Changes in molecular structure of biodegradable plastics during degradation in soils estimated by FT-IR and NMR

Among the biodegradable plastic specimens (poly-(3-hydroxy-butylate-valerate) (PHB / V), poly-(epsilon-caprolactone) (PCL), poly-(butylene succinate) (PBS), poly-(butylene succinate and adipate) (PBSA), and poly-lactide (PLA)) that were placed in soils for 1 year at nineteen sites in Japan, plastic specimens with appreciable biodegradation were studied for the transformation of the chemical structure by FT-IR, H-1-NMR, and C-13-NMR. No appreciable differences in the main absorbency-bands of the atomic groups were recognized by FT-IR for any of the plastic specimens tested. However, both H-1-NMR and C-13-NMR analyses suggested that molecular structure of the PHB; / V specimens changed after 1 year placement in soils. Based on the assignment of the respective signals of chemical shifts derived from valerate, selective degradation of the valerate moiety in the PHB, / V specimens was observed. In contrast, although weight loss, and / or a decrease in tensile strength and elongation were observed after the placement in soils for the PCL, PBS, PBSA, and PLA specimens, the analyses of these specimens by FT-IR, H-1-NMR, and C-13-NMR did not reveal any changes in their molecular structure.