ASTM_F_2214_-_02_2008.pdf

Designation:F221402(Reapproved 2008)Standard Test Method forIn Situ Determination of Network Parameters of CrosslinkedUltra High Molecular Weight Polyethylene(UHMWPE)1This standard is issued under the fixed designation F2214;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.1.Scope1.1 This test method describes how the crosslink density,molecular weight between crosslinks,and number of repeatunits between crosslinks in ultra-high molecular weight poly-ethylene(UHMWPE)crosslinked by ionizing radiation or bychemical means can be determined by measuring the swellingratio of samples immersed in o-xylene.Examples of experi-mental techniques used to make these measurements arediscussed herein.1.2 The test method reported here measures the change inheight of a sample specimen while it is immersed in thesolvent.Volumetric swell ratios assume that the sample iscrosslinked isotropically,and that the change in dimension willbe uniform in all directions.This technique avoids uncertaintyinduced by solvent evaporation or temperature change.1.3 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.4 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.2.Referenced Documents2.1 ASTM Standards:2D2765 Test Methods for Determination of Gel Content andSwell Ratio of Crosslinked Ethylene PlasticsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 crosslink density,dthe theoretical average numberof crosslinks per unit volume mol/dm3.3.1.2 molecular weight between crosslinks,Mcthe theo-retical average molecular weight between crosslinks g/mol.3.1.3 swell ratio,qsthe ratio of the volume of the samplein an equilibrium swollen state to its volume in the unswollenstate.4.Summary of Test Method4.1 The height of a cubic specimen is measured,and thespecimen is placed in a dry chamber.A selected solvent ischosen according to the Flory network theory and is introducedinto the chamber.The chamber is heated to the referencetemperature.The sample height is monitored as a function oftime until steady state(equilibrium)is achieved.The swellratio is calculated from the final steady state(equilibrium)height and the initial height.5.Significance and Use5.1 This test method is designed to produce data indicativeof the degree of crosslinking in ultra high molecular weightpolyethylene that has been crosslinked chemically or byionizing radiation.5.2 The results are sensitive to the test temperature,solvent,and method used.For the comparison of data betweeninstitutions,care must be taken to have the same test conditionsand reagents.5.3 The data can be used for dose uniformity analysis,fundamental research,and quality assurance testing.6.Apparatus6.1 The apparatus shall include any device that allows anon-invasive measurement of the change in one dimension ofthe sample as it swells in the solvent.This measurement couldinclude,but is not limited to:6.1.1 Mechanical measurements,such as linear variabledisplacement transducers(LVDTs).1This test method is under the jurisdiction ofASTM Committee F04 on Medicaland Surgical Materials and Devicesand is the direct responsibility of SubcommitteeF04.15 on Material Test Methods.Current edition approved May 1,2008.Published June 2008.Originallyapproved in 2002.Last previous edition approved in 2002 as F2214 02.DOI:10.1520/F2214-02R08.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.1.1.1 If a mechanical probe is used,it must be constructedof a material that exhibits little thermal expansion,such asquartz or ceramic.6.1.2 Optical measurements,such as cameras or laser mi-crometers.6.1.2.1 Optical measurements should be insensitive to anyrefractive index changes in the UHMWPE sample,given thechanging temperature of the system.6.1.3 Inductive measurements,such as proximity sensors.Inductive measurements must be insensitive to temperature orsolvent composition.6.2 The sensitivity of the measurement shall be 1%of theinitial height of the sample,H0.An uncertainty analysis hasdemonstrated that this sensitivity will produce a relative errorin crosslink density less than 10%for samples swollen to