Fourier Transform Infrared Photoacoustic Spectroscopy (FT-IR-PAS) Combined with Two-Trace Two-Dimensional Correlation...

This study demonstrates the use of Fourier transform infrared photoacoustic spectroscopy (FT-IR-PAS) to investigate surface structural changes in biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) films during marine microbial degradation. FT-IR-PAS, a non-contact and surface-sensitive technique, enables the analysis of brittle or rough surfaces without pretreatment and offers clear advantages over conventional attenuated total reflection infrared (ATR-IR) for degraded films. To enhance spectral interpretation, FT-IR-PAS was combined with two-trace two-dimensional (2T2D) correlation analysis, which allowed the detection of subtle spectral variations associated with microbial degradation. This approach revealed changes in the carbonyl stretching bands (1675-1775 cm^-1) linked to the molecular order of the PHBH chains, enabling the detection of changes in the proportion of crystalline and amorphous regions on the surface. Asynchronous 2T2D correlation spectra for PHBH residues revealed specific cross-peaks at (1726 cm^-1, 1743 cm^-1), indicating preferential degradation of amorphous regions. Furthermore, the asynchronous correlation intensities at these positions showed a positive relationship with the PHBH film weight loss resulting from microbial degradation. These findings highlight FT-IR-PAS coupled with 2T2D analysis as a powerful, non-destructive approach for elucidating the surface degradation mechanisms of biodegradable polymers under marine conditions.