ISO 11357-6 specifies methods for determining oxidation induction time (OIT) and oxidation induction temperature in plastics using differential scanning calorimetry (DSC). It is used to assess the oxidative stability of materials, supporting quality control and durability assessment in industries like pipe manufacturing.
Scope and focus of the standard
ISO 11357-6 is an international standard titled “Plastics — Differential scanning calorimetry (DSC) — Part 6: Determination of oxidation induction time (isothermal OIT) and oxidation induction temperature (dynamic OIT).” This part of ISO 11357 establishes procedures for testing plastic materials, including polyethylene pipes, by using differential scanning calorimetry to determine their resistance to oxidative degradation. The primary aim is to measure either the oxidation induction time (OIT) under isothermal conditions or the oxidation induction temperature during dynamic heating. This information is crucial for assessing the long-term thermal stability of polymers that are exposed to heat and oxygen during processing or in service.
Classification of procedures
ISO 11357-6 specifies two main testing procedures: isothermal OIT and dynamic OIT. Isothermal OIT evaluates the time until oxidative degradation begins at a constant elevated temperature, while dynamic OIT determines the temperature at which oxidation starts as the sample is heated at a uniform rate. Both methods are used to assess the effectiveness of antioxidants present in plastic formulations or to monitor material aging during manufacturing and service life.
Importance in the plastic pipe industry
This standard is often referenced in the plastic pipe industry as part of quality assurance protocols for ensuring long-term thermal oxidation stability, especially in applications such as water and gas supply. Regulatory bodies and industry specifications may require compliance with ISO 11357-6 for product certification or acceptance.
Takeaway
ISO 11357-6 provides a structured, reliable approach for assessing the oxidative stability of plastics using DSC, contributing to consistent product quality and longevity.
Overview of the DSC-based OIT and dynamic OIT process
The procedures described in ISO 11357-6 rely on differential scanning calorimetry (DSC) to determine either the oxidation induction time at constant temperature (isothermal OIT) or oxidation induction temperature under a controlled heating rate (dynamic OIT). The test provides a precise indication of the thermal oxidation resistance of polymer samples, assisting in evaluating material composition, antioxidant effectiveness, and the effects of processing or aging.
Key steps in isothermal and dynamic OIT measurement
To perform the test as outlined by ISO 11357-6, a typical workflow includes careful sample preparation, instrument calibration, stepwise temperature control, and accurate interpretation of the DSC signal for the onset of oxidation.
Considerations for reliable results
Ensuring accurate, reproducible results requires attention to factors such as sample size, crucible type, gas purity, and heating rates. Following standard recommendations minimizes variations that could affect the detected OIT or oxidation induction temperature. Consistent results rely on controlled test conditions and careful interpretation of the observed exothermic peak in the DSC curve.
Reporting and using test data
The standard specifies the format for reporting oxidation induction time or temperature, including test conditions, signifying the stability of the material. This data can inform material selection, assess the effects of processing, and validate the effectiveness of stabilizers in pipe-grade plastics.
Best practice recommendations
Laboratories performing ISO 11357-6 tests should maintain rigorous quality assurance, including routine calibration and reference material checks, to ensure compliance and meaningful results. Proper training and periodic review of the procedure help optimize both the precision and repeatability of measurements, supporting manufacturers in meeting regulatory and industry-specific requirements.
Summary
Adhering to ISO 11357-6 ensures reliable assessment of the oxidative stability of plastics used in pipes and fittings. The stepwise procedure covers every aspect from sample handling to result interpretation, providing vital information for both quality control and product development in the plastics industry.
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