ISO 182-4:1993

Overview

ISO 182-4:1993 specifies the potentiometric method for determining the tendency of PVC (vinyl chloride homopolymers and copolymers) compounds and products to evolve hydrogen chloride (HCl) and other acidic products at elevated temperatures. The method measures chloride ion concentration (reported as pCl) in an absorbing solution while a test portion is heated in a nitrogen gas stream. It is mainly recommended for compounded PVC materials and products, including plasticized and colored formulations, and can be adapted for powders under agreed conditions.

Key topics and requirements

• Principle: maintain a test portion at an agreed elevated temperature in a dry nitrogen stream, absorb evolved HCl in a measured solution, and determine HCl by potentiometric pCl measurement.
• Essential apparatus and reagents:
  • Dehydrochlorination cells (re-usable Cell A or disposable Cell B), heating oil bath (170–210 °C range), measurement cell, stirrer, flowmeter.
  • Specific chloride electrode (AgCl-based) with a precision of at least 0.01 pCl, and a suitable reference electrode (e.g., calomel or mercurous sulfate) with salt bridge where required.
  • Pure nitrogen: < 6 ppm O2 and < 0.1 ppm CO2; typical flow ~120 cm³/min ±4 cm³/min.
  • Support electrolyte and standard chloride solutions calibrated over the measurement pCl range.
• Typical test parameters:
  • Sample mass: 2 g prepared according to material type (films, pellets, plastisols).
  • Preferred test temperatures: 200 °C for unplasticized PVC and many insulating materials; 180–200 °C for plasticized PVC depending on stabilization.
  • Endpoint: record stability time (ts) as time to attain a pCl value of 3.8 in the absorbing solution.
• Precision and repeatability: perform at least two determinations per sample; follow specified calibration and electrode temperature compensation practices.
• Safety notice: method involves hazardous materials and high temperatures - users must follow appropriate safety procedures.

Applications and who uses it

• Quality control during manufacture and conversion of PVC compounds and finished products.
• Comparative evaluation of heat-stabilizing systems, plasticizers and additives by measuring dehydrochlorination tendency.
• Testing of electrical and fiber-optic insulation, coatings, films, sheets and molded PVC parts where discoloration tests are unsuitable.
• Typical users: materials laboratories, polymer producers, QC/QA engineers, testing and certification bodies, and product developers assessing thermal stability of PVC formulations.

Related standards

• ISO 182 (series) - Parts 1–3: Part 1 (Congo red), Part 2 (pH method, ISO 182-2:1990), Part 3 (conductometric, ISO 182-3:1993).
• Cited normative references include ISO 565 (test sieves), ISO 4793 (sintered filters), ISO 6353-2 (reagent specs) and ISO 5725 (precision of test methods).

Keywords: ISO 182-4:1993, potentiometric method, PVC testing, dehydrochlorination, hydrogen chloride, pCl, chloride ion, thermal stability, plastics standards.