1、BRITISH STANDARD BS 7164-23.1: 1993 ISO 6528-1: 1992 Chemical tests for raw and vulcanized rubber Part 23: Methods for determination of total sulfur content Section 23.1 Oxygen combustion flask methodBS7164-23.1:1993 This British Standard, having been prepared under the direction of thePlastics and
2、Rubber StandardsPolicy Committee, waspublished under the authorityof the Standards Boardand comes into effect on 15 January 1993 BSI 06-1999 The following BSI references relate to the work on this standard: Committee reference PRM/23 Draft announced in BSI News December 1992 ISBN 0 580 21512 1 Commi
3、ttees responsible for this British Standard The preparation of this British Standard was entrusted by the Plastics and Rubber Standards Policy Committee (PRM/-) to Technical Committee PRM/23, upon which the following bodies were represented: Institute of Water and Environmental Management Laboratory
4、 of the Government Chemist Ministry of Defence Royal Society of Chemistry Rubber and Plastics Research Association Amendments issued since publication Amd. No. Date CommentsBS7164-23.1:1993 BSI 06-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Princip
5、le 1 3 Reagents and materials 1 4 Apparatus 2 5 Preparation of test sample 2 6 Safety precautions 2 7 Procedure 3 8 Expression of results 4 9 Test report 4 Annex A (informative) Bibliography 8 Figure 1 Form of paper for wrapping test portions 5 Figure 2 Cut form of paper for wrapping test portions (
6、forusewithsmallerplatinum baskets) 5 Figure 3 Typical combustion apparatus for the determination ofsulfurbytheoxygen combustion flask method 6 Figure 4 Typical combustion device for use in the oxygen combustion flaskmethod 7 Table 1 Repeatability data 4BS7164-23.1:1993 ii BSI 06-1999 National forewo
7、rd This Section of BS 7164 has been prepared under the direction of the Plastics and Rubber Standards Policy Committee and is identical with ISO 6528-1:1992 Rubber Determination of total sulfur content Part 1: Oxygen combustion flask method, published by the International Organization for Standardiz
8、ation (ISO). BS 7164 rationalizes all the methods that deal with chemical analysis of raw, compounded and vulcanized rubber, some of which have previously been published in BS 903, BS 1673 and BS 5923. Relevant Parts of those standards will be withdrawn or deleted by amendment, as appropriate, when
9、superseded by Parts and Sections of BS 7164. This Section of BS 7164 supersedes Part B6, Section 3 of BS 903-B6:1958 to BS903-B10:1958, which is deleted by amendment. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible
10、 for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to8 and a back cover. This standard has been updated (see copyright date)
11、and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS7164-23.1:1993 BSI 06-1999 1 1 Scope This part of ISO 6528 specifies an oxygen combustion flask method for the determination of the total sulfur content of rubber. The method is applic
12、able for the determination of all the sulfur present in a rubber or rubber product, except that contained in barium sulfate. It is applicable to NR, CR, SBR, BR, IR, IIR, EPDM, NBR and ebonite. (The meanings of these designations are given in ISO 1629:1987, Rubber and latices Nomenclature.) This met
13、hod gives unreliable (usually low) results in the presence of lead, antimony, zinc, barium and calcium compounds. If calcium carbonate is the only calcium compound present, good results can be obtained by modifying the absorbing solution. 2 Principle A test portion is ignited in an atmosphere of oxy
14、gen in an oxygen combustion flask containing hydrogen peroxide, the carbon and hydrogen of the organic matter being oxidized and the sulfur being converted to sulfuric acid. If necessary, the resulting solution is passed through a cation-exchange column to remove interfering metals. The eluate is ti
15、trated with barium perchlorate using thorin indicator. WARNING All recognized health and safety precautions shall be observed when carrying out this method of analysis. 3 Reagents and materials During the analysis, use only reagents of recognized analytical grade and only distilled water or water of
16、 equivalent purity. NOTE 1Two methods are described for the preparation of the indicator (3.8). The analyst may choose that best suited to his experience, equipment and needs. 3.1 Absorbing solution 3.1.1 Hydrogen peroxide, 2 % (m/m), absorbing solution. Dilute 1 volume of 30 % (m/m) hydrogen peroxi
17、de solution (H 2 O 2 ) to 15 volumes with water. WARNING 30 % (m/m) hydrogen peroxide solution is very corrosive to the skin. Wear rubber or plastic gloves and goggles when handling it. 3.1.2 Hydrogen peroxide/hydrochloric acid Dilute 4 volumes of 30 % (m/m) hydrogen peroxide solution (H 2 O 2 ) to
18、60 volumes with water and add 5 volumes of concentrated hydrochloric acid,( 20 =1,18 Mg/m 3 ), and mix thoroughly. 3.2 Hydrochloric acid, 0,5 mol/dm 3solution. 3.3 2-Propanol. 3.4 Barium perchlorate, 0,01 mol/dm 3solution. 3.4.1 Preparation Dissolve 3,363 g of barium perchlorate Ba(ClO 4 ) 2 in 200
19、cm 3of water. Adjust the pH to about 3,5 with hydrochloric acid solution (3.2). Make up to 1 dm 3with 2-propanol (3.3). 3.4.2 Standardization Standardize the barium perchlorate solution as follows. Weigh, to the nearest 0,1 mg, 0,10 g of anhydrous sodium sulfate (Na 2 SO 4 ) and dissolve the sodium
20、sulfate in 10 cm 3of water in a 100 cm 3volumetric flask. Dilute to the mark with water. Pipette exactly 10 cm 3of this solution into a small flask or beaker, add 40 cm 3of 2-propanol (3.3) to make the solution 80 % (V/V) alcoholic and titrate as specified in 7.3.3. The concentration c of the barium
21、 perchlorate solution, expressed in moles per cubic decimetre, is given by the equation where 3.4.3 Storage Barium perchlorate solutions deteriorate on storage and should be standardized sufficiently often so as to be able to detect changes in concentration of0,0005 mol/dm 3 . 3.5 Cation exchange re
22、sin, strongly acidic, containing nuclear sulfonic acid active groups. Before filling the column (4.6), allow the resin to stand in a beaker of distilled water to absorb water and become swollen. Check that the following requirements are fulfilled before use and after regeneration (because of the lar
23、ge capacity of the resin to remove interfering cations, it may be used five to ten times before regeneration becomes necessary): a) 10 cm 3of 0,02 mol/dm 3sulfuric acid solution shall be completely eluted with 15 cm 3of water (test the last portion of the eluate for the absence of sulfate using thor
24、in solution); m 1 is the mass, in grams, of sodium sulfate used; V s is the volume, in cubic centimetres, of the barium perchlorate solution required for the titration. c 01 , m 1 1000 142,06V s - =BS7164-23.1:1993 2 BSI 06-1999 b) the ion exchange column shall be capable of removing 0,1 g of zinc,
25、which is the most commonly interfering cation in rubber analyses. Regenerate the resin by passing 10 cm 3of 2 mol/dm 3hydrochloric acid (3.6) through the resin bed, at the rate of 2 to 3 drops per second, then wash the resin bed with 20 cm 3of water at a faster rate. Test the last few drops of the w
26、ashings for the absence of sulfate using thorin solution. 3.6 Hydrochloric acid, 2 mol/dm 3solution. 3.7 Oxygen, compressed, from a cylinder with an outlet suitable for introduction into the combustion flask (4.1). 3.8 Indicator Two types of indicator are described, both of which are suitable for us
27、e with the procedure described in this part of ISO 6528, i.e. thorin alone (3.8.1) and thorin plus methylene blue (3.8.2). The thorin used shall be a uniform red powder and shall give a clear, orange, aqueous solution. 3.8.1 Thorin 4-(2-arsonophenyl)azo-3-hydroxy- 2,7-naphthalenedisulfonic acid, dis
28、odium salt,0,2% (m/m) solution. Dissolve 0,2 g of thorin in 100 cm 3of water. 3.8.2 Thorin/methylene blue mixed indicator 3.8.2.1 Thorin, 0,5 % (m/m) solution. Dissolve 0,5 g of thorin in 100 cm 3of water. 3.8.2.2 Methylene blue 3,7-bis(dimethylamino)-5- phenothiazinium chloride, Cl 52015, 0,012 % (
29、m/m) solution. Dissolve 0,012 g of methylene blue in 100 cm 3of water. 3.9 Potassium nitrate (KNO 3 ), 0,4 % (m/m) solution. Dissolve 0,4 g of potassium nitrate in 100 cm 3water. 3.10 Black or white paper, for wrapping the test portions. NOTE 2The papers are usually supplied in the form shown in Fig
30、ure 1. For use with smaller platinum baskets, they may be cut as shown in Figure 2. Although most commercial papers are readily combustible, the papers may be cut from regular filter papers and impregnated with the potassium nitrate solution (3.9) to aid combustion of the rubber. Drain the excess so
31、lution and dry the papers at 100 C. If these treated papers are used, the procedure described in 7.3.2.2 shall be followed after the combustion. NOTE 3Papers used in electrical ignition units do not require the extension shown in Figure 1 and Figure 2. NOTE 4Black papers usually ignite more rapidly
32、with infra-red igniters. 4 Apparatus Usual laboratory equipment, and 4.1 Oxygen combustion flask (Schniger flask), thick-walled, of capacity 1 dm 3 , with a platinum sample carrier (basket) and a strong pinch clamp or fastening device. 4.2 Combustion device, infra-red safety type with enclosed safet
33、y cabinet and door, and with electrical igniter or alcohol burner (see Figure 3 and Figure 4). The infra-red igniter is the preferred apparatus because it is self-contained and properly shields the flask during combustion. All apparatus shall be operated in accordance with the manufacturers instruct
34、ions for safe operation. 4.3 Microburette, of capacity 5 cm 3or 10 cm 3 , graduated in 0,01 cm 3divisions. 4.4 Magnetic stirrer. 4.5 High-intensity lamp (optional). 4.6 Ion-exchange column, comprising a small tube, about 170 mm long with an internal diameter of10mm, provided with a stopcock or sinte
35、red-glass disc at one end. The bottom shall be filled to a depth of about 10 mm with glass wool, and the rest of the column shall be filled with the resin (3.5). 4.7 Balance, capable of weighing to 0,1 mg. 5 Preparation of test sample 5.1 Finely mill the test sample on a laboratory roll mill and tho
36、roughly homogenize it. 5.2 Due to the small masses of the test portions, the rubber and paper used for wrapping shall be protected from contamination. The use of forceps for handling the test portion and paper reduces the risk of contamination. 6 Safety precautions The oxygen combustion flask has be
37、en in use in many laboratories for a number of years and has an excellent safety record. Provided that the safety precautions are rigorously observed, there is little danger of explosion. 6.1 Flasks of capacity 1 dm 3shall not be used for test portions of mass greater than 80 mg. Larger flasks are a
38、vailable for larger test portions, but successive burning in the same flask over the same liquid is effectively the same as using a larger flask and larger test portions. It is also safer. 6.2 Flasks shall be inspected for minute cracks before use. Destroy imperfect flasks. 6.3 The flask shall conta
39、in no residues of organic solvent or vapours. This could cause an explosion. Any such solvents used for cleaning shall be repeatedly rinsed out with water.BS7164-23.1:1993 BSI 06-1999 3 6.4 Pressure, generated by the rapid combustion of organic material, could cause the flask to explode, and combust
40、ion shall, therefore, be carried out behind a safety shield or hood. The hands and face of the operator shall be behind a shield before the flame reaches the test portion. Goggles or a face shield shall be worn during combustion. A self-contained safety chamber is, therefore, highly recommended. 6.5
41、 The flask shall be left in the safety chamber until the last spark is extinguished. When it is removed, goggles or a face shield are recommended, since a slight vacuum is formed. 7 Procedure Carry out the determination in duplicate. 7.1 Test portion Weigh 40 mg to 80 mg of the test sample (seeclaus
42、e5) for sulfur contents up to about4%(m/m) or an appropriately smaller mass in the case of higher sulfur contents. (The test portion shall not contain more than 3 mg of sulfur.) 7.2 Preparation of the apparatus If calcium carbonate is absent, place 5 cm 3of hydrogen peroxide absorbing solution (3.1.
43、1) in the combustion flask (4.1). If the presence of calcium carbonate is suspected, place 5 cm 3of hydrogen peroxide/hydrochloric acid absorbing solution(3.1.2) in the combustion flask. If using a stirring bar, place the stirring bar in the flask. Wrap the test portion (see 7.1) in the paper (3.10)
44、 and fold so that the test portion is adequately contained and the paper extension extends above the platinum basket when placed therein. Do not allow the paper to become wet with absorbing solution. Insert a tube from the oxygen cylinder (3.7) almost to the bottom of the flask and blow in oxygen st
45、rongly for at least 30 s. (Avoid splashing the ab sorbing solution.) Quickly remove the oxygen tube, close the flask with the combustion device and firmly attach the pinch clamp or fastening device. 7.3 Determination 7.3.1 Combustion Place the flask in the safety chamber with the paper extension in
46、line with the focal point of the infra-red igniter beam. Ensure that the paper does not touch the side of the flask. If using electrical ignition, attach the flask to the proper connections. Ignite the paper and allow combustion to proceed to completion. When the test portion and paper have been com
47、pletely incinerated, remove the flask from the safety chamber and examine for black carbon deposits. If these are noted, repeat the whole procedure using a new test portion. (The object of combustion is to attain as high a temperature as possible and to burn the paper and test portion completely.) W
48、hen proper combustion has been achieved, place the sealed flask on the magnetic stirrer (4.4), if one is being used, and stir for 1 h. If no stirrer is used, allow the flask to stand for 2 h, to allow the gases to be absorbed by the absorbing solution. Occasional shaking may speed up absorption. 7.3
49、.2 Elimination of interfering substances 7.3.2.1 If interfering cations are absent, pour the contents of the flask into a 250 cm 3beaker or flask. Wash down the sides of the combustion flask and sample carrier with 5 cm 3of water and collect the washings in the same 250 cm 3container. Repeat the washing twice more. Collect the solution and water from the washings in a 100 cm 3conical flask and boil to decompose the excess hydrogen peroxide. Evaporate the solution to 5 cm 3to 10 cm 3volume and
