Thermal Stability and Miscibility of Poly(hydroxybutyrate) and Methanol-Soluble Soda Lignin Blends

Poly(3-hydroxybutyrate), PHB is a biodegradable and biocompatible polymer generally produced by algae and bacteria. The main disadvantages of PHB include: (a) prohibitive cost, (b) poor processability, and (c) thermal instability during processing. Lignin (obtained from sugarcane fibre) has been blended with PHB to ascertain improvements in PHB properties. The properties of the blends were investigated by differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), scanning electron microscopy (SEM) and Fourier transform infra-red spectroscopy (FTIR) over the entire range of composition. The addition of methanol-soluble lignin increases the thermal stability of PHB over a wide temperature range. A single glass transition temperature (Tg), which depicts miscibility, was obtained for blends containing up to 40 wt% lignin. At up to 30 wt% lignin, the experimental data fitted the Gordon-Taylor and Kwei models. The Tg results correlate with the SEM and FTIR data. The FTIR data show that the miscibility of the blends is probably associated with specific hydrogen bonding interactions between the reactive functional groups in lignin and the carbonyl groups of PHB.