ISO 17744:2004

Overview

ISO 17744:2004 - Plastics: Determination of specific volume as a function of temperature and pressure (pvT diagram) - Piston apparatus method defines procedures to measure the specific volume (v) of plastics in both molten and solid states using a piston-equipped measurement cell. The standard describes isobaric (constant-pressure) and isothermal (constant-temperature) test modes to generate pvT diagrams and to derive volumetric properties such as compressibility and thermal-expansion coefficients. Results support polymer processing simulation and dimensional‑shrinkage prediction.

Key topics and technical requirements

• Test principle: A known-mass sample is confined in a cylindrical measurement cell and pressurized by a piston; piston movement is translated to volume change as temperature or pressure is varied.
• Measurement modes:
  • Isobaric (constant pressure) - temperature varied (note: in constant-pressure mode, the standard restricts heating/cooling rates to ≤ 5 °C/min unless corrected for thermal gradients).
  • Isothermal (constant temperature) - pressure varied.
• Outputs: pvT diagrams; volumetric compressibility (βv); volumetric thermal-expansion coefficient (αv); identification of first-order and glass transitions as functions of temperature and pressure.
• Apparatus requirements (select highlights):
  • Measurement cell inside diameter 5–12 mm, constant to ±0.01 mm; inside surface hardness ≥ 800 HV30 and roughness Ra < 0.25 µm.
  • Piston hardness lower than cylinder but ≥ 375 HV30; seals inert and temperature‑resistant (e.g., PTFE up to ~280 °C).
  • Piston position accuracy ±5 µm; temperature sensor resolution 0.1 °C; pressure-sensor calibration error ≤ 1% of range (load cell class 1 per ISO 7500-1).
• Calibration & corrections: Equipment pvT behaviour (cell, piston, seals) must be characterized and subtracted; sampling, pre‑compression and thermal gradients are identified error sources.
• Data integrity: The standard prescribes reporting conventions, precision information and test‑report content to ensure reproducible pvT data.

Applications and who uses it

• Polymer processing engineers and simulation specialists use pvT data for injection‑moulding and extrusion simulations to predict packing, shrinkage and dimensional change.
• Materials scientists and R&D labs characterize phase transitions (glass and crystallization) under pressure/temperature conditions.
• Quality-control laboratories validate lot‑to‑lot consistency of thermophysical properties.
• Test-house and instrument manufacturers design and calibrate piston‑type pvT apparatus to meet ISO 17744:2004 requirements.

Related standards

• ISO 17282 - Guide for acquisition and presentation of design data (recommended isobaric cooling practice for processing design).
• ISO 1183, ISO 4287, ISO 6507-1, ISO 7500-1 - referenced for density, surface texture, hardness and force‑measurement verification.

Keywords: ISO 17744:2004, pvT diagram, piston apparatus method, specific volume, plastics testing, isobaric measurement, isothermal measurement, volumetric compressibility, thermal-expansion coefficient, polymer processing.