Rubber and rubber products -- Determination of chlorine and bromine content

This document specifies methods for the determination of chlorine and/or bromine present in raw rubber as well as vulcanized or unvulcanized rubber compounds. The methods are applicable to natural rubbers and to the following synthetic rubbers: isoprene, styrene-butadiene, butadiene, butyl, halogenated butyl, nitrile, ethylene-propylene, chloroprene and epichlorohydrin.

Caoutchouc et produits à base de caoutchouc -- Détermination de la teneur en brome et en chlore

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Published
Publication Date
22-Jan-2020
Current Stage
6060 - International Standard published
Start Date
06-Dec-2019
Completion Date
23-Jan-2020
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INTERNATIONAL ISO
STANDARD 7725
Second edition
2020-01
Rubber and rubber products —
Determination of chlorine and
bromine content
Caoutchouc et produits à base de caoutchouc — Détermination de la
teneur en brome et en chlore
Reference number
ISO 7725:2020(E)
ISO 2020
---------------------- Page: 1 ----------------------
ISO 7725:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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below or ISO’s member body in the country of the requester.
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Published in Switzerland
ii © ISO 2020 – All rights reserved
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ISO 7725:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 1

5 Sample preparation ........................................................................................................................................................................................... 2

5.1 Sampling ....................................................................................................................................................................................................... 2

5.2 Sample solutions ................................................................................................................................................................................... 2

6 Method A — Ion chromatography ....................................................................................................................................................... 2

6.1 Reagents........................................................................................................................................................................................................ 2

6.2 Apparatus .................................................................................................................................................................................................... 3

6.3 Determination ......................................................................................................................................................................................... 3

6.3.1 Setting up the ion chromatograph .................................................................................................................... 3

6.3.2 Preparation of the calibration curve ............................................................................................................... 3

6.3.3 Measuring blank solutions and sample solutions ............................................................................... 3

6.4 Calculation .................................................................................................................................................................................................. 4

7 Method B — Potentiometric titration ............................................................................................................................................. 4

7.1 Reagents........................................................................................................................................................................................................ 4

7.2 Apparatus .................................................................................................................................................................................................... 5

7.3 Determination ......................................................................................................................................................................................... 5

7.4 Calculation .................................................................................................................................................................................................. 6

8 Precision ....................................................................................................................................................................................................................... 7

9 Test report ................................................................................................................................................................................................................... 7

Annex A (normative) Preparation of sample solutions by the tubular furnace combustion

method ............................................................................................................................................................................................................................ 8

Annex B (normative) Preparation of sample solutions by the oxygen combustion flask method ....11

Annex C (normative) Preparation of sample solutions by the oxygen combustion bomb method ..14

Annex D (informative) Conditions for ion chromatography .....................................................................................................16

Annex E (informative) Precision results from an interlaboratory test programme ........................................18

Bibliography .............................................................................................................................................................................................................................20

© ISO 2020 – All rights reserved iii
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ISO 7725:2020(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

The committee responsible for this document is ISO/TC 45, Rubber and rubber products, Subcommittee

SC 2, Testing and analysis.

This second edition cancels and replaces the first edition (ISO 7725:1991), which has been technically

revised. The main changes compared to the previous edition are as follows:
— the ion chromatography method has been added in Clause 6;
— the titration procedure has been improved in Clause 7;

— the tubular furnace combustion method for sample preparation has been added in Annex A;

— the oxygen combustion flask method for sample preparation has been improved in Annex B;

— the oxygen combustion bomb method for sample preparation has been added in Annex C;

— mercury nitrate and hydrazine are no longer used due to their hazardous properties.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved
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ISO 7725:2020(E)
Introduction

The two test methods in this document for quantitative analysis can be used for any type of rubbers

(i.e. raw rubber, vulcanized rubber or unvulcanized rubber) containing chlorine and/or bromine in any

form of existence, such as an element of polymer chain, chemical additives or a part of contaminations.

Three combustion methods are given for preparation of sample solution, i.e. tubular furnace

combustion method, oxygen combustion flask method and oxygen combustion bomb method. After

sample solutions are prepared, a content determination procedure, i.e. either ion chromatography or

potentiometric titration, follows. The most convenient and efficient method from the testing time and

safeness points of view, is the combination of tubular furnace combustion and ion chromatography, as

ion chromatography is widely used in quality control of polymer/rubber products or in environmental

analysis.
© ISO 2020 – All rights reserved v
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INTERNATIONAL STANDARD ISO 7725:2020(E)
Rubber and rubber products — Determination of chlorine
and bromine content

WARNING 1 — Persons using this document should be familiar with normal laboratory practice.

This document does not purport 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

determine the applicability of any other restrictions.

WARNING 2 — Certain procedures specified in this document might involve the use or generation

of substances, or the generation of waste, that could constitute a local environmental hazard.

Reference should be made to appropriate documentation on safe handling and disposal after use.

1 Scope

This document specifies methods for the determination of chlorine and/or bromine present in raw

rubber as well as vulcanized or unvulcanized rubber compounds.

The methods are applicable to natural rubbers and to the following synthetic rubbers: isoprene,

styrene-butadiene, butadiene, butyl, halogenated butyl, nitrile, ethylene-propylene, chloroprene and

epichlorohydrin.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 1795, Rubber, raw natural and raw synthetic — Sampling and further preparative procedures

ISO 3696, Water for analytical laboratory use — Specification and test methods

ISO 4661-2, Rubber, vulcanized — Preparation of samples and test pieces — Part 2: Chemical tests

3 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at http:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Principle

A sample solution is obtained by combustion of a test piece either burnt in a tubular furnace with

a stream of oxygen-containing gas and passed into a prepared solution or burnt in an oxygenic

atmosphere in a flask or a bomb which contains a solution to absorb the combustion gas. The sample

solution is then analysed by ion chromatography (method A) or potentiometric titration (method B) to

determine the content of chlorine and/or bromine in a sample.

For rubber samples of very low halogen content, method A is preferable since the inflection point might

not be obtained by method B.
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ISO 7725:2020(E)
5 Sample preparation
5.1 Sampling
For raw rubber, carry out sampling in accordance with ISO 1795.
For rubber compounds, carry out sampling in accordance with ISO 4661-2.

NOTE Chlorine and bromine contained in additives or contaminants can be detected by these sampling

methods, unless previously removed by extraction.
5.2 Sample solutions

To prepare sample solutions by the tubular furnace combustion method, follow the method specified in

Annex A. Repeat the procedure to create two solutions for each sample.

To prepare sample solutions by the oxygen combustion flask method, follow the method specified in

Annex B. Repeat the procedure to create two solutions for each sample.

To prepare sample solutions by the oxygen combustion bomb method, follow the method specified in

Annex C. Repeat the procedure to create two solutions for each sample.

If incomplete combustion, such as soot generation during combustion, is expected by the oxygen

combustion flask method, it is preferable to use the tubular furnace combustion method or the oxygen

combustion bomb method.
6 Method A — Ion chromatography
6.1 Reagents
6.1.1 Water, of grade 1 or higher. It shall be as specified in ISO 3696.

6.1.2 Chloride ion standard stock solution, of a commercial standard solution with a certified

chloride ion concentration, e.g. 1 000 mg/l of chloride, traceable to national standards. Comply with the

manufacturer’s expiration date or recommended shelf-life.

6.1.3 Chloride ion calibration solution, prepared by diluting the chloride ion standard stock solution

(6.1.2) with water (6.1.1). Prepare at least four solutions of different concentration of chloride ion covering

the expected concentration from the sample. The solutions shall be prepared every analytical day.

6.1.4 Bromide ion standard stock solution, of a commercial standard solution with a certified

bromide ion concentration, e.g. 1 000 mg/l of bromide, traceable to national standards. Comply with the

manufacturer’s expiration date or recommended shelf-life.

6.1.5 Bromide ion calibration solution, prepared by diluting the bromide ion standard stock solution

(6.1.4) with water (6.1.1). Prepare at least four solutions of different concentration of bromide ion covering

the expected concentration from the sample. The solutions shall be prepared every analytical day.

6.1.6 Mixed calibration solution, for measuring chloride ion and bromide ion at the same time,

prepared by mixing chloride ion (6.1.2) and bromide ion (6.1.4) with water (6.1.1). Prepare at least four

solutions of different concentration of chloride ion and bromide ion covering the expected concentration

from the sample. The solutions shall be prepared every analytical day.

6.1.7 Eluent solution, capable of eluting chloride ion and bromide ion to a proper retention time in

selected column. Follow the column manufacturer’s instructions.
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ISO 7725:2020(E)
NOTE Some examples of eluent are provided in Annex D.
6.2 Apparatus

6.2.1 Ion chromatograph, consisting of a pump to supply eluent, a sample injector, a column and a

conductivity detector specified as follows:

— pump: capable of delivering a constant flow within the range of 0,1 ml/min to 2,0 ml/min;

— sample injector: capable of injecting a constant volume of solution;

— column: filled with anion exchange resin suitable for resolving chloride ion and bromide ion from

other inorganic anions;
— suppressor: used for reducing the conductivity of high ionic eluent;
— detector: for detecting conductivity.
NOTE Some examples of commercially available column are provided in Annex D.

An ion chromatograph fitted with a suppressor as Figure 1 is suitable for sensitive analysis. The

suppressor is attached between a column and a detector.
An ion chromatograph without a suppressor as Figure 2 may also be selected.
Figure 1 — Example of basic ion chromatography system with suppressor
Figure 2 — Example of basic ion chromatography system without suppressor
6.3 Determination
6.3.1 Setting up the ion chromatograph
Set up the ion chromatograph in accordance with the manufacturer’s instructions.
6.3.2 Preparation of the calibration curve

Inject the calibration solutions in increasing order of concentration and measure the conductivity of

chloride ion and bromide ion peak area in each solution. Determine the correlation formula (calibration

curve) by plotting the peak area as a function of concentration by means of linear regression.

6.3.3 Measuring blank solutions and sample solutions

Inject the blank solution and sample solutions (created in 5.2) to measure the peak areas in sequence.

Then determine the chloride ion and bromide ion concentration of the blank (C and C , respectively)

B1 B2

as well as the concentration of the individual sample solution (C and C , respectively) by using the

S1 S2
calibration curve determined in 6.3.2.
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ISO 7725:2020(E)
6.4 Calculation

Calculate the chlorine content (w ) and/or bromine content (w ), in percentage by mass, by

1 2

Formulae (1) and (2), using the two determination values in 6.3. Average the results and round to the

second decimal place.
CC− ×V
SB11
w = ×100 (1)
W×1000
CC− ×V
SB22
w = ×100 (2)
W×1000
where
W is the mass of the test piece, in mg (see A.4.2, B.4.1 or C.4.1);
C is the chloride ion concentration of the sample solution, in mg/l;
C is the chloride ion concentration of the blank solution, in mg/l;
C is the bromide ion concentration of the sample solution, in mg/l;
C is the bromide ion concentration of the blank solution, in mg/l;
V is the fixed amount of the solution, in ml (see A.4.5, B.4.9 or C.4.8).
7 Method B — Potentiometric titration
7.1 Reagents
7.1.1 Water, of grade 1 or higher. It shall be as specified in ISO 3696.
7.1.2 Nitric acid, concentrated, ρ = 1,42 g/cm .

7.1.3 0,5mol/l Nitric acid, c(HNO ) = 0,5 mol/l, obtained by diluting 30 ml of concentrated nitric acid

(7.1.2) to 1 000 ml with water (7.1.1).
NOTE Commercially available 0,5 mol/l nitric acid can be used.
7.1.4 Silver nitrate standard volumetric solution, c(AgNO ) = 0,02 mol/l.

Standardize a silver nitrate solution obtained by dissolving 3,4 g of silver nitrate in 1 000 ml of water

(7.1.1) as follows:

Take a measured volume (between 1 ml and 5 ml) of sodium chloride solution (7.1.5), dilute with water

(7.1.1) to 25 ml in a 50 ml beaker, and add 2 ml of 0,5 mol/l nitric acid (7.1.3) along with a stirring

bar. Place the solution on a stirrer (7.2.2) and titrate with the silver nitrate solution (7.1.4) using an

automatic titrator (7.2.3). Read the volume from the automatic titrator. Determine the factor ( f) from

the averaged result in duplicating the same procedure.

Commercially available 0,02 mol/l silver nitrate standard volumetric solution and its guaranteed

factor ( f ) can be used.

7.1.5 Sodium chloride solution, traceable to national standards. c(NaCl) = 0,02 mol/l.

Alternatively, dissolve 1,168 g of sodium chloride in 1 000 ml of water (7.1.1).
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ISO 7725:2020(E)
7.1.6 Aluminium nitrate, of analytical reagent grade.

NOTE Aluminium nitrate is used to minimize the mutual interference caused by co-precipitation of chloride

and bromide.
7.1.7 Ethanol, of analytical reagent grade.
Alternatively, 2-propanol may be substituted wherever ethanol is specified.
7.2 Apparatus
7.2.1 Electronic balance, capable of weighing to the nearest 0,01 mg.
7.2.2 Magnetic stirrer and a stirring bar.
7.2.3 Automatic titrator.
7.2.4 Silver electrode, to be used as a measuring electrode.
7.2.5 Reference electrode, of the salt bridge type.

NOTE It is possible to use a combined electrode instead of the silver electrode and the reference electrode.

7.3 Determination

7.3.1 Transfer the blank solutions and sample solutions (created in 5.2) obtained quantitatively to a

300 ml beaker each with several washes water. Place a magnetic stirring bar in the beaker and place the

assembly on the magnetic stirrer (7.2.2).

7.3.2 Add 2 ml of the 0,5 mol/l nitric acid (7.1.3) and 2 g of the aluminium nitrate (7.1.6). Continue

stirring to dissolve the aluminium nitrate, then add 160 ml of ethanol (7.1.7).

7.3.3 Insert the electrode pair (7.2.4 and 7.2.5) into the solution and titrate with the silver nitrate

solution (7.1.4) with an automatic titrator (7.2.3).

NOTE The problem is least when bromine is in excess. At its worst, when chlorine is in excess, the bromine

concentration might appear high, to an extent of 5 % of the chloride ion content. The problem can be minimized

[2]

by carrying out the titration at 60 °C and keeping the rate of addition of titrant to a minimum .

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ISO 7725:2020(E)

7.3.4 The first inflection point on the titration curve represents the bromide ion end point and the

volume of titrant for bromide ion (V ). The second inflection represents the chloride ion end point and

the volume of titrant for chloride ion (V ). A typical titration curve is given in Figure 3.

Key
X volume of AgNO3 solution (ml)
Y potential difference (mV)
1 Br end point
2 Cl end point
Figure 3 — Example of titration curve

NOTE The kind of ion can be identified by initially measuring the potential difference at the end point of

each solution which contains chlorine alone and bromine alone.

7.3.5 Determine the volume of the silver nitrate solution required to titrate a blank solution to the

inflection point (V ).
7.4 Calculation

Calculate the chlorine content (w ) and/or bromine content (w ), in percentage by mass, by Formulae (3)

3 4

and (4), using the two determination values in 7.3.4 and 7.3.5. Average the results and round to the

second decimal place.
VV−−Vh××f×35,45
21 b
w = ×100 (3)
CC− ×V
SB22
w = ×100 (4)
W×1000
where
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ISO 7725:2020(E)

V is the volume, in ml, of silver nitrate solution required to titrate to the first inflection point;

V is the volume, in ml, of silver nitrate solution required to titrate to the second inflection point;

V is the volume, in ml, of silver nitrate solution of blank titration;
h is the concentration, in mol/l, of the silver nitrate solution;
f is the factor obtained in 7.1.4;
W is the mass of the test piece, in mg (see A.4.2, B.4.1 or C.4.1).
8 Precision
See Annex E.
9 Test report
The test report shall include the following information:
a) sample details:
1) full description of the sample and its origin;

2) method of preparation of the test piece from the sample, for example moulded or cut;

b) test method:
1) a full reference to the test method used, e.g. method A of ISO 7725:2020;

2) preparation method, i.e. tubular furnace combustion method, oxygen combustion flask method

or oxygen combustion bomb method;
3) determination procedure of halogen content, i.e. method A or method B;
4) details of any procedures not specified in this document;

c) results of the determination, expressed in % and rounded to the second decimal place;

d) date of the test.
© ISO 2020 – All rights reserved 7
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ISO 7725:2020(E)
Annex A
(normative)
Preparation of sample solutions by the tubular furnace
combustion method
A.1 General

This annex gives the preparation procedure of sample solutions by the tubular furnace combustion

method.
A.2 Reagents and materials
A.2.1 Water, of grade 1 or higher. It shall be as specified in ISO 3696.
A.2.2 Hydrogen peroxide, 30 % (m/m) solution, of analytical reagent grade.
A.2.3 Sodium carbonate, of analytical reagent grade.
A.2.4 Sodium hydrogen carbonate, of analytical reagent grade.

A.2.5 Absorbent solution, obtained by dissolving 2,0 ml hydrogen peroxide (A.2.2), 0,286 g sodium

carbonate (A.2.3) and 0,025 g sodium hydrogen carbonate (A.2.4) in 1 000 ml of water (A.2.1).

The absorbent solution shall be prepared every analytical day.
A.2.6 Oxygen, of mass fraction > 99,7 %.
A.2.7 Argon, of mass fraction > 99,98 %.
A.2.8 Air, of certified quality in contamination and purity.

NOTE Air is an alternative to the combustion gas of oxygen mixed with argon. The certification of the air

quality can be judged by individual laboratories in so far as it does not affect the test result.

A.2.9 Membranous filter, of pore size 0,45 µm.
A.3 Apparatus

Apparatus consists of a combustion furnace, a quartz tube and an absorbing vessel, as shown in

Figure A.1. Other types of apparatus than those specified in A.3.1 to A.3.4 may be used when they are

proven to give the same result.

A.3.1 Combustion furnace, with an electric heater capable of heating at a temperature of 1 000 °C and

maintaining the temperature for a certain period of time.
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ISO 7725:2020(E)

A.3.2 Quartz tube, having heat-resistance enough to be heated at the maximum temperature (e.g.

1 000 °C) and capable of holding a sample boat inside.

A gas of oxygen mixed with argon, or air which is supplied by the system, passes through the tube.

A.3.3 Sample boat, made of quartz, ceramic, or platinum and capable of carrying a test piece.

It shall have heat-resistance enough to be heated by the electric heater at the maximum temperature

(e.g. 1 000 °C).

A.3.4 Absorption vessel, made of borosilicate glass with sufficient volume to allow the gas to bubble

through the absorbent solution in it when it is filled at a certain level.
A.3.5 Electronic balance, capable of weighing to the nearest 0,01 mg.
Key
1 flow of combustion gas
2 quartz tube
3 sample boat
4 absorption vessel
5 combustion furnace
Figure A.1 — Example of the tubular combustion furnace
A.4 Procedure

A.4.1 Burn the sample boat at the combustion maximum temperature and weigh it to the nearest

0,1 mg after cooling it down.

A.4.2 Weigh out a test piece of 10 mg to 150 mg taken from the test sample prepared in 5.1 and place

it in the sample boat. Weigh the boat with the test piece to the nearest 0,1 mg and determine the mass of

the test piece, W, by subtracting the mass measured in A.4.1.

A.4.3 Follow the procedure a) to c) below unless manufacturer's instructions are available:

a) Insert the sample boat into the combustion furnace.
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ISO 7725:2020(E)

b) Put 15 ml of the absorbent solution (A.2.5) in the absorption vessel and connect it to the combustion

furnace.

c) Start the flow of the argon and oxygen gas, or air, and turn on the combustion furnace to burn the

test piece completely. An example of the combustion condition is as follows:
— temperature: 1 000 °C;
— flow rate of argon gas: 200 ml/min;
— flow rate of oxygen gas: 400 ml/min.

NOTE If the conditions are specified in manufacturer's instructions, the amount of the absorbed liquid, the

combustion temperature and the gas flow rate can be set accordingly.

A.4.4 After the completion of burning, wash through the whole tube and collect the washes into the

absorption vessel together with the absorbent solution to use as a sample solution.

A.4.5 For potentiometric titration, use the solution (A.4.4).

For ion chromatography analysis, adjust the solution volume (A.4.4) to a fixed amount, V, using a

specified volume vessel. If necessary, filter out a particulate matter in the sample solution with a

membranous filter (A.2.9) before injecting the solution into the ion chromatograph. To avoid possible

contamination, wash the membranous filter with a small quantity of the absorbent solution (A.2.5).

NOTE If any specific conditions are provided by manufacturer's instructions, the fi

...

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