1、BRITISH STANDARD BS 7164-24: 1996 ISO 7269:1995 Incorporating Technical Corrigendum No. 1 Chemical tests for raw and vulcanized rubber Part 24: Determination of free sulfur ICS 83.060 BS 7164-24:1996 This British Standard, having been prepared under the direction of the Sector Board for Materials an
2、d Chemicals, was published under the authority of the Standards Board and comes into effect on 15 May 1996 BSI 10 December 2002 First published September 1990 Second edition May 1996 The following BSI references relate to the work on this standard: Committee reference PRI/23 Draft announced in BSI N
3、ews February 1996 ISBN 0 580 25611 1 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee PRI/23, Chemical testing of rubber, upon which the following bodies were represented: Malaysian Rubber Producers Research Association Mi
4、nistry of Defence RAPRA Technology Ltd. Royal Society of Chemistry Amendments issued since publication Amd. No. Date Comments 13980 Technical Corrigendum No. 1 10 December 2002 Changes to formulae in 5.4 and 7.4BS 7164-24:1996 BSI 10 December 2002 i Contents Page Committees responsible Inside front
5、cover National foreword ii Introduction 1 1S c o p e 1 2 Normative references 1 3 Principle 1 4 Limitations 2 5 Copper spiral method A 2 6 Copper spiral method B 4 7 Sulfite method 5 8 Test report 6 Annex A (normative) Determination of free-sulfur content Effect of various commercial accelerators on
6、 the copper spiral and sulfite methods of analysis 10 Figure 1 Typical apparatus for extraction of free sulfur by copper spiral method A 7 Figure 2 Typical apparatus for determination of free sulfur by copper spiral method A 8 Figure 3 Typical apparatus for determination of free sulfur by copper spi
7、ral method B 9BS 7164-24:1996 ii BSI 10 December 2002 National foreword This Part of BS 7164 has been prepared by Technical Committee PRI/23 and is identical with ISO 7269:1995 Rubber Determination of free sulfur, including Technical Corrigendum 1 May 2002, published by the International Organizatio
8、n for Standardization (ISO). It supersedes BS 7164-24:1990 which is withdrawn. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Corresponden
9、ce Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. The Technical Committee has reviewed the provisions of ISO 383:1976 to which normative reference is made in the text, and has decided that it is acceptable for use in conjunction with this st
10、andard. A related British Standard to ISO 383:1976 is BS 572:1991 Specification for interchangeable conical ground glass joints. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Stand
11、ard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 10, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last
12、 issued.BS 7164-24:1996 BSI 10 December 2002 1 Introduction The free-sulfur content of an unvulcanized rubber compound (i.e. the amount of uncombined sulfur present in the compound) should represent all the added, elemental, sulfur. As the vulcanization proceeds and sulfur is gradually combined with
13、 the rubber, the free-sulfur content gradually decreases, so its level in any particular product bears some relation to its state of vulcanization, provided the formulation is known and the correct proportion of elemental sulfur (and other ingredients) has been incorporated. Vulcanizates containing
14、higher proportions of free sulfur than the rubber can dissolve are liable to bloom sulfur, hence certain product specifications include a maximum figure for free sulfur. WARNING Persons using this International Standard should be familiar with normal laboratory practice. This standard does not purpo
15、rt 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 1.1 This International Standard specifies three methods for t
16、he determination of free sulfur in vulcanized rubber: two versions of the copper spiral method, and the sodium sulfite method. 1.2 The copper spiral methods are also applicable, subject to the limitations described in clause 4, to unvulcanized compounds. 1.3 Annex A gives a table listing the sulfur
17、contribution, as a percentage by mass, to these free-sulfur methods for various commercial accelerators. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the edit
18、ions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently
19、 valid International Standards. ISO 383:1976, Laboratory glassware Interchangeable conical ground joints. ISO 1407:1992, Rubber Determination of solvent extract. 3 Principle 3.1 Copper spiral methods A and B 3.1.1 Method A The free sulfur in a test portion is extracted with acetone as in the determi
20、nation of solvent extract, described in ISO 1407, except that a spiral of clean copper gauze is placed in the flask containing the acetone. The copper reacts with the extracted sulfur, forming copper sulfide. When extraction is complete, the acetone solution is drawn off through a filter and discard
21、ed. The acetone-insoluble copper and copper sulfide remaining in the flask are treated with hydrochloric acid. The resulting hydrogen sulfide is passed through cadmium acetate solution, and the cadmium sulfide formed is determined iodometrically. 3.1.2 Method B Rapid copper spiral method B is the sa
22、me as copper spiral method A except that the extraction time is reduced by using a vapour-jacketed Soxhlet of reduced capacity (6 cm 3 ) to increase the extraction temperature. 3.2 Sulfite method The free sulfur in a test portion is reacted with aqueous sodium sulfite and the sodium thiosulfate so f
23、ormed is determined iodometrically.BS 7164-24:1996 2 BSI 10 December 2002 4 Limitations 4.1 The copper spiral methods generally determine elemental sulfur only, although certain sulfur-donating curatives, such as thiuram disulfide and diaminosulfides, can give rise to slightly high results. In addit
24、ion, the copper spiral methods are unsuitable for unvulcanized compounds if the added elemental sulfur is of the form insoluble in acetone, i.e. the so-called “insoluble” or amorphous sulfur. The total mass of free sulfur in the test portion shall be in the range 0,2 mg to 10 mg. 4.2 The sulfite met
25、hod is excessively sensitive to the presence of sulfur-donating curatives and to antioxidants, and shall not be used for unvulcanized compounds. 4.3 In the absence of sulfur-donating curatives, the methods are comparable in accuracy and precision. NOTE 1 In practice, in addition to determining free
26、elemental sulfur, some coordinately bound reactive sulfur such as that in thiuram disulfide and polysulfides may also give positive responses. 5 Copper spiral method A 5.1 Reagents and materials During the analysis, use only reagents of recognized analytical reagent grade and only distilled water or
27、 water of equivalent purity. 5.1.1 Acetone 5.1.2 Cadmium acetate, buffered solution. Dissolve 25 g of cadmium acetate dihydrate (CH 3 COO) 2 Cd2H 2 O and 25 g of sodium acetate trihydrate (CH 3 COONa3H 2 O) in water, add 100 cm 3of glacial acetic acid and make up to 1 dm 3with water. 5.1.3 Copper ga
28、uze, 250 m to 420 m (40 mesh to 60 mesh). 5.1.4 Filter paper or polyamide cloth, to wrap the rubber test portion. 5.1.5 Hydrochloric acid, diluted 1 + 1. Add 1 volume of concentrated 36 % (m/m) hydrochloric acid, c(HCl) = 10 mol/dm 3( 20 =1 , 18Mg/ m 3 ), to 1 volume of water. 5.1.6 Nitric acid, c(H
29、NO 3 ) = 10 mol/dm 3 . Add 10 volumes of concentrated 70 % (m/m) nitric acid, c(HNO 3 ) = 16 mol/dm 3( 20= 1,42Mg/m 3 ), to 6 volumes of water. 5.1.7 Iodine solution, c(I 2 ) 0,025 mol/dm 3 . 5.1.8 Sodium thiosulfate, accurately standardized solution, c(Na 2 S 2 O 3 ) = 0,05 mol/dm 3 . 5.1.9 Starch,
30、 1 g/100 cm 3solution. 5.1.10 Pure nitrogen gas. 5.1.11 Glycerol, general laboratory grade. 5.2 Apparatus Ordinary laboratory apparatus and the items specified in 5.2.1 to 5.2.10 are required for assembly of the apparatus shown in Figure 1 and Figure 2. Substitutions may be made if they perform the
31、same function as the items listed. All ground-glass joints shall comply with the requirements of ISO 383 and shall be sealed by applying glycerol (5.1.11) before assembling. 5.2.1 Extraction flask (A), of capacity 150 cm 3 , with 34/35 conical ground-glass joint. 5.2.2 Soxhlet extractor (Y), with 34
32、/35 socket and 34/35 cone. Capacity of extractor (P) 20 cm 3to 30 cm 3 . 5.2.3 Graham condenser (Z), with 34/35 angle drip cone. 5.2.4 Reduction adapter (D), with 14/23 socket, 34/35 cone, and a gas inlet tube to reach to within 3 mm of the bottom of the extraction flask (5.2.1) when assembled. 5.2.
33、5 Conical flask (J), of capacity 250 cm 3 , with 24/29 conical ground-glass joint.BS 7164-24:1996 BSI 10 December 2002 3 5.2.6 Gas-washing bottles (K and L). 5.2.7 Receiver adapter (E), with 10/19 socket, 24/29 cone and internal sealed dip-tube. 5.2.8 Condenser, Liebig type (F), effective length app
34、roximately 22 cm, with 14/23 angle drip cone, 14/23 socket and side arm with 10/19 cone. 5.2.9 Dropping funnel (G), of capacity 100 cm 3 , with 14/23 cone, modified stem and 14/23 stopper. 5.2.10 Micro-immersion filter (Emich pattern) (H), stem approximately 75 mm long, diameter of disc 10 mm, poros
35、ity grade 3. 5.2.11 Laboratory mill. 5.3 Procedure 5.3.1 Preparation of copper spiral 5.3.1.1 Cut about 5 g of the copper gauze (5.1.3) to form a 10 mm wide strip and loosely roll to form a spiral approximately 20 mm in diameter, the turns being conveniently held in place by a loop of copper wire. 5
36、.3.1.2 Clean the spiral, immediately before use, by dipping in cold dilute nitric acid (5.1.6) for a few seconds, sufficient to cause the copper to become clean and bright. Remove all traces of acid by thoroughly and repeatedly washing in water. Wash with acetone (5.1.1) and dry. 5.3.2 Extraction of
37、 free sulfur 5.3.2.1 Prepare the rubber by finely cutting to pass through a 1,70 mm sieve or thinly milling to a thickness not exceeding 0,5 mm and weigh a test portion of approximately 1 g to the nearest 0,1 mg (mass m). If there is evidence of sulfur bloom, weigh a 0,5 g test portion to the same t
38、olerance. If the rubber is unvulcanized, weigh a test portion which will contain not more than 10 mg of free sulfur. 5.3.2.2 Place the copper spiral, prepared as specified in 5.3.1, in the 150 cm 3extraction flask (A) (5.2.1) and extract the test portion for not less than 4 h, following the procedur
39、e specified in 5.3.2.3. 5.3.2.3 Roll the weighed test portion in the filter paper or polyamide cloth (5.1.4) (previously extracted with acetone) to form a loose roll from which the rubber cannot fall and so that no part of the rubber is anywhere in contact with any other part of the rubber. Place th
40、e roll in the Soxhlet extractor (Y) (5.2.2) and pour into the extraction flask (A) 75 cm 3of acetone. Assemble the apparatus and adjust the rate of heating such that the quantity of acetone distilled will fill the extractor 10 to 20 times per hour. 5.3.2.4 If, at the end of the extraction period, th
41、e spiral is heavily blackened, add a second spiral prepared as specified in 5.3.1 and continue the extraction for a further 2 h. If no blackening is apparent, it will suffice to add a further piece of copper gauze about 10 mm square and continue the extraction for 1 h. 5.3.2.5 Disconnect the extract
42、ion flask, remove the reduction adapter (D) (5.2.4) and filter off the acetone through the micro-immersion filter (H) (5.2.10). Wash the spirals with three portions of about 20 cm 3of hot acetone, removing the washings each time through the micro-immersion filter. 5.3.3 Determination of extracted fr
43、ee sulfur 5.3.3.1 Assemble the extraction flask (A) now containing the copper spirals, together with the micro-immersion filter (H) and reduction adapter (D), into the apparatus of Figure 2. Introduce 100 cm 3of cadmium acetate solution (5.1.2) into the receiver (J) (5.2.5) and fill the gas-washing
44、bottles (K and L) (5.2.6) to a depth of about 10 mm with the same solution. Pass a stream of nitrogen (5.1.10) through the apparatus to displace the air and then adjust the flow to about one bubble per second in flask J.BS 7164-24:1996 4 BSI 10 December 2002 5.3.3.2 Introduce 50 cm 3of dilute hydroc
45、hloric acid (5.1.5) slowly from the dropping funnel (G) (5.2.9) into flask A, heat slowly to boiling and continue to boil gently for 20 min to 30 min. Towards the end of this period, increase the flow of nitrogen to sweep over all traces of hydrogen sulfide. The solution in gas-washing bottle K shou
46、ld be clear and colourless; if this is not so, it is an indication that the gas flow has been too rapid and the determination shall be repeated using a smaller test portion or slower rate of gas flow. Disconnect the receiver adapter (E) (5.2.7) from the condenser side arm and, whilst holding it at a
47、n angle, add from a pipette a measured volume (V) of iodine solution (5.1.7) (usually 20 cm 3is a suitable quantity) to flask J, so that excess iodine is present. 5.3.3.3 Allow the iodine to react with any precipitate adhering to the entry tube and, when all the precipitate has dissolved, remove and
48、 rinse the tube. Cool the solution to approximately 15 C. Titrate the excess iodine with sodium thiosulfate solution (5.1.8) (volume V 1 ), using starch solution (5.1.9) as the indicator. 5.3.3.4 Carry out a blank test using all the reagents, including a volume V (see 5.3.3.2) of iodine solution (5.
49、1.7) and 100 cm 3of cadmium acetate solution (5.1.2), but omitting the test portion. Record the volume of standard sodium thiosulfate solution needed (V 2 ). 5.3.3.5 The difference between the volume of sodium thiosulfate used in the blank test and that used in the determination is equivalent to the iodine which has reacted with the cadmium sulfide. 5.4 Expression of results Calculate the free-sulfur content, expressed as a percentage by mass, from the formula: 6 Copper spiral
