ISO-14897-2002.pdf

Reference number ISO 14897:2002(E) © ISO 2002 INTERNATIONAL STANDARD ISO 14897 Second edition 2002-06-15 Plastics Polyols for use in the production of polyurethane Determination of water content Plastiques Polyols pour la production du polyuréthanne Dosage de l'eau ISO 14897:2002(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this area. Adobe is a trademark of Adobe Systems Incorporated. Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. © ISO 2002 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.ch Web www.iso.ch Printed in Switzerland ii © ISO 2002 All rights reserved -,-,- ISO 14897:2002(E) © ISO 2002 All rights reserved iii Contents Page Foreword.iv 1 Scope1 2 Normative references1 3 Terms and definitions .1 4 Principle2 5 Application .2 6 Interferences 2 7 Reagents.2 8 Apparatus.3 9 Sampling.4 10 Standardization of reagent .5 11 Procedure.5 12 Expression of results6 13 Precision and bias.6 14 Test report7 Annex A (informative) Interlaboratory precision studies8 -,-,- ISO 14897:2002(E) iv © ISO 2002 All rights reserved 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. Each member body interested in a subject for which a technical committee has been established has the right to be represented 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. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3. The main task of technical committees is to prepare International Standards. 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. Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 14897 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 12, Thermosetting materials. This second edition cancels and replaces the first edition (ISO 14897:2000), which has been technically revised. The principal technical change is the incorporation of significantly improved precision data. The standard is based on ASTM D 4672, Standard Test Methods for Polyurethane Raw Materials Determination of Water Content of Polyols. -,-,- INTERNATIONAL STANDARD ISO 14897:2002(E) © ISO 2002 All rights reserved 1 Plastics Polyols for use in the production of polyurethane Determination of water content CAUTION Persons using this International Standard should be familiar with normal laboratory practice. This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and to ensure compliance with any national regulatory conditions prior to use. 1 Scope This International Standard specifies methods used to measure the water content of polyols employed as polyurethane raw materials. Method A is a manual amperometric method which has been included to better define the principles of the Karl Fischer measurement. Amperometric methods are applicable to a wide range of polyols, including those which have enough colour to obscure a visual end-point. Method B includes an automated amperometric procedure and an automated coulometric procedure. The coulometric procedure is an absolute method that does not require calibration and gives improved sensitivity compared with amperometric methods. 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 3696:1987, Water for analytical laboratory use Specification and test methods ISO 6353-1:1982, Reagents for chemical analysis Part 1: General test methods ISO 6353-2:1983, Reagents for chemical analysis Part 2: Specifications First series ISO 6353-3:1987, Reagents for chemical analysis Part 3: Specifications Second series 3 Terms and definitions For the purposes of this International Standard, the following terms and definitions apply. 3.1 polyol an organic compound containing two or more hydroxyl groups suitable for reaction with isocyanates 3.2 polyurethane a polymer prepared by the reaction of an organic di- or polyisocyanate with compounds containing two or more hydroxyl groups NOTE Polyurethanes may be thermosetting, thermoplastic, rigid or soft and flexible, cellular or non-cellular. -,-,- ISO 14897:2002(E) 2 © ISO 2002 All rights reserved 4 Principle 4.1 Methods A and B are based on amperometric or coulometric titrations with Karl Fischer reagent. The sulfur dioxide in the reagent first reacts with the alcohol to form an ester which is neutralized by the base present in the reagent. The anion of the alkyl sulfurous acid is the reactive component. The titration of water present constitutes the oxidation of the alkyl sulfite to alkyl sulfate by the iodine, which consumes the water. The reaction can be formulated as follows:1) ROH + SO2 + R¢N (R¢NH)SO3R H2O + I2 + (R¢NH)SO3R + 2R¢N (R¢NH)SO4R + 2(R¢NH)I 4.2 To determine water, Karl Fischer reagent a solution of iodine, sulfur dioxide, ethylene glycol monomethyl ether (HOCH2CH2OCH3) and pyridine or a pyridine substitute is added to a solution of the test portion in methanol or another alcohol until all of the water present has been consumed. In an amperometric titration, this is evidenced by a current-measuring device that indicates the depolarization of a pair of platinum electrodes. In coulometric titrations, the iodine reagent is generated electrically, thus eliminating the need for standardization of the reagent. 5 Application These test methods are suitable for quality control, as a specification test for products, and for research. The water content of a polyol is important because water reacts with isocyanates to form carbon dioxide and an amine which consumes additional isocyanate. NOTE The description of the manual system presented below is principally for reference purposes and has been included in order to better define the principles of the Karl Fischer measurement. Commercially available automated Karl Fischer titrators of the type described in Method B are used extensively. Additional details and diagrams are available in ISO 760:1978, Determination of water Karl Fischer method (General method). 6 Interferences 6.1 Oxides, hydroxides and strongly basic compounds react with Karl Fischer reagent, producing an equivalent amount of water, thus giving falsely high results. Therefore, this method shall not be used for crude polyols containing KOH or other highly basic products unless corrections are made for the excess water produced. 6.2 Amine-based polyols may shift the pH of the Karl Fischer system into the alkaline range, causing incorrect results. This problem may be circumvented by adding salicylic or benzoic acid in greater than stoichiometric amounts before carrying out the titration. Tests should be run to determine the suitability of the procedure for a particular polyol type. 7 Reagents 7.1 Purity of reagents Reagent-grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of ISO 6353-1, ISO 6353-2 and ISO 6353-3. Other grades may be used, provided that it is first determined that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination. 1) Scholz, Eugen: Karl Fischer Titration, Springer-Verlag, Berlin, Heidelberg, New York, 1984. -,-,- ISO 14897:2002(E) © ISO 2002 All rights reserved 3 7.2 Purity of water Unless otherwise indicated, references to water shall be understood to mean grade 3 water as defined in ISO 3696. 7.3 Reagents for Method A (manual titration) 7.3.1 Karl Fischer reagent, equivalent to 2,5 mg to 3,5 mg of water/ml. Dilute commercially available stabilized Karl Fischer reagent (6 mg of water/ml) with an equal volume of anhydrous ethylene glycol monomethyl ether (containing less than 0,1 % of water). NOTE Improved, pyridine-free Karl Fischer reagents have been made available and are highly recommended as a replacement for the previous reagents. 7.3.2 Titration solvent (anhydrous methanol): Unless the methanol is extremely dry, it will require a large amount of dilute Karl Fischer reagent to react with its residual water. For this reason, dry the solvent further by adding undiluted Karl Fischer reagent (6 mg of water/ml) to a bottle of methanol until a light red-brown colour persists. Then add methanol until the solution is a pale yellow. A 100 ml portion of the treated solvent should require 1 ml to 10 ml of dilute Karl Fischer reagent. 7.4 Reagent for Method B 7.4.1 Karl Fischer reagent: Commercial reagents and reagent systems of various types are available for use with autotitrators for water determination. These pyridine-free reagents have improved stability and a less objectionable odour than the conventional Karl Fischer reagent. Reagents can be purchased in split or composite forms in different concentrations to fit various ranges of water content. A composite reagent contains all of the components required for a Karl Fischer titration in a single solution. A split reagent implies separate solutions of the solvent and titrant. 8 Apparatus 8.1 Apparatus for Method A (manual titration) 8.1.1 Titration vessel: A vessel of approximately 300 ml capacity, such as a tall-form, lipless beaker provided with a tight-fitting closure to protect the reaction mixture from atmospheric moisture. The vessel shall also be fitted with a nitrogen inlet tube, a 10 ml burette, a stirrer (preferably magnetic) and a port that may be opened momentarily for sample and solvent addition, or removal of electrodes. It is convenient to provide a vacuum line leading to a 1 litre trap bottle for drawing off the titrated solution. Pass the nitrogen through a drying tube containing anhydrous calcium sulfate before it enters the titration vessel. 8.1.2 Instrument electrodes, platinum, with a surface equivalent of two No. 26 wires, 4,76 mm long. The wires shall be 3 mm to 8 mm apart and inserted in the vessel so that 75 ml of solution will cover them. 8.1.3 Instrument depolarization indicator, having an internal resistance of less than 5 000 W, consisting of a means of applying and indicating a voltage of 20 mV to 50 mV across the electrodes, and capable of indicating a current flow of 10 µA to 20 mA by means of a galvanometer or ratio tuning circuit. 8.1.4 Burette assembly, for Karl Fischer reagent, consisting of a 10 ml burette with 0,05 ml subdivisions and connected by means of glass or polyethylene (not rubber) connectors to a source of reagent. Various types of automatic dispensing burette may be used. Since the reagent loses strength when exposed to moist air, all vents shall be protected against atmospheric moisture by adequate drying tubes containing anhydrous calcium sulfate. All stopcocks and joints shall be lubricated with an inert lubricant. 8.1.5 Weighing pipette, approximately 1 ml. 8.1.6 Syringes, 1 ml and 10 ml, suitable for weighing and delivering viscous liquid samples. -,-,- ISO 14897:2002(E) 4 © ISO 2002 All rights reserved 8.1.7 Analytical balance, capable of weighing to 0,1 mg. 8.2 Apparatus for Method B (automated titration) 8.2.1 Autotitrator: Several commercial autotitrators are available for amperometric or coulometric titrations and provide results equivalent to or better than those of the manual procedure described in Method A. These instruments consist of an automated burette assembly, a sealed titration vessel with appropriate electrodes and associated circuitry, and a means for removal of solution after analysis. These automated systems provide several advantages. Atmospheric-moisture contamination can be more closely controlled, calibration is simplified and the preneutralization step is automatic. Titrations are rapid and reagent consumption is low. The newer autotitrators automatically calculate and display or print out the water concentration. 8.2.2 Syringes, 1 ml and 10 ml, suitable for weighing and delivering viscous liquid samples. 8.2.3 Analytical balance, capable of weighing to 0,1 mg. 9 Sampling 9.1 It is essential to avoid changes in the water content of the material during sampling operations. Many polyols are quite hygroscopic, and errors from this source are particularly significant in the determination of the small amount of water usually present. It has been demonstrated that increases in the water content of hygroscopic liquids