What is the TGA test for rubber products?

Many rubber parts look similar, but the compound inside can be totally different and even unknown.

The TGA test (thermogravimetric analysis) for rubber measures weight loss of a sample as temperature rises, so we can understand polymer type, fillers, volatiles, and thermal stability in a rubber compound.

When I work with new customers, they sometimes send me old samples without any data sheet. In these cases, TGA is one of my favorite tools. It helps me “see inside” the rubber without cutting it open in a chemical lab.

How does the TGA test work for rubber compounds?

Rubber burns, smokes, and loses weight when it gets hot, but this process actually follows a pattern.

In a TGA test, a small piece of rubber is heated in a controlled atmosphere on a sensitive balance, and the instrument records how the sample weight changes with temperature or time.

🧪 What really happens inside a TGA test?

I will describe the process in simple steps, the same way I explain it to buyers during a factory visit.

1️⃣ Prepare a small sample

I cut or punch a tiny piece of rubber, usually a few milligrams.

• I avoid metal inserts and big contamination.
• I note the sample ID, part number, and batch.

This piece goes into a small open pan in the TGA instrument¹.

2️⃣ Place the sample on a micro-balance²

Inside the TGA, a very sensitive balance holds the pan.

• The balance can “feel” microgram-level weight changes.
• The system controls temperature and gas flow at the same time.

Typical gases are nitrogen (inert) or air/oxygen (oxidative).

3️⃣ Heat according to a program

The instrument heats the sample at a set rate, such as 10 °C per minute.

There are two common modes:

• 🔥 Nitrogen first, then air

  • Nitrogen shows polymer decomposition³.
  • Air then burns away carbon and shows ash content.

• 🔥 Only nitrogen or only air

  • Used for special studies or when we only care about one effect.

4️⃣ Record weight loss vs temperature

As the sample heats, it may lose:

• Volatile components and moisture.
• Plasticizers, softeners, processing oils.
• Polymer mass as the chain breaks down.
• Carbon black leaving only ash and minerals.

The TGA software draws a curve:

• The TGA curve⁴ shows remaining mass vs temperature.
• The DTG curve⁵ (derivative) shows where weight loss is fastest.

5️⃣ Analyze the curve

From the steps and plateaus in the curve, I can estimate:

• How much volatile content or oil is present.
• Approximate polymer fraction.
• Amount of fillers and ash.
• Thermal stability and decomposition start temperature.

🧾 Simple process overview

Step	What the instrument does	What I learn from it
Loading	Weighs sample at room temp	Initial mass
Heating 1	Heats to medium temp in N₂	Volatiles, plasticizers, early changes
Heating 2	Heats to high temp in N₂	Main polymer decomposition3
Switch gas	Changes to air / O₂	Oxidation of carbon black
Final step	Heats to burn off carbon	Ash, minerals, metal oxides left over

Once you see this sequence a few times, reading a TGA curve becomes much easier.

What information does TGA give about rubber materials?

On the surface, TGA is just a curve. In practice, it is a fingerprint of the compound.

TGA gives information about volatile content, polymer and oil fraction, filler and ash content⁶, thermal stability⁷, and decomposition behavior of rubber, so we can compare compounds and detect suspicious or low-quality formulations.

📈 What can I see in a TGA curve for rubber?

I normally split the curve into “zones”. Each zone tells me something different.

🔍 Typical TGA zones for a filled rubber

Temperature Zone (°C)	What Often Happens	What It May Indicate
25–150	Moisture, very light volatiles	Drying, small volatile loss
150–350	Plasticizers, process oils, softeners	Oil content, low-molecular components
350–550 (N₂)	Main polymer breakdown	Polymer type and thermal stability
550–800 (air)	Carbon black burns, leaving ash	Filler system, ash content, minerals

Not every material has clear steps in each zone, but many industrial compounds do.

🧱 Key things I learn from TGA

✅ Volatile and oil content
If the mass drops significantly in lower temperature zones, I know the compound contains more oil or softener. Very high volatile content can mean:

• Lower mechanical strength.
• Higher risk of fogging or outgassing.
• Stability problems at service temperature.

✅ Polymer fraction and stability
The main decomposition step shows:

• Around what temperature the polymer starts to break down.
• How sharp or broad the decomposition is.

This helps me compare different compounds:

• A high-quality EPDM⁸ for hot water may show higher onset temperature.
• A very cheap compound may start to decompose earlier.

✅ Filler and ash content
The final plateau after burning carbon black and organic parts tells me:

• Remaining mass = ash and mineral fillers.
• I can compare it with recipes or previous batches.

If I see high ash content where I expect low filler, I know the formulation is very different.

🧪 When TGA is especially useful

I find TGA very helpful when:

• A buyer sends an old seal and wants “same quality” from our factory.
• We suspect that a market part is underfilled or overloaded with chalk.
• We want to check if a supplier changed the compound without telling us.

In these cases, even a simple TGA comparison gives strong evidence.

How is TGA used in rubber quality control⁹ and failure analysis¹⁰?

Most people think TGA is only for R&D labs. In my experience, it is also a strong support for QC and complaint handling.

In rubber quality control and failure analysis, TGA is used to verify compound identity, compare batches, check filler and oil levels, and investigate failed parts for signs of wrong material or contamination.

🛠️ TGA in daily QC and “special cases”

I do not run TGA for every batch. However, I use it strategically.

✅ 1. Compound identity and change detection

When we freeze a compound recipe for a long-running project, I like to keep a reference TGA curve.

• This is our “fingerprint”.
• Future curves should look very similar.

If I see a different curve for a new batch, it may mean:

• Wrong material was loaded.
• Filler or oil levels changed.
• A new raw material supplier is used without approval.

✅ 2. Supplier comparison and reverse engineering¹¹

Sometimes buyers ask me:

“Can you match this gasket from my current supplier?”

I use TGA along with other tests (hardness, density, tensile) to estimate:

• Approximate filler content.
• Volatile and oil level.
• Basic thermal behavior¹².

I do not copy exact formulas, but I can design a compound in the same “class” of quality.

✅ 3. Failure analysis for claims

When a part fails in the field, I want to know if the material is the real problem.

TGA helps me check:

• Is this the correct polymer family?
• Did the failed part have unusual oil/filler content?
• Is the ash or residue showing contamination, such as metal salts or dirt?

I once had a case where rubber seals turned hard very quickly. TGA and other tests showed the competitor had used a very high filler content and low polymer fraction. This explained the poor ageing. The buyer understood why our quote was slightly higher: our compound was richer and more stable.

🧩 Role of TGA in a QC toolbox

TGA is not a stand-alone decision tool. I always combine it with:

• Hardness and density.
• Tensile and elongation.
• Compression set and ageing.

However, when material identity and filler system matter, TGA is one of the fastest ways to get clear insight.

How should I interpret a TGA curve for rubber?

A TGA graph can look scary at first, full of lines and numbers. The good news is that you do not need to be a scientist to see the main points.

To interpret a TGA curve for rubber, you should look for mass-loss steps, note their temperature ranges and sizes, check the final ash content, and compare these features with reference curves or expected formulation.

📉 Simple way to read a TGA curve as a buyer

When I send a TGA report to a customer, I walk them through it in three simple steps.

1️⃣ Look at the starting mass and final residue

• Start: 100% (by definition).
• End: maybe 20% or 40% or 5%, depending on formulation.

End mass = ash and stable inorganic materials.

If you know your normal ash level (for example, 35%), and you suddenly see 55%, you know something changed.

2️⃣ Count the “steps” in the curve

Each clear step in the curve shows a loss event.

Observation on Curve	Possible Meaning
Small drop below 150 °C	Moisture, very light volatiles
Big drop 150–350 °C	Oils, plasticizers, low-boiling parts
Major drop 350–550 °C	Polymer decomposition
Slow loss in air above 550 °C	Carbon black burning

The DTG curve (first derivative) shows peaks at each event. The peak temperature is the point of fastest loss.

3️⃣ Compare curve shape with reference

I always encourage buyers to compare:

• New batch vs reference batch.
• Competitor sample vs our sample.

If curves overlay nicely, formulations are similar. If not, there is a meaningful difference.

📊 Example: comparing two EPDM compounds

Imagine two EPDM gasket materials tested by TGA.

Feature	EPDM A (high-quality)	EPDM B (cheaper)
Volatile loss < 250 °C	3%	10%
Main polymer loss region	380–500 °C	350–470 °C
Final ash residue13	30%	50%

From this, I suspect:

• EPDM B has more oil and lower polymer fraction.
• EPDM B has more cheap filler (ash).
• EPDM A may have better thermal stability⁷ and mechanical behavior.

Even without exact recipes, you see why one compound costs more and behaves better. This kind of clear comparison helps buyers explain internal decisions to their own teams.

When should B2B buyers ask suppliers for TGA data?

You do not need TGA for every small rubber plug. But in some cases, asking for TGA is very smart and very strategic.

B2B buyers should ask for TGA data when they qualify new critical materials, switch suppliers, suspect compound changes, or need objective proof of filler and polymer levels in high-risk rubber parts.

✅ Typical situations where I recommend TGA

🧾 1. First article approval for critical seals

If your project involves:

• High temperature.
• Aggressive media (oil, coolant, chemicals).
• Long lifetimes or warranty.

Then I suggest including a TGA curve in the approval package. It becomes your baseline.

🔁 2. Supplier change or second source

When you add a new supplier, TGA helps you check if:

• Their “equivalent” material truly has similar filler and oil level.
• They did not cut quality to win the order.

You can save these curves as part of your internal technical file.

⚠️ 3. Suspicion of unapproved compound change

Sometimes customers tell me:

“The latest batch feels different from before.”

In this case, you can ask for TGA from the current batch and compare it with earlier batches, or we can run TGA from retained samples. If the curves differ strongly, that is objective evidence of a change.

💡 4. Reverse engineering and benchmarking

If you want to understand market alternatives better, TGA is a powerful comparison tool:

• Your existing part vs competitors.
• Different price levels vs compound richness.

You gain technical arguments instead of only price talk.

📋 What to request from your supplier

When you ask for TGA, I suggest you be specific:

• Ask for the TGA and DTG curves as graphs.
• Ask for test conditions¹⁴ (gas, heating rate, temperature range).
• Ask for calculated percentages of volatile loss, polymer loss, and ash.

You do not need to become a TGA expert. You only need to know when and how to use this data to support your quality decisions.

Conclusion

The TGA test for rubber is like an X-ray of the compound. It reveals polymer, filler, and thermal behavior, so buyers and engineers can see beyond hardness and color and make safer, smarter choices.

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