This standard specifies the method for determining the content of boric acid in concentrated natural rubber latex. This standard applies to concentrated natural rubber latex produced from Hevea brasiliensis latex. GB/T 8294-2001 Determination of boric acid content in concentrated natural rubber latex GB/T8294-2001 Standard download decompression password: www.bzxz.net

GB/T 8294--2001
This standard is equivalent to the international standard ISO1802.1992 "Concentrated natural latex". This standard is consistent with the previous version in terms of technical content, with only slight editorial changes. This standard replaces GB/T8294--1987 from the date of implementation. This standard is proposed by the Ministry of Agriculture of the People's Republic of China. Determination of boric acid content".
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, and Food Quality Supervision, Inspection and Testing Center of the Ministry of Agriculture (Zhanjiang). The main drafters of this standard are: Zhou Jiang, Huang Maofang, and Chen Ying. This standard was first issued in July 1987, and this edition is the second edition. This standard is interpreted by the Natural Rubber Sub-Technical Committee of the National Technical Committee for Standardization of Rubber and Rubber Products. 81
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GB/T8294—2001
ISO Foreword
ISO (International Organization for Standardization) is a worldwide federation of national standards bodies (ISQ member bodies). The work of formulating international standards is usually carried out by ISO's technical committees. Any member body interested in the project of an established technical committee has the right to participate in the committee. All governmental and non-governmental international organizations in contact with ISO may also participate in this work. In all aspects of electrotechnical standardization, ISO works closely with the International Electrotechnical Commission (IEC). Draft international standards adopted by the technical committee are sent to member bodies for voting. To be published as an international standard, at least 75% of the voting member bodies must vote in favor.
International Standard ISO1802 was prepared by ISO/TC45 Rubber and Rubber Products Technical Committee SC3 Rubber Industry Raw Materials (including Latex) Subcommittee.
This third edition of the standard slightly modifies the second edition (ISO1802:1985), abolishes and replaces the second edition. 82
1 Scope
National Standard of the People's Republic of China
Determination of boric acid content in concentrated natural rubber latex
Natural rubber latex concentralDetermination of boric acid content This standard specifies the method for determining the boric acid content in concentrated natural rubber latex. This standard applies to concentrated natural rubber latex produced from Hevea brasiliensis latex. 2 Referenced standards
GB/T 8294--2001
idt ISo 1802:1992
Replaces GB/T8294-1987
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 are subject to revision, and 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 (negISO123:1985) 3 Principle
The pH of a latex sample containing about 0.02g of boric acid is adjusted to 7.50, at which time the boric acid is basically in an undissociated state. Then an excess of mannitol is added to form a strongly acidic boric acid-mannitol complex, thereby releasing hydrogen ions equivalent to the amount of boric acid in the latex, causing the pH to drop. Add alkali to restore the pH of the sample to 7.50, and the boric acid content can be measured based on the amount of alkali added. 4 Reagents
This standard recommends the use of only confirmed analytically pure reagents, distilled water or water of equivalent purity. 4.1 Hydrochloric acid, 2% (m/m) solution.
4.2 Stabilizer solution, containing 5% (m/m) ethylene oxide condensate type non-ionic stabilizer. 4.3 Mannitol.
4.4 Boric acid solution. Weigh about 5g of boric acid (H.BO,) to the nearest 1mg, dissolve in water and dilute to 1000mL in a volumetric flask. 4.5 Sodium hydroxide standard solution, c(NaOH)~0.05mol/L. 4.5.1 Calibration of solution
Use a pipette (5.2) to take 5mL of boric acid solution (4.4) and place it in a 250mL beaker, add 2mL of stabilizer solution (4.2) and 50mL of water. Use a pH meter (5.1) to measure the pH of the solution. If the pH value exceeds 5.5, add hydrochloric acid solution (4.1) drop by drop while stirring continuously to reduce the pH value to the range of 5.5 to 2.5. Let the solution stand for 15min, and add sodium hydroxide solution (4.5) to pH 7.50 using a burette (5.3) while stirring continuously. Then add 4g of mannitol (4.3) while continuing to stir, and the pH value will drop immediately. Then accurately titrate the burette (5.3) with sodium hydroxide solution and record the volume of sodium hydroxide solution required to restore the pH value to 7.50. 4.5.2 Calculation of concentration
Use formula (1) to calculate the concentration c of sodium hydroxide solution, expressed in moles per liter c = 0. 081×
Approved by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China on July 20, 2001
(1)www.bzxz.net
Implemented on December 1, 2001
GB/T8294-2001
Where: m-mass of boric acid in 1000mL boric acid solution (4.4) + g; V,.-volume of sodium hydroxide solution required to restore the pH to 7.50, mL. 5 Instruments
Ordinary laboratory instruments and:
a) pH meter, capable of measuring the pH during the test to an accuracy of 0.01 unit. b) Pipette with a capacity of 2mL, 5mL and 50mL. c) Burette with an appropriate capacity.
6 Sampling
Sampling shall be carried out in accordance with the method specified in GB/T8290. 7 Operating Procedure
Weigh about 10g of concentrated latex to an accuracy of 0.1g. Place it in a 250mL beaker and add 2mL of stabilizer solution (4.2) and 50mL of water. Add hydrochloric acid solution (4.1) dropwise while stirring continuously until the pH of the concentrated latex is less than 5.5 but greater than 2.5 when measured with a pH meter (5.1). After standing for 15 minutes, add sodium hydroxide solution (4.5) to pH 7.50 with a burette (5.3) while stirring continuously. Then add 4g of mannitol (4.3) and continue stirring. The pH will drop immediately. Use a burette (5.3) to add sodium hydroxide solution and titrate accurately, and record the volume of sodium hydroxide solution required to restore the pH to 7.50. 8 Expression of results
Use formula (2) to calculate the boric acid (H,BO.) content of concentrated latex, expressed as mass fraction: 6.18cV2× 100
Boric acid content (%) -
Where: c - the actual concentration of sodium hydroxide solution (4.5) calculated according to 4.5.2, mol/L; V2 - the volume of sodium hydroxide solution required to restore the pH of latex to 7.50, mL; m. - the mass of concentrated latex sample, g. The difference between the two determination results shall not exceed 0.01%, and the average shall be taken. The result shall be expressed to two decimal places. 9 Test report
The test report shall include the following:
a) This standard number;
b) All details required to identify the sample;
c) The measurement result and its unit;
d) Any abnormal phenomenon noticed during the measurement;
e) Any operation that is not included in this standard but is considered to be applicable;
f) The test date.
. (2)
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