BS ISO 7781:2017 pdf download.Styrene-butadiene rubber, raw – Determination of soap and organic-acid content.
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, Labo ratory glass ware — Single-volume pipettes
ISO 1042, Labo ratory 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 After making up to a standard volume, an aliquot portion of the extract is withdrawn and titrated with acid-base titration.
5 Reagents
During the analysis, use only reagents of recognized analytical grade and only distilled water or water
of equivalent purity.
5.1 Ethanol-toluene azeotrope (ETA).
Mix seven volumes of absolute ethanol with three volumes of toluene. Alternatively, mix seven volumes of commercial-grade ethanol with three volumes of toluene, and boil the mixture with anhydrous calcium oxide (quicklime) under reflux for 4 h. Cool to room temperature and decant through No. 42 filter paper.
5.2 Ethanol-toluene-water mixture.
Mix 95 cm3 of ETA (5d) and 5 cm3 of water.
5.3 Sodium hydroxide solution, c(NaOH) = 0,1 mol/dm3, accurately standardized.
5.4 Thymol blue indicator.
Dissolve 0,06 g of thymol blue in 6,45 cm3 of 0,02 mol/dm3 sodium hydroxide solution and dilute to 50 cm3 with water.
5.5 Hydrochloric acid, c(HCI) = 0,05 mol/dm3. accurately standardized.
6 Apparatus
Use ordinary laboratory apparatus and the following.
6.1 Balance, accurate to 1 mg.
6.2 Hotplate.
6.3 Wide-mouthed conical flask, of capacity 400 cm3 to 500 cm3.
6.4 Volumetric flask, of capacity 250 cm3, complying with the requirements of ISO 1042.
6.5 Reflux condenser, complying with the requirements of ISO 4799.
7 Sampling and sample preparation
Sheet out 2 g to 6 g of rubber, selected and prepared in accordance with ISO 1795 . Cut into pieces no larger than 2 mm x 2 mm or strips no longer than 10 mm and no wider than 5 mm. Weigh a test portion of approximately 2 g to the nearest 0,001 g.
8 Procedure
8.1 Preparation of the test solution
Place a circular filter paper in the bottom of the wide-mouthed conical flask (63). and add 100 cm3 of ETA extraction solvent (5J.) 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 (fz.S) 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 cm3 portion of extraction solvent under reflux for 1 h. Add this extract also to the volumetric flask. Rinse the strips with three successive 10 cm3 portions of extraction solvent, add these washings to the volumetric flask and, after cooling to room temperature, adjust the final volume to 250 cm3 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 (5j) or ethanol-toluene-water mixture (52) under reflux for a minimum of 4 h.
8.2 Method A — Titration method using indicator reagent
8.2.1 Procedure for determination of soap content
After thorough mixing, pipette 100 cm3 of the diluted extract into the 250 cm3 conical flask (&6), add six drops of thymol blue indicator (SA) and titrate the solution with hydrochloric acid solution (5.5) to the first colour change (V i).
Carry out a blank titration on 100 cm3 of extraction solvent taken from the same stock as was used for the test portion and using the same indicator as used for titration of the test portion (V2).
8.2.2 Procedure for determination of organic-acid content
Proceed exactly as in 82.1. but titrate the aliquot portion with sodium hydroxide solution (53), again using thymol blue indicator (SA) (V3).
Carry out a blank titration on 100 cm3 of extraction solvent using the same method (V4).BS ISO 7781 pdf download.