ISO 11235 pdf download.Rubber compounding ingredients — Sulfenamide accelerators — Test methods
1 Scope
1.1 This International Standard specifies the methods to be used for the evaluation of sulfenamide accelerators. 1.2 The analytical methods are applicable for most commercial sulfenamide accelerators: – Sulfenamides of primary amines (type I) – Sulfenamides of unhindered secondary amines (type II) – Sulfenamides of hindered secondary amines (type III) 1.2.1 MBTS: Benzothiazyl disulfide NOTE Although MBTS is not a sulfenamide, it is the primary decomposition product of these accelerators and quantitatively determined by the method specified in 4.2. 1.2.2 CBS: N -cyclohexylbenzothiazole-2-sulfenamide 1.2.3 TBBS: N – tert -butylbenzothiazole-2-sulfenamide 1.2.4 DIBS: N , N ‘-diisopropylbenzothiazole-2-sulfenamide 1.2.5 DCBS: N , N ‘-dicyclohexylbenzothiazole-2-sulfenamide 1.2.6 MBS: N -oxydiethylenebenzothiazole-2-sulfenamide
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 385-1 :1 984, Laboratory glassware — Burettes — Part 1 : General requirements . ISO 648:1 977, Laboratory glassware — One-mark pipettes . ISO 1 772:1 975, Laboratory crucibles in porcelain and silica . ISO 381 9:1 985, Laboratory glassware — Beakers
4 Test methods for purity
4.1 Method to determine purity by reduction with MBT and titration 4.1.1 Scope The following method is suitable for determining the purity and free amine in sulfenamides commonly used in the rubber industry and is applicable to CBS, DCBS, MBS and TBBS. 4.1.2 Principle After neutralization of the free amine, the sulfenamide is reduced by means of a solution of mercaptobenzothiazole (MBT). An excess of hydrochloric acid is added and the unreacted hydrochloric acid is then titrated with sodium hydroxide using one of the two following methods: – method A: potentiometric titration; – method B: titration using an indicator. 4.1.3 Reagents During the analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity. 4.1.3.1 Basic reagents for methods A and B 4.1.3.1.1 Mercaptobenzothiazole (MBT), min. assay 99,0 %. 4.1.3.1.2 Absolute ethanol. 4.1.3.1.3 Toluene. 4.1.3.1.4 Hydrochloric acid, standard volumetric solution, c(HCl) = 0,1 mol/dm 3 . 4.1.3.1.5 Hydrochloric acid, standard volumetric solution, c(HCl) = 0,5 mol/dm 3 . 4.1.3.1.6 Sodium hydroxide, standard volumetric solution, c(NaOH) = 0,1 mol/dm 3 , carbonate free. 4.1.3.1.7 Sodium hydroxide, standard volumetric solution, c(NaOH) = 0,5 mol/dm 3 , carbonate free. 4.1.3.1.8 Bromophenol blue, 1 0 g/dm 3 solution. Dissolve 1 g of bromophenol blue with a small volume of ethanol (4.1 .3.1 .2). Transfer to a 1 00 cm 3 volumetric flask and neutralize with the sodium hydroxide solution (4.1 .3.1 .6) to a green colour. Dilute to the mark with ethanol (4.1 .3.1 .2). 4.1.3.2 Prepared reagent for method A 4.1.3.2.1 Mercaptobenzothiazole, 40 g/dm 3 solution, freshly prepared. Weigh a suitable quantity of MBT (4.1 .3.1 .1 ) to the nearest 0,1 g and dissolve in absolute ethanol (4.1 .3.1 .2). If the MBT does not dissolve completely, heat the solution to a temperature no higher than (55 ± 2) °C (not exceeding 57 °C) to ensure complete dissolution. 4.1.5.1.1 Grind a sample and weigh a test portion of approximately 2 g of the blended powder to the nearest 0,1 mg. For TBBS, weigh approximately 1 ,6 g of the test sample. Transfer it to the beaker (4.1 .4.4). 4.1.5.1.2 Add 50 cm 3 of ethanol (4.1 .3.1 .2) and stir until dissolved. If needed, heat the solution to a temperature no higher than 55 °C. A slight turbidity may remain. 4.1.5.1.3 Cool to room temperature. Add 3 drops of indicator (4.1 .3.1 .8) and titrate the free amine with 0,1 mol/dm 3 hydrochloric acid (4.1 .3.1 .4) to the blue-green-colour end point (V 1 ). 4.1.5.1.4 Add 50 cm 3 of the MBT solution (4.1 .3.2.1 ) and immediately pipette 25 cm 3 of 0,5 mol/dm 3 hydrochloric acid (4.1 .3.1 .5), exactly measured. 4.1.5.1.5 Stir the solution in a temperature-controlled bath (4.1 .4.5) maintained at (55 ± 2) °C for exactly 5 min, timed with the stop-watch (4.1 .4.6). 4.1.5.1.6 Titrate potentiometrically the unreacted hydrochloric acid with the 0,5 mol/dm 3 sodium hydroxide (4.1 .3.1 .7). With continued stirring, add the sodium hydroxide stepwise in increments of 1 cm 3 , and record the resultant equilibrium potential (mV) after each addition. Approaching the end point, add titrant in increments of 0,1 cm 3 , recording the potential (mV) 20 s after each addition until the end point has been passed. The end point of the titration is the point of inflection of the titration curve, plotted automatically or manually as the measured potential (mV) against the volume in cubic centimetres of sodium hydroxide solution. At this point, the first derivative curve reaches a maximum whilst the second derivative curve is zero (falling from a positive to a negative value). The end point shall be calculated from the second derivative on the assumption that the change from a positive to a negative value bears a linear relationship with the addition of sodium hydroxide in the 0,1 cm 3 interval (V 3 ) passing through the inflection point.