1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 127:2012Rubber, natural latexconcentrate Determinationof KOH numberBS ISO 127:2012 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 1
2、27:2012. Itsupersedes BS 6057-3.5:1996 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee PRI/50/-/1, Rubber - Latex.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to inclu
3、de all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2012. Published by BSI StandardsLimited 2012ISBN 978 0 580 73936 1ICS 83.040.10Compliance with a British Standard cannot confer immunity fromlegal obligations.This Britis
4、h Standard was published under the authority of theStandards Policy and Strategy Committee on 31 May 2012.Amendments issued since publicationDate Text affectedBS ISO 127:2012 ISO 2012Rubber, natural latex concentrate Determination of KOH numberLatex concentr de caoutchouc naturel Dtermination de lin
5、dice de potasseINTERNATIONAL STANDARDISO127Fourth edition2012-04-15Reference numberISO 127:2012(E)BS ISO 127:2012ISO 127:2012(E)ii ISO 2012 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2012All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utiliz
6、ed in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCase postale 56 CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 2
7、2 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished in SwitzerlandBS ISO 127:2012ISO 127:2012(E) ISO 2012 All rights reserved iiiContents PageForeword iv1 Scope 12 Normative references . 13 Terms and definitions . 14 Reagents 15 Apparatus 26 Sampling 27 Procedure 28 Expression of results . 39
8、 Precision 310 Test report . 3Annex A (informative) Determination of formaldehyde 5Annex B (informative) Example of a typical titration and calculation of the end-point . 6Annex C (informative) Precision statement . 8Bibliography .10BS ISO 127:2012ISO 127:2012(E)ForewordISO (the International Organi
9、zation for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been establishe
10、d has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.I
11、nternational Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publi
12、cation as an International Standard requires approval by at least 75 % of the member bodies casting a vote.Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent ri
13、ghts.ISO 127 was prepared by Technical Committee ISO/TC 45, Rubber and rubber products, Subcommittee SC 3, Raw materials (including latex) for use in the rubber industry.This fourth edition cancels and replaces the third edition (ISO 127:1995), in which the following modifications have been undertak
14、en: the normative references have been updated; the first sentence in Clause 8 has been modified.It also incorporates the Amendment ISO 127:1995/Amd.1:2006, the precision data from which have been included as a new informative annex (Annex C);iv ISO 2012 All rights reservedBS ISO 127:2012INTERNATION
15、AL STANDARD ISO 127:2012(E)Rubber, natural latex concentrate Determination of KOH numberWARNING Persons using this International Standard should be familiar with normal laboratory practice. This standard does not purport to address all of the safety problems, if any, associated with its use. It is t
16、he 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 KOH number of natural rubber latex concentrate which is preserved who
17、lly 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 other than Hevea brasiliensis, or for latices of synthetic rubber, compo
18、unded 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. For undated references, the latest edition of the referenced docume
19、nt (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 Polymer dispersions and rubber latices Determination of pHISO 1802, Natura
20、l 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 acid radicals combined with ammonia in latex containing 100 g of tot
21、al 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 volumetric solution, c(KOH) = 0,1 mol/dm3, carbonate-free.4.2 Potassium hyd
22、roxide, standard volumetric solution, c(KOH) = 0,5 mol/dm3, carbonate-free. ISO 2012 All rights reserved 1BS ISO 127:2012ISO 127:2012(E)4.3 Formaldehyde, 45 g to 50 g in 1 dm3of solution c(HCHO) = 1,5 mol/dm3to 1,67 mol/dm3, acid-free, prepared by diluting concentrated formaldehyde with water and ne
23、utralizing 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 ApparatusStandard laboratory glassware, plus the following:5.1 pH-meter, conforming to ISO 976
24、 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 automatic titrator may be used provided it has been checked as giving the same result as the stan
25、dard 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 alkalinity (A) of the latex are not known, determine them in accordance with ISO 124 and ISO 125
26、, 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 a test portion (mass m) of the test sample containing approximately 50 g of total solids.
27、 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 cubic centimetres, of formaldehyde solution to be added from the equationVmwAcfTS100HCHO
28、=()()()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 concentration, expressed in moles per cubic decimetre, of the formaldehyde solution (4.3).Dilute the
29、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/dm3potassium hydroxide solution (4.2) while stirring slowly with the glass paddle or magnetic s
30、tirrer (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 equilibrium pH after each addition. Continue until the end-point has been passed.2 ISO 20
31、12 All rights reservedBS ISO 127:2012ISO 127:2012(E)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.The end-point of the titration is the point of infl
32、exion 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 positive to a negative value. The end-point shall b
33、e 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 calculation of the end-point is given in Annex B.
34、The results of duplicate determinations shall agree to within 5 % (by mass).8 Expression of resultsCalculate the KOH number, K, using the equationKcVwm=561TSwherec is the actual concentration, expressed in moles of KOH per cubic decimetre, of the potassium hydroxide solution (4.2);V is the volume, i
35、n 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.If the latex concentrate contains boric acid, s
36、ubtract 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 mass;wTSis the total solids content, expressed as a
37、 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;c) all details necessary for complete identifica
38、tion of the pH-meter used;d) the result obtained; ISO 2012 All rights reserved 3BS ISO 127:2012ISO 127:2012(E)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.4 ISO 2012 All ri
39、ghts reservedBS ISO 127:2012ISO 127:2012(E)Annex A (informative) 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 bee
40、n widely used due to the fact that standard solutions 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 de
41、termine the concentration of the diluted formaldehyde, 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, analyt
42、ical grade.A.1.2 Sulfuric acid, standard volumetric solution, 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
43、(A.1.1) in 500 cm3of water and dilute to 1 dm3. Transfer 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/dm3sulfuri
44、c acid (A.1.2) to the first colourless end-point using 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 2
45、10121, VV cm() ()HSO24whereV1is the volume, in cubic 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 H2SO
46、4per cubic decimetre, of the sulfuric acid;m1is the mass, 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. ISO 2012 All rights reserved 5BS ISO 127:2012ISO 127:2012(E)Annex B (
47、informative) Example of a typical titration and calculation of the end-pointTable B.1 Example 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
48、 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 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-diffe
49、rence values, i.e. 0,07/(0,07 + 0,01) = 0,875 of the difference between 11 cm3and 12 cm3, i.e. 11,875 cm3.Figure B.1 presents these data graphically to show the point of inflexion.6 ISO 2012 All rights reservedBS ISO 127:2012ISO 127:2012(E)KeyX volume of potassium hydroxide solution (cm3)Y pH1 end-pointFigure B.1 Illustrative curve showing change of pH during titration ISO 2012 All rights reserved 7BS ISO 127:2012ISO 127:2012(E)Annex C (informative) Precision statementC.1 BackgroundC.1.1 The precision o
