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Thermogravimetric Analysis (TGA)

Tire Rubber Chemistry by TGA

Thermal Gravimetric Analysis (TGA) works by monitoring the weight loss of a sample as a function of Time, Temperature, and Gas Environment allows the components of a product to be quantified. The Automated Gas Switching System typically is set to start the run in an inert gas (high purity nitrogen) and then later in the run change to air. This allows the quantification of combustible components that will not pyrolyze and the rubber component that falls into this category is carbon black.

For a rubber sample analyzed by TGA, the run starts in nitrogen and ramps the temperature up to 600 °C at 10 °C per minute. Between room temperature and 300 °C weight is lost due to the volatization of plasticizers, lubricants, stabilizers, and other small molecules. Between 300 °C and 600 °C, the polymer backbone cracks down into volatile fragments and the weight loss in this stage is taken as the polymer content. After a few minutes at 600 °C in nitrogen, the gas is switched to air and the carbon black is combusted with the weight loss after 15 minutes in air at 600 °C is directly related to the carbon black content. The temperature is again ramped up at 10 °C per minute to 900 °C and any calcium carbonate present decarboxylates leaving calcium oxide. Based on the molecular weight ratios of calcium oxide and calcium carbonate, the CaCO3 content can be calculated from the weight lost in this step. The remaining mass of material is all mineral ash content (subject to the carbonate loss) and the ash can be analyzed by SEM-EDXS for elemental coposition.

The required sample size is usually 10 to15 milligrams for each run and we always run samples in duplicate. If duplicate runs are not identical, we run more until we have consistent results.

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