EXPRESS: Spectroscopic Study of Solution Crystallization of a Biodegradable Polyester Streamlined with a Correlation Filter (CF)

Due to the growing interest in high-purity bioplastics for emerging applications, we investigated the solution crystallization of poly(3-hydroxybutyrate-<i>co</i>-3-hydroxyhexanoate) (PHBHx) from a chloroform solution using advanced spectroscopic techniques. Compared to melt crystallization, solution crystallization proved to be a more complex process. Solvent evaporation led to the formation of amorphous PHBHx and less-ordered crystallites. Subsequently, a distinct intermediate species of slightly disordered crystals formed, eventually transforming into more ordered crystalline structures. To analyze the time-dependent attenuated total reflection infrared (ATR-IR) spectra during crystallization, we employed two-dimensional correlation spectroscopy (2D-COS) and codistribution spectroscopy (2D-CDS). To streamline the 2D analysis of this complex dynamic system, we utilized a correlation filter (CF) technique to attenuate interfering contributions from overlapping peaks.