、nds can be forced from a reservoirthrough a capillary die. The temperature, pressure entering the die, and flow rate through the die can be controlled and accuratelymeasured.3.1.5 corrected shear rate (w) )the actual shear rate at the wall of the capillary die determined by applying theRabinowitsch
22、correction for non-Newtonian materials, s1.3.1.5.1 DiscussionThe Rabinowitsch correction mathematically adjusts the shear-rate values to compensate for non-Newtonian behavior of thepolymer. To obtain corrected shear rate, at least two measurements of apparent shear stress and apparent shear rate are
23、 made. Thisis generally accomplished by increasing the rate of extrusion (Q) while using the same measuring capillary.3.1.5.2 DiscussionD5422 172As 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 onlytwo measurements ar
24、e made), or by a regression method (for a greater number of points), the equation in 3.1.11 is solved for n,using the corrected shear stress (w).3.1.5.3 DiscussionThe corrected shear rate ( w) is determined by the following:w 5F3n 114nGa (3)For most thermoplastics and thermoplastic compounds, the ma
25、gnitude of shear sensitivity (n) will vary, depending on ma-terial composition.3.1.6 corrected shear stress (W) )the actual shear stress at the wall of the capillary die, Pa. The corrected shear stress isobtained by applying the Bagley Correction Factor (E) to the apparent shear stress (see 3.1.7.1
26、and 3.1.7.2). The Bagley correctioncompensates for energy losses at the entrance and exit of the die.3.1.6.1 DiscussionThis correction is often applied as though it were an additional length of capillary. The correction is often termed “end effect.”Capillary entrance angle and geometry have great in
27、fluence on the magnitude of this correction.3.1.6.2 DiscussionThe Bagley correction will also remove the influence of any static pressure in the system that does not vary with die length.3.1.6.3 DiscussionSince the magnitude of correction is a function of shear rate, data for this correction are obt
28、ained by using two or more dies ofdifferent length, but of the same diameter (and thus the same apparent shear rate, as calculated in 3.1.4.2). If the data from theseadditional dies are compared, either graphically or mathematically, a linear relationship of extrusion pressure with die geometryis us
29、ually obtained in the following form:P 5cFLD1EG (4)where:E = the Bagley Correction Factor. (This term is often called “end effect.” It is expressed as the equivalent length of capillarynecessary to extrapolate the pressure-line value on the P versus L/D plot to zero, mm.)c = slope of the line.The Ba
30、gley Correction Factor (E) and the slope (c) are functions of the thermoplastic compound and the shear rate. Correctedshear stress is therefore as follows: w 5 P4L/D!1E# (5)3.1.6.4 DiscussionEach value of corrected shear stress must be annotated with the shear rate with which it is measured.3.1.7 co
31、rrected viscosity ()the ratio of corrected shear stress to corrected shear rate, Pas.3.1.7.1 DiscussionSince both the material properties and the correction equations are functions of shear rate, it is very important to state the particularvalue of shear rate at which each measurement is made.3.1.7.
32、2 DiscussionD5422 173Other corrections to measured values are often made in rheological research studies to compensate for the effects of pressure,viscous heating, compressibility, time effects, etc. The terms “true shear stress,” “true shear rate,” and “true viscosity” are oftenused for the results
33、 of such exhaustive calculations. This test method addresses only the two most important corrections, Bagleyand Rabinowitsch.3.1.8 die entrance pressure (P)the pressure in the reservoir at the die entrance.3.1.9 newtonian fluida material for which the measurement of viscosity is not changed by chang
34、ing the shear rate. Simpleliquids, such as water, are considered Newtonian whereas most polymeric materials are not.3.1.10 power-law fluida material for which the viscosity varies with the shear rate in accordance with the following knownrelationship:a 5Ka!n (6)where:a = apparent shear stress, Pa,a
35、= apparent shear rate, s1 ,K = a material constant, often called “consistency index,” andn = shear sensitivity, dimensionless.Most non-Newtonian fluids follow this relationship for at least short ranges of the shear rate variable. The power-law equationis generally used in its logarithmic form as fo
36、llows:log a! 5logK!1n log a! (7)3.1.11 shear sensitivity (n)a dimensionless material parameter, also called the “power-law index,” that represents themagnitude of the shear sensitivity of a polymer. It is equal to 1.00 for Newtonian fluids, and generally less than 0.8 fornon-Newtonian fluids.3.1.11.
37、1 DiscussionMathematically, the shear sensitivity is given by the following:n 5dlogw!dloga!(8)where:d log(w) = the change in log corrected shear stress over varying extrusion rates, anddlog(a)= the change in log apparent shear rate over varying extrusion rates.4. Summary of Test Method4.1 The thermo
38、plastic material is fed into a laboratory extruder, the barrel of which is equipped with a temperature control. Theoutput end of the extruder is equipped with a capillary die containing an insert of specified dimensions. Temperatures of theextruder barrel and capillary die are normally kept constant
39、. (It may be necessary to alter the die-set temperature only tocompensate for shear heating of the material at different extrusion rates.)4.2 A suitable pressure transducer and temperature-measuring device, such as a thermocouple, are positioned in the die justbefore the entrance to the insert.4.3 T
40、he rate of material extrusion, or mass throughput (Q) is determined by collecting extrudate over a timed interval and thenweighing it. The extrusion rate is controlled by adjusting the drive speed.4.4 In order to calculate the flow properties of the material, extrusion is performed at a minimum of t
41、wo different drive speedsthrough an insert of specified dimensions (Die A). Then, extrusion is performed again, at the same drive speeds, through at leastone additional die insert of different specified dimensions (Die B or Die C).4.5 This procedure allows for the determination of apparent shear rat
42、e, apparent shear stress, apparent viscosity, corrected shearstress, corrected shear rate, corrected viscosity, shear sensitivity, and entrance/exit effects.5. Significance and Use5.1 This test method is useful for the characterization of thermoplastics and thermoplastic compounds, in terms of visco
43、sity, orresistance to flow.D5422 1745.2 The data produced by this test method has been found useful in both quality-control testing and compound development.However, direct correlation with factory conditions is not implied.5.3 Flow-performance data permits quality control of incoming thermoplastics
44、 and thermoplastic compounds because the flowparameters are sensitive to molecular weight and molecular-weight distribution. Therefore, this test method may distinguishdifferences between lots.5.4 The shear viscosity or flow viscosity of thermoplastics and thermoplastic compounds will not only be se
45、nsitive to theraw-polymer molecular properties, but will also be affected by the type and amount of filler, additive, plasticizer, or stabilizer, bythe type of copolymer blend, and by the addition of other compounding materials. This test method can serve as a quality-controltool for either incoming
46、 materials or for in-house quality-assurance checks on production mixing. This test method is useful to theresearch and development of new products in that the rheological behavior of a yet uncharacterized thermoplastic or thermoplasticcompound can be measured and considered for comparative analysis
47、.6. Interferences and Precautions6.1 Since the flow properties of non-Newtonian materials are not linear, capillary rheometers should be operated at conditionsof flow (temperature, pressure, and rate) similar to those of selected commercial processes. These processes include mixing,calendering, mold
48、ing, and extrusion of thermoplastics and thermoplastic compounds.6.2 Screw-extrusion-type rheometers impart significant amounts of energy to the thermoplastic or thermoplastic compoundbefore the measurement is made. Interpretation of the data for factory operations such as production extrusion, cale
49、ndering, orinjection molding is therefore more straightforward than for compression-molding operations, where factory-work input is quitesmall.6.3 Increasing the rate of extrusion will induce shear heating, and therefore may alter the temperature of the material flowingthrough the capillary die. It is essential to maintain a constant melt temperature in the die in order to perform accurate viscositymeasurements. It may be necessary to compensate for shear heating by manually adjusting
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