FT-Raman investigation of biodegradable polymers: Poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

This work presents a FT-Raman study (λ0 = 1064 nm) of naturally occurring polyester poly[(R)-3-hydroxybutyrate] (PHB) and its copolymer poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] (PHBV) with 5, 8 and 12 mol % of HV (hydroxyvalerate). The FT-Raman spectra of films indicate that full width at half height of the band centered at 1725 cm−1 and relative intensity of bands at 1443 and 1458 cm−1 can be use to estimate the crystalline degree in film samples. The similarity between Raman spectra of molten PHB and PHBV and theirs CDCl3 solutions suggested that molten polymers present similar conformation than polymers in solution. Raman data of these samples showed that bands at 1220, 1402, 1725, 2998 and 3009 cm−1 are due to crystalline helical structure and the bands at 1453, 1740, 2881, 2938 and 2990 cm−1 are originated from disordered domains. It is shown that composition of PHBV samples can be estimated by analyzing the ratio of the intensity of the bands at 2938 cm−1 (νC–H) and 1740 cm−1 (νCO) in the spectra of solutions and of bands at 1354 (wCH2) and 1740 cm−1 (νCO) in spectra of molten polymers.