Effect of aqueous medium on the molecular mobility of polylactide

Abstract

The coefficient of diffusion of distilled and sea water in polylactide of two grades at 23°C was calculated. The diffusion coefficient of water was (0.63–0.85) × 10^–10 cm²/s for both polylactide samples, which corresponds to hydrophobic polymers. The temperature dependence of the water diffusion coefficient at 23, 30, and 50°C was obtained. The activation energy of the diffusion of distilled water was determined to be 38 and 36 kJ/mol, respectively, for both polylactide samples. A differential scanning calorimetry (DSC) study showed that after exposure to distilled and sea water at 23°C for 120 days, the melting point decreased by 2–3°C, and the degree of crystallinity increased by 5–9% in the experiment with distilled water for both samples. In an electron paramagnetic resonance (EPR) study it was determined that after hydrolysis, the correlation time of radical rotation in amorphous regions slightly decreased for both samples.