Overview
EN ISO 119:1998 defines a standardized iodometric method for the semi-quantitative determination of free phenols in phenol-formaldehyde plastics mouldings. This international standard, developed by CEN in alignment with ISO 119:1977, is crucial for assessing the chemical composition and safety of phenolic moulded products. The method focuses on extracting free phenols from powdered samples via hot water, followed by iodination and back titration of excess iodine with a volumetric sodium thiosulphate solution. Accurate measurement of free phenol content is essential due to its influence on the degree of cure and potential contamination risks when phenolic plastics contact foodstuffs or other sensitive materials.
Key Topics
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Scope and Field of Application
- Suitable for phenol-formaldehyde mouldings made from thermosetting plastics.
- Provides a semiquantitative measure of free phenols affecting product quality and safety.
- Important for quality control during manufacturing and for regulatory compliance.
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Method Principle
- Extraction of free phenols using hot water from powdered test material.
- Iodination of the aqueous extract in presence of sodium tetraborate.
- Back titration of unreacted iodine with standard sodium thiosulphate solution using starch as an indicator.
- Calculation based on the stoichiometric reaction between iodine and phenol molecules.
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Sample Preparation
- Mouldings reduced to powder by filing, milling, grinding, or drilling, carefully avoiding heating.
- Sieved to obtain a uniform particle size (nominal aperture of 250 µm).
- Extraction performed within 1 hour of powder preparation to ensure consistent results.
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Chemical Reagents and Apparatus
- Reagents include sodium tetraborate, iodine solution (~0.05 N), sulphuric acid (2 N), standard sodium thiosulphate solution, and starch indicator.
- Typical laboratory glassware and equipment like pipettes, burettes, sieve, flasks, and analytical balance are required.
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Calculation and Reporting
- Results expressed as percentage by mass of phenol (C6H5OH).
- Test report must include sample identification, method details, free phenol amount, and date of test.
- Method influenced by sample powdering approach, which should be agreed upon when used as a referee method.
Applications
Related Standards
- ISO 565 - Test sieves for particle size standardization, applicable to sample preparation.
- ISO/R 385 - Requirements for precision laboratory burettes used in volumetric analysis.
- ISO 648 - Laboratory glassware specifications, including single-mark pipettes essential to this procedure.
- ISO/TC 61 - Technical Committee on plastics responsible for developing related plastics testing standards.
Keywords: phenol-formaldehyde mouldings, free phenols determination, iodometric method, phenolic plastics testing, CEN standard, ISO 119:1977, thermosetting plastics, chemical analysis, volumetric titration, phenol content testing.