ISO 16947:2026

Natural rubber latex concentrate — Determination of zinc oxide stability time (ZST)

This document specifies a method for determining the zinc oxide stability time (ZST) of natural rubber latex concentrate.

Concentré de latex de caoutchouc naturel — Détermination du temps de stabilité de l'oxyde de zinc (ZST)

General Information

• Status: Published
• Publication Date: 23-Feb-2026
• ICS: 83.040.10 - Latex and raw rubber
• Technical Committee: ISO/TC 45/SC 3 - Raw materials (including latex) for use in the rubber industry
• Drafting Committee: ISO/TC 45/SC 3 - Raw materials (including latex) for use in the rubber industry
• Current Stage: 6060 - International Standard published
• Start Date: 24-Feb-2026
• Due Date: 20-Mar-2026
• Completion Date: 24-Feb-2026

Overview

ISO 16947:2026 - Natural Rubber Latex Concentrate - Determination of Zinc Oxide Stability Time (ZST) is an internationally recognized standard developed by the International Organization for Standardization (ISO). This standard specifies a detailed method for determining the zinc oxide stability time (ZST) of natural rubber latex concentrate. ZST is a key indicator of latex stability when zinc oxide is introduced, helping manufacturers and laboratories assess the quality and processability of latex products. Precise determination of ZST supports the rubber industry in maintaining high standards for raw material quality, performance, and safety.

Key Topics

• Zinc Oxide Stability Time (ZST):
  Defines the time in seconds for a latex concentrate sample to show visible flocculation after zinc oxide addition under specified conditions.
• Method Principle:
  Latex is prepared under controlled alkalinity, dilution, and temperature, then stirred at high speed with added zinc oxide until flocculation is observed.
• Sample Preparation and Test Procedure:
  Standardizes sample handling, reagent use, pH adjustment, temperature conditioning, and mechanical stirring protocols.
• Result Expression and Reporting:
  Specifies how to calculate, validate, and report the mean ZST value from duplicate determinations, ensuring result consistency.
• Precision Assessment:
  Includes guidelines for repeatability and reproducibility of the test across different laboratories, based on interlaboratory studies.

Applications

ISO 16947:2026 is essential for industries that process and manufacture natural rubber products using latex concentrate, including:

• Quality Control in Latex Production:
  Helps producers ensure that latex batches maintain desired stability when exposed to zinc oxide, reducing the risk of premature coagulation during product manufacturing.
• Product Development:
  Supports formulation design for latex gloves, medical devices, foam products, and adhesives, where latex stability is critical for performance.
• Procurement and Compliance:
  Enables buyers and suppliers to harmonize quality standards when specifying or receiving natural rubber latex concentrates.
• Research and Laboratory Analysis:
  Provides a scientific basis for comparing raw material batches, troubleshooting manufacturing issues, and validating new processing conditions or additives.
• Regulatory Compliance:
  Assists in meeting international trade and safety requirements for latex materials through standardized testing protocols.

Related Standards

For comprehensive latex quality evaluation and consistency with international best practices, consider these related ISO standards:

• ISO 35: Natural rubber latex concentrate - Determination of mechanical stability
  Procedures for assessing the mechanical stability of latex under stress.
• ISO 123: Rubber latex - Sampling
  Guidance on representative sampling methods for latex.
• ISO 124: Latex, rubber - Determination of total solids content
  Methods for quantifying the total solids within latex samples.
• ISO 976: Rubber and plastics - Polymer dispersions and rubber latices - Determination of pH
  Standardized approaches to measuring pH in latex systems.
• ISO 3310-1: Test sieves - Technical requirements and testing - Part 1: Test sieves of metal wire cloth
  Specifications for laboratory sieving apparatus used in latex testing.
• ISO 1382: Rubber - Vocabulary
  Reference for rubber and latex terminology.
• ISO 19983: Rubber - Determination of precision of test methods
  Guidance on statistical approaches for test method validation.

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Adhering to ISO 16947:2026 enables natural rubber latex producers and users worldwide to consistently assess ZST, optimizing material performance and product safety across diverse applications. For further details or access to the complete standard, visit iso.org.

Standards Content (Sample)

International
Standard
ISO 16947
First edition
Natural rubber latex concentrate —
2026-02
Determination of zinc oxide
stability time (ZST)
Concentré de latex de caoutchouc naturel — Détermination du
temps de stabilité de l'oxyde de zinc (ZST)
Reference number
© ISO 2026
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
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 2
6 Apparatus . 2
7 Sampling . 2
8 Procedure . 2
9 Expression of results . 3
10 Precision . 3
11 Test report . 4
Annex A (informative) Precision . 5
Bibliography . 7

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 through
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The procedures used to develop this document and those intended for its further maintenance are described
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This document was prepared by Technical Committee ISO/TC 45, Rubber and rubber products, Subcommittee
SC 3, Raw materials (including latex) for use in the rubber industry.
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
International Standard ISO 16947:2026(en)
Natural rubber latex concentrate — Determination of zinc
oxide stability time (ZST)
WARNING — Persons using this document should be familiar with normal laboratory practice. This
document does not purport to address all of the safety problems, if any, associated with its use. It
is the responsibility of the user to establish appropriate safety and determine the applicability of
regulatory limitations prior to use.
1 Scope
This document specifies a method for determining the zinc oxide stability time (ZST) of natural rubber latex
concentrate.
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 35, Natural rubber latex concentrate — Determination of mechanical stability
ISO 123, Rubber latex — Sampling
ISO 124, Latex, rubber — Determination of total solids content
ISO 976, Rubber and plastics — Polymer dispersions and rubber latices — Determination of pH
ISO 3310-1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
zinc oxide stability time
ZST
time required to initiate visible flocculation after the addition of zinc oxide when the latex is stirred at high
speed
Note 1 to entry: The zinc oxide stability time is expressed in seconds.
4 Principle
A test portion, under specified alkalinity, dilution and temperature is stirred at high speed after the addition
of zinc oxide until visible flocculation is observed. The time required to initiate visible flocculation is
recorded, this
...