Complete Materials Deformulation Using TGA-IR

Significance of the topic

Deformulation of complex materials is a routine requirement in failure analysis, competitor benchmarking and product development across polymers, rubbers, coatings and related industries. Coupling thermal gravimetric analysis (TGA) with Fourier-transform infrared spectroscopy (FT‑IR) converts weight‑loss profiles into chemically specific vapor identifications. This hybrid approach yields actionable chemical intelligence—identifying volatile reaction intermediates, residual monomers, blowing agents and degradation products—that informs formulation control, process adjustments and material selection.

Objectives and overview of the study

The application note demonstrates practical use of TGA‑IR combined with automated multi‑component spectral searching (OMNIC Specta) to deformulate three industrial scenarios:

• Fresh two‑part epoxy during cure and thermal breakdown.
• Two black rubber formulations used for gaskets, with different thermal gas evolution behavior.
• Two blown polymeric foams made with different blowing agents where one emitted noxious vapor.

The aim was to show how TGA weight‑loss timing and FT‑IR vapor identification together resolve formulation differences and supply rapid, confident chemical assignments even when multiple gases evolve simultaneously.

Methodology

General experimental approach:

• Small samples (10–50 mg) were placed in pre‑tared platinum pans and analyzed by TGA while an inert purge gas carried evolved vapors, via a heated transfer line, into a heated gas cell in the FT‑IR.
• FT‑IR spectra were collected at 4 cm−1 resolution. Background and Gram‑Schmidt (GS) basis vectors were recorded immediately before timed collections to visualize total spectral change.
• TGA and FT‑IR data acquisition were synchronized using a trigger link and a single controlling computer; Gram‑Schmidt traces provided rapid visualization of evolving gas intensity versus time.
• Multi‑component spectral searches were performed by exporting FT‑IR time‑resolved spectra to OMNIC Specta, using an HR vapor‑phase library to identify overlapping gas mixtures automatically.

Instrumentation used

• Thermal gravimetric analyzer: TA Instruments Q5000 TGA with autosampler.
• Sample pans: pre‑tared platinum pans.
• FT‑IR spectrometer: Thermo Scientific Nicolet iS™10 FT‑IR with Nicolet iZ™10 sampling module and in‑sample TGA accessory (double‑pass gas cell heated to 220 °C).
• Software: OMNIC Series for FT‑IR acquisition and Gram‑Schmidt visualization; OMNIC Specta for multi‑component spectral searching; TA Universal Analysis (UA) used for data import/export.

Main results and discussion

Epoxy system:

• A single drop of mixed two‑part epoxy was ramped from ambient to 500 °C at 15 °C/min. Early emissions (≈190–210 °C) were dominated by water and CO2 (bubble evolution). At higher temperature (≈250 °C and above) more complex spectra appeared.
• OMNIC Specta multicomponent searches identified unreacted base and hardener constituents (including bisphenol‑A), ester formation indicative of curing, and later low‑molecular‑weight breakdown products such as methane accompanying bisphenol‑A release.
• The 3‑D time–wavenumber–intensity view showed substantial overlap of emissions; OMNIC Specta reconstructed composite spectra closely matching experimental spectra in under a minute per time point.

Black rubber comparison:

• Two raw rubber samples (light and dark, carbon‑filled) were analyzed with a two‑step TGA ramp. Gram‑Schmidt and derivative weight‑loss traces correlated strongly, allowing confident alignment of spectral features with temperature and mass loss events.
• Both rubbers released similar chemical species, but the dark (high carbon‑filled) rubber evolved many gases at lower temperatures than the light rubber—an important indicator of formulation differences or processing treatments that could explain performance variance.
• Narrow‑range multi‑component searches resolved species such as CO, CO2, water, butenes, methanol and methyl‑ethyl ketone among small spectral features. The study emphasized that atmospheric suppression of CO2/water should be avoided in TGA‑IR because these species are informative sample emissions.

Blown polymeric foam and blowing agents:

• Two blowing agents (Agent 1 and Agent 2) plus base polymer and finished covers were compared with TGA‑IR up to 200 °C to capture blowing‑related gas release without polymer decomposition.
• Agent 1 displayed a single rapid, sharp gas release containing more than one species; OMNIC Specta identified isocyanate as a significant component (with a small CO shoulder).
• Agent 2 exhibited two transitions and both transitions produced CO2 only; the finished cover blown with Agent 2 mirrored Agent 2’s transitions.
• Because the base polymer alone showed none of these emissions, the noxious gases were traced to the blowing agent choice—providing a clear, actionable differentiation that weight‑loss profiles alone could not provide.

Benefits and practical applications of the method

• Direct chemical identification of evolved gases linked to precise temperature/time points—enables root‑cause analysis for failures and formulation differences.
• Automated multi‑component spectral searching reduces operator expertise requirements and analysis time (searches completed in under a minute), improving throughput and consistency.
• Applicable across plastics, rubbers, coatings, adhesives and pharmaceuticals for deformulation, QA troubleshooting, supplier comparison and safety screening (identification of toxic volatiles like isocyanates).
• Flexible TGA control (ramp, hold, purge composition) allows designed thermal treatments to probe reactions or simulate processing conditions.

Limitations and best practice notes

• Gas‑phase IR spectra depend on temperature, pressure and mixture: band shapes and relative intensities can differ from library spectra; minor mismatches are expected.
• Avoid automatic atmospheric corrections or spectral subtractions that remove CO2/water signals since these are sample‑derived in TGA‑IR experiments; maintain constant purge conditions during runs.
• Quantitation of evolved gases requires calibration strategies; the study focuses on qualitative identification and comparative behavior.

Future trends and opportunities

Potential developments to expand the power and utility of TGA‑IR deformulation include:

• Integration with mass spectrometry (TGA‑FTIR‑MS) or GC‑MS for orthogonal confirmation and improved identification of small or weakly IR‑active species.
• Library expansion with vapor‑phase spectra collected under controlled temperature/pressure conditions to improve match fidelity.
• Automated, quantitative calibration protocols for absolute evolved gas measurements and emission rates.
• Real‑time process monitoring and in‑line thermal screening with compact TGA‑IR modules for manufacturing QA.
• Machine‑learning assisted deconvolution and predictive models that correlate gas‑evolution profiles to performance or failure probabilities.

Conclusions

The case studies demonstrate that coupling TGA with FT‑IR and using automated multi‑component searches (OMNIC Specta) delivers rapid, reliable, and chemically specific deformulation outcomes. This combined workflow outperforms TGA mass‑loss profiles alone by identifying volatile and semi‑volatile species responsible for curing behavior, degradation and noxious emissions. Results are sufficiently actionable to support material selection, supplier assessment and process changes.

References

• Bradley M. Complete Materials Deformulation Using TGA‑IR. Thermo Fisher Scientific Application Note 51694, 2008. (Thermo Fisher Scientific, Madison, WI)