1、BSI Standards Publication Rubber and plastics Polymer dispersions and rubber latices Determination of pH BS ISO 976:2013National foreword This British Standard is the UK implementation of ISO 976:2013. It supersedes BS 6057-3.9:1996 which is withdrawn. The UK participation in its preparation was ent
2、rusted to Technical Committee PRI/50, Rubber Raw, natural and synthetic, including latex and carbon black. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users
3、 are responsible for its correct application. The British Standards Institution 2013. Published by BSI Standards Limited 2013 ISBN 978 0 580 77195 8 ICS 83.040.10 Compliance with a British Standard cannot confer immunity from legal obligations. This British Standard was published under the authority
4、 of the Standards Policy and Strategy Committee on 31 December 2013. Amendments/corrigenda issued since publication Date Text affected BRITISH STANDARD BS ISO 976:2013 ISO 2013 Rubber and plastics Polymer dispersions and rubber latices Determination of pH Caoutchouc et plastiques Dispersions de poly
5、mres et latex de caoutchouc Dtermination du pH INTERNATIONAL STANDARD ISO 976 Fourth edition 2013-12-01 Reference number ISO 976:2013(E) BS ISO 976:2013 ISO 976:2013(E)ii ISO 2013 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2013 All rights reserved. Unless otherwise specified, no part of th
6、is publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in t
7、he country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland BS ISO 976:2013 ISO 976:2013(E) ISO 2013 All rights reserved iii Contents Page Foreword iv 1 Scope . 1 2 N
8、ormative references 1 3 Reagents 1 4 Apparatus . 2 5 Sampling 2 6 Procedure. 2 6.1 General . 2 6.2 Maintenance of the electrode . 3 6.3 Calibration of the pH-meter . 4 6.4 Measurement of the pH of the test sample . 5 7 Expression of results 6 8 Test report . 6 Annex A (informative) Precision . 7 Bib
9、liography 9 BS ISO 976:2013 ISO 976:2013(E) Foreword ISO (the International Organization 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 membe
10、r body interested in a subject for which a technical committee has been established 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 Elec
11、trotechnical Commission (IEC) on all matters of electrotechnical standardization. The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types
12、of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives). 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 he
13、ld responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents). Any trade name used in this document is informati
14、on given for the convenience of users and does not constitute an endorsement. For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the f
15、ollowing URL: Foreword - Supplementary information The committee responsible for this document is 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 976:1996), whic
16、h has been technically revised. It also incorporates the Amendment (ISO 976:1996/Amd.1:2006). The following are the main changes: the normative references were updated; in (subclause) 4.2, the contact details of a provider of combined electrodes were deleted; the precision data were updated.iv ISO 2
17、013 All rights reserved BS ISO 976:2013 INTERNATIONAL ST ANDARD ISO 976:2013(E) Rubber and plastics Polymer dispersions and rubber latices Determination of pH WARNING Persons using this International Standard should be familiar with normal laboratory practice. This International Standard does not pu
18、rport to address 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 Scope This International Standard specifies a method for the det
19、ermination of the pH of polymer dispersions and rubber latices (natural and synthetic) by means of a pH-meter equipped with a combined glass and silver reference electrode. The method is also suitable for prevulcanized latex and compounds containing polymer dispersions or rubber latices, including a
20、dhesives. NOTE The accuracy of the method decreases at pH values above 11. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated ref
21、erences, the latest edition of the referenced document (including any amendments) applies. ISO 123, Rubber latex Sampling ISO 3696, Water for analytical laboratory use Specification and test methods ISO 15528, Paints, varnishes and raw materials for paints and varnishes Sampling 3 Reagents Use comme
22、rcially available analytical-grade buffer solutions of known pH or, in the absence of commercial buffer solutions, prepare the solutions required (3.1, 3.2 and 3.3) using only reagents of recognized analytical grade and carbon dioxide-free distilled water or water of equivalent purity (grade 3 as de
23、fined in ISO 3696). 3.1 Buffer solution, of nominal pH 7. Dissolve 3,40 g of potassium dihydrogen phosphate (KH 2 P0 4 ) and 3,55 g of disodium hydrogen phosphate (Na 2 HP0 4 ) in water and make up to 1 000 cm 3in a volumetric flask. The pH of this solution is 6,87 at 23 C. Store the solution in a g
24、lass or polyethylene vessel, which is resistant to chemicals. 3.2 Buffer solution, of pH 4. Dissolve 10,21 g of potassium hydrogen phthalate (KOOC C 6 H 4COOH) in water and make up to 1 000 cm 3in a volumetric flask. The pH of this solution is 4,00 at 23 C. Store the solution in a glass or polyethyl
25、ene vessel, which is resistant to chemicals. ISO 2013 All rights reserved 1 BS ISO 976:2013 ISO 976:2013(E) 3.3 Buffer solution, of nominal pH 9 Dissolve 3,814 g of sodium tetraborate decahydrate (Na 2 B 4 O 710H 2 O) in water and make up to 1 000 cm 3in a volumetric flask. The pH of this solution,
26、when freshly prepared, is 9,20 at 23 C. Store the solution in a glass or polyethylene vessel, which is resistant to chemicals, and fitted with a soda-lime carbon dioxide trap. Replace the solution after one month. Alkaline buffer solutions are unstable; they absorb carbon dioxide from the atmosphere
27、. W hen an alkaline buffer has been used for calibration, the accuracy can be verified by means of the buffer solution of pH 4. 3.4 Reference electrolyte. Use 3 mol/dm 3potassium chloride solution saturated with silver chloride. 4 Apparatus Use usual laboratory equipment and the following. 4.1 pH-me
28、ter, with an input impedance of at least 10 12Q, a resolution of 0,01 pH units and equipped for temperature compensation. 4.2 Combined electrode, in which the glass electrode is surrounded concentrically by the silver reference electrode. The reference electrolyte (3.4) is kept in electrical contact
29、 with the test sample by a chemically inert diaphragm, e.g. a retractable sleeve made of polytetrafluoroethylene or glass. This is supplied with the electrode by the electrode manufacturer. A typical combined electrode is shown in Figure 1. The glass electrode used shall be one recommended by the ma
30、nufacturer as suitable over the pH range to be encountered (0 to 14 in the case of polychloroprene latices). Electrical contact between the electrolyte and the test sample is maintained through a thin film of electrolyte between the sleeve and the electrode. The electrode functions linearly between
31、pH 0 and the appearance of the alkaline error, which, depending on the sodium ion concentration, usually does not appear until the pH is over 11. 4.3 Magnetic stirrer and magnetic bar. 4.4 Electrode holder. 5 Sampling Carry out the sampling of the rubber latex or polymer dispersion in accordance wit
32、h one of the methods specified in ISO 123 or ISO 15528. 6 Procedure 6.1 General In order to reduce thermal and electrical hysteresis effects, ensure that the temperatures of the test samples, electrode, demineralized or distilled rinsing water and buffer solutions are as close to one 2 ISO 2013 All
33、rights reserved BS ISO 976:2013 ISO 976:2013(E) another as possible. The temperatures of the test samples and buffer solutions shall not differ by more than 1 C. The temperature for the determination shall be 23 C 3 C (27 C 3 C in tropical countries). NOTE The pH variation over the range of 20 C to
34、30 C is negligible. In addition, the temperature compensator in the instrument should be set at the actual temperature. 6.2 Maintenance of the electrode The combined electrode (4.2) shall be maintained following the manufacturers instructions, paying particular attention to the following points. a)
35、Refill the electrode with the reference electrolyte (3.4) through the filling hole, first removing the filling cap if one is fitted. Slightly withdraw the seated sleeve to eliminate any latex deposits and allow a drop of the electrolyte to appear before reseating the sleeve. Prior to calibration and
36、 measurement, remove the cap on the electrolyte filling hole to allow the reference electrolyte to be at atmospheric pressure. b) When it is not in use, keep the electrode with the junction immersed in the electrolyte. ISO 2013 All rights reserved 3 BS ISO 976:2013 ISO 976:2013(E) Key 1 sliding head
37、 6 reference electrolyte (3.4) 2 filling hole 7 seated PTFE or glass diaphragm (sleeve) 3 connector 8 internal buffer 4 reference electrode 9 membrane 5 internal electrode Figure 1 Typical combined electrode 6.3 Calibration of the pH-meter 6.3.1 Switch on the pH-meter (4.1) and allow the electronic
38、circuit to stabilize. Calibrate the pH-meter following the manufacturers instructions. If not available, proceed as follows. 6.3.2 Select two commercial buffer solutions (see Clause 3), one of nominal pH 7 (i.e. close to the zero point of the electrode) and the other differing from the first by abou
39、t 3 pH units and of a higher or lower pH corresponding to the sample to be tested. In the event that commercial buffer solutions are not available, use the appropriate prepared buffer solutions (3.1 and 3.2 or 3.3).4 ISO 2013 All rights reserved BS ISO 976:2013 ISO 976:2013(E) 6.3.3 Allow the temper
40、ature of the buffer solutions, the test sample, and the electrode to equilibrate at the specified temperature (see 6.1). Record the temperature and adjust the temperature correction on the pH-meter to correspond. 6.3.4 Rinse the electrode with distilled or demineralized water (see Clause 3), and the
41、n with the buffer solution of nominal pH 7, so that the liquid runs down the length of the electrode. 6.3.5 Introduce an adequate volume of the same buffer solution into a suitable clean, dry glass or inert plastic vessel. Immerse the electrode in it, taking care that the level of reference electrol
42、yte in the electrode remains about 5 cm higher than the level of the buffer solution to prevent any contamination of the electrode. Stir gently and allow the reading to stabilize. Adjust the pH-meter using the zero-point adjustment control, so that the reading corresponds to the pH of the buffer sol
43、ution. Withdraw the electrode and discard the portion of buffer solution. 6.3.6 Rinse the electrode with water, followed by the chosen buffer solution, pH 4 (3.2) or pH 9 (3.3), as described in 6.3.4. Instead of the prepared solution of pH 9 (3.3), commercial buffer solution with a pH in the range 9
44、 to 11 can also be used, if available. 6.3.7 Immerse the electrode in a quantity of the chosen buffer solution as described in 6.3.5. Allow the reading to stabilize before adjusting the meter to the pH of the buffer solution, using the gradient adjustment control and without touching the zero-point
45、control. Ensure that the electrode gradient is in the range -55,6 mV/pH unit to - 61,5 mV/pH unit, i.e. between 95 % and 103 % of the theoretical value (- 58,57 mV/pH unit at 23 C). If the electrode is outside this range, carry out the maintenance procedure specified in 6.2. Discard the portion of b
46、uffer solution. 6.4 Measurement of the pH of the test sample 6.4.1 Mix the test sample thoroughly to ensure that it is homogeneous. 6.4.2 Rinse the electrode and measuring vessel, first with distilled or demineralized water, and then with some of the sample to be tested, as described in 6.3.4. Trans
47、fer an adequate volume into the vessel (an additional clean, dry vessel can be used) and immerse the electrode in it as described in 6.3.5. Stir gently. Allow the pH-meter reading to stabilize and record the pH. Clean the electrode by rinsing with distilled or demineralized water to remove any latex
48、 before it dries. 6.4.3 Repeat the operations specified in 6.4.2 with a fresh portion of the test sample. If the new reading does not differ from the first by more than 0,1 pH unit, the determination is complete. If the two readings differ by more than 0,1 pH unit, make two further determinations, h
49、aving first carried out all the checks necessary to detect any sources of error. If a series of consecutive determinations is to be made, recalibrate the pH-meter in accordance with 6.3 at 30 min intervals or more frequently depending on the change found at each successive check. ISO 2013 All rights reserved 5 BS ISO 976:2013 ISO 976:2013(E) 7 Expression of results Calculate the mean of the two readings that agree and round to the nearest 0,1 of a pH unit. Express the results in units of pH at 23
