ISO 458-2:1985

Overview

ISO 458-2:1985 is an international standard developed by the International Organization for Standardization (ISO) that specifies a method for determining the torsional stiffness of flexible plastic materials. This part of the ISO 458 series focuses specifically on plasticized compounds of homopolymers and copolymers of vinyl chloride (PVC). It provides a precise procedure for measuring torsional stiffness over a temperature range, corresponding to key stiffness values relevant for practical applications of flexible PVC materials. The standard complements the general testing methods outlined in ISO 458-1 by addressing the particular behavior of PVC compounds when subjected to torsion.

Key Topics

• Scope and Purpose: Applies ISO 458-1 general procedures to plasticized vinyl chloride homopolymers and copolymers with an angle of deflection between 55° and 65°.
• Characteristic Stiffness Values: The standard identifies three key values of torsion stiffness to be determined:
  • 300 MPa (high stiffness region)
  • 23 MPa (intermediate stiffness)
  • 4 MPa (low stiffness region)
• Temperature Determination: The temperatures at which these stiffness values occur are established to characterize the material’s flexibility and rigidity properties over different thermal conditions.
• Test Specimens: Specifies the use of test specimens with distinct thickness ranges for accurate measurement near each stiffness value:
  • 1.8 to 2 mm
  • 2 to 5 mm
  • 4 to 5 mm
• Testing Procedure: Detailed steps for applying torque and measuring angular deflection to calculate stiffness, followed by plotting torsional stiffness logarithm against temperature to analyze the material’s behavior.
• Application of the Method: Focus on the "S-shaped" curve of stiffness versus temperature common in plasticized PVC materials, defining zones of high stiffness, intermediate transition, and low stiffness for comprehensive analysis.

Applications

ISO 458-2:1985 is critical for manufacturers, quality control laboratories, and researchers working with flexible PVC compounds, particularly when evaluating:

• Material Performance Under Temperature Variations: Understanding how plasticized PVC loses stiffness and gains flexibility at different temperatures aids in product design.
• Flexibility and Durability Analysis: Essential for products such as flexible films, curtains, tablecloths, and waterproof materials where mechanical torsional properties influence usability.
• Standardized Testing for Compliance: Enables consistent and comparable torsional stiffness results across different batches and suppliers.
• Material Development and Optimization: Helps in modifying plasticizer content or polymer blends to achieve desired flexibility properties suited for specific end-use conditions.
• Quality Assurance: Ensures materials meet stiffness requirements critical for manufacturing processes and final product performance.

Related Standards

• ISO 458-1: Plastics - Determination of stiffness in torsion of flexible materials - Part 1: General method
  Provides the foundational testing method on which ISO 458-2 builds its specific application for PVC compounds.

• ISO/R 458-1965
  The previous version of the stiffness determination method, now superseded by ISO 458-1 and ISO 458-2, reflecting updated technical revisions.

• Other ISO Standards on Plastic Testing
  Standards related to mechanical and thermal property evaluation of plastics for comprehensive material characterization.

Keywords: ISO 458-2, torsion stiffness, plasticized PVC, flexible plastics, homopolymers of vinyl chloride, copolymers of vinyl chloride, plasticized compounds, plastics testing, torsional rigidity, temperature-dependent stiffness, standard test method, ISO plastics standards.