BS 7164-7.1:1990

Committees responsible
National foreword
Method
0 Introduction
1 Scope
2 Normative references
3 Principle
4 Reagents
5 Apparatus
6 Sampling
7 Procedure
8 Expression of results
9 Test report
Tables
1 Degree of interference of rubber compounding
   ingredients
2 Behaviour of rubber-like materials in chromic acid
   oxidation procedure
Figures
1 Digestion and distillation assembly
2 Aeration assembly

Method for natural or synthetic isoprene rubber, with some modification if halogenated rubbers are present. Not to be used if vinyl acetate polymers are present.

1.1 This International Standard specifies a method for the determination of polyisoprene occurring as natural isoprene rubber (NR)²⁾, synthetic isoprene rubber (IR), balata and gutta percha, in the total solids from NR or IR latices, in solid raw rubbers, or in cured or uncured compounds.

The method is applicable to these isoprene rubbers alone or in blends. It cannot be used for hard rubber (ebonite) without modification.

1.2 Compounding ingredients, such as carbon black, mineral oil and sulfur, in soft rubbers do not interfere (see Table 1) (but see also 8.2). If vinyl acetate polymers are present, the method should not be used.

1.3 The method is applicable to blends of the rubbers mentioned in 1.1 with SBR, BR and NBR.

If halogenated rubbers are present, a slightly modified procedure, described in 7.7.3, is used. Some interference may be expected, because these rubbers react with chromic acid in a manner similar to polyisoprene. If these interfering rubbers are the major part of the blend, they may impede the reaction of the polyisoprene with the chromic acid. The digestion shall then be checked for completeness on known mixtures of these interfering rubbers.

Milling of the test portion as finely as possible is advisable.

1.4 The method may be used for the determination of polyisoprene in reclaimed rubbers, but it has been found to give consistently lower values than the previously accepted estimates for the polyisoprene content.

1.5 If rubbers other than those mentioned in 1.3 are present (CSM, EPDM, IIR, CIIR and BIIR), the digestion time shall be modified. The estimates shall be corrected by comparison with results from similar rubber blends. If these interfering rubbers are present in the blend, they may impede the reaction of the polyisoprene with the chromic acid and the method is not applicable. Greatest deviations are found if polysulfide rubbers are present as part of the mixture. (See Table 2.)