Investigation of the 3-hydroxyvalerate content and degree of crystallinity of P3HB-co-3HV cast films using Raman spectroscopy

The structural properties of extruded cast films of poly-3-hydroxybutyrate (P3HB) and poly-3-hydroxybutyrate-co-3-hydroxyvalerate (P3HB-co-3HV) were analysed by Raman spectroscopy. A sensitive band for the side chain of the 3HV was found at 844 cm⁻¹ (νCC, νC-COO). Using an internal standard at 1101 cm⁻¹ (ν_sC-O-C, ρCH₃), a model for calculation of the 3HV content was developed. This was based on analysis of samples with a 3HV content of 0–12 mol%. Additionally, P3HB-co-3HV samples were tempered in order to create different degrees of crystallinity. The induced changes in the Raman spectra were analysed. The Raman model to determine the degree of crystallinity considers the sensitive band at 2999 cm⁻¹ (ν_asCH₂) and the internal standard at 1059 cm⁻¹ (νC-O, νC-CH₃, ρCH₂). The investigated crystallinity was in a range of 0.69–0.86.