Overview
EN ISO 182-2:1999 specifies a pH method for assessing the thermal stability of compounds and products based on vinyl chloride homopolymers and copolymers (PVC). The standard measures the tendency of PVC materials to evolve hydrogen chloride (HCl) and other acidic decomposition products at elevated temperatures. It defines the concept of stability time (tS) and is intended primarily as a quality-control and characterization test for compounded PVC materials, including coloured compounds.
Key topics and requirements
- Test principle: maintain a weighed test portion at an agreed elevated temperature in a flowing inert gas stream; absorb evolved HCl in a 0.1 mol/L sodium chloride (NaCl) solution and record the change in pH to determine the amount of acid evolved.
- Stability time (tS): time measured from test start until the absorbing solution reaches a predetermined pH (commonly pH 3.8) - used as the stability/time-to-dehydrochlorination indicator.
- Apparatus & consumables:
- Dehydrochlorination cells (re-usable Cell A or disposable Cell B) and a measurement cell with magnetic stirring.
- Supply of dry, high-purity nitrogen (specified purity limits) and flow control (typical flow ~120 cm3/min ±4 cm3/min).
- pH-meter with suitable electrodes (accuracy to 0.01 pH) and chart/recorder.
- Reagents: 0.1 mol/L NaCl absorbing solution, standard NaOH and HCl for pH adjustment.
- Temperatures: typical test temperatures specified include 200 °C for unplasticized PVC and cable products, and 180 °C for plasticized PVC compounds (subject to agreement between parties).
- Sample preparation: comminution to specified particle sizes; e.g., plastisol test portions (2 g) or ground material passing through defined sieves. The method is not recommended for dry blends because of possible inhomogeneity.
- Limitations: other decomposition products can affect absorbing-solution pH; when chloride-ion measurement is required, use the conductometric/potentiometric methods (see related parts).
Applications and users
- Quality control during manufacture and conversion of PVC compounds and products.
- Materials characterization for assessing heat‑stabilizer performance and comparative thermal stability.
- Useful to R&D teams, test laboratories, cable and insulation manufacturers, compounders, and converters who need an objective measure of dehydrochlorination tendency for product development or incoming material inspection.
- Particularly valuable for coloured PVC compounds where visual discoloration tests are unsuitable.
Related standards
- ISO 182 series:
- Part 1: Congo red method
- Part 3: Conductometric method
- Part 4: Potentiometric / chloride-ion determination (recommended when other decomposition products affect pH)
- Other referenced methods for laboratory reagents and sample preparation (e.g., ISO 3696, ISO 4793, ISO 565).
Safety note: the procedure may involve hazardous materials and high temperatures - appropriate safety controls and local regulations must be followed.
