ISO 1628-2:2020

Overview

ISO 1628-2:2020 specifies a standardized laboratory method for measuring the viscosity of poly(vinyl chloride) (PVC) resins in dilute solution using capillary viscometers. The standard defines how to determine the reduced viscosity (viscosity number) and the K‑value of PVC powders (homopolymers and vinyl‑chloride‑based copolymers) dissolved in cyclohexanone under controlled conditions. It also explains limitations (volatility, solubility) and reporting rules to ensure comparable test results.

Key topics and technical requirements

• Scope and applicability
  • Applies to PVC resins in powder form where vinyl chloride is the main constituent.
  • Excludes resins with volatile‑matter content > 0.5 % ± 0.1 % (ISO 1269) or those not fully soluble in cyclohexanone.
• Solvent and materials
  • Cyclohexanone with specified kinematic viscosity and boiling point (≈155 °C); store protected from light.
• Solution preparation
  • Typical test solution: 0.250 g resin in a 50 ml volumetric flask → concentration 5 kg/m3 (5 g/L).
  • Dissolve by agitation at 80–85 °C for 1 hour, cool to 25 °C ± 1 °C, then make up to mark.
• Apparatus and conditions
  • Capillary viscometer model 1C (capillary ≈0.77 mm) as reference (ISO 3105).
  • Controlled bath temperature: 25.0 °C ± 0.5 °C, stability ±0.05 °C.
  • Filtration before viscometer filling; strict cleaning and verification procedures.
• Measurement and calculation
  • Measure efflux times for solvent (t0) and solution (t); discard first reading.
  • Reduced viscosity I calculated as I = (t − t0) / (t0 · c).
  • K‑value computed per ISO 1628‑1 formula (reported to 1 decimal); tables in Annex A aid lookup for the standard concentration.
  • Precision checks: repeat determinations, tolerance limits (e.g., successive solution times within 0.25 %, solvent times within 0.2 s).
• Limitations
  • Reduced viscosity and K‑value are related to molecular mass but not directly interchangeable across different copolymer types or concentrations.
  • Limiting viscosity number is not used for PVC resins.

Applications and users

• Quality control and batch acceptance at PVC resin manufacturers
• Incoming inspection for compounders, formulators and converters
• Analytical and R&D labs assessing molecular‑mass-related properties
• Comparative testing of recovered polymer fractions from chemical analysis (with caution about impurities)
• Regulatory and procurement specifications where standardized viscosity/K‑value reporting is required

Related standards

• ISO 1628‑1:2009 - General principles for dilute‑solution viscosity measurements
• ISO 1269 - Determination of volatile matter in PVC
• ISO 1042 - One‑mark volumetric flasks
• ISO 3105 - Glass capillary kinematic viscometers

Keywords: ISO 1628-2:2020, PVC resins, poly(vinyl chloride), reduced viscosity, K‑value, capillary viscometer, cyclohexanone, polymer viscosity testing.