Overview
CEN ISO/TR 20659-2:2024 addresses rheological test methods focusing on the fundamentals and interlaboratory comparisons of time-dependent structural changes, specifically thixotropy, in materials. Thixotropy describes the reversible and time-dependent decrease in shear viscosity at a constant shear rate or stress, a key property in many industrial materials such as paints, varnishes, coatings, and formulated products. This technical report, developed by CEN and based on ISO guidance, provides best practices for measuring thixotropy using various test methods, ensuring comparability and reliability between laboratories.
Standardized evaluation of thixotropy is essential for product performance in sectors such as paints, coatings, adhesives, and other materials where flow behavior under stress impacts application and final use. CEN ISO/TR 20659-2:2024 provides structured procedures and evaluation techniques for interlaboratory comparisons, supporting consistency and reproducibility in rheological testing.
Key Topics
- Definition of Thixotropy: Focuses on its characterization as a time-dependent, reversible drop in viscosity under constant shear.
- Measuring Techniques: Outlines rotational and oscillatory rheometry protocols for determining thixotropy, including profiles with ramped or stepwise changes in shear.
- Evaluation Methods: Describes how to assess hysteresis area between up and down flow curves, structural recovery rates, and indices based on viscosity or elastic moduli recovery.
- Interlaboratory Comparison: Addresses requirements for test profiles, sample preparation, calibration, and data evaluation to facilitate precision and reliability across different laboratories.
- Boundary Conditions and Controls: Emphasizes documenting temperature, shear load, sample preparation, and device calibration as crucial for reproducible results.
Applications
CEN ISO/TR 20659-2:2024 is highly relevant to industries that formulate, process, or apply materials whose structure changes over time under mechanical stress. Key applications include:
- Paints and Varnishes: Predicting leveling, sagging, brush-mark resistance, and film thickness in wet paint applications.
- Rheological Additives: Assessing the effectiveness of thixotropic agents designed to modify flow and recovery behavior.
- Coatings and Inks: Enhancing application characteristics, pigment orientation, and final surface quality.
- Construction Materials: Ensuring structural stability and pumpability of materials like mortars and adhesives during processing.
- Cosmetics, Foods, and Pharmaceuticals: Controlling application texture, shelf stability, and user experience by managing time-dependent structural changes.
By providing robust frameworks for thixotropy assessment, the standard supports product development, quality assurance, and regulatory compliance in these and related sectors.
Related Standards
Organizations and laboratories using CEN ISO/TR 20659-2:2024 should be aware of these relevant international standards:
- ISO 3219-1, Rheology - Part 1: Vocabulary and symbols for rotational and oscillatory rheometry, foundational for consistent terminology and methodology.
- ISO 3219-2: Further details on absolute measurement geometries for rheological testing.
- CEN ISO/TR 20659-1: Part 1 of this series, covering fundamentals and interlaboratory comparisons focused on yield stress and structural strength.
- ICS 87.040: Relevant to paints, varnishes, and related coatings, ensuring alignment with broader industry standardization efforts.
Using CEN ISO/TR 20659-2:2024 with related standards enhances the reliability and comparability of rheological property data, underpinning product performance and consistency in demanding industrial applications.