Standardization of Fourier transform infrared (FTIR) fingerprint region for paints and assessment on the reproducibility using different spectrophotometers were investigated. While selective fingerprint regions may be confusing for technicians/analysts who are non‐chemists, we attempt to generalize these regions (e.g., 1300–1000 cm−1 for Epoxy part A and 1400–1000 cm−1 for Epoxy part B) by choosing a universal region (2000–900 cm−1) that works for different paints. Comparison result using a paired student t‐test shows that the degree of similarity (r) values from the studied regions are not statistically different. The paint fails the screening analysis occasionally on‐site when analyzed using handheld FTIR due to the higher level of noise that gives low r values (r < 0.900 ± 0.002). The same samples were analyzed using a benchtop FTIR and the r values are above 0.900 ± 0.002. While the screening may lead to a false rejection of the sample on‐site, there could be occurrence of false acceptance. The on‐site screening of EPZ part A with different formulations, for instance, shows that the r values over the entire IR spectrum are above 0.900 ± 0.002 when analyzed using handheld FTIR. After the samples were analyzed using the benchtop, the r values fall below 0.900 ± 0.002.

This study aims to correlate the molecular structure consistency of unmixed paints and the performance of 2-pack three-layer protective dried coatings (mixed and cured paints) in various aging conditions (fresh, aged and expired paints) stored under different conditions. All the physical tests (density, solid content, viscosity and sag resistance) of paints fulfil the required specifications. However, these tests cannot tell if the chemical formulation of retained paints (aged and expired) has undergone changes due to storage. The conformity analysis by Fourier-transform infrared (FTIR) spectroscopy coupled with squared derivative algorithm was employed for molecular structure analysis comparison of the fresh and retained paints. FTIR results show high degree of similarity (r), with r ≥ 0.900 for the properly stored retained paints when compared against its fresh paints using high sensitivity compare algorithm. This finding is validated with a paired Student’s t-test and it turns out that the r values of properly stored paints are not statistically different from the fresh paints. Moreover, the performance test (pull off adhesion and salt-spray) of dried coatings indicates good durability when the properly stored retained paints with high degree of structural similarity are applied on the substrate according to end user specifications. This approach offers a practical solution for the paint manufacturer and user to employ a rapid and non-destructive FTIR structural analysis for the confirmation of structural consistency of retained paints before application instead of disposing the polymeric paint without verification.

Inorganic and metallic compounds are often added in the paint formulation to improve the performance of protective coatings. Since some of these materials are infrared (IR) inactive in the mid‐IR region, the applicability of far‐IR as an additional quality assurance or quality control (QA/QC) tool to ensure the batch‐to‐batch consistency or fingerprinting/authentication of inorganic raw materials or paints with inorganic component(s) supplied to the job sites is instigated. Results suggest that the degree of similarity (r) in the far‐IR region can be used to differentiate the inorganic polymorph mixtures of rutile and anatase TiO2, which are attested by desummation of the superimposed absorbance bands for the same purpose. However, far‐IR region for authentication of inorganic compounds is challenging for paints with small amount of inorganic component(s). Mid‐IR spectroscopy is still practical to be used as the QA/QC tool for the batch‐to‐batch consistency or authentication of polymeric wet paints with or without inorganic component(s) coupled with other physical analyses.