1、Designation: D1991 15Standard Test Method forRubber Chemicals2-Mercaptobenzothiazole (MBT)Assay1This standard is issued under the fixed designation D1991; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A
2、 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 a procedure for the assay of2-mercaptobenzothiazole (MBT). It is based on a potentiomet-ric titration of MBT w
3、ith sodium hydroxide.1.2 The assay is determined as percent by mass.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
4、 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:2D4483 Practice for Evaluating Precision for Test MethodStandards in the Rubber a
5、nd Carbon Black ManufacturingIndustries3. Summary of Test Method3.1 A sample of MBT is dissolved in ethanol. The solutionis titrated potentiometrically using a solution of sodium hy-droxide as the titrant.4. Significance and Use4.1 MBT is commonly used as an accelerator for rubber andlatex vulcaniza
6、tion. The purity of MBT may be of importancein predicting performance in rubber compounds and this testmethod is designed to assess the purity of MBT.4.2 This test method may be used as a quality control tooland for research and development work.5. Apparatus5.1 Erlenmeyer Flask, 250-cm3.5.2 Analytic
7、al Balance, having a sensitivity of 60.1 mg.5.3 Potentiograph.5.4 Glass pH Electrode, and reference electrode.5.5 Graduated Cylinder, 200-cm3.6. Reagents6.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform
8、to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.36.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean distilled water or water ofequal purity.6.3 Aqueous Sodium Hydroxide
9、Solution (40 g NaOH in1dm3of solution)Standardize by accepted analytical tech-niques to ensure that the maximum error of the normalizationfactor is not more than 0.001.6.4 Ethanol, denatured with toluene (in the ratio of 100volumes ethanol to 1 volume toluene).6.5 Toluene.7. Sampling7.1 Sampling sha
10、ll be at the discretion of the analyst toobtain as representative a sample as possible, of the lot to betested.8. Procedure8.1 Weigh (to nearest 0.001 g) about5gofthespecimen,and transfer into a 250-cm3Erlenmeyer flask. Using a gradu-ated cylinder, add 125 cm3denatured ethanol (6.4). Titrate the1Thi
11、s 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 June 1, 2015. Published July 2015. Originally approvedin 1991. Last previous edition approved in 2010 as D1991 05 (2010). DOI:1
12、0.1520/D1991-15.2For 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
13、 Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial
14、Convention, Inc. (USPC), Rockville,MD.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1solution potentiometrically, using a glass electrode system,with NaOH (6.3) as the titrant (A) (see Fig. 1).9. Calculation9.1 From the plot of pH ve
15、rsus millilitres of NaOH, asillustrated in Fig. 1, the equivalence point for the potentiomet-ric titration is defined as the inflection point of the curve. Thisinflection point may be estimated by determination of themidpoint of the tangent slope.9.1.1 This inflection point is identified as follows:
16、9.1.1.1 Draw a tangent through the steepest part of thecurve. Determine the two points at which the curve departsfrom this tangent line. The midpoint of the line segmentbetween these two points represents the equivalence point.9.2 Calculate the MBT content by the following equation:MBT content, % 51
17、67.2 3 A 3 N 3100W 31000(1)where:A = volume of sodium hydroxide to the equivalencepoint, cm3,167.2 = molecular mass of MBT,W = mass g of specimen, andN = normality of titrant.10. Report10.1 Report the following information:10.1.1 Proper identification of the sample, and10.1.2 Results obtained from t
18、wo individual determinationsand their average, reported to the nearest 0.1 %.11. Precision and Bias11.1 This precision and bias section has been prepared inaccordance with Practice D4483. Refer to this practice forterminology and other statistical calculation details.11.2 The precision results in th
19、is precision and bias sectiongive an estimate of the precision of this test method with thematerials used in the particular interlaboratory programs asdescribed below. The precision parameters should not be usedfor acceptance/rejection testing of any group of materialswithout documentation that they
20、 are applicable to those par-ticular materials and the specific testing protocols that includethis test method.11.3 A Type 1 (interlaboratory) precision was evaluated in1988. Both repeatability and reproducibility are short term. Aperiod of a few days separates replicate test results.Atest resultis
21、the mean of the assay results.11.4 An MBT sample was analyzed in ten laboratories ontwo different days.11.5 The results of the precision calculations for repeatabil-ity and reproducibility are shown in Table 1.11.6 RepeatabilityThe repeatability, r, of this test methodhas been established as the val
22、ue tabulated in Table 1.Twosingle test results, obtained under normal test methodprocedures, that differ by more than the tabulated r (for anygiven level) must be considered as derived from different ornonidentical sample populations.11.7 ReproducibilityThe reproducibility, R, of this testmethod has
23、 been established as the value tabulated in Table 1.Two single test results obtained in two different laboratories,under normal test method procedures, that differ by more thanthe tabulated R (for any given level) must be considered tohave come from different or nonidentical sample populations.11.8
24、Repeatability and reproducibility expressed as a per-centage of the mean level, (r) and (R), have equivalentapplication statements as above for r and R. For the (r) and (R)statements, the difference in the two single test results isexpressed as a percentage of the arithmetic mean of the two testresu
25、lts.11.9 BiasIn test method terminology, bias is the differencebetween an average test value and the reference (or true) testproperty value. Reference values have not been evaluated forthis test method. Bias therefore cannot be determined.12. Keywords12.1 accelerators; assay; mercaptobenzothiazole (
26、MBT);thiazoleFIG. 1 Potentiometric Titration Using NaOH as the TitrantTABLE 1 MBT AssayAMaterialAverage%Within Laboratories Between LaboratoriesSr r (r) SR R (R)MBT 97.56 0.286 0.810 0.83 1.675 4.74 4.86ASr = repeatability standard deviation,r = repeatability2.83 the square root of the repeatability
27、 variance,(r) = repeatability (as percentage of material average),SR = reproducibility standard deviation,R = reproducibility2.83 the square root of the reproducibilityvariance, and(R) = reproducibility (as percentage of material average).D1991 152ASTM International takes no position respecting the
28、validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is
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30、quarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This sta
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