Crystallization Behavior of Poly(3-hydroxybutyrate) (PHB), Poly(ε-caprolactone) (PCL) and Their Blend (50:50 wt.%) Studied by 2D FT-IR Correlation Spectroscopy

Variable-temperature FT-IR spectra of poly(3-hydroxybutyrate) (PHB), poly(epsilon-caprolactone) (PCL) and a PHB/PCL (50:50 wt.%) blend were analyzed by two-dimensional correlation spectroscopy (2DCOS). For this purpose the nu(C=O) region was employed to characterize in some detail the crystallization behavior of the investigated polymer systems during cooling from the melt. The asynchronous 2D correlation spectra clearly captured the existence of three components in the crystallinity-sensitive region of the C=O stretching mode for PHB and PCL, respectively: a well-ordered, an inter-mediate and a less ordered crystalline state. Furthermore, by 2DCOS application a sequential order of the observed structural changes could be proposed for the whole temperature range during the crystallization of both polymers. In the case of the PHB/PCL (50:50 wt.%) polymer blend, we have split up the spectral data set in the sub-sets between 200-120 degrees C and 70-30 degrees C for a more detailed 2DCOS analysis. In this way we could separate the crystallization process of PHB and PCL in the polymer blend.