ENStarting point
FTIR provides spectral information associated with molecular composition; DSC observes thermal events; TGA tracks mass changes; XRF measures elements under the method's conditions. These techniques can complement one another. No isolated reading demonstrates complete identity, absence of contaminants and part performance simultaneously.
Start with the question that changes the decision
A batch may require polymer identification, impurity investigation, comparison with a reference or assessment of a relevant substance. Define which conclusion would allow the material to be released, blocked or sent for another test. Requesting every available test without a hypothesis often produces lengthy reports and little clarity about the next action.
Describe origin, batch, physical form, preparation and the observed symptom. If the investigation starts with a failed part, preserve both the part and material from the corresponding period. The laboratory needs to know the question without being given a premature conclusion that unduly steers interpretation. Distinguish what was observed from a merely suspected cause.
Use FTIR to investigate identity and compositional differences
Fourier-transform infrared spectroscopy, FTIR, allows comparison of bands associated with molecular structures. Thermo Fisher's technical resources present applications in polymer identification and contaminant investigation. A library match is analytical information whose interpretation depends on signal quality, the acquisition technique and the sample. [1]
In ATR measurements, the condition of the region touching the accessory matters. A coating, dirt or surface layer may give a different reading from the interior. Compare regions and fractions where this addresses the hypothesis. A dominant classification does not automatically quantify minor components; estimating composition requires an appropriate method, with calibration and validation for that purpose.
Read DSC with thermal history in mind
Differential scanning calorimetry, DSC, observes events associated with thermal behaviour. The scope of the ISO 11357 series includes glass transition, melting, crystallisation and other phenomena. Part 1 establishes general principles, while specific procedures belong to the corresponding parts. The result must state the conditions used, without treating every curve as directly comparable to another. [2]
Preparation, conditioning and material history may influence interpretation. A first analysis may reflect both composition and processing history; additional sequences should be defined by the method and question. An unexpected event warrants investigation, but does not by itself identify its cause or the proportion of another polymer. Avoid using the absence of a peak as universal proof of no contamination.
Relate TGA to the mass that changes during the test
Thermogravimetry, TG or TGA, tracks mass changes under programmed conditions. ISO 11358-1 describes its use in investigating physical effects and reactions associated with these changes, including decomposition and the assessment of volatiles, additives or fillers. The atmosphere, thermal programme and preparation must accompany the result. [3]
An educational example: a 12 mg sample leaves 2.4 mg at the end of a defined procedure. The residue corresponds to 20% of the initial mass under those conditions. This does not in itself prove the presence of 20% of a specific mineral filler. The residue's composition and what occurred during the programme require interpretation and, where necessary, further tests.
Use XRF without confusing elements with substances
X-ray fluorescence, XRF, provides elemental information according to the method's capability and calibration. Studies screening plastics from electrical and electronic equipment use elements such as bromine and antimony as relevant indicators. Identifying total bromine does not automatically identify the flame retardant or prove compliance with a restriction on a specific compound. [4]
The sample must be suitable for the procedure: heterogeneity, thickness and surface condition may affect the reading's representativeness. Where the decision depends on a substance, confirm which method is needed to identify or quantify it. Do not turn a measurement below the detection limit into a declaration of absolute absence; the report should state the method's scope and basis for interpretation.
Combine results without expecting them to say the same thing
One technique may indicate a predominant matrix while another reveals behaviour inconsistent with the reference. This calls for investigation, not arbitrary selection of the most convenient result. The tests observe different properties and may have been performed on different portions of a heterogeneous batch.
Organising each technique's contribution
Technique
- FTIR
- Main information
Bands and matches with structures or references
- What it cannot conclude alone
The complete percentage composition of a mixture
- DSC
- Main information
Thermal events under the method's conditions
- What it cannot conclude alone
The part's complete functional performance
- TGA
- Main information
Mass change and residue from the procedure
- What it cannot conclude alone
The chemical identity of the entire residual fraction
- XRF
- Main information
Elements measurable in the matrix and under the adopted conditions
- What it cannot conclude alone
The identity of all compounds containing those elements
Together, the results should converge on the initial question, with a conclusion that recognises confirmed findings, hypotheses and information still needed.
Investigate the deviation with consistent samples and references
Imagine a batch sold as a styrenic material that shows different processing behaviour from usual. FTIR indicates a compatible matrix, while DSC shows an additional event in some samples. One hypothesis is the presence of another fraction; others include differences in preparation or thermal history. The next step should distinguish these possibilities with the laboratory.
Compare samples from the suspect batch, a reference batch and, where available, the separated fractions. Preserve identification and preparation conditions. Repeats on the same portion investigate the measurement; new portions help investigate material distribution. The article on waste and plastics sampling explains why these two activities are not interchangeable.
Turn the report into a quality decision
The investigation report should identify samples, methods, conditions, results, limitations and a relevant conclusion. Avoid reducing the document to an “approved” label without stating the requirement concerned. Where the cause remains unresolved, indicate the next analysis and its reason, rather than accumulating tests without a close-out criterion.
Industrial approval may require mechanical tests, processing and functional verification in addition to these techniques. In PCR resin qualification, characterisation and qualification play complementary roles. The former helps understand the material; the latter demonstrates its suitability for the application under defined conditions. The control plan should preserve this relationship across batches.
Sources and references
References accessed on 30 September 2026. The numbering in the text indicates the concepts supported by each source.
References to ISO standards use their publicly available scopes; full requirements should be consulted in the respective standards.
- Thermo Fisher Scientific. FTIR Spectroscopy Resources — Applications in polymers and contaminants. Manufacturer technical material.
- ISO 11357-1:2023 — Plastics: differential scanning calorimetry, general principles. Publicly available scope of the standard.
- ISO 11358-1:2022 — Plastics: thermogravimetry of polymers, general principles. Publicly available scope of the standard.
- Chaine, C. et al. Optimized industrial sorting of WEEE plastics: development of fast and robust h-XRF technique for hazardous components. Case Studies in Chemical & Environmental Engineering, 2023. Abstract in the University of the West of Scotland repository.
Circuvia corporate content to support project discussions. Methods, acceptance criteria and applicable requirements are defined within the scope of each operation.
