Evaluation of the Relationship between Crystal Orientation and Enzymatic Degradation Rate of Poly[(<i>R</i>)-3-hydroxybutyrate-<i>co</i>-(<i>R</i>)-3-hydroxyhexanoate] Banded Spherulites via FT-IR Imaging

Poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (PHBH) is a semicrystalline thermoplastic with biodegradable and biocompatible properties. In this study, Fourier transform infrared spectroscopy (FT-IR) imaging measurements were performed on PHBH banded spherulites as a model material to quantitatively evaluate the relationship between crystal orientation and enzymatic degradation rate. In a spherulite, lamellar crystals are cooperatively twisted in the radial direction, resulting in periodic changes in crystal orientation. Taking advantage of this structural feature, 25,600 data sets of crystal orientation and degradation rate, corresponding to the number of pixels in FT-IR image, were obtained in a single measurement to cover all various orientation states. Based on numerous data sets, a clear correlation between crystal orientation and degradation rate was confirmed, indicating that the degradation rate of flat-on lamellar crystals was approximately three times greater than that of edge-on lamellar crystals. The proposed method could be applied to predict the degradation rate of oriented materials in various degradation systems.