GB/T 8297-2001 Determination of potassium hydroxide (KOH) value of concentrated natural rubber latex
Some standard content:
ICS.83.040.10
National Standard of the People's Republic of China
GB/T 82972001
idtIS0127:1995
Concentrated natural rubber latex
Determination of potassium hydroxide (KOH) value
Natural rubber latex concentrate-Determination of KOH number
Issued on 2001-07-20
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
Implementation on 2001-12-01
GB/T 8297-2001
This standard adopts the international standard IS0127:1995°Concentrated natural rubber latex. This standard has made the following revisions to the previous version:
Determination of KOH value".
- Added Chapter 5 Instruments and specified the accuracy of the instruments;- The operating procedures chapter was greatly revised, and specific provisions were made on the titration process and the judgment of the endpoint; Appendix A "Determination of formaldehyde" and Appendix B "Titration and endpoint calculation examples" were added. This standard will replace GB/8257-[987 from the date of implementation. Appendix A and Appendix B of this standard are both indicative appendices. This standard was proposed by the Ministry of Agriculture of the People's Republic of China. This standard is under the jurisdiction of the Natural Rubber Sub-Technical Committee of the National Technical Committee for Standardization of Rubber and Rubber Products. The drafting units of this standard are: South China Tropical Agricultural Products Processing Design Institute, Food Quality Supervision, Inspection and Testing Center of the Ministry of Agriculture (Zhanjiang). The main drafters of this standard are Huang Maofang, Xu Sui, Chen Xiaoguang, Wang Guilan, and Chen Ying. This standard is the second edition, and the first edition was first issued in July 1987. This standard is entrusted to the Natural Rubber Sub-Technical Committee of the National Technical Committee for Standardization of Rubber and Rubber Products for interpretation. GB/T 8297—2001
ISOForeword
ISO (International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out by ISO technical committees. Any member body interested in a project for which a technical committee has been established has the right to represent it. International organizations, governmental and non-governmental, in liaison with ISO may also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards adopted by the technical committees The draft shall be sent to the member groups for voting. Publication as an international standard requires at least 75% of the voting member groups to vote in favor.
International Standard ISO127 is prepared by ISO/TC45 Rubber and Rubber Products Technical Committee. The third edition of this standard has made technical revisions to the second edition (1S0127:1984), abolishing and replacing the second edition. Appendices A and B of this international standard are for reference only. National Standard of the People's Republic of China
Concentrated natural latex
Determination of potassium hydroxide (KOH) value
Natural rubber latex concentrate-Determination f KoH number
GB/T 8297—2001
idt ISo 127: 1995
Replaces GB/T 8297—1987
Notice: Personnel using this standard should be familiar with the operating procedures of regular laboratories. This standard does not cover all safety issues that may arise from the use of this standard. It is the user's responsibility to develop appropriate safety and health systems and ensure compliance with relevant national regulations. 1 Scope
This standard specifies the method for determining the KOH value of concentrated natural latex preserved in whole or in part with nitrogen. This standard is applicable to latex containing acid. It is not applicable to latex preserved with potassium hydroxide, nor to natural latex, compound latex, vulcanized latex and artificial latex other than Brazilian rubber tree latex. 2 Referenced standards
The provisions contained in the following standards constitute the provisions 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/T8290--1987 Sampling of natural concentrated latex (neuISO123:1985) GB/T8294-2001 Determination of acid content of concentrated natural latex (idtISO1802.1992) GB/T8298-2001 Determination of total solid content of concentrated natural latex GB/T8300-2001 Determination of alkalinity of concentrated natural latex (idtISO125:1990) GB/T18012-1999 Determination of pH of natural latex (neqIS976:1996) 3 Definitions
This standard adopts the following definitions.
KOH value of latex
The number of grams of potassium hydroxide equivalent to the acid radicals combined with ammonia in concentrated latex containing 100 total solids. 4 Reagents
In the analysis, use only reagents of confirmed analytical grade and distilled water or water of equivalent purity that does not contain carbon dioxide. 4.1 Potassium hydroxide, standard titration solution, c(KOH) = 0.1mol/L, does not contain carbonates. 4.2 Potassium hydroxide, standard titration solution, c(KOH) = 0.5 mol/L, does not contain carbonates. 4.3 Formaldehyde, 45 g/L to 50 g/L acid-free formaldehyde solution [e(HCHO) = 1.5 mol/L to 1.67 mal/L], prepared by diluting concentrated formaldehyde with water and neutralizing with 0.1 mol/L potassium hydroxide solution (4.1), using phenolic acid as an indicator, and a pale pink color as the end point, and determining the formaldehyde concentration as described in Appendix A.
Approved by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China on July 20, 2001, implemented on December 1, 2001
5 Instruments
GB/T 8297 2001
5.1 pH meter, conforming to the requirements of GB/T 18012, readable to 0.01 pH unit. 5.2 Glass electrode, of a type suitable for use in solutions with a pH of up to 12.0. 5.3 Mechanical stirrer, equipped with a grounded motor and glass paddles. Electromagnetic stirrer can also be used. Note: If a white dynamic titrator is used, it can be used after calibration if its effect is the same as that of the standard method. 6 Sampling
Sampling is performed according to the method described in GB/T8290. 7 Operating procedures
Use the method recommended in GB/T18012 to calibrate the pH meter. If the total solid content (W) and alkalinity (A) are unknown, they shall be determined according to GR/T8298 and GB/T8300 respectively. If the latex contains boric acid and its content is unknown, it shall be determined according to GB/T8294. Perform parallel duplicate determinations.
Weigh a latex sample containing about 50g of total solids and place it in a 400mL beaker as the test material (mass m), accurate to 0.1g. If necessary, add the required amount of formaldehyde solution (4.3) while stirring to adjust the alkalinity to (0.5±0.1)% ammonia (measured in water phase). The volume of formaldehyde solution to be added is calculated by formula (1): Volume of formaldehyde solution = m(100 - Wrs)(A ~ 0.5)1134c(HCHO)
-actual concentration of formaldehyde solution (4.3), mol/L. Where: c(HCHO)—
Dilute the latex with water to about 30% total solids,
Insert the electrode of the pH meter (5.1) into the diluted latex and record the pH value. (1)
If the initial pH is lower than 10.3, slowly add 5 mL of 0.5 mol/L potassium hydroxide solution (4.2). Stir slowly with a glass paddle. Record the pH reading when equilibrium is reached. While continuing to stir, regularly add 0.5 mol/L potassium hydroxide solution, 1 mL each time, at regular intervals (e.g. 15a). Record the pH value when equilibrium is reached each time potassium hydroxide solution is added until it exceeds the endpoint. If the initial pH is 10.3 or higher, skip the initial 5 mL addition and directly add 0.5 mol/L potassium hydroxide solution.Steps of 1 mL\ at a time. The endpoint of the titration is the inflection point of the titration curve of pH versus titration volume of potassium hydroxide solution (in mL). At this point, the slope of the curve (i.e., the first-order differential) reaches a maximum value, and the second-order differential changes from positive to negative. Assuming that the change from positive to negative of the second-order differential is linear with each addition of 1 mL of potassium hydroxide, the endpoint should be calculated based on the second-order differential. Appendix B gives a typical example of titration and calculation of the endpoint. The difference between the results of parallel duplicate determinations should not be greater than 5% (m/m). 8 Results
Calculate the KOH value of the concentrated latex according to formula (2): KOH value =
561e·V
Wherein: ---actual concentration of potassium hydroxide solution (4.2), mol/L; ---volume of 0.5mol/L potassium hydroxide solution (4.2) required to reach the end point, mL; Wrs---total solid content of concentrated latex, expressed in mass percentage; m
-mass of the sample.
(2))
If the condensed latex contains oxadiazine, the KOH value obtained in formula (2) should be subtracted from the KOH value equivalent to the oxadiazine content. The KOH value equivalent to the oxadiazine content is calculated according to formula (3): 2
Wherein: WBa—
9 Test report
boric acid content.
The test report should include the following contents:
a) The number of this standard:
b) All details required to identify the sample:
c) All details of the pH meter used for marking: d) The result of the measurement,
e) Whether a calibration with code acid is used,
GB/T 8297—2001
KOH value = 91×
f) Any operation not included in this standard but considered to be applicable, g) Test date.
（3）
A1 Reagents
A1.1 Anhydrous sodium sulfite, analytical grade
GB/T.8297—2001
Appendix A
(Suggested Appendix)
Determination of formaldehyde
A1.2 Sulfuric acid, standard titration solution, c(H,SO,)=0.25mol/L. A1.3 Thymol, indicator solution, dissolve 80mg thymol acid in 100mL ethanol, then dilute with 100mL distilled water. A2 Method
Dissolve 125g anhydrous sodium sulfate (A1.1) in 500mL water, then dilute to 1L. Take 100mL of the solution and place it in a 500mL beaker. Then accurately weigh 6.0g to 8.0g of formaldehyde solution (4.3) with a nominal concentration of 50g/. and add it to the beaker. Shake thoroughly and leave for 5 minutes. Then use thymol as an indicator and titrate with 0.25mol/L sulfuric acid (A1.2) until the first colorless state appears. Use sodium sulfite solution as a blank. A3 Results
Calculate the formaldehyde content in the formaldehyde solution by formula (A1), expressed as mass percentage: 30.03(V1 - V,) × 2c(H,S0))Formaldehyde (%) =
Wherein: Vi—volume of sulfuric acid (A1.2) consumed in titrating the formaldehyde solution sample, mL; V
volume of sulfuric acid (A1.2) consumed in the blank, mL; c(H,SO,)actual concentration of sulfuric acid solution, mol/l; mibzxZ.net
-mass of the formaldehyde solution sample, g.
Appendix B
(Suggested Appendix)
Examples of Titration and Endpoint Calculation
Table B1 gives typical examples of pH changes in titration. Table B1 Typical examples of pH changes during titration KOH added
Volume of solution
pH reading
1 When analyzing concentrated methanol solution, it is more convenient to take 1.8 g to 2.2 g of solution for plating. 4
First-order differential
ApH/nL
Second-order differential
ApH/mL
(Al)
Volume of KOH added
pH reading
GB/T 8297—2001
Table B1 (end)
First-order differential
Second-order differential
a\pH/mL
In this example, the first-order differential reaches a maximum value of 0.31 when the amount of potassium hydroxide solution added is between 11 mL and ~12 mL. The exact inflection point can be calculated from the ratio of two adjacent second-order differentials, such as 0.07/(0.07+0.01)=0.875 is the ratio of the second-order differentials between 11 mL and 12 mL, that is, the inflection point is 11.875 mL. Figure BI shows the inflection point in the form of a graph. 12.2
68101121314
Volume reduced by potassium hydroxide, mL
Figure B1 Curve of pH change during titrationFigure 5
GB/T 8297-2001
National Standard of the People's Republic of China
Concentrated natural rubber latex
Determination of potassium hydroxide (KOH) value
GB/T 8297 2001
Published by China Standards Press
No. 16 Hebei Street, Lanli, Fuxingmenwai, Beijing
Postal Code: 100045
Tel: 6852304668517548
Printed by Qinhuangdao Printing Factory of China Standards Press Distributed by Beijing Distribution Office of Xinhua Bookstore Distributed by Xinhua Bookstores in various places*
Format: 880×12301/16:3/4 Number of words: 14,000 words 2(December 2001, first edition, December 2001, first printing, print run: 1-2,000
Book number: 155066:1-17975 Price: 8.00 yuan Network certificate: bzcbs.com
Keywords: 590 -543
Copyright exclusive. Infringement will be investigated
Report phone number: (010)68533533) Actual concentration of sulfuric acid solution, mol/l; mi
-mass of formaldehyde solution sample, g.
Appendix B
(Suggested Appendix)
Titration and endpoint calculation examples
Table B1 gives typical examples of pH changes during titration. Table B1 Typical examples of pH changes during titration
Volume of KOH added
pH reading
1 When analyzing concentrated formaldehyde solution, it is more convenient to take 1.8 g to 2.2 g of solution for plating. 4
First-order differential
ApH/nL
Second-order differential
ApH/mL
(Al)
Volume of KOH added
pH reading
GB/T 8297—2001
Table B1 (end)
First-order differential
Second-order differential
a\pH/mL
In this example, the first-order differential reaches a maximum value of 0.31 when the amount of potassium hydroxide solution added is between 11 mL and ~12 mL. The exact inflection point can be calculated from the ratio of two adjacent second-order differentials, such as 0.07/(0.07+0.01)=0.875 is the ratio of the second-order differentials between 11 mL and 12 mL, that is, the inflection point is 11.875 mL. Figure BI shows the inflection point in the form of a graph. 12.2
68101121314
Volume reduced by potassium hydroxide, mL
Figure B1 Curve of pH change during titrationFigure 5
GB/T 8297-2001
National Standard of the People's Republic of China
Concentrated natural rubber latex
Determination of potassium hydroxide (KOH) value
GB/T 8297 2001
Published by China Standards Press
No. 16 Hebei Street, Lanli, Fuxingmenwai, Beijing
Postal Code: 100045
Tel: 6852304668517548
Printed by Qinhuangdao Printing Factory of China Standards Press Distributed by Beijing Distribution Office of Xinhua Bookstore Distributed by Xinhua Bookstores in various places*
Format: 880×12301/16:3/4 Number of words: 14,000 words 2(December 2001, first edition, December 2001, first printing, print run: 1-2,000
Book number: 155066:1-17975 Price: 8.00 yuan Network certificate: bzcbs.com
Keywords: 590 -543
Copyright exclusive. Infringement will be investigated
Report phone number: (010)68533533) Actual concentration of sulfuric acid solution, mol/l; mi
-mass of formaldehyde solution sample, g.
Appendix B
(Suggested Appendix)
Titration and endpoint calculation examples
Table B1 gives typical examples of pH changes during titration. Table B1 Typical examples of pH changes during titration
Volume of KOH added
pH reading
1 When analyzing concentrated formaldehyde solution, it is more convenient to take 1.8 g to 2.2 g of solution for plating. 4
First-order differential
ApH/nL
Second-order differential
ApH/mL
(Al)
Volume of KOH added
pH reading
GB/T 8297—2001
Table B1 (end)
First-order differential
Second-order differential
a\pH/mL
In this example, the first-order differential reaches a maximum value of 0.31 when the amount of potassium hydroxide solution added is between 11 mL and ~12 mL. The exact inflection point can be calculated from the ratio of two adjacent second-order differentials, such as 0.07/(0.07+0.01)=0.875 is the ratio of the second-order differentials between 11 mL and 12 mL, that is, the inflection point is 11.875 mL. Figure BI shows the inflection point in the form of a graph. 12.2
68101121314
Volume reduced by potassium hydroxide, mL
Figure B1 Curve of pH change during titrationFigure 5
GB/T 8297-2001
National Standard of the People's Republic of China
Concentrated natural rubber latex
Determination of potassium hydroxide (KOH) value
GB/T 8297 2001
Published by China Standards Press
No. 16 Hebei Street, Lanli, Fuxingmenwai, Beijing
Postal Code: 100045
Tel: 6852304668517548
Printed by Qinhuangdao Printing Factory of China Standards Press Distributed by Beijing Distribution Office of Xinhua Bookstore Distributed by Xinhua Bookstores in various places*
Format: 880×12301/16:3/4 Number of words: 14,000 words 2(December 2001, first edition, December 2001, first printing, print run: 1-2,000
Book number: 155066:1-17975 Price: 8.00 yuan Network certificate: bzcbs.com
Keywords: 590 -543
Copyright exclusive. Infringement will be investigated
Report phone number: (010)68533533
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