ASTM_D_5422_-_09.pdf

Designation:D542209Standard 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.NOTE1There 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(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 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 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 DiscussionMathematically,the apparent shear rateat the wall of the capillary for a Newtonian fluid at the capillarywall is given by the following:a532QD3(1)where:a=apparent shear rate,s1,Q=quantity of fluid extruded per time,mm3/s,=3.142,andD=diameter of the measuring capillary,mm.3.1.2 apparent shear stress(a)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 DiscussionMathematically,apparent shear stressis given by the following:1This test method is under the jurisdiction of ASTM 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 serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards 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 States1 a5P4L/D!(2)where:a=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(a)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 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 die.The temperature,pressureentering the die,and flow rate through the die can be controlledand accurately measured.3.1.5 corrected shear rate(w)the actu