ISO 1158:1998

Overview

ISO 1158:1998 specifies laboratory methods for determining the chlorine content of vinyl chloride homopolymers and copolymers (PVC and related resins) that do not contain plasticizers or other additives. The standard defines two combustion-based procedures to convert bound chlorine to chloride, which is then quantified by titration. It is intended for routine quality control and analytical assessment of raw polymer material.

Key topics and technical requirements

• Two prescribed methods
  • Method A - Bomb combustion: oxidation with sodium peroxide in a combustion bomb (gas or electric ignition). Typical test load: ~0.25 g sample mixed with ~0.16 g combustion aid and layered with ~7–7.5 g sodium peroxide.
  • Method B - Oxygen flask combustion: ignition of a small (25–35 mg) sample on filter paper inside a round-bottom flask under an oxygen flow; liquid absorbent captures the released HCl.
• Chloride measurement
  • Chlorides produced are determined by potentiometric titration or the Volhard titration using silver nitrate (AgNO3) solution (0.1 mol/L or 0.05 mol/L).
• Reagents and apparatus
  • Analytical-grade reagents (AgNO3, HNO3, Na2O2, KOH, H2O2, NaNO3, oxygen gas).
  • Equipment includes a combustion bomb or suitable flask with platinum ignition wire, precision balances (0.1 mg for method A; 0.01 mg for method B), drying oven, and titration setup.
• Sample preparation
  • Samples as powder or granules; cut to 1–3 mm if required.
  • Drying: 2 h at 75 °C or 16 h at 50 °C before testing.
• Procedure controls
  • Run a blank for each method using the same reagents but no sample.
  • Report the mean of two determinations that do not differ by more than 0.2% (absolute).
• Safety and fidelity
  • Standard contains explicit safety precautions for combustion methods. Interlaboratory precision data were not available at publication; fidelity is to be established later.

Applications and who uses it

• Quality control in PVC resin manufacturing to verify chlorine (vinyl chloride) content and consistency of homopolymers and copolymers.
• Independent testing laboratories performing compositional analyses of thermoplastic resins.
• Research and development groups studying polymer composition or degradation.
• Regulatory and compliance labs requiring standardized, reproducible methods for material characterization.

Related standards and context

• Prepared by ISO/TC 61 (Plastics), SC 9 (Thermoplastic materials). For broader polymer test methods, consult other ISO plastics standards produced by ISO/TC 61. Use ISO 1158:1998 when testing unplasticized vinyl chloride polymers; other test methods may apply when additives or plasticizers are present.

Keywords: ISO 1158:1998, chlorine content, vinyl chloride homopolymers, PVC, combustion method, silver nitrate titration, potentiometric titration, Volhard, polymer quality control.