EN ISO 7327:1997

Plastics - Hardeners and accelerators for epoxide resins - Determination of free acid in acid anhydride (ISO 7327:1994)

The principle of the method specified is reacting a small amount of free acid present in a test portion of acid anhydride hardener or accelerator with rhodamine 6G to colour the test solution pink, measuring the absorbance of the coloured solution at a wavelength of about 510 nm using a spectrometer, determining the free-acid content from a calibration curve. The method is suitable for most anhydrides except for polyester and oligomeric anhydrides which may give too wide a scatter of results.

Kunststoffe - Härter und Beschleuniger für Epoxidharze - Bestimmung der freien Säure in Säurenanhydrid (ISO 7327:1994)

Dieser Internationale Norm beschreibt ein Verfahren zur Bestimmung der freien Säure in Säure-Anhydrid-Härtern und -Beschleunigern für Epoxidharze.

Plastiques - Durcisseurs et accélérateurs pour résines époxydes - Détermination de l'acide libre dans l'acide-anhydrique (ISO 7327:1994)

La présente Norme internationale prescrit une méthode pour la détermination de l'acide libre dans les durcisseurs acide-anhydride pour résines époxydes.  
NOTE 1 La méthode convient à la plupart des anhydrides, à l'exception des anhydrides polyester et oligomériques qui peuvent donner des résultats trop dispersés.

Polimerni materiali – Utrjevala in pospeševala za epoksidne smole – Določevanje proste kisline v kislinskem anhidridu (ISO 7327:1994)

General Information

• Status: Published
• Publication Date: 17-Jun-1997
• Withdrawal Date: 30-Dec-1997
• ICS: 83.080.10 - Thermosetting materials
• Technical Committee: CEN/TC 249 - Plastics
• Drafting Committee: CEN/TC 249/SC 1/WG 13 - Thermosets
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 18-Jun-1997
• Completion Date: 18-Jun-1997
• Ref Project: SIST EN ISO 7327:1999 - Plastics - Hardeners and accelerators for epoxide resins - Determination of free acid in acid anhydride (ISO 7327:1994)

Overview

EN ISO 7327:1997 (ISO 7327:1994) specifies a chemical test method for the determination of free acid in acid anhydride hardeners and accelerators for epoxide (epoxy) resins. The method reacts any free acid present with rhodamine 6G to produce a pink coloured complex whose absorbance is measured spectrometrically at about 510 nm. The free-acid concentration is obtained from a calibration curve. The procedure is suitable for most acid anhydrides but is not recommended for polyester or oligomeric anhydrides because they may give widely scattered results.

Key topics and technical requirements

• Analytical principle: formation of a coloured complex between free acid and rhodamine 6G; spectrometric measurement of absorbance at ~510 nm and calculation by calibration curve.
• Reagents and solvent purity: use analytical-grade reagents and distilled or equivalent water; dried butan-2-one (MEK) and toluene are specified - solvents must contain ≤ 20 ppm water (checked by Karl Fischer titration, ISO 760).
• Sample and reagent preparation:
  • Typical test portion: 0.2 g of sample dissolved in a solvent mixture (95 parts dried toluene : 5 parts dried butan-2-one).
  • Rhodamine 6G solution prepared and extracted into toluene as described in the method.
  • Standard free-acid solution prepared from a hydrolysed sample (procedure given in the standard) for calibration.
• Instrumentation: UV‑Vis spectrometer with 10 mm path length absorption cells; zero with dried toluene; measure absorbance within 5 minutes of colour formation because the absorbance changes with time.
• Calibration and calculation: blank correction, plot corrected absorbance vs. mass of free acid in calibration solutions, draw a calibration curve through the origin, and compute free-acid content (expressed as % mass).
• Limitations: unsuitable for certain polymeric anhydrides (polyester/oligomeric) due to poor reproducibility.

Applications and users

• Quality control and acceptance testing of acid anhydride hardeners and accelerators used in epoxy resin systems.
• Users: chemical manufacturers, resin formulators, contract testing laboratories, R&D teams in composites and coatings industries, and regulatory/compliance laboratories that require accurate free-acid quantification.
• Typical use cases: incoming raw-material inspection, batch release testing, troubleshooting curing performance linked to residual acid content, and comparative supplier evaluation.

Related standards

• ISO 760 - Determination of water (Karl Fischer) - referenced for solvent drying and water-content verification.
• EN adoption note: this method is published as EN ISO 7327:1997 under CEN adoption of ISO 7327:1994.

Keywords: EN ISO 7327:1997, ISO 7327, free acid determination, acid anhydride hardeners, epoxide resins, rhodamine 6G, spectrometer 510 nm, calibration curve, solvent drying, Karl Fischer.

Standards Content (Sample)

SLOVENSKI STANDARD
01-maj-1999
3ROLPHUQLPDWHULDOL±8WUMHYDODLQSRVSHãHYDOD]DHSRNVLGQHVPROH±'RORþHYDQMH
SURVWHNLVOLQHYNLVOLQVNHPDQKLGULGX,62
Plastics - Hardeners and accelerators for epoxide resins - Determination of free acid in
acid anhydride (ISO 7327:1994)
Kunststoffe - Härter und Beschleuniger für Epoxidharze - Bestimmung der freien Säure
in Säurenanhydrid (ISO 7327:1994)
Plastiques - Durcisseurs et accélérateurs pour résines époxydes - Détermination de
l'acide libre dans l'acide-anhydrique (ISO 7327:1994)
Ta slovenski standard je istoveten z: EN ISO 7327:1997
ICS:
83.080.10 Duromeri Thermosetting materials
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL
ISO
STANDARD 7327
First edition
1994-07-01
Plastics - Hardeners and accelerators for
epoxide resins - Determination of free
acid in acid anhydride
Plas tiques - Durcisseurs et acc6Mrateurs pour r&ines 6poxydes -
DAtermination de I ’acide libre dans I ’acide-anhydride
Reference number
ISO 7327: 1994(E)
ISO 7327:1994(E)
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 ISO
technical committees. Esch member body interested in a subject for
which a technical committee has been established has the right to be re-
presented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard ISO 7327 was prepared by Technical Committee
lSO/TC 61, Plastics, Subcommittee SC 12, Thermosetting materials.
0 ISO 1994
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronie or mechanical, including photocopying and
microfilm, without Permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-I 211 Geneve 20 l Switzerland
Printed in Switzerland
ii
INTERNATIONAL STANDARD 0 ISO ISO 7327:1994(E)
Plastics - Hardeners and accelerators for epoxide
resins - Determination of free acid in acid anhydride
1 Scope 4 Reagents
This International Standard specifies a method for the During the analysis, unless otherwise stated, use only
determination of free acid in acid anhydride hardeners reagents of recognized analytical grade and only dis-
tilled water or water of equivalent purity.
and accelerators for epoxide resins.
NOTE 1 This method is suitable for most anhydrides ex-
4.1 Butan-i-one (methyl ethyl ketone), dried us-
cept for Polyester and oligomeric anhydrides which may
give too wide a scatter of results. ing the following procedure:
Put 100 g of molecular sieve 4A into 1 litre of
butan-2-one. After allowing to settle for 24 h, decant
2 Normative reference
off the supernatant liquid, taking care that it does not
contain any molecular sieve 4A particles.
The following Standard contains provisions which,
through reference in this text, constitute provisions
Determine the water content of the dried butan-2-one
of this International Standard. At the time of publica-
by the Karl Fischer method (see ISO 760). Reject
tion, the edition indicated was valid. All Standards are
butan-2-one containing more than 20 ppm of water.
subject to revision, and Parties to agreements based
on this International Standard are encouraged to in-
4.2 Toluene, dried using the following procedure:
vestigate the possibility of applying the most recent
edition of the Standard indicated below. Members of
Put 100 g of molecular sieve 4A into 1 litre of toluene.
IEC and ISO maintain registers of currently valid
After allowing to settle for 24 h, decant off the
International Standards.
supernatant liquid, taking care that it does not contain
any molecular sieve 4A particles.
ISO 760: 1978, Determination of water - Karl Fischer
method (General method).
Determine the water content of the dried toluene us-
ing the Karl Fischer method (see ISO 760). Reject
toluene containing more than 20 ppm of water.
3 Principle
4.3 Rhodamine 6G solution.
The small amount of free acid present in a test portion
of acid anhydride hardener or accelerator is reacted
with rhodamine 6G to colour the test Solution pink.
4.3.1 Preparation
The absorbance of the coloured Solution is measured
at a wavelength of about 510 nm using a Disperse 20 mg of rhodamine 6G in IO ml of a buffer
spectrometer, and the free-acid content determined Solution [0,1 g of sodium Phosphate (Na,PO,) dis-
from a calibration curve. solved
...