1、March 2014Translation by DIN-Sprachendienst.English price group 9No part of this translation may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).ICS 83
2、.040.10!%,l%“2097302www.din.deDDIN ISO 127Rubber, natural latex concentrate Determination of KOH number (ISO 127:2012),English translation of DIN ISO 127:2014-03Naturkautschuk-Latex-Konzentrat Bestimmung der KOH-Zahl (ISO 127:2012),Englische bersetzung von DIN ISO 127:2014-03Latex concentr de caoutc
3、houc naturel Dtermination de lindice de potasse (ISO 127:2012),Traduction anglaise de DIN ISO 127:2014-03SupersedesDIN ISO 127:2008-06www.beuth.deIn case of doubt, the German-language original shall be considered authoritative.Document comprises 12 pages02.14 A comma is used as the decimal marker. C
4、ontents Page National foreword .3 National Annex NA (informative) Bibliography .3 1 Scope .4 2 Normative references .4 3 Terms and definitions 4 4 Reagents 4 5 Apparatus 5 6 Sampling 5 7 Procedure 5 8 Expression of results .6 9 Precision 6 10 Test report .6 Annex A (informative) Determination of for
5、maldehyde 7 Annex B (informative) Example of a typical titration and calculation of the end-point 8 Annex C (informative) Precision statement 10 Bibliography . 12 2DIN ISO 127:2014-03National foreword This standard (ISO 127:2012) has been prepared by Technical Committee ISO/TC 45 “Rubber and rubber
6、products” (Secretariat: DSM, Malaysia), Subcommittee SC 3 “Raw materials (including latex) for use in the rubber industry”. The responsible German body involved in its preparation was the Normenausschuss Materialprfung (Materials Testing Standards Committee), Working Committee NA 062-04-35 AA Rohmat
7、erialien (ein-schlielich Latex) fr die Kautschukindustrie. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. DIN and/or DKE shall not be held responsible for identifying any or all such patent rights. The DIN Standards corresponding
8、 to the International Standards referred to in this document are as follows: ISO 123 DIN ISO 123 ISO 125 DIN ISO 125 ISO 976 DIN ISO 976 ISO 1802 DIN ISO 1802 Amendments This standard differs from DIN ISO 127:2008-06 as follows: a) normative references have been updated; b) the precision statement h
9、as been moved to Annex C. Previous editions DIN 53566: 1965-11, 1987-04 DIN ISO 127: 1999-04, 2008-06 National Annex NA (informative) Bibliography DIN ISO 123, Rubber latex Sampling DIN EN ISO 125, Natural rubber latex concentrate Determination of alkalinity DIN ISO 976, Rubber and plastics Polymer
10、dispersions and rubber latices Determination of pH DIN ISO 1802, Rubber latex, natural, concentrate Determination of boric acid content 3DIN ISO 127:2014-03WARNING Persons using this International Standard should be familiar with normal laboratory practice. This standard does not purport to address
11、all of the safety problems, if any, associated with its use. It is the responsibility of the user to establish appropriate safety and health practices and to ensure compliance with any national regulatory conditions.1 ScopeThis International Standard specifies a method for the determination of the K
12、OH number of natural rubber latex concentrate which is preserved wholly or in part with ammonia. The method is applicable to latices containing boric acid. The method is not applicable to latices preserved with potassium hydroxide. It is not necessarily suitable for latices from natural sources othe
13、r than Hevea brasiliensis, or for latices of synthetic rubber, compounded latex, vulcanized latex or artificial dispersions of rubber.2 Normative referencesThe following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies.
14、 For undated references, the latest edition of the referenced document (including any amendments) applies.ISO 123, Rubber latex SamplingISO 124, Latex, rubber Determination of total solids contentISO 125, Natural rubber latex concentrate Determination of alkalinityISO 976, Rubber and plastics Polyme
15、r dispersions and rubber latices Determination of pHISO 1802, Natural rubber latex concentrate Determination of boric acid content3 Terms and definitionsFor the purposes of this document, the following terms and definitions apply.3.1KOH numbernumber of grams of potassium hydroxide equivalent to the
16、acid radicals combined with ammonia in latex containing 100 g of total solidsISO 1382:20084 ReagentsDuring the analysis, use only reagents of recognized analytical grade and only distilled water free of dissolved carbon dioxide, or water of equivalent purity.4.1 Potassium hydroxide, standard volumet
17、ric solution, c(KOH) = 0,1 mol/dm3, carbonate-free.4.2 Potassium hydroxide, standard volumetric solution, c(KOH) = 0,5 mol/dm3, carbonate-free.Rubber, natural latex concentrate Determination of KOH number 4DIN ISO 127:2014-034.3 Formaldehyde, 45 g to 50 g in 1 dm3of solution c(HCHO) = 1,5 mol/dm3to
18、1,67 mol/dm3, acid-free, prepared by diluting concentrated formaldehyde with water and neutralizing with 0,1 mol/dm3potassium hydroxide solution (4.1), using as indicator the faint pink colour of phenolphthalein.Determine the concentration of the formaldehyde solution as described in Annex A.5 Appar
19、atusStandard laboratory glassware, plus the following:5.1 pH-meter, conforming to ISO 976 but capable of being read to 0,01 units.5.2 Glass electrode, of a type suitable for use in solutions of pH up to 12,0.5.3 Mechanical stirrer, with earthed motor and glass paddle, or magnetic stirrer.An automati
20、c titrator may be used provided it has been checked as giving the same result as the standard method.6 SamplingCarry out the sampling in accordance with one of the methods specified in ISO 123.7 ProcedureCalibrate the pH-meter by the method specified in ISO 976. If the total solids (wTS) and alkalin
21、ity (A) of the latex are not known, determine them in accordance with ISO 124 and ISO 125, respectively. If the latex contains boric acid and the content is not known, determine it in accordance with ISO 1802.Carry out the determination in duplicate.Weigh, to the nearest 0,1 g, into a 400 cm3beaker
22、a test portion (mass m) of the test sample containing approximately 50 g of total solids. If necessary, adjust the alkalinity to (0,5 0,1) % ammonia calculated with respect to the water phase by adding, while stirring, the required quantity of formaldehyde solution (4.3).Calculate the volume, Vf, in
23、 cubic centimetres, of formaldehyde solution to be added from the equationVmwAcfTS100HCHO=()()()05113 4,wherem is the mass, in grams, of the test portion;wTSis the total solids content, expressed as a percentage by mass, of the latex concentrate;A is the alkalinity;c(HCHO) is the actual concentratio
24、n, expressed in moles per cubic decimetre, of the formaldehyde solution (4.3).Dilute the latex with water to about 30 % total solids.Insert the electrodes of the pH-meter (5.1) into the diluted latex concentrate and record the pH.If the initial pH is less than 10,3, slowly add 5 cm3of 0,5 mol/dm3pot
25、assium hydroxide solution (4.2) while stirring slowly with the glass paddle or magnetic stirrer (5.3). Record the resultant equilibrium pH reading. With continued stirring, add 0,5 mol/dm3potassium hydroxide solution (4.2) in 1 cm3increments at regular (e.g. 15 s) intervals, recording the resultant
26、equilibrium pH after each addition. Continue until the end-point has been passed.If the initial pH is 10,3 or higher, omit the initial addition of 5 cm3at one time and proceed directly to “add 0,5 mol/dm3potassium hydroxide solution (4.2) in 1 cm3increments” as described above.5DIN ISO 127:2014-03Th
27、e end-point of the titration is the point of inflexion of the titration curve of the pH-value against the volume, in cubic centimetres, of potassium hydroxide solution. At this point, the slope of the curve, i.e. the first differential, reaches a maximum and the second differential changes from a po
28、sitive to a negative value. The end-point shall be calculated from the second differential on the assumption that the change from a positive to a negative value bears a linear relation to the addition of potassium hydroxide during the 1 cm3interval involved.An example of a typical titration and the
29、calculation of the end-point is given in Annex B.The results of duplicate determinations shall agree to within 5 % (by mass).8 Expression of resultsCalculate the KOH number, K, using the equationKcVwm=561TSwherecis the actual concentration, expressed in moles of KOH per cubic decimetre, of the potas
30、sium hydroxide solution (4.2);V is the volume, in cubic centimetres, of the nominally 0,5 mol/dm3potassium hydroxide solution (4.2) required to reach the end-point;wTSis the total solids content, expressed as a percentage by mass, of the latex concentrate;m is the mass, in grams, of the test portion
31、.If the latex concentrate contains boric acid, subtract the KOH number equivalent to the boric acid from the KOH number obtained above. Calculate the KOH number equivalent to the boric acid present, KBA, from the equationKwwBABATS=91wherewBAis the boric acid content, expressed as a percentage by mas
32、s;wTSis the total solids content, expressed as a percentage by mass, of the latex concentrate.9 PrecisionSee Annex C.10 Test reportThe test report shall include the following information:a) a reference to this International Standard;b) all details necessary for complete identification of the sample;
33、c) all details necessary for complete identification of the pH-meter used;d) the result obtained;e) the correction applied for boric acid, if present;f) details of any operation not included in this International Standard or regarded as optional;g) the date of the test.6DIN ISO 127:2014-03Annex A (i
34、nformative) Determination of formaldehydeThe method, using a standard solution of ammonia, given in the first and second editions of this International Standard for determining the concentration of the formaldehyde solution appears not to have been widely used due to the fact that standard solutions
35、 of ammonia are considered to be unsatisfactory. Having regard to the consistent quality of analytical-grade concentrated formaldehyde solution, the majority of users prepare a standard solution of formaldehyde directly.Where it is necessary to determine the concentration of the diluted formaldehyde
36、, a variety of methods exist and users are referred to the Encyclopaedia of Industrial Chemical Analysis, Vol. 13, published by Interscience (1971). The method given below is for information only.A.1 ReagentsA.1.1 Sodium sulfite, anhydrous, analytical grade.A.1.2 Sulfuric acid, standard volumetric s
37、olution, c(H2SO4) = 0,25 mol/dm3.A.1.3 Thymolphthalein, indicator solution.Dissolve 80 mg of thymolphthalein in 100 cm3of ethyl alcohol and dilute with 100 cm3of distilled water.A.2 ProcedurePrepare a solution of 125 g of anhydrous sodium sulfite (A.1.1) in 500 cm3of water and dilute to 1 dm3. Trans
38、fer 100 cm3of the solution to a 500 cm3conical flask. Accurately weigh into the flask 6,0 g to 8,0 g of the nominally 50 g/dm3formaldehyde solution (4.3)1)and swirl to mix thoroughly. Allow to stand for 5 min, then titrate with 0,25 mol/dm3sulfuric acid (A.1.2) to the first colourless end-point usin
39、g thymolphthalein (A.1.3) as indicator. Run a blank determination with the sodium sulfite solution.A.3 Expression of resultsCalculate the formaldehyde content, expressed as a percentage by mass, of the formaldehyde solution from the formula30 03 210121, VV cm() ()HSO24whereV1is the volume, in cubic
40、centimetres, of sulfuric acid (A.1.2) used for the titration of the test portion of formaldehyde solution;V2is the volume, in cubic centimetres, of sulfuric acid (A.1.2) required for the blank;c(H2SO4) is the actual concentration, in moles of H2SO4per cubic decimetre, of the sulfuric acid;m1is the m
41、ass, in grams, of the test portion of formaldehyde solution.1) When analysing concentrated formaldehyde solution, 1,8 g to 2,0 g of solution is a more convenient amount to take.7DIN ISO 127:2014-03Annex B (informative) Example of a typical titration and calculation of the end-pointTable B.1 Example
42、of a typical titration to show variation in pHVolume of KOH solution addedcm3pH reading First differencepH/cm3Second differencepH/cm3Initial 10,095 10,460,096 10,55 0,010,107 10,65 0,010,118 10,76 0,030,149 10,90 0,040,1810 11,08 0,060,2411 11,32 0,070,3112 11,63 0,010,3013 11,93 0,090,2114 12,14In
43、this example, the first difference reaches a maximum of 0,31 between 11 cm3and 12 cm3of potassium hydroxide solution. The precise point of inflexion is calculated from the ratio of the adjacent second-difference values, i.e. 0,07/(0,07 + 0,01) = 0,875 of the difference between 11 cm3and 12 cm3, i.e.
44、 11,875 cm3.Figure B.1 presents these data graphically to show the point of inflexion.8DIN ISO 127:2014-03KeyX volume of potassium hydroxide solution (cm3)Y pH1 end-pointFigure B.1 Illustrative curve showing change of pH during titration9DIN ISO 127:2014-03Annex C (informative) Precision statementC.
45、1 BackgroundC.1.1 The precision of this method was determined in accordance with ISO/TR 9272:1986. Refer to this document for terminology and explanations of statistical concepts.C.1.2 The precision details in this precision statement give an estimate of the precision of this test method with the ma
46、terials used in the particular interlaboratory programme as described below. The precision parameters should not be used for acceptance/rejection testing of any group of materials without documentation that the parameters are applicable to those particular materials and the specific test protocol of
47、 this test method.C.1.3 The precision results are given in Table C.1. The precision is expressed on the basis of a 95 % confidence level for the values established for repeatability r and reproducibility R.C.1.4 The results contained in Table C.1 are mean values and give an estimate of the precision
48、 of this test method as determined in an interlaboratory test programme (ITP) conducted in 2001. Thirteen laboratories performed triplicate analyses on two samples, A and B, which were prepared from highly ammoniated latex. The bulk latex was strained and then homogenized by thorough blending and st
49、irring prior to being subsampled into 1-litre bottles labelled A and B. Thus, essentially, samples A and B were the same and were treated as such in the statistical computations. Each participating laboratory was required to carry out the test using these two samples on the dates which had been given to the participants in the ITP.C.1.5 A type 1 precision was determined, based on the sampling method used for the latex samples in the ITP.C.2 Repeatabil
