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1、BRITISH STANDARD BS 6057-3.12: 1992 ISO 1802:1992 Rubber latices Part 3: Methods of test Section 3.12 Determination of boric acid content of natural rubber latex concentrate NOTEAttention is drawn to BS 6057-0 General introduction, issued separately. Licensed Copy: sheffieldun sheffieldun, na, Wed D
2、ec 06 15:21:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6057-3.12:1992 This British Standard, having been prepared under the direction of the Plastics and Rubber Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 15 August 1992 BSI 10-1
3、999 First published January 1984 Second edition February 1988 Third edition August 1992 The following BSI references relate to the work on this standard: Committee reference PRM/51 Draft announced in BSI News, July 1992 ISBN 0 580 21086 3 Committees responsible for this British Standard The preparat
4、ion of this British Standard was entrusted by the Plastics and Rubber Standards Policy Committee (PRM/-) to Technical Committee PRM/51, upon which the following bodies were represented: British Rubber Manufacturers Association Malaysian Rubber Producers Research Association Medical Sterile Products
5、Association Tropical Growers Association Amendments issued since publication Amd. No.DateComments Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 15:21:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6057-3.12:1992 BSI 10-1999i Contents Page Committees responsibleInside front cover National
6、forewordii 1Scope1 2Normative reference1 3Principle1 4Reagents1 5Apparatus1 6Sampling1 7Procedure2 8Expression of results2 9Test report2 List of referencesInside back cover Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 15:21:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6057-3.12:1992 ii
7、 BSI 10-1999 National foreword This Section of BS 6057 has been prepared under the direction of the Plastics and Rubber Standards Policy Committee and is identical with ISO 1802:1992 Natural rubber latex concentrate Determination of boric acid content, published by the International Organization for
8、 Standardization (ISO). It supersedes BS 6057-3.12:1988, which is withdrawn. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself conf
9、er immunity from legal obligations. Cross-reference International StandardCorresponding British Standard ISO 123:1985BS 6057 Rubber latices Part 2:1987 Sampling (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 and 2, an inside back co
10、ver and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 15:21:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6
11、057-3.12:1992 BSI 10-19991 1 Scope This International Standard specifies a procedure for the determination of boric acid in natural rubber latex concentrate. The procedure is not necessarily suitable for latices from natural sources other than Hevea brasiliensis or for latices of synthetic rubber, c
12、ompounded latex, vulcanized latex or artificial dispersions of rubber. 2 Normative reference The following standard contains provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the edition indicated was valid. All standa
13、rds are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 123
14、:1985, Rubber latex Sampling. 3 Principle The pH of a test portion containing about 0,02 g of boric acid is adjusted to 7,50, at which value boric acid exists substantially in the undissociated form. Mannitol is then added in excess to form the strongly acidic boric-acid/mannitol complex. Hydrogen i
15、ons equivalent to the boric acid present in the latex are thus liberated and the pH falls. Boric acid is determined from the amount of alkali required to restore the pH of the test portion to 7,50. 4 Reagents During the analysis, use only reagents of recognized analytical quality, and only distilled
16、 water or water of equivalent purity. 4.1 Hydrochloric acid, 2 % solution (m/m). 4.2 Stabilizer solution, containing 5 % (m/m) of a suitable non-ionic stabilizer of the ethylene oxide condensate type. 4.3 Mannitol 4.4 Boric acid solution Weigh, to the nearest 1 mg, about 5 g of boric acid (H3BO3), d
17、issolve in water and dilute to 1 000 cm3 in a volumetric flask. 4.5 Sodium hydroxide, standard solution, c(NaOH) . 0,05 mol/dm3. 4.5.1 Standardization of the solution Using a pipette (5.2), introduce 5 cm3 of the boric acid solution (4.4) into a 250 cm3 beaker. Add 2 cm3 of the stabilizer solution (
18、4.2) and 50 cm3 of water. If the pH of the solution, measured using the pH-meter (5.1), exceeds 5,5, add hydrochloric acid solution (4.1), drop by drop, with constant stirring, to reduce the pH to a value between 5,5 and 2,5. Allow the solution to stand for 15 min. Add sodium hydroxide solution (4.5
19、) from a burette (5.3), with constant stirring, until the pH is 7,50. Add 4 g of the mannitol (4.3) with continued stirring. The pH falls. Titrate accurately with sodium hydroxide solution from the burette (5.3) and record the volume of solution required to restore the pH to 7,50. 4.5.2 Calculation
20、of the concentration Calculate the concentration c, expressed in moles per cubic decimetre, of the sodium hydroxide solution using the formula where 5 Apparatus Ordinary laboratory apparatus and 5.1 pH-meter, capable of measuring the pH found during the test to the nearest 0,01 units. 5.2 Pipettes,
21、of capacity 2 cm3, 5 cm3 and 50 cm3. 5.3 Burettes, of suitable capacity. 6 Sampling Carry out sampling in accordance with one of the methods specified in ISO 123. mis the mass, in grams, of boric acid in 1 000 cm3 of boric acid solution (4.4); V1is the volume, in cubic centimetres, of sodium hydroxi
22、de solution required to restore the pH to 7,50. 0,081 m V1 - - Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 15:21:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6057-3.12:1992 2 BSI 10-1999 7 Procedure Weigh, to the nearest 0,1 g, about 10 g of latex concentrate into a 250 cm3 beaker. Ad
23、d 2 cm3 of the stabilizer solution (4.2) and 50 cm3 of water. Add hydrochloric acid solution (4.1), drop by drop, with constant stirring, until the pH of the latex concentrate, measured using the pH-meter (5.1), is below 5,5 and above 2,5. Allow to stand for 15 min. Adjust the pH to 7,50 by adding s
24、odium hydroxide solution (4.5) from a burette (5.3), with constant stirring. Add 4 g of the mannitol (4.3) with continued stirring. The pH falls. Titrate accurately with sodium hydroxide solution from the burette (5.3), and record the volume of solution required to restore the pH to 7,50. NOTE 1The
25、pH falls gradually as the mannitol dissolves. 8 Expression of results Calculate the boric acid (H3BO3) content of the latex concentrate, expressed as a percentage by mass, using the formula. where A difference of 0,01 % (m/m) boric acid between the results of duplicate determinations shall not be co
26、nsidered significant. 9 Test report The test report shall include the following particulars: a) a reference to this International Standard; b) all details necessary for identification of the test sample; c) the results, and the units in which they have been expressed; d) any unusual features noted d
27、uring the determination; e) any operation not included in this International Standard or in the International Standard to which reference is made, as well as any operation regarded as optional. cis the actual concentration, expressed in moles per cubic decimetre, of the sodium hydroxide solution (4.
28、5), calculated in accordance with 4.5.2; V2is the volume, in cubic centimetres, of sodium hydroxide solution required to restore the pH of the latex to 7,50; m0is the mass, in grams, of the latex concentrate test portion. 6,18 cV2 m0 - Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 15:21:17
29、GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6057-3.12:1992 BSI 10-1999 List of references See national foreword. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 15:21:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6057-3.12: 1992 ISO 1802:1992 BSI 389 Chiswick High Road London W4 4AL BSI
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