TGA continuously weighs a material as it is heated; therefore, it records all weight losses versus the temperature at which they occur. Water evaporates first, followed by volatile components and plasticizers; then the polymer itself breaks down, and the residue is filler and ash. One experiment with a 10 mg sample divides everything. MatX Lab conducts TGA on plastics, rubber formulations, coatings, powders, and composite materials.
What Is Thermogravimetric Analysis?
A microbalance holds the sample inside a furnace under a controlled atmosphere and can detect very small mass changes, down to fractions of a microgram. As the temperature increases, each component decomposes at its own characteristic temperature, causing the trace to step down.
The derivative of this trace provides much of the useful information. What may appear as a single event on the mass curve can often separate into two distinct peaks on the derivative curve. These two peaks can help distinguish between a single polymer and a polymer blend.
Switching between atmospheres allows separating the rest. The sample is initially heated in nitrogen to about 600 °C. This decomposes the organic part but does not burn the carbon. The atmosphere is switched to air, oxidizing the carbon black and leaving inorganic ash as the residue. This sequence enables separation of the polymer, carbon black, and mineral filler in one experiment.
Thermogravimetric Analysis Applications and Sample Types
Almost any solid or viscous material can be tested as long as it fits in the pan. If the material tends to foam, spit, or expand violently when heated, use a smaller sample with a suitable lid arrangement.
Where TGA does the work:
- Filling and reinforcement materials. Determination of glass, mineral, or carbon loadings in a mixture directly, without calcination in a muffle furnace and loss of volatile information.
- Moisture and residual solvent. Quantifying what leaves below 200 °C, which often explains a molding defect nobody could otherwise account for.
- Material identification support. Using decomposition profile and residue alongside DSC and infrared work to confirm what a material is.
- Incoming and failure checks. Comparing a suspect lot or a failed part against a known-good reference on the same program.
- Rubber compositional analysis. Separation of oil, polymer, carbon black, and ash in a single step, on which the ASTM D6370 method relies.
- Rubber compositional analysis. Separation of oil, polymer, carbon black, and ash in a single step, on which the ASTM D6370 method relies.
- Thermal stability order. Onset of degradation and mass loss at 5% temperatures are compared among alternative materials. When the focus is on transitions and enthalpy rather than mass changes, differential scanning calorimetry (DSC) under ASTM D3418 is appropriate. If the aim is to identify the gases released during the process rather than simply quantify them, TGA can be coupled with infrared spectroscopy or mass spectrometry to provide that information.
How Thermogravimetric Analysis Works
Sample size and heating rate need to be balanced. Smaller samples and slower heating rates help separate and resolve overlapping events, while larger samples and faster heating rates allow samples to be processed more quickly.
| Step | What happens |
| Sampling | A representative piece is taken. On a filled compound, this matters more than usual, since filler distribution is rarely perfectly uniform. |
| Sample loading | Place 5 mg to 20 mg in a platinum or alumina pan, ensuring good contact with the pan base and no material touching the walls. |
| Baseline and calibration | Balance baseline and temperature calibration are verified, and a blank pan run corrects for buoyancy where precision demands it. |
| Purge setup | Nitrogen purges the furnace at a constant recorded flow, with the switch point to air programmed where compositional analysis is required. |
| Heating programme | The furnace ramps at a set rate, commonly 10 °C/min to 20 °C/min, through the full range required. |
| Atmosphere switch | At the programmed temperature, the purge switches to air, oxidizing carbonaceous residue and separating it from inorganic ash. |
| Data collection | Mass, temperature, and time are logged continuously, and the derivative curve is generated from the mass trace. |
| Evaluation | Step sizes are integrated as mass percentages, onset and peak temperatures are extracted, and residue is reported at the final temperature. |
Limitations: The heating rate changes the temperature at which decomposition is recorded. A decomposition onset measured at 10 °C/min, for example, will differ from one measured at 20 °C/min, so use the same heating rate when comparing results from different laboratories.
In blends and complex compounds, two or more decomposition steps can occur at similar temperatures, making them hard to distinguish. The derivative curve can make these changes easier to see, but it does not always separate them completely. TGA shows the change in mass, but it does not tell you what caused that change. A mass loss at 300 °C, for instance, could come from a plasticizer, oil, or a low-molecular-weight fraction. To identify the material, TGA needs to be combined with another technique or used alongside complementary analysis. Sample size can affect the result as well. If the sample is less than 5 mg, small mass changes may be difficult to pick up. With a larger sample, heat can take longer to reach the whole sample, and some of the gases produced during decomposition may get trapped. Decomposing fillers can add another source of mass loss. Calcium carbonate, for example, releases carbon dioxide above roughly 600 °C. If the filler is not known to be present, this loss could be mistaken for polymer decomposition. Sample inhomogeneity is another issue. A 10 mg sample taken from a compound containing 30% filler may not represent the material evenly.
Thermogravimetric Analysis Detection Limits and Capabilities
| Capability | Typical performance |
| Balance resolution | Fractions of a microgram |
| Sample mass | 5 mg to 20 mg typical, adjusted for inhomogeneous materials |
| Quantification | Mass percentage per step, typically to a few tenths of a percent |
| Isothermal capability | Hold at temperature to measure mass loss against time |
| Material supplied | 1 g minimum, more for inhomogeneous or filled compounds |
Send more material than the pan needs. Representative sampling on a filled compound means taking several pieces from different locations. A single 20 mg chip cut from one spot describes that spot and nothing else.
Tell us what you expect to find in the sample. If we know, for example, that a compound contains calcium carbonate or that a coating contains a solvent, we can set the temperature program and atmosphere change accordingly, so the different events can be seen separately rather than running together.
Thermogravimetric Analysis Data Output and Reporting
Your report provides the mass loss curve and its derivative for each specimen, with each step quantified as a percentage of the original mass.
Step temperatures are reported with the basis named, covering onset, midpoint, and derivative peak. The residue at the final temperature is reported, along with the temperature and atmosphere under which it was measured. Where compositional analysis was the purpose, the report breaks out volatiles, polymer, carbonaceous residue, and inorganic ash as separate figures.
Every trace includes the run conditions, including sample mass, pan material, heating rate, purge gases and flow rates, and the point at which the atmosphere is switched. If something in the trace does not match the expected profile, it is noted and described. In many cases, an unexplained step turns out to be the most important finding.
Thermogravimetric Analysis FAQs
Can TGA tell me what polymer this is?
The decomposition profile and the amount of residue can narrow down the possibilities considerably. When combined with DSC and infrared analysis, the results usually give a clear answer. On its own, though, TGA only shows mass loss and does not identify the chemistry involved.
How accurate is filler content?
Good to a few tenths of a percent on a homogeneous sample. The limiting factor is almost always sampling rather than the instrument, which is why we ask for enough material to take several specimens.