This standard specifies the determination of free sulfur content in rubber by potentiometric titration. This standard is applicable to the determination of free sulfur content in unvulcanized rubber and vulcanized rubber. ? GB/T 15253-1994 Determination of free sulfur in rubber Potentiometric titration method GB/T15253-1994 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Determination of free sulfur in rubber
Potentiometic titration method
Rubber--Determination of free sulpher-Potentiometic titration method Subject content and scope of application
This standard specifies the determination of free sulfur content in rubber by potentiometric titration. This standard is applicable to the determination of free sulfur content in unvulcanized rubber and vulcanized rubber. 2 Reference standards
GB/T601 Preparation of standard solution for titration analysis (volume analysis) of chemical reagents GB/T3516 Determination of solvent extracts in rubber 3 Principle
GB/T15253-94
Free sulfur extracted from rubber with acetone is treated with potassium cyanide to generate potassium thiocyanate. A silver electrode is used as the indicator electrode and a double salt bridge calomel electrode is used as the reference electrode to form a working cell, and potassium thiocyanate is titrated potentiometrically with a silver nitrate standard titration solution. Reaction formula: S+KCN=KCNS
KCNS+AgNO,=AgCNS+KNO,
4 Reagents and materials
Analytical reagents and distilled water or water of equal purity should be used during the analysis. 4.1 Acetone (GB/T 686).
4.2 95% ethanol (GB/T 679).
4.3 Potassium cyanide solution, β=10g/L, beware of highly toxicity! For treatment of potassium cyanide waste liquid, see Appendix A (reference). 4.4 Gelatin solution, P=0.1g/L.
4.5 Starch solution, Q=10g/L.
4.6 Silver nitrate standard titration solution (c（AgNO.)=0.1mol/L): Prepare and calibrate according to GB/T 601 4.7 Silver nitrate standard titration solution [c（AgNO,）0.004mol/L: Accurately pipette 20.00mL of silver nitrate standard titration solution (4.6) into a 500mL volumetric flask, and dilute to the mark with water (dilute before use). The concentration of the solution is given by formula (1). C,
Where: c-
The molar concentration of the silver nitrate standard titration solution [c（AgNO,)=0.1mol/L>, mol/L; The molar concentration of the silver nitrate standard titration solution after dilution, mol/L. 4.8 Qualitative filter paper.
National Technical Supervision Kitchen 1994-09-24 approved 834
: (1)
1995-08-01 implementation
5 Instruments and Equipment
5.1 Automatic Potentiometric Titrator:
5.1.1 Main Parameters:
Amplifier: Measurement accuracy is ±0.5%.
b. Potentiometric Controller: Accuracy is ±5mV. GB/T15253-94
c Automatic Burette: Accuracy is ±0.2% within 0~100% volume. d. Recorder: When the paper feed speed is adjusted to 20cm/10000 pulses, each centimeter of recording paper is equivalent to dripping 1mL of titrant. 5.2216 type silver electrode.
5.3217 type double salt bridge calomel electrode.
5.4 Extraction device: see the rapid extraction device in GB/T3516. 5.5 Electric constant temperature water bath.
5.6 Analytical balance: accuracy is 0.1mg. 5.7 Volumetric flask (brown): 1000mL.
5.8 Pipette: 20mL.
5.9 Conical flask with stopper: 125mL.
6 Analysis steps
Weigh a certain amount (about 1g for vulcanized rubber, 0.3~0.5g for unvulcanized rubber) of the sample cut into particles of about 1mm, accurate to 0.1mg, wrap it with filter paper, and extract it with acetone for 4h according to the method specified in GB/T3516. After cooling, remove the extraction bottle, pour the extract into a stoppered conical flask, wash the extraction bottle with 15mL acetone, add the washing liquid into the stoppered conical flask, place the flask on a water bath, evaporate to dryness in a fume hood, and take it out. Add 10mL ethanol, shake well to dissolve the residue, then add 2.mL potassium cyanide solution (when the free sulfur content is too high, the amount of potassium ferrite solution can be appropriately increased), heat on a water bath at about 80℃, and shake from time to time to further dissolve the residue, then transfer all the solution into a titration beaker, add 50mL water and 2mL gelatin solution, and measure on an automatic potentiometric titrator in a constant temperature chamber at 20±2℃.
7 Potentiometric titration
Titrate the test solution with silver nitrate standard titration solution (4.7) according to the operating method specified in the potentiometric titrator manual. 7.1 Titration method
Use the first differential method (as shown in Figure 1) or the recording titration plotting method (as shown in Figure 2) to determine the potentiometric titration endpoint. 7.2 Recorder adjustment
Range 500mV, zero point adjusted to the left, paper speed 20cm/10000 pulses; each centimeter of recording paper is equivalent to dripping 1mL of titrant. 7.3 Instrument adjustment
-Subdifferential titration
Titration amplifier: Select the first differential switch. Titration device: Select the manual switch.
Manual controller: The speed is 0.2mL/min. Electrode: 216 type silver electrode and 217 type double salt bridge calomel electrode. 7.3.2 Recording titration
Titration amplifier: Select the recording titration switch. Titration device: Select the manual switch. bzxz.net
Manual controller: The speed is 0.2mL/min. Electrode: 216 type silver electrode and 217 type double salt bridge calomel electrode. 835
Figure 1 Secondary differential titration
8 Expression of analysis results
GB/T15253-94
8.1 The content of free sulfur is expressed as mass percentage and is given by formula (2). a
500,mv
Record titration
(V2 - V) X c X 0. 032 07
S(%,m/m) =
Where: m——mass of sample, g,
concentration of standard silver nitrate titration solution, mol/L, V,—total volume of standard silver nitrate titration solution consumed by titrating the sample solution, mL; V,—volume of standard silver nitrate titration solution consumed by titrating excess cyanide, mL, (2)
0.03207——mass of sulfur equivalent to 1.00mL standard silver nitrate titration solution [c(AgNO,)=1.000mol/L), expressed in grams.
Analysis results should be rounded to two significant figures.
GB/T 15253-94
Appendix A
Treatment of cyanide-containing waste liquid
(reference)
Cyanide is a highly toxic substance. This waste liquid cannot be lost at will, otherwise it will cause irreversible poisoning accidents. Therefore, CN-containing substances must be handled carefully. Add NaOH to a small amount of dilute cyanide solution to adjust the pH to above 10, and then add a few grams of potassium permanganate (3%) to oxidize and decompose CN-. If the CN~ content is high, it can be treated by alkaline oxidation method: first adjust the pH to above 10, and then add sodium hypochlorite. Additional remarks:
This standard is proposed by the Ministry of Chemical Industry of the People's Republic of China. This standard is under the jurisdiction of the Beijing Rubber Industry Research and Design Institute of the Ministry of Chemical Industry. This standard is drafted by the Shanghai Rubber Products Research Institute. The main drafters of this standard are Cao Hui and Xi Renfen. This standard refers to ISO/DPSAM-1983 "Determination of free sulfur in compound rubber or vulcanized rubber (potentiometric titration method)". 837
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