ISO 2781-2018 PDF

Full title and description

ISO 2781:2018 — Rubber, vulcanized or thermoplastic — Determination of density. This International Standard specifies two laboratory methods for determining the density of solid vulcanized and thermoplastic rubbers; it is used for quality control, material specification and calculating mass from volume for rubber products.

Abstract

This document specifies two methods of test for the determination of the density of solid vulcanized and thermoplastic rubbers. Such determinations are important for quality control of rubber compounds and for calculating the mass of rubber required to produce a given volume. The document does not cover the determination of relative density (ratio to pure water at a stated temperature).

General information

• Status: Published — International Standard (confirmed in systematic review).
• Publication date: 2018-06 (published 25 June 2018).
• Publisher: International Organization for Standardization (ISO).
• ICS / categories: 83.060 (Rubber).
• Edition / version: Edition 5 (2018).
• Number of pages: 10 (ISO edition content length).

Key bibliographic and lifecycle information (status, edition, pages and confirmation history) are published on the ISO catalogue entry.

Scope

ISO 2781:2018 applies to the determination of the density of solid vulcanized and thermoplastic rubbers and gives two test methods for that purpose. It excludes the determination of relative density expressed as a ratio to the mass of an equal volume of pure water at a stated temperature. The standard is intended for routine laboratory and production quality-control use.

Key topics and requirements

• Two standardized methods: Method A (buoyancy/immersion on an analytical balance with pan straddle) and Method B (density-bottle/pycnometer technique for samples that must be cut into pieces, e.g., narrow tubing or cable insulation).
• Apparatus requirements: analytical balance (precision to about ±1 mg), balance pan straddle or suspension arrangement, density bottle (pycnometer) where applicable, beakers and suitable suspension filament or sinker for immersion tests.
• Test-piece requirements: smooth, crack-free specimens; typical minimum mass about 2.5 g per test piece; duplicate tests recommended.
• Conditioning and temperature: specified laboratory conditioning and test temperatures (typical reference 23 °C ±2 °C; alternative specified conditions can apply); minimum ageing/interval requirements between forming/vulcanization and testing (e.g., minimum 16 h) to ensure comparable results.
• Test media and procedure notes: use freshly boiled then cooled distilled/deionized water for immersion; ensure removal of entrained air from the specimen (surface wetting, brief alcohol dip, gentle agitation or detergent trace as allowed) and account for filament/sinker buoyancy when calculating density.
• Calibration and precision: the standard includes precision information (informative annex) and a calibration schedule (normative annex). Laboratories are expected to follow calibration guidance (e.g., ISO calibration guides) and to report results with the required expression of results and test-report information.
• Limitations: does not provide methods for relative density (water-based ratio) and is focused on solid vulcanized and thermoplastic rubbers; alternate liquids may be used if sample density < 1 Mg/m3 and non-interaction is verified.

Summary of procedural and apparatus details and the two-method approach as specified in the standard.

Typical use and users

Routine quality-control and materials laboratories in rubber manufacturing and processing plants; product development and R&D groups characterizing compounds; test houses and certification laboratories performing property verification for specifications and purchase contracts; standards committees and technical experts referencing a harmonized method for density reporting. Laboratories use the standard to ensure repeatable density measurements for specification, mass/volume calculations and material comparisons.

Related standards

Standards commonly referenced alongside ISO 2781 include ISO 23529 (general procedures for preparing and conditioning test pieces for physical test methods) and ISO 18899 (guide to calibration of test equipment); ISO 2782 series (permeability) and other ISO/TC 45 test-method standards may be relevant for a laboratory’s full test program. National adoptions and identical national standards (e.g., BS/SS/NEN adoptions) reproduce the ISO method text with national forewords.

Keywords

density; mass per unit volume; volumetric mass; rubber; vulcanized rubber; thermoplastic rubber; buoyancy method; pycnometer; density bottle; analytical balance; conditioning; quality control; ISO 2781

FAQ

Q: What is this standard?

A: ISO 2781:2018 is the International Standard that specifies two laboratory methods for determining the density of solid vulcanized and thermoplastic rubbers.

Q: What does it cover?

A: It covers test principles, required apparatus, test-piece preparation and conditioning, test temperatures, calibration guidance, procedural steps for the two methods (immersion/buoyancy and density-bottle/pycnometer), expression of results and reporting. It does not cover relative density defined as a ratio to pure water.

Q: Who typically uses it?

A: Materials and QC laboratories in rubber production, R&D groups, test houses and conformity-assessment bodies that need standardized, repeatable density measurements for specification, production control and mass/volume calculations.

Q: Is it current or superseded?

A: ISO 2781:2018 is the current edition (Edition 5, published June 2018). The ISO catalogue shows the standard was last reviewed and confirmed in 2024 and remains current; it superseded the 2008 edition.

Q: Is it part of a series?

A: It is part of ISO/TC 45 test-method deliverables for rubber; related methods and documents (conditioning, calibration, permeability test series ISO 2782, etc.) form the wider family of physical test methods for rubber.

Q: What are the key keywords?

A: density, volumetric mass, buoyancy, pycnometer, rubber, vulcanized, thermoplastic, analytical balance, conditioning, quality control.