Complete Materials Deformulation Using TGA-IR

Significance of the Topic

The combined use of Thermal Gravimetric Analysis (TGA) with Fourier Transform Infrared (FT-IR) spectroscopy addresses a frequent need in materials analysis: deformulation and failure investigation of multi-component materials (polymers, rubbers, foams, resins). TGA provides sensitive, quantitative mass-loss profiles as a function of temperature, while FT-IR identifies the vapors evolved during heating. Linking these techniques yields actionable chemical information to explain differences in material performance, guide process adjustments, and select safer or more stable feedstocks.

Objectives and Study Overview

This application note demonstrates the power and workflow of TGA-IR coupled with modern multi-component spectral searching (OMNIC Specta) through three industrially relevant case studies:

• An epoxy system monitored from fresh mixing through curing and thermal breakdown.
• Comparison of two black rubber samples (light versus carbon-filled dark) to reveal formulation-dependent evolution behavior.
• Evaluation of two blowing agents used in polymeric foam production to identify noxious emissions and inform selection.

The goal is to show how combining quantitative TGA weight-loss data with rapid multi-component gas-phase FT-IR identification produces rapid, reliable deformulation results.

Methodology

General measurement strategy and data processing:

• Samples (10–50 mg) were placed in pre-tared platinum pans and analyzed under an inert purge gas while heated with controlled temperature ramps.
• FT-IR spectra of the evolving vapors were collected concurrently via a heated transfer line feeding an in-sample TGA gas-sampling accessory and a heated double-pass gas cell mounted in the FT-IR sampling module.
• Spectra were acquired at 4 cm-1 resolution. Background scans and Gram–Schmidt (GS) basis vectors were collected immediately prior to each run. GS traces were used to visualize total spectral change over time.
• TGA weight-loss profiles and derivative traces were synchronized with the IR time-base to correlate thermal events with gas evolution.
• Multi-component spectral deconvolution and library searching were performed using OMNIC Specta with a HR (High Resolution) Nicolet TGA Vapor Phase library to automatically identify overlapping gas-phase absorptions.

Used Instrumentation

Key instruments and accessories used in the experiments:

• TA Instruments Q5000 TGA with autosampler (temperature programming and mass-loss measurement).
• In-sample TGA vapor sampling accessory with heated transfer line and double-pass gas cell (gas cell heated to 220 °C).
• Thermo Scientific Nicolet iS10 FT-IR spectrometer with Nicolet iZ10 sampling module.
• OMNIC Series spectroscopy software and OMNIC Series time-base for FT-IR data collection; TA Universal Analysis (UA) software for TGA data export/import; OMNIC Specta for multi-component spectral searching.

Main Results and Discussion

Epoxy system:

• TGA-IR run from ambient to 500 °C at 15 °C/min on a freshly mixed two-part epoxy revealed early evolution of CO2 and water (~190–210 °C) and larger complex emissions starting ~250 °C.
• Single instantaneous spectra showed overlapping gas components; OMNIC Specta quickly (under one minute) identified multiple components including bisphenol-A (unreacted monomer), ester species consistent with curing, and methane plus low bisphenol-A at higher temperatures indicating thermal breakdown.
• Multi-component searching provided excellent composite fits despite slight spectral differences arising from gas-phase collection conditions (temperature, pressure, mixtures).

Black rubber samples:

• Two rubbers (light vs. carbon-filled dark) showed similar types of evolved species but with markedly different temperatures of release: the dark, high-carbon sample released comparable gases at lower temperatures.
• GS traces correlated closely with TGA derivative peaks, enabling confident temperature–spectral assignment.
• Targeted narrow-range multi-component searches identified species such as butenes, methanol and methyl ethyl ketone in addition to CO, CO2 and water, revealing subtle formulation differences likely responsible for performance variation.
• Result: chemical similarity in composition but differences in thermal stability/processing history—important for failure analysis and product qualification.

Blown polymeric foam and blowing agents:

• Two blowing agents gave distinct gas-evolution patterns when analyzed to 200 °C (chosen to avoid base-polymer decomposition): Agent 1 produced a single rapid-onset emission containing multiple gases including isocyanate and CO, whereas Agent 2 produced two transitions dominated by CO2.
• Blown cover material reflected the agent-specific emission profile, confirming trapped-agent behavior rather than polymer decomposition.
• OMNIC Specta identified isocyanate evolution from Agent 1, flagging a potential source of noxious emissions despite acceptable mechanical properties for both agents.
• Conclusion: weight-loss profiles alone would not distinguish the agents; FT-IR identification was decisive for selecting the safer blowing agent (Agent 2).

Benefits and Practical Applications of the Method

• Combines quantitative thermal data with direct chemical identification to offer high-confidence deformulation results useful for failure analysis, competitive benchmarking, and feedstock qualification.
• OMNIC Specta multi-component searching removes much of the manual spectral interpretation required for overlapping gas-phase spectra, shortening analysis time and reducing operator dependence.
• Applicable across industries: plastics, rubbers, coatings, resins, pharmaceuticals, and any situation where evolved gases inform composition, curing, degradation, or safety concerns.
• Enables process- and materials-level decisions based on concrete chemical evidence rather than mass-loss patterns alone.

Future Trends and Potential Applications

Promising directions and extensions for TGA-IR deformulation workflows:

• Improved and expanded vapor-phase spectral libraries (including temperature- and matrix-matched entries) to increase identification confidence.
• Integration with complementary detectors such as mass spectrometry (TGA-IR-MS) or GC–MS for orthogonal confirmation and improved sensitivity for trace species.
• Advanced chemometric and machine-learning approaches for automated deconvolution, quantitative speciation, and pattern recognition across large sample sets.
• Development of calibrated quantitative protocols for converting IR absorbance into evolved-species mass or concentration for regulatory or occupational-exposure assessment.
• Real-time in-line monitoring and process control applications where thermal events and emitted vapors inform manufacturing adjustments (e.g., curing profiles, additive dosing).

Conclusions

TGA-IR, when combined with robust multi-component spectral searching (OMNIC Specta), is a powerful and general-purpose tool for materials deformulation. The method couples precise thermal decomposition or desorption profiles with definitive molecular identification of evolved gases. Case studies on epoxy curing/breakdown, black rubbers, and blown foams demonstrate that this approach provides rapid, reliable, and actionable insights that cannot be obtained from TGA weight-loss data alone. OMNIC Specta considerably reduces the need for expert spectral interpretation and supports consistent, reproducible results appropriate for quality assurance, failure analysis, and formulation development.

References

1. Bradley M. Complete Materials Deformulation Using TGA-IR. Thermo Fisher Scientific Application Note 51694; 2008.