ASTM_D_5051_-_06_2012.pdf

Designation:D505106(Reapproved 2012)Standard Test Method forRubber Compounding MaterialsBenzothiazyl Disulfide(MBTS)Assay1This standard is issued under the fixed designation D5051;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 covers the determination of assay ofbenzothiazyl disulfide(MBTS).It is based on a titration of freeiodine liberated upon reduction of MBTS,with potassiumiodide(KI)in acid medium.1.2 The assay is determined as mass percent.1.3 Free 2-mercaptobenzothiazole(MBT)content is notdetermined.1.4 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.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.2.Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD4483 Practice for Evaluating Precision for Test MethodStandards in the Rubber and Carbon Black ManufacturingIndustries3.Summary of Test Method3.1 In an acid medium,MBTS is reduced with KI to MBTand free iodine.The free iodine is titrated with standard sodiumthiosulfate solution.3.2 MBTS is sparingly soluble in any organic solvent;whileMBT,formed during the reaction of MBTS with KI is verysoluble.Therefore after reagents are added as indicated in theprocedure,continue to stir till all MBTS has reacted.4.Significance and Use4.1 The test method is designed to assess the purity ofMBTS,which is used for rubber and latex vulcanizationacceleration.The amount of MBTS is of importance inpredicting performance in rubber compounds and for rawmaterial purchase and control.4.2 This test method may be used as a quality control tooland for research and development work.5.Interferences5.1 KI-reducible contaminants interfere with the results.6.Apparatus6.1 Erlenmeyer Flask,300 cm3.6.2 Graduated Cylinder,5 cm3.6.3 Magnetic Stirrer,with hot plate.6.4 Buret,50-cm3capacity.6.5 Analytical Balance,having a sensitivity of 60.1 mg.7.Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests.Unless otherwise indicated,it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.3Other grades may beused,provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.7.2 Purity of WaterUnless otherwise indicated,referencesto water shall be understood to mean reagent water as definedby Types I,II,or III of Specification D1193.7.3 Acetic Acid,100%,analytical reagent.7.4 Isopropanol,analytical reagent.1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand is the direct responsibility of Subcommittee D11.11 on Chemical Analysis.Current edition approved May 1,2012.Published July 2012.Originally approvedin 1990.Last previous edition approved in 2006 as D5051 06.DOI:10.1520/D5051-06R12.2For 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.3Reagent Chemicals,American Chemical Society Specifications,AmericanChemical Society,Washington,DC.For suggestions on the testing of reagents notlisted by the American Chemical Society,see Analar Standards for LaboratoryChemicals,BDH Ltd.,Poole,Dorset,U.K.,and the United States Pharmacopeiaand National Formulary,U.S.Pharmaceutical Convention,Inc.(USPC),Rockville,MD.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 7.5 Toluene,analytical reagent.7.6 Potassium Iodide(KI),analytical reagent.7.7 Sodium Thiosulfate(Na2S2O3)(0.1 N).7.8 Starch Indicator SolutionSlurry 2 g of soluble starchwith 10 cm3of water and dilute with 90 cm3of boiling water.7.9 Hydrochloric Acid(HCl)(2 N).7.10 Solvent:Mix 5 volumes isopropanol with 3 volumestoluene.8.Sampling8.1 Depending upon the purposes of the testing,samplingshall be at the discretion of the analyst to obtain as represen-tative a sample as possible of the lot to be tested.9.Procedure9.1 Accurately weigh about 0.5 g of the test specimen to thenearest 0.1 mg and carefully transfer it to a 300-cm3Erlen-meyer flask.9.2 Add 50 cm3of solvent to the specimen,which may notdissolve completely.9.3 With stirring,add the reagents in the following se-quence:50 cm3of distilled water,about 6 g of KI,25 cm3of2 N HCl,and 25 cm3of acetic acid(see 3