ISO 7781:2017 pdf download

ISO 7781:2017 pdf download.Styrene-butadiene rubber, raw — Determination of soap and organic-acid content
1 Scope
This document specifies three methods for the determination of the soap and organic-acid content of raw styrene-butadiene rubber (SBR).
— Method A is the titration method using indicator reagent.
— Method B is the titration method using an automatic potentiometric titrator.
— Method C is the back titration method using an automatic potentiometric titrator.
Since the soaps and organic acids present in the rubber are not single chemical compounds, the method gives only an approximate value for the soap and organic-acid content.
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 385, Laboratory glassware — Burettes
ISO 648, Laboratory glassware — Single-volume pipettes
ISO 1042, Laboratory glassware — One-mark volumetric flasks
ISO 1795, Rubber, raw natural and raw synthetic — Sampling and further preparative procedures
ISO 4799, Laboratory glassware — Condensers
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:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
4 Principle
A weighed test portion of the rubber, in the form of thin strips, is extracted using an ethanol-toluene azeotrope, or, for alum-coagulated rubber, using an ethanol-toluene-water mixture. After making up to a standard volume, an aliquot portion of the extract is withdrawn and titrated with acid-base titration.
— Method A: Titrate with standard acid for the determination of soap and with standard alkali for the determination of organic acid using indicator reagent.
— Method B: Titrate with standard acid for the determination of soap and with standard alkali for the determination of organic acid using automatic potentiometric titrator. The titration equivalence point is determined by inflection point.
8.1 Preparation of the test solution
Place a circular filter paper in the bottom of the wide-mouthed conical flask (6.3), and add 100 cm 3 of ETA extraction solvent (5.1) for all rubbers except alum-coagulated rubbers. For alum-coagulated rubbers, use an ethanol-toluene-water mixture (5.2). Introduce the strips of rubber separately into the flask, swirling after each addition so that the strips are thoroughly wetted with solvent and sticking is minimized. Fit the reflux condenser (6.5) to the flask and boil the solvent very gently under reflux for 1 h. Transfer the extract to the volumetric flask (6.4), and treat the rubber with a second 100 cm 3 portion of extraction solvent under reflux for 1 h. Add this extract also to the volumetric flask. Rinse the strips with three successive 10 cm 3 portions of extraction solvent, add these washings to the volumetric flask and, after cooling to room temperature, adjust the final volume to 250 cm 3 with appropriate extraction solvent. Alternatively, the weighed strips of sample can be wrapped in filter paper and placed in a Soxhlet extractor (see Note to 6.6) and extracted with an ETA (5.1) or ethanol-toluene-water mixture (5.2) under reflux for a minimum of 4 h.