1、BRITISH STANDARD BS7164-22.2: 1992 ISO7725:1991 Chemical tests for raw and vulcanized rubber Part 22: Methods for determination of bromine and chlorine content Section 22.2 Oxygen flask combustion technique for determination of bromine and chlorineBS7164-22.2:1992 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 into effect on 28 February1992 BSI08-1999 The following BSI references relate to the work on this standard: Committee reference PRM/23 Draft for commen
3、t89/35456 DC ISBN 0 580 20647 5 Committees 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 an
4、d Environmental Management Laboratory of the Government Chemist Ministry of Defence Royal Society of Chemistry Rubber and Plastics Research Association Amendments issued since publication Amd. No. Date CommentsBS7164-22.2:1992 BSI 08-1999 i Contents Page Committees responsible Inside front cover Nat
5、ional foreword ii Introduction 1 1 Scope 1 2 Principle 1 3 Interference 1 4 Reagents and materials 1 5 Apparatus 2 6 Selection and preparation of intermediate test portion 3 7 Procedure 3 8 Expression of results 4 9 Test report 6 Annex A (informative) Bibliography 7 Figure 1 Paper configurations for
6、 wrapping test portions for oxygen combustion 3 Figure 2 Typical titration curve 5 Publication(s) referred to Inside back coverBS7164-22.2:1992 ii BSI 08-1999 National foreword This Section of BS7164 has been prepared under the direction of the Plastics and Rubber Standards Policy Committee and is i
7、dentical with ISO7725:1991 “Rubber and rubber products Determination of bromine and chlorine content Oxygen flask combustion technique”, published by the International Organization for Standardization (ISO). BS7164 rationalizes all the methods that deal with chemical analysis of raw, compounded and
8、vulcanized rubber, some of which have previously been published in BS903, BS1673 and BS5923. Relevant Parts of those standards will be withdrawn or deleted by amendment, as appropriate, when superseded by Parts and Sections of BS7164. This Section of BS7164 supersedes3.4 of PartB12 of BS903-B11 and
9、BS903-B12:1960 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 for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligati
10、ons. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1to8, an inside back cover 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 insid
11、e front cover.BS7164-22.2:1992 BSI 08-1999 1 Introduction This International Standard describes an oxygen flask combustion technique for the destruction of rubber, followed by either a potentiometric titration for chlorine and bromine if they occur singly or together, or a visual titration for bromi
12、ne only or chlorine only. Mutual interference, caused by co-precipitation, can be a problem in the potentiometric titration with silver nitrate. This is largely overcome though not completely eliminated by the addition of aluminium nitrate. The problem is least when bromine is in excess. At its wors
13、t, when chlorine is in excess, the bromine concentration may appear high, to an extent of5% of the chlorine content. The problem may be minimized by carrying out the titration at60 C, and keeping the rate of addition of titrant to a minimum. During combustion of bromine-containing compounds, a small
14、 proportion of the bromine appears as bromate instead of bromide. Bromine results can therefore be low by about1% of the bromine content. This can be overcome in the case of the potentiometric finish only by treating the solution obtained on combustion with hydrazine sulfate. The potentiometric titr
15、ation (see7.2.1) is sensitive down to64g of bromine or34g of chlorine when these are present singly. The visual titration (see7.2.2) lower limits are down to0,2mg of bromine or0,1mg of chlorine. When both chlorine and bromine are present, the lower limits are604g of bromine and304g of chlorine. Thes
16、e limits are dependent on the electrical sensitivities of the individual instruments used (see5.3 to5.5). 1 Scope This International Standard specifies methods for the determination of chlorine and/or bromine present in raw rubber, uncured mixes or vulcanizates. The methods are applicable to natural
17、 rubbers and to the following synthetic rubbers: isoprene, styrene-butadiene, butadiene, chlorinated, butyl, halogenated butyl, nitrile, ethylene-propylene, polychloroprene and epichlorohydrin. 2 Principle The test portion is ignited in an atmosphere of oxygen in an oxygen combustion flask containin
18、g potassium hydroxide and hydrogen peroxide. The carbon and hydrogen of any organic matter are oxidized and halogen is converted to the potassium salt. These potassium salts are titrated potentiometrically with silver nitrate solution to determine the amount of chlorine and bromine, when they occur
19、together in a rubber sample, or are titrated visually with mercuric nitrate solution to give either chlorine or bromine, when only one halogen is present. 3 Interference 3.1 Iodine will interfere but Zn 2+ , S, CN and do not. 3.2 Bromine and chlorine contained in additives/contaminants will be deter
20、mined by this method, unless previously removed by extraction. 4 Reagents and materials WARNING All recognized health and safety precautions shall be in effect when carrying out the operations specified in this International Standard. Failure to heed the directions contained in this International St
21、andard or those of the manufacturer of the devices used may result in explosions. During the analysis, use only reagents of recognized analytical reagent grade and only distilled water or water of equivalent purity. 4.1 Hydrogen peroxide, 6% (m/m) solution. Dilute20cm 3of30% (m/m) aqueous hydrogen p
22、eroxide solution to100cm 3with water. WARNING 30%(m/m) hydrogen peroxide is very corrosive to the skin. Wear rubber or plastic gloves and eye protection when handling. 4.2 Potassium hydroxide, solution, c(KOH)=0,5mol/dm 3 Dissolve2,8g of potassium hydroxide in100cm 3of water. 4.3 Nitric acid, concen
23、trated, =1,42Mg/m 3 . 4.3.1 Nitric acid, dilute, c(HNO 3 )=2mol/dm 3 . Dilute approximately120cm 3of concentrated nitric acid(4.3) to1dm 3with water. 4.3.2 Nitric acid, dilute, c(HNO 3 )=0,5mol/dm 3 . Dilute30cm 3of concentrated nitric acid(4.3) to1dm 3with water. 4.3.3 Nitric acid, dilute,0,2% (V/V
24、). CO 2 3BS7164-22.2:1992 2 BSI 08-1999 Dilute2cm 3of concentrated nitric acid(4.3) to1dm 3with water. 4.4 Silver nitrate, standard volumetric solution, c(AgNO 3 )=0,02mol/dm 3 . Prepare from commercial ampoules or dissolve3,4g of silver nitrate in1dm 3of water. Standardize the silver nitrate soluti
25、on as follows: Take a measured volume of between1cm 3and5cm 3of sodium chloride solution(4.5), dilute with water to25cm 3in a50cm 3beaker, add2 drops of sulfuric acid(4.11) along with a stirring bar, place on a stirrer(5.8) and titrate manually or with an automatic titrator(5.9). Plot the reading in
26、 millivolts versus the volume of silver nitrate to find the inflection point, or read the volume from the automatic titrator. Carry out the standardization in duplicate. Besides determining the concentration of the silver nitrate, this operation serves to alert the analyst to the proper functioning
27、of the millivoltmeter(5.3) and indicates the proper inflection point for chlorine. 4.5 Sodium chloride, standard reference solution, c(NaCl)=0,02mol/dm 3 . Prepare from commercial ampoules or dissolve1,17g of sodium chloride in1dm 3of water. 4.6 Methyl orange indicator, solution. Dissolve0,2g of met
28、hyl orange in100cm 3of water. 4.7 Aluminium nitrate, with low halide content. 4.8 Diphenylcarbazone indicator, solution. Dissolve1,5g of diphenylcarbazone in100cm 3of ethanol. Heat to dissolve, if necessary. 4.9 Bromophenol blue indicator, solution. Dilute5cm 3of a1g/100cm 3ethanolic solution of bro
29、mophenol blue to100cm 3with ethanol. 4.10 Mercury(II) nitrate, standard volumetric solution, c(Hg(NO 3 ) 2 .0,5H 2 O)=0,01mol/dm 3 . Dissolve3,4g of mercury(II) nitrate in1dm 3of water containing2cm 3of0,2% (V/V) nitric acid(4.3.3). Adjust the pH to1,7, using a pH-meter and adding the nitric acid dr
30、opwise. Standardize the mercury(II) nitrate solution as follows: Weigh and record, to the nearest0,1mg,40mg to60mg of potassium chloride and make up to100cm 3with water in a graduated flask. Transfer10cm 3of this solution to a250cm 3conical flask. Add20cm 3of water and80cm 3of ethanol(4.14) and stir
31、 magnetically at moderate speed. Add5 drops of the bromophenol blue indicator solution(4.9) and then add0,5mol/dm 3nitric acid(4.3.2) dropwise until the yellow end-point is reached, plus3 drops in excess. Add5 drops of the diphenylcarbazone indicator solution(4.8) and titrate with the mercury(II) ni
32、trate solution to the first appearance of a permanent pink colour. Carry out the standardization in duplicate. Carry out a blank titration, omitting the potassium chloride. Calculate the concentration c 1 , expressed in moles of Hg(NO 3 ) 2 .0,5H 2 O per cubic decimetre, using the equation 4.11 Sulf
33、uric acid, concentrated, =1,84Mg/m 3 . 4.12 Supply of oxygen 4.13 Potassium chloride, with low bromide content. 4.14 Ethanol Alternatively2-propanol may be substituted wherever ethanol is specified. 4.15 Hydrazine sulfate, 20g/dm 3solution (only for use in7.2.1). 5 Apparatus Ordinary laboratory appa
34、ratus, plus the following: 5.1 Oxygen combustion flask (Schniger flask), thick-walled,1000cm 3capacity, with a platinum sample carrier and a strong pinch clamp or fastening device (see5.2, note1). 5.2 Igniter, suitable for igniting the flammable material in which the test portion is contained in the
35、 tightly closed combustion flask. Common types are electrical and infra-red, both of which are suitable for use in this determination. where m 1 is the mass, in milligrams, of potassium chloride weighed out; V 1 is the volume, in cubic centimetres, of mercury(II) nitrate solution used for the titrat
36、ion of the potassium chloride; V 2 is the volume, in cubic centimetres, of mercury(II) nitrate solution used for the titration of the blank.BS7164-22.2:1992 BSI 08-1999 3 NOTE 1There are many types of oxygen combustion flask assembly, complete with igniter, that are commercially available and that a
37、re suitable for this determination provided they are operated in accordance with the manufacturers instructions. 5.3 Millivoltmeter, with high input impedance: e.g.a pH-meter with a millivolt scale. 5.4 Silver electrode, to be used as a measuring electrode. WARNING Do not coat the electrode with hal
38、ogen. 5.5 Reference electrode, of the salt bridge type: mercury(I) sulfate or any other type with a potassium sulfate salt bridge. 5.6 Burette, 10cm 3or25cm 3capacity. 5.7 Balance, capable of weighing to0.01mg. 5.8 Magnetic stirrer and stirring bar. 5.9 Automatic titrator 5.10 Wrappers, of black or
39、white paper, or cellulose capsules, suitable for oxygen combustion purposes. Typical paper configurations are illustrated in Figure 1. The test portion is placed in the centre of the large section and the paper folded over it to enclose it completely. The narrow strip is allowed to protrude to reach
40、 a flame or the beam of an infra-red igniter or an igniting electrode. 5.11 Safety chamber 6 Selection and preparation of intermediate test portion 6.1 Selection Cut from the sample an intermediate test portion of between0,5g and2,0g depending on the expected halogen level, if necessary from more th
41、an one place so that proper representation of the whole sample is achieved. 6.2 Preparation Pass the intermediate test portion six times between the cold rolls of a laboratory mill set to a nip not exceeding0,5mm. If it is not possible to pass it through the mill, the intermediate test portion may b
42、e cut into pieces less than1mm per side. 7 Procedure 7.1 Combustion 7.1.1 Weigh40mg to50mg of rubber to 0,1mg and place this test portion in a capsule or wrap in paper(5.10). Due to the small test portion size, the rubber and paper or capsule used for containing the test portion shall be protected f
43、rom contamination. Handle with forceps or plastic gloves. The test portion shall contain at least0,25mmol of halogen. If it is known that the amount of halogen is small, it is advisable to combust several (maximum4)80mg to100mg test portions of rubber in the same flask, consecutively, over the same
44、absorbing solution (see7.1.8). 7.1.2 Place1,0cm 3of the potassium hydroxide solution(4.2),5cm 3of the hydrogen peroxide solution(4.1) and10cm 3of water into the combustion flask and insert the test portion. Figure 1 Paper configurations for wrapping test portions for oxygen combustionBS7164-22.2:199
45、2 4 BSI 08-1999 7.1.3 Flush the flask for1min with oxygen(4.12), using a flow rate of at least2l/min. 7.1.4 Firmly close the flask with the clamps or closures recommended and place the flask in the safety chamber(5.11). 7.1.5 Ignite and burn the test portion. WARNING Leave the flask In the safety ch
46、amber until the last spark is extinguished. At this point, it can be removed, but since a slight vacuum is formed, hand and eye protection is recommended. 7.1.6 After removing the flask from the igniter assembly(5.2), insert a stopper and allow it to stand for1h or until all of the vapours have cond
47、ensed into the absorbing solution. If black residual carbon is noted at this point, repeat the procedure with a smaller test portion. 7.1.7 Remove the stopper from the flask, and rinse all the stopper surfaces with water into the combustion flask. 7.1.8 If more than one test portion is to be combust
48、ed in the same flask, wrap the next test portion, insert it in the flask and repeat the operations described in7.1.3 to7.1.7. 7.1.9 Boil the contents of the flask for a short time to decompose the hydrogen peroxide, but do not allow the flask to boil to dryness. 7.2 Titration 7.2.1 Potentiometric ti
49、tration for bromine and/or chlorine (present singly or together) 7.2.1.1 Transfer the solution obtained as described in7.1.9 quantitatively to a50cm 3beaker with several washes of water. The total volume should be about20cm 3 . Place a magnetic stirring bar in the beaker and place the assembly on the magnetic stirrer(5.8). When bromine is present, add5 drops of hydrazine sulfate solution(4.15). 7.2.1.2 Add a few drops of the methyl orange solution(4.6) and, while stirring, add0,5mol/dm 3nitric acid(4.3.2) until a colour change is noted, indicating
