Three-DimensionalRaman Imaging of Marine Biodegradationin Poly(3-hydroxybutyrate) and Its Copolymer in Seawater

The marine biodegradation behavior of poly(3-hydroxybutyrate) (P(3HB)) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) films was successfully visualized using two- and three-dimensional Raman imaging in both high- and low-frequency regions through laboratory experiments using seawater, marine field experiments, and in situ measurements. Raman imaging was used to investigate changes in the crystallinity of the P(3HB) and P(3HB-co-4HB) films based on the area ratio of the C═O stretching bands in the crystalline and amorphous regions (high-frequency region). Furthermore, the strength of intermolecular hydrogen bonding was evaluated based on the peak position at 79 cm–1 (low-frequency region). Changes in crystallinity of P(3HB) and P(3HB-co-4HB) films observed by Raman imaging suggested that marine biodegradation initially occurs in the amorphous regions, leading to an increase in crystallinity. Low-frequency Raman imaging revealed that significant changes at the film surface were correlated with pronounced alterations in intermolecular hydrogen bonding. These changes were observed not only in laboratory marine biodegradation experiments but also in field experiments and during continuous hourly measurements.