BS 7164 is a series on chemical tests for raw and vulcanized rubber. Raw and vulcanized rubber is any type of rubber that's been hardened through the use of heat and sulfur. BS 7164-7.1 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.
The method is applicable to blends of the rubbers mentioned in BS 7164-7.1 with SBR, BR and NBR. If halogenated rubbers are present, a slightly modified procedure, described in BS 7164-7.1, 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 a major part of the blend, they may impede the reaction of the polyisoprene with the chromic acid. The digestion is checked for completeness on known mixtures of these interfering rubbers. Milling the test portion as finely as possible is advisable.
BS 7164-7.1 on methods of determination of polymer content is useful for:
Raw and vulcanized rubber is made via a curing process in which the rubber's elastomers harden in response to heat and sulfur. BS 7164-7.1 describes the method that 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. If rubbers other than those mentioned in BS 7164-7.1 are present (CSM, EPDM, IIR, CIIR and BIIR), the digestion time is modified. The estimates are 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.
The greatest deviations are found if polysulfide rubbers are present as part of the mixture. BS 7164-7.1 states the principle that Quantitative oxidation of the polyisoprene present in a test portion with a hot digestion mixture of sulfuric and chromic acids; a distillation of the acetic acid formed, aeration of the distillate to remove carbon dioxide and titration of the acetic acid with sodium hydroxide solution. The calculation is based on the observation that a 75 % yield of acetic acid is always obtained in the oxidation of the isoprene unit under the specified test conditions. Using BS 7164-7.1 you can understand the methods of determination of polymer content.
ISO 5945:1989