ISO 18373-2:2008

Overview

ISO 18373-2:2008 specifies a laboratory method for measuring the enthalpy of fusion of crystallites in rigid PVC pipes using differential scanning calorimetry (DSC). The procedure quantifies the latent heat absorbed when secondary PVC crystallites melt, providing insight into the pipe's thermal history and processing quality. The method is suitable for all types of rigid PVC pipes and can be adapted for other extruded rigid PVC products with appropriate sampling.

Key topics and technical requirements

• Scope: Determination of the enthalpy of fusion (∆H, in J/g) of secondary crystallites in rigid PVC pipe samples via DSC.
• Apparatus: Calibrated DSC instrument with software, aluminium sample pans, inert purge gas (e.g., nitrogen/argon), analytical balance (±0.01 mg), and low‑speed cutting tools to avoid heating or stressing samples.
• Sampling and sample prep:
  • Take at least four samples from the pipe centre at 0°, 90°, 180° and 270° around the circumference.
  • Test piece mass: (20 ± 10) mg; maximize contact between sample and pan (thin disks recommended).
• Test parameters:
  • Start temperature: (35 ± 15) °C
  • End temperature: 225 °C
  • Heating rate: (20 ± 1) °C/min
  • Purge gas flow: (20 ± 5) ml/min
• Measurement and data handling:
  • Identify A‑onset (secondary crystallite melting, typically 100–120 °C) and B‑onset (close to maximum processing temperature).
  • Enthalpy ∆H is the net area between A‑onset and B‑onset after subtracting additive peaks; normalize ∆H for PVC content (divide by PVC mass fraction).
  • Use instrument zoom and baseline subtraction; discard noisy or irregular scans.
• Quality control:
  • Repeat samples: if standard deviation from three repeats at the same location > 1 J/g, discard the furthest outlier and retest; persistent variance may indicate recalibration or sample issues.
  • Watch for additive peaks and other thermal events (see Annexes on sources of error and additive effects).

Applications and users

• Applications:
  • Assessing processing quality and thermal history of rigid PVC pipes.
  • Detecting local variations in crystallinity around the pipe circumference.
  • Supporting product development, process optimization and quality control.
• Who uses it:
  • Materials scientists, polymer analysts and laboratory technicians working on PVC pipes.
  • QC/QA teams in pipe manufacturing and extrusion facilities.
  • R&D groups evaluating compound formulations, stabilizers or processing changes.
  • Certification bodies and testing laboratories performing standardized PVC pipe tests.

Related standards

• ISO 18373-1 (Part 1): Measurement of the processing temperature - complements Part 2 by defining processing temperature determination.
• Other DSC and PVC characterization literature referenced in the standard (for instrument technique and interpretation).

Keywords: ISO 18373-2:2008, rigid PVC pipes, DSC, differential scanning calorimetry, enthalpy of fusion, PVC crystallites, processing temperature, PVC quality control.