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 BS6057-0 General introduction, issued separately.BS6057-3.12:1992 This British Standard, having been
2、 prepared under the directionof the Plastics and Rubber Standards Policy Committee, was published underthe authority of the Standards Board and comes intoeffect on 15 August 1992 BSI 10-1999 First published January 1984 Second edition February 1988 Third edition August 1992 The following BSI referen
3、ces 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 preparation of this British Standard was entrusted by the Plastics and Rubber Standards Policy Committee (PRM/-) to Techn
4、ical Committee PRM/51, upon which the following bodies were represented: British Rubber Manufacturers Association Malaysian Rubber Producers Research Association Medical Sterile Products Association Tropical Growers Association Amendments issued since publication Amd. No. Date CommentsBS6057-3.12:19
5、92 BSI 10-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Normative reference 1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Sampling 1 7 Procedure 2 8 Expression of results 2 9 Test report 2 List of references Inside back coverBS6057-3.12:1992 ii BSI 10
6、-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 ISO1802:1992 Natural rubber latex concentrate Determination of boric acid content, published by the International Organization for Standar
7、dization (ISO). It supersedes BS6057-3.12:1988, which is withdrawn.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 confer immuni
8、ty from legal obligations. Cross-reference International Standard Corresponding British Standard ISO 123:1985 BS 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, pages1and 2, an inside back cover and a
9、 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.BS6057-3.12:1992 BSI 10-1999 1 1 Scope This International Standard specifies a procedure for the determination of boric a
10、cid 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, compounded latex, vulcanized latex or artificial dispersions of rubber. 2 Normative reference The following standard c
11、ontains provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investi
12、gate 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 123:1985, Rubber latex Sampling. 3 Principle The pH of a test portion containing about0,02g of boric acid is adjusted to
13、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 ions equivalent to the boric acid present in the latex are thus liberated and the pH falls. Boric acid is determined from
14、 the amount of alkali required to restore the pH of the test portion to7,50. 4 Reagents During the analysis, use only reagents of recognized analytical quality, and only distilled water or water of equivalent purity. 4.1 Hydrochloric acid,2% solution (m/m). 4.2 Stabilizer solution, containing5% (m/m
15、) of a suitable non-ionic stabilizer of the ethylene oxide condensate type. 4.3 Mannitol 4.4 Boric acid solution Weigh, to the nearest1mg, about5g of boric acid (H 3 BO 3 ), dissolve in water and dilute to1000cm 3in a volumetric flask. 4.5 Sodium hydroxide, standard solution, c(NaOH). 0,05mol/dm 3 .
16、 4.5.1 Standardization of the solution Using a pipette (5.2), introduce5cm 3of the boric acid solution (4.4) into a250cm 3beaker. Add2cm 3of the stabilizer solution (4.2) and50cm 3of water. If the pH of the solution, measured using the pH-meter (5.1), exceeds5,5, add hydrochloric acid solution (4.1)
17、, drop by drop, with constant stirring, to reduce the pH to a value between5,5 and2,5. Allow the solution to stand for15min. Add sodium hydroxide solution (4.5) from a burette (5.3), with constant stirring, until the pH is7,50. Add4g of the mannitol (4.3) with continued stirring. The pH falls. Titra
18、te accurately with sodium hydroxide solution from the burette (5.3) and record the volume of solution required to restore the pH to7,50. 4.5.2 Calculation of the concentration Calculate the concentration c, expressed in moles per cubic decimetre, of the sodium hydroxide solution using the formula wh
19、ere 5 Apparatus Ordinary laboratory apparatus and 5.1 pH-meter, capable of measuring the pH found during the test to the nearest0,01units. 5.2 Pipettes, of capacity2cm 3 ,5cm 3and50cm 3 . 5.3 Burettes, of suitable capacity. 6 Sampling Carry out sampling in accordance with one of the methods specifie
20、d in ISO123. m is the mass, in grams, of boric acid in1000cm 3of boric acid solution (4.4); V 1 is the volume, in cubic centimetres, of sodium hydroxide solution required to restore the pH to7,50. 0,081 m V 1 - BS6057-3.12:1992 2 BSI 10-1999 7 Procedure Weigh, to the nearest0,1g, about10g of latex c
21、oncentrate into a250cm 3beaker. Add2cm 3of the stabilizer solution (4.2) and50cm 3of 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 below5,5 and above2,5. Allow to stand for15min. Adjust
22、the pH to7,50 by adding sodium hydroxide solution (4.5) from a burette (5.3), with constant stirring. Add4g 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
23、pH to7,50. NOTE 1The pH falls gradually as the mannitol dissolves. 8 Expression of results Calculate the boric acid (H 3 BO 3 ) content of the latex concentrate, expressed as a percentage by mass, using the formula. where A difference of0,01% (m/m) boric acid between the results of duplicate determi
24、nations shall not be considered 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 u
25、nusual features noted during 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. c is the actual concentration, expressed in moles per cubic decimetre, of the sodiu
26、m hydroxide solution (4.5), calculated in accordance with4.5.2; V 2 is the volume, in cubic centimetres, of sodium hydroxide solution required to restore the pH of the latex to7,50; m 0 is the mass, in grams, of the latex concentrate test portion. 6,18 cV 2 m 0 -BS6057-3.12:1992 BSI 10-1999 List of
27、references See national foreword.BS 6057-3.12: 1992 ISO 1802:1992 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on standards in Europe and at the international level. It
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