Thermogravimetric Analysis (TGA) is a core thermal characterization technique that measures the mass change of a chemical material as a function of temperature or time under a precisely controlled atmosphere. For polymers, rubber, composites, catalysts, and inorganic chemicals, TGA provides quantitative data on thermal stability, compositional makeup, filler and ash content, and decomposition behavior. Accredited third-party laboratories perform TGA testing in accordance with ISO, ASTM, and GB standards to support quality control, material verification, failure analysis, and product development.
Technical Overview
Thermogravimetric Analysis (TGA), also known as thermogravimetry, is a thermal analysis technique in which the mass of a specimen is continuously monitored while it is subjected to a controlled temperature program. The resulting mass-versus-temperature curve, together with its first derivative (DTG curve), reveals dehydration, desorption, oxidation, and decomposition events, as well as the residue remaining at the end of the test. Because every mass change is recorded quantitatively, TGA is one of the most reliable techniques for determining the composition and thermal robustness of chemical materials.
Measurement Principle
A small sample, typically 5 to 20 mg, is placed in a crucible suspended from a highly sensitive microbalance inside a furnace. The furnace follows a predefined temperature program, usually a linear ramp at 5 to 20 °C/min from ambient temperature up to 600–1000 °C. The atmosphere around the sample is tightly controlled by purge gases such as nitrogen, argon, air, or oxygen, and can be switched dynamically during a run. Any mass loss or gain caused by volatilization, decomposition, oxidation, or reaction is recorded in real time with microgram-level resolution.
Instrumentation and Capability
A modern TGA instrument consists of the following key elements:
- A precision microbalance with resolution down to 0.1 µg, isolated from the furnace by a protective gas curtain.
- A programmable furnace, typically capable of 25 °C to 1000 °C, with some systems extending to 1500 °C for ceramics and refractory materials.
- A gas control module for inert, oxidative, or reactive atmospheres, including automatic gas switching mid-run.
- A cooling system, typically forced air or circulating water, to reset the furnace between tests.
- Optional coupling to FTIR or mass spectrometry for evolved gas analysis (TGA-FTIR, TGA-MS), which identifies the chemical nature of decomposition products.
Key calculated results include the onset temperature of decomposition, temperatures at 5% and 10% mass loss, the DTG peak temperature of maximum degradation rate, residual mass at high temperature, and step-by-step mass losses attributable to moisture, volatiles, polymer matrix, and inorganic residue.
Testing Samples
TGA is applicable to virtually any chemical material that is thermally active and can be sampled in milligram quantities. Typical sample categories submitted to accredited third-party laboratories include:
Polymers and Plastics
Commodity plastics such as PE, PP, PVC, PS, and PET; engineering plastics such as PA, PC, POM, PBT, and PMMA; and high-performance polymers such as PEEK, PPS, PI, PTFE, and silicone. TGA quantifies thermal stability, filler loading, and volatiles content.
Rubber and Elastomers
Natural rubber, SBR, NBR, EPDM, butyl rubber, silicone elastomers, and thermoplastic elastomers. TGA determines oil content, polymer fraction, carbon black content, and ash content in a single run.
Composites and Filled Materials
Glass-fiber and carbon-fiber reinforced plastics, mineral-filled compounds, nanocomposites, and flame-retardant formulations, where accurate measurement of reinforcement or filler fraction is essential for batch consistency.
Coatings, Adhesives, and Sealants
Thermosetting resins, epoxy systems, polyurethane adhesives, and powder coatings, for evaluating curing residue, solvent content, and degradation thresholds.
Inorganic and Specialty Chemicals
Catalysts and catalyst supports, adsorbents such as molecular sieves and activated carbon, ceramics and ceramic precursors, metal oxides, hydrates, and pharmaceutical or fine-chemical intermediates, for assessing hydration states, purity, and oxidation-reduction behavior.
Testing Items
Common TGA test items for chemical materials include:
- Thermal stability evaluation: onset decomposition temperature, T5%, T10%, and maximum-rate degradation temperature (Tmax).
- Compositional analysis: moisture and volatile content, polymer or matrix content, carbon black or carbonaceous residue, and inorganic filler or ash content.
- Carbon black content in polyolefins and rubber compounds, measured by pyrolysis in nitrogen followed by combustion in air.
- Ash content and residue-on-ignition determination.
- Moisture and solvent content, including adsorbed and crystal water.
- Oxidative stability and oxidation onset temperature (OOT) under oxygen or air atmospheres.
- Comparative degradation kinetics, including apparent activation energy via multiple heating-rate methods such as Ozawa–Flynn–Wall or Kissinger analysis.
- Thermal endurance screening for long-term service temperature extrapolation of insulating and polymeric materials.
- Evolved gas characterization when TGA is coupled with FTIR or mass spectrometry.
Testing Methods
Applicable Standards
TGA testing of chemical materials is commonly performed according to the following international and national standards:
- ISO 11358-1 and ISO 11358-2: Thermogravimetry of plastics, general principles and activation energy determination.
- ISO 9924-1 and ISO 9924-2: Determination of composition of rubber and rubber products by TGA.
- ASTM E1131: Compositional analysis by thermogravimetry.
- ASTM D6370: Compositional analysis of rubber by thermogravimetry.
- ASTM E2550: Thermal stability by thermogravimetric analysis.
- ASTM D3850: Rapid degradation of solid electrical insulating materials by TGA.
- ASTM E1582 and ASTM E2040: Temperature and mass calibration of TGA apparatus.
- GB/T 33047 series and GB/T 14837: Chinese national standards for thermogravimetric analysis of plastics and rubber composition.
- IEC 60216 series and UL 746B: Referenced frameworks for thermal endurance and long-term properties of insulating and polymeric materials, for which TGA data provide supporting evidence.
Typical Test Procedure
A standard compositional analysis run proceeds as follows:
- Sample preparation: 5–20 mg of representative material is cut, ground, or punched into small pieces and loaded into an alumina or platinum crucible.
- Conditioning: an equilibration hold at 30–50 °C may be used to stabilize the instrument and purge atmosphere.
- Stage one, drying or devolatilization: heating under nitrogen to approximately 105–300 °C to quantify moisture and volatile components.
- Stage two, pyrolysis: continued heating in nitrogen to 550–650 °C to decompose the organic matrix, with the mass loss corresponding to polymer and oil fractions.
- Stage three, combustion: switching to air or oxygen and holding at 600–900 °C to burn off carbon black or carbonaceous char, leaving the inorganic ash as final residue.
- Data processing: mass losses are assigned to each component, and DTG peaks are matched to individual decomposition events to produce a full compositional profile.
Data Interpretation
Interpretation is based on the step heights of the TGA curve, the positions of DTG peaks, and the final residue. Overlapping decomposition events may be resolved by slower heating rates or by modulated TGA techniques. Results are influenced by heating rate, sample mass, particle size, and atmosphere, so laboratories report full method parameters alongside the data to ensure comparability between tests.
Applications
TGA data are used across the chemical industry for a wide range of practical purposes:
- Incoming material verification and batch-to-batch quality control of resins, compounds, and masterbatches by confirming filler and volatile content against specifications.
- Deformulation and competitive benchmarking of molded parts, films, and compounds by quantifying polymer, plasticizer, carbon black, and mineral filler fractions.
- Failure analysis of degraded or discolored parts by comparing decomposition profiles of failed and reference materials.
- Flame-retardant development, tracking char yield and decomposition shifts when additives are incorporated.
- Lifetime and service-temperature estimation for wires, cables, and electrical insulation based on thermal degradation kinetics.
- Catalyst and adsorbent characterization, including moisture uptake, coking, and regenerability studies.
- Support of regulatory submissions, material data sheets, and supplier qualifications with standards-compliant test reports from accredited third-party laboratories.
FAQ
How much sample is required for a TGA test?
A typical test requires only 5 to 20 mg of material. Because such a small quantity is analyzed, it is important that the submitted sample be homogeneous and representative of the bulk material, especially for filled or reinforced compounds.
What is the difference between TGA and DSC?
TGA measures mass changes with temperature and is ideal for compositional and stability analysis, while DSC measures heat flow and is used for transitions such as melting, crystallization, glass transition, and curing. The two techniques are complementary and are frequently performed together for complete material characterization.
Can TGA distinguish carbon black from inorganic filler?
Yes. Under nitrogen pyrolysis both remain as residue, but when the atmosphere is switched to air at high temperature the carbon black combusts while mineral fillers and glass fiber remain. The mass loss in the air stage corresponds to carbon black, and the final residue corresponds to inorganic filler or ash.
What heating rate and atmosphere are normally used?
The most common condition is 10 °C/min under nitrogen for stability testing, followed by an air switch for residue determination. However, parameters are adjusted to match the governing standard and the material being tested, and heating-rate studies at several rates are used when kinetic analysis is required.
Can TGA predict product service lifetime?
TGA degradation kinetics allow thermal endurance estimates through methods such as Ozawa–Flynn–Wall or Kissinger analysis, and these results are widely used as screening inputs for frameworks such as IEC 60216. For definitive lifetime ratings, TGA data are normally combined with long-term aging studies.
How long does a TGA analysis take?
A single standard run from room temperature to 900 °C with atmosphere switching typically takes 1.5 to 3 hours, including cooling. Studies involving multiple heating rates, isothermal holds, or evolved gas coupling require additional time, and accredited third-party laboratories generally report results within a few working days.
