FTIR conformity analysis and performance testings of fresh, aged and expired polymeric paints under different storage conditions

Abstract

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.