GB/T 8657-2000 Determination of soap and organic acid content in styrene-butadiene rubber
Some standard content:
GB/T 8657—2000
This standard is equivalent to the international standard IS(）7781:1996 "Determination of soap and organic acid content of styrene-butadiene rubber", and amends GB/T8657-1992 "Determination of soap and organic acid content of styrene-butadiene rubber". The main difference between this standard and the international standard ISO7781:1996: This standard adds the potentiometric titration method. The international standard only stipulates the determination of styrene-butadiene rubber soap and organic acid content by the indicator method. The main differences between this standard and the previous version:
1. Changes in the scope of application: This standard is applicable to styrene-butadiene rubber, divided into method A and method B. Method B is more suitable for styrene-butadiene rubber filled with high aromatic oil;
2. Method A of this standard uses thymol blue as an indicator. GB/T8657-1992 uses meta-cresol purple as an indicator, and thymol blue as an indicator for alum-coagulated rubber;
3. The end point of potentiometric titration for determining soap content by method B of this standard is pH 4.8, while that of GB/T8657-1992 is pH 2.8; this standard shall replace GB/T8657-1992 from the date of implementation. This standard is proposed by China Petrochemical Corporation. This standard is under the jurisdiction of the Synthetic Rubber Sub-Technical Committee of the National Technical Committee for Standardization of Rubber and Rubber Products. The drafting units of this standard are: Chemical Research Institute of Lanzhou Petrochemical Company, Lanzhou University. The main drafters of this standard are: Guo Hongda, Wang Xingguo, Wang Jin, Zhang Yuan. This standard was first issued as the national standard GB/T8657--1988 in 1988 and revised for the first time in 1992. 730
GB/T8657—2000
ISOForeword
ISO (International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing international standards is usually carried out by ISO technical committees. Any member body interested in the subject of an established technical committee has the right to participate in the committee. International organizations, both governmental and non-governmental, in liaison with ISO may also participate in the work. ISO works closely with the International Electrotechnical Commission (IEC) on all aspects of electrotechnical standardization. Draft international standards adopted by the technical committees are circulated to member bodies for voting. Publication as an international standard requires a vote of at least 75% of the member bodies voting.
International Standard ISO 7781 was prepared by ISO/TC45, Technical Committee on Rubber and Rubber Products. This second edition is a technically revised version of the first edition and it repeals and replaces the first edition (ISO 7781:1986). Annex A to this international standard is a prompt annex. 731
National Standard of the People's Republic of China
Styrene-butadiene raw rubber
Determination of soap and organic-acid content
Rubber, raw styrene-butadiene-Determination of soap and organic-acid contentGB/T 8657—2000
eqv ISO 7781: 1996
Replaces GB/T8657--.1992
Warning: Personnel using this standard should be familiar with formal laboratory operating procedures. This standard does not intend to cover all safety issues that may arise from the use of this standard. It is the user's responsibility to establish appropriate safety and health systems and ensure compliance with national regulations. 1 Scope
This standard specifies the method for the determination of soap and organic acid content in styrene-butadiene raw rubber. This standard is applicable to styrene-butadiene raw rubber, divided into method A and method B. Method B is more suitable for styrene-butadiene rubber filled with high aromatic oil.
2 Referenced Standards
The clauses contained in the following standards constitute the clauses of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised. Parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T15340-1994 Sampling and sample preparation methods for natural and synthetic raw rubber (idtISO1795:1992) 3 Principle
This method uses solvent to extract soap and organic acid in rubber, divides the extract into several parts, and determines the soap and organic acid content respectively. Titrate with standard acid solution to determine the soap content: R—COO+H+→R-COOH
Titrate with standard alkali solution to determine the organic acid content: R-CO0H+OH-—→R-COO-+H,O
Since soap and organic acid in rubber are not single chemical substances, this method only gives approximate values of soap and organic acid content. 4 Reagents
This standard uses analytical reagents and distilled water or water of equivalent purity. 4.1 Extraction agent
4.1.1 Ethanol-toluene azeotrope (ETA): Mix 7 volumes of anhydrous ethanol with 3 volumes of toluene; 4.1.2 Ethanol-toluene-water mixture: Mix 95 mL of ETA (4.1.1) with 5 mL of distilled water. 4.2 Standard hydrochloric acid titration solution: r(HC1)=0.05 mol/L. 4.3 Standard sodium hydroxide titration solution: c(NaOH)==0.1 mol/L. 4.4 pH7 standard buffer solution: Dissolve 3.40 g of potassium dihydrogen phosphate (KH,PO,) and 3.55 g of disodium hydrogen phosphate (NazHPO,) in distilled water and dilute to 1000 mL in a volumetric flask. At 23°C, the pH value of the freshly prepared solution is 6.87. 4.5 pH 4 standard buffer solution: Dissolve 10.21 g potassium hydrogen phthalate (KHCgH,O4) in distilled water and dilute to 1000 mL in a volumetric flask. At 23°C, the pH value of the freshly prepared solution is 4.00. 4.6 pH 9 standard buffer solution: Dissolve 3.81 g sodium tetraborate decahydrate (borax, Na2B,O, ·10H.O) in distilled water and dilute to 1000 mL in a volumetric flask. At 23°C, the pH of the freshly prepared solution is 9.20. 4.7 Thymol blue indicator: Dissolve 0.06 g of thymol blue in 6.45 mL of 0.02 mol/L sodium hydroxide titration solution and dilute to 50 mL with distilled water.
5 Instruments
5.1 Balance: minimum reading 1mg;
5.2 Heater: constant temperature water bath;
5.3 Wide-mouth conical flask: 400~500mL,
5.4 Reflux condenser: spherical or serpentine water condenser: 5.5
Acidity meter: accuracy of 10mV (or 0.1pH), with calomel electrode, glass electrode; 5.6 Magnetic stirrer;
5.7 Volumetric flask: 250mL;
5.8 Pipette: 100mL;
5.9 Conical flask, 250mL,
5.10 Burette: 25 mL, 1 mL;
5.11 Beaker: 250mL.
6 Sample preparation
Prepare the sample according to the method specified in GB/T15340 and cut it into thin strips with a length not exceeding 10mm and a width not exceeding 5mm. Weigh about 2g of the sample, accurate to 1mg.
7 Analysis steps
7.1 Preparation of test solution
Put a round filter paper at the bottom of a wide-mouth conical flask (5.3) and add 100mL of extractant (4.1). Note: Generally, ethanol-toluene azeotropic solution (4.1.1) is used. For rubber coagulated by alum, use ethanol-toluene-water mixture (4.1.2). Put the prepared samples into the wide-mouth conical flask one by one. After each addition, rotate the wide-mouth conical flask to make the extractant completely infiltrate the sample and reduce adhesion. Install the reflux condenser (5.4) on the wide-mouth conical flask and heat it. After slowly boiling for 1h under reflux conditions, transfer the extract to a volumetric flask (5.7). Add 100mL of extractant again, boil for another 1h, and transfer this extract to a volumetric flask. Wash the gel sample 3 times with 10mL of extractant respectively, and transfer the washing solution to a volumetric flask. After cooling to room temperature, dilute to 250mL with extractant, mix, and the result is the test solution.
7.2A Method: Indicator Method
7.2.1 Soap Content Analysis Steps
Use a pipette (5.8) to draw 100mL of test solution into a conical flask (5.9), add 6 drops of thymol blue indicator (4.7), and titrate with a standard hydrochloric acid solution (4.2) until the color changes suddenly. Draw another 100mL of extractant and perform a blank test in the same way. 7.2.2 Organic Acid Content Analysis Steps
Use a pipette to draw 100mL of test solution into a conical flask, add 6 drops of thymol blue indicator, and titrate with a standard sodium hydroxide solution (4.3) Titrate until the color changes suddenly. Take another 100mL of extractant and perform a blank test in the same way. 7.3B Method: Potentiometric Titration
7.3.1 Soap Content Analysis Steps
Connect the acidometer (5.5). Calibrate the acidometer with pH7 standard buffer solution (4.4) and pH4 standard buffer solution (4.5) in turn. Use a pipette to take 100ml of the test solution into a beaker (5.11), and place a magnetic stirrer in the beaker, and place it on a magnetic stirrer (5.6)733
GB/T 8657-2000
. Insert the glass electrode and calomel electrode into the beaker containing the test solution, start stirring, and titrate the test solution with hydrochloric acid standard titration solution under stirring until the pH is 4.8 as the end point. When approaching the end point, the titration speed should be slowed down until the titration end point is reached. Record the volume of hydrochloric acid standard titration solution consumed. Take another 100 mL of extractant and perform a blank test in the same way. 7.3.2 Analysis steps for organic acid content
Use pH 7 standard buffer solution and pH 9 standard buffer solution (4.6) to calibrate the acidometer in turn. Titrate the test solution with sodium hydroxide standard titration solution to pH 11.0 as the end point according to the analysis steps described in 7.3.1. Record the volume of sodium hydroxide standard titration solution consumed. Take another 100 mL of extractant and perform a blank test in the same way. 8 Expression of analysis results
8.1 Soap content Ws is expressed as mass percentage, which is given by the calculation formula (1): Ws = 0. 25(V - Va)G · Ks
Where: V,--the volume of hydrochloric acid standard titration solution consumed by titrating the test solution, mL; V.--the volume of hydrochloric acid standard titration solution consumed by titrating the blank test solution, mL.; C1\---the actual concentration of hydrochloric acid standard titration solution, mol /L; - the mass of the sample, g.
Ks value is appropriately selected from the following coefficients:
306, when the soap is sodium stearate;
368, when the soap is sodium rosinate;
337, when the soap is a 50:50 mixture of sodium stearate and sodium rosinate; 322, when the soap is potassium stearate;
384, when the soap is potassium rosinate,
353, when the soap is a 50,50 mixture of potassium stearate and potassium rosinate; 345, when the soap is a 50:50 mixture of sodium stearate and potassium rosinate or potassium stearate and sodium rosinate. The result should be expressed to two decimal places.
8.2 Organic acid content W. It is expressed as mass percentage and is given by the calculation formula (2): W = 0.25(V. - Vac - K.
Wherein: V3—the volume of sodium hydroxide standard titration solution consumed by the titration test solution, mL; V—the volume of sodium hydroxide standard titration solution consumed by the titration blank test, mL; C2—the actual concentration of sodium hydrofluoride standard titration solution, mol /L; m----sample mass, g. bzxz.net
K. The value is appropriately selected from the following coefficients:
284, when the acid is stearic acid;
346, when the acid is rosin acid;
315, when the acid is a 50:50 mixture of stearic acid and rosin acid. The result should be expressed to two decimal places.
9-Tolerance
When the soap content is 0-0.55%, the difference between the two parallel results shall not exceed 0.03%; when the organic acid content is 3.00%~～8.00%, the difference between the two parallel results shall not exceed 0.15%. 9.2B method
GB/T8657—2000
When the soap content is 0~0.05%, the parallel The difference between the two results of parallel determination is not greater than 0.01%; when the soap content is between 0.06% and 0.55%, the difference between the two results of parallel determination is not greater than 0.03%; when the organic acid content is between 3.00% and 8.00%, the difference between the two results of parallel determination is not greater than 0.12%. 10 Test report
The test report should include the following:
a) The number of this standard;
b) Detailed description of the sample;
c) The method used in the analysis process (Method A or Method B); d) Expression of test results and units (specify Ks, K. values); e) Any abnormal phenomena observed during the test; f) Any optional operations not included in this standard or referenced standards; g) Test date.
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