ISO 21490:2022

Rubber and rubber products — Determination of 2-mercaptobenzothiazole content by high performance liquid chromatography (HPLC)

This document specifies a quantitative test method to determine the 2-mercaptobenzothiazole content in rubber and rubber products by high performance liquid chromatography (HPLC). This document delivers a method for quantifying 2-mercaptobenzothiazole in rubber products for a better selection of curing conditions. This document provides a method to follow the curing of rubber with sulfur- and benzothiazole-based accelerators using a chemical measurement which is complementary to the classical rheometric technique.

Caoutchouc et produits à base de caoutchouc — Détermination de la teneur en 2-mercaptobenzothiazole par chromatographie en phase liquide haute performance

General Information

• Status: Published
• Publication Date: 20-Jan-2022
• ICS: 83.060 - Rubber
• Technical Committee: ISO/TC 45/SC 2 - Testing and analysis
• Drafting Committee: ISO/TC 45/SC 2/WG 5 - Chemical tests
• Current Stage: 6060 - International Standard published
• Start Date: 21-Jan-2022
• Completion Date: 21-Jan-2022

Overview

ISO 21490:2022 sets out a standardized quantitative method for the determination of 2-mercaptobenzothiazole (2-MBT) content in rubber and rubber products using high performance liquid chromatography (HPLC). Developed by the International Organization for Standardization (ISO), this standard aims to provide a reliable chemical analysis technique to monitor and optimize the curing process of rubber compounds, particularly those using sulfur- and benzothiazole-based accelerators. The method described complements classical rheometric techniques, allowing manufacturers and laboratories to make data-driven decisions for improved product performance and quality assurance within the rubber industry.

Key Topics

• 2-Mercaptobenzothiazole (2-MBT) Analysis: Specifies a precise HPLC-based test method to quantify 2-MBT content in rubber materials and products.
• Sample Preparation and Extraction: Details the procedures for collecting, preparing, and extracting rubber samples to ensure accurate analysis.
• Chromatographic Conditions: Outlines recommended chromatographic parameters, including column selection, mobile phases, and detection wavelength, for consistent and reproducible results.
• Calibration and Quantitative Assessment: Provides guidance on preparation of standard working solutions and calibration curves, essential for accurate quantitation of 2-MBT.
• Data Reporting and Precision: Includes requirements for reporting test results, such as content values under various curing conditions, and offers information on method repeatability and reproducibility based on interlaboratory studies.

Applications

ISO 21490:2022 is highly practical across the rubber manufacturing sector and analytical laboratories engaged in:

• Quality Control: Ensuring consistent 2-mercaptobenzothiazole content in rubber batches to meet product specifications.
• Optimization of Curing Conditions: Monitoring 2-MBT levels during the sulfur vulcanization process enables precise adjustment of temperature, time, and accelerator dosage, leading to better material properties such as tensile strength and hardness.
• Regulatory Compliance: Supporting compliance with international standards regarding chemical content in rubber products.
• Research and Development: Providing a reliable method to track chemical changes during the development of new rubber compounds or formulations.
• Complementing Rheometric Techniques: Offering a chemical measurement method that supports and adds confidence to physical measurements obtained via rheometry.

Related Standards

For a comprehensive approach to rubber testing and analysis, the following international standards are frequently referenced and can complement ISO 21490:2022:

• ISO 3696: Water for analytical laboratory use - Specification and test methods; ensures the purity of water used in analytical procedures.
• ISO 4661-2: Rubber, vulcanized - Preparation of samples and test pieces - Part 2: Chemical tests; provides guidance on sample preparation for chemical analysis in rubber.
• ISO 19983:2017: Rubber - Determination of precision of test methods; referenced for evaluating precision and reliability in laboratory testing procedures.

Summary

ISO 21490:2022 delivers a reliable, standardized protocol for the determination of 2-mercaptobenzothiazole content by HPLC in rubber and rubber products. Its adoption enhances analytical accuracy, supports process optimization, and ensures product quality and compliance throughout the rubber industry. By applying this standard, organizations can achieve better control over the curing process, improve product performance, and align with global best practices in rubber analytics.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 21490
First edition
2022-01
Rubber and rubber
products — Determination of
2-mercaptobenzothiazole content
by high performance liquid
chromatography (HPLC)
Caoutchouc et produits à base de caoutchouc — Détermination de la
teneur en 2-mercaptobenzothiazole par chromatographie en phase
liquide haute performance
Reference number
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
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or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: [phone]
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and materials . 1
6 Apparatus . 2
7 Sampling . 2
8 Procedure .2
8.1 Sample preparation . 2
8.2 Chromatographic conditions . 3
8.3 Preparation of standard working solutions and the calibration curve . 3
8.4 HPLC-DAD testing . 3
9 Test results . . 3
9.1 Calibration curve . 3
9.2 Calculation . 4
10 Precision . 4
11 Test report . 4
Annex A (informative) Schematic chemical reactions during curing or rubber with
sulfenamide that gives 2-MBT . 5
Annex B (informative) A gradient programme of HPLC . 6
Annex C (informative) Calibration . 7
Annex D (informative) Spectrum and chromatogram of 2-MBT . 9
Annex E (informative) Precision .11
Bibliography .12
iii
Foreword
ISO (the 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
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electrotechnical standardization.
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described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
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expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by ISO/TC 45, Rubber and rubber products, Subcommittee SC 2, Testing
and analysis.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
2-Mercaptobenzothiazole (sometimes also referred to as: MBT; 2-MBT; 2-benzothiazolethione, or BTSH)
is used in the rubber industry as a curing agent. MBT is in the group of thiazoles and is considered as
scorch fast when used as a primary accelerator.
2-Mercaptobenzothiazole as the acidic sulfur accelerator is widely used in rubber materials because of
its good characteristics: stable sulfides, good vulcanization, and a low critical temperature to accelerate
vulcanization so that the rubber product can reach higher tensile strength and hardness levels.
Measuring 2-mercaptobenzothiazole concentration in rubber compounds at different stages of curing
the rubber product is an excellent means to define the optimal curing conditions of temperature and
time in order to obtain the right properties for the products at the best cost.
During the curing of rubber compounds sulfenamides are used as accelerators, which chemically
react at an early stage of the curing to produce 2-mercaptobenzothiazole and other species.
2-Mercaptobenzothiazole then contributes to the initiation of the mechanism which creates the sulfur
crosslinks between the rubber macromolecules at the end (an example is given in Figure A.1). To ensure
continuous progress, it is important to know the chemical mechanisms involved at each stage. Thus,
it is necessary to quantify the content of 2-mercaptobenzothiazole during the decomposition of the
sulfenamide and to know whether 2-mercaptobenzothiazole has disappeared in any further chemical
reactions.
v
INTERNATIONAL STANDARD ISO 21490:2022(E)
Rubber and rubber products — Determination of
2-mercaptobenzothiazole content by high performance
liquid chromatography (HPLC)
1 Scope
This document specifies a quantitative test method to determine the 2-mercaptobenzothiazole content
in rubber and rubber products by high performance liquid chromatography (HPLC).
This document delivers a method for quantifying 2-mercaptobenzothiazole in rubber products for a
better selection of curing conditions.
This document provides a method to follow the curing of rubber with sulfur- and benzothiazole-
based accelerators using a chemical measurement which is complementary to the classical rheometric
technique.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4661-2, Rubber, vulcanized — Preparation of samples and test
...