Overview
EN ISO 8975:1995 (ISO 8975:1989) specifies a standardized laboratory method for the determination of pH of phenolic resins used in plastics manufacturing and on the market. The method covers liquid phenolic resins at the manufacturing stage and includes an informative annex (Annex A) giving a variant procedure for solid phenolic resins. The standard was prepared by ISO/TC 61 (Plastics) and is published as identical in national editions (e.g., SIST EN ISO 8975:1999).
Key topics and technical requirements
- Principle: pH is measured potentiometrically using a glass measuring electrode and a reference electrode; the potential difference is converted to pH by a calibrated pH‑meter.
- Test temperature: All measurements are carried out at 23 °C ± 0.5 °C.
- Calibration: Use two buffer or standard solutions bracketing the expected pH. Typical solutions referenced in the standard:
- Potassium hydrogen phthalate buffer, pH = 4.00 (0.05 mol/L).
- Hydrogen phosphate buffer, pH = 6.88 (≈0.025 mol/L KH2PO4 + Na2HPO4).
- Sodium tetraborate (borax) standard, pH = 9.22 (0.01 mol/L).
- Apparatus & electrodes: pH‑meter accurate to 0.1 pH units; glass measuring electrode and calomel reference electrode; follow manufacturer maintenance and reconditioning instructions.
- Sample preparation (liquid resins): Prepare a 50% (m/m) resin solution in water. If phase separation occurs, collect the aqueous phase for pH measurement. Viscous resins (>2 Pa·s) may require magnetic stirring.
- Solid resins (Annex A): Prepare an organo‑aqueous solution using a solvent mixture (water:methanol:acetone ≈ 20 g : 40 g : 40 g). Neutralize the solvent mixture to pH 7, dissolve 20 g ±1 g of finely ground resin in 80 g ±1 g solvent mix, stir with a magnetic mixer, then measure.
- Expression of results: Mean of two measurements, rounded to 0.1 pH unit.
- Test report must include: reference to the standard, resin identification, test result (and test temperature if not 23 °C), and date.
Applications and who uses it
- Quality control and production laboratories in phenolic resin manufacturing.
- Textile, adhesives, molding compound, and composite producers that use phenolic resins and require consistent pH specifications.
- Third‑party testing laboratories verifying product conformity for procurement or regulatory purposes.
- Standards and compliance teams ensuring accepted test methods are used for material certification and product data sheets.
Related standards / notes
- Prepared by ISO/TC 61 (Plastics). Published internationally as ISO 8975:1989 and adopted regionally as EN ISO 8975:1995 (also published as SIST EN ISO 8975:1999 in Slovenia).
- Annex A provides a validated alternative for solid phenolic resins and should be consulted when testing non‑liquid forms.
Keywords: EN ISO 8975:1995, ISO 8975:1989, phenolic resins pH determination, pH measurement of resins, liquid and solid phenolic resins, pH‑meter calibration, glass electrode, calomel reference electrode.