ISO 11358 Plastics - Thermogravimetry (TG) of Polymers

The “ISO 11358 Plastics - Thermogravimetry (TG) of Polymers” standard, developed by the International Organization for Standardization (ISO), essentially consists of the following three sections published under the same title:

• “ISO 11358-1 Part 1: General principles” standard describes the general conditions for the analysis of polymers using thermogravimetric methods. It is valid for liquids or solids. Solid materials can be in the form of pellets, granules or powders. Manufactured shapes that have been reduced to a suitable sample size can also be analyzed by this method. This standard specifies methods for investigating physical effects and chemical reactions associated with mass changes. In addition, this standard is used to determine the temperature and speed of decomposition of polymers and to measure the amount of volatile matter, additives and fillers they contain. Also, this standard is valid for measurements in dynamic mode (temperature or time according to mass change under programmed temperature conditions) or isothermal mode (time according to mass change at constant temperature). This standard is valid for measurements in different test atmospheres, such as the separation of decomposition from oxidative degradation in an inert atmosphere.

For the purposes of this standard, the following terms and definitions apply:

• Dynamic mass change determination is the technique of recording the change in mass of a test sample with temperature as it changes at a programmed rate.
• Isothermal mass change determination is a technique of recording the change in mass of a test sample with time at constant temperature.
• Curie temperature refers to the temperature at which a ferromagnetic material transitions from a ferromagnetic state to a paramagnetic state or vice versa.

A test sample is heated at specified rates by a controlled temperature program and the change in mass is measured as a function of temperature (dynamic mass change determination). Alternatively, the sample is held at a specified constant temperature and the change in mass is measured as a function of time for a specified period of time (isothermal mass change determination).

During measurement, the test sample is held in a controlled inert, oxidizing, or otherwise reactive atmosphere. In general, reactions that cause the mass of a test sample to change are decomposition or oxidation reactions or evaporation of a component. In some cases, measurements with special reaction gases may also be made.

The change in mass is recorded as a thermogravimetric (TG) curve with respect to temperature or time. The change in mass of a material with respect to temperature and the extent of this change are indicators of the thermal stability of the material. Therefore, thermogravimetric data can be used to assess the relative thermal stability of polymers in the same general family and polymer-polymer or polymer-additive interactions using measurements made under the same test conditions.

• The standard “ISO 11358-2 Part 2: Determination of activation energy” describes a test method for determining the activation energy of the Arrhenius formula for the separation of polymers using a thermogravimetric technique. This method is applicable only if the reaction proceeds by a single mechanism. This method can be applied to multistage reactions if the reaction consists of clearly separated single-stage steps.

For the purposes of this standard, the following terms and definitions apply:

• The Arrhenius formula is a formula that represents the temperature dependence of the rate constant of a reaction.
• Activation energy is the energy above the ground state that must be added to an atomic or molecular system to allow a particular process to occur.
• Degree of conversion refers to the amount of product present at a given time and temperature during a reaction compared to the final amount of products.

Test samples are heated at several different heating rates and the mass change is measured as a function of temperature. For each heating rate, temperatures corresponding to given degrees of transformation are determined. For a given degree of transformation, the logarithm of the heating rate is plotted against the inverse of the absolute temperature and the activation energy is calculated from the slope of the line thus obtained.

• The standard “ISO 11358-3 Part 3: Determination of activation energy using the Ozawa-Friedman plot and analysis of reaction kinetics” describes an analysis method for determining activation energy using the Ozawa-Friedman plot. This standard also specifies the preparation of master plots for the verification of reaction kinetics determined by thermogravimetry. The Ozawa-Friedman plot (logarithm of the inverse of the absolute temperature with the mass loss rate at a specified mass loss) is a derivative method that can be applied to data obtained with any mode of temperature change in thermal analysis. For example, isothermal, constant heating rate, sample controlled thermal analysis, temperature jump and repeated temperature sweep.

For the purposes of this standard, the formulas for conversion, generalized time, and generalized conversion rate are given in the standard. In addition, the term master curve refers to a graph that can be used to evaluate results and investigate reaction kinetic models. Examples of master curves include conversion vs. generalized time, conversion vs. generalized conversion rate, and generalized conversion rate vs. generalized time.

Test samples are heated using any temperature profile and the change in mass is measured as a function of temperature and time. At a given transformation, the logarithm of the transformation rate is compared with the inverse of the absolute temperature and the activation energy is calculated from the slope of the straight line fitted to the data thus obtained. At least two of the master curves provide confirmation of the reaction kinetic analysis.

Our organization, which has been trying to support businesses from every sector with its wide range of testing, measurement, analysis and evaluation studies for years, has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. In this context, testing services in accordance with the "ISO 11358 Plastics - Thermogravimetry of Polymers (TG)" standard are also provided to businesses.