Miscibility, thermal properties, and enzymatic degradability of binary blends of poly[(R)-3-hydroxybutyric acid] with poly(epsilon-caprolactone-co-lactide)

The miscibility, morphology, and biodegradability of binary blends of poly[(R)-3-hydroxybutyric acid] (P[(R)-3HB]) (M(n) = 300 000) with poly(epsilon-caprolactone-co-lactide) (P(CL-co-LA)) (M(n) = 1500-40 000) have been studied by means of differential scanning calorimetry (DSC), optical microscopy, scanning electron microscopy (SEM), enzymatic hydrolysis, and biodegradation in river water. Copolymers of epsilon-caprolactone (CL) and (R,S)-lactide (LA) with a wide range of compositions were prepared by ring-opening copolymerization of epsilon-caprolactone with (R,S)-lactide in the presence of aluminum triisopropoxide as an initiator. The P(CL-co-LA) samples were found to have a random sequence distribution of monomer units by C-13 NMR analysis. The P(CL-co-LA) films were hydrolyzed by a lipase from Rhizopus delemar, and the rates of enzymatic hydrolysis were higher than that of PCL homopolymer. DSC analysis revealed that the solid-state structure of P[(R)-3HB]/P(CL-co-LA) blends was strongly dependent on the copolymer composition of the P(CL-co-LA) component. The miscible blends of P[(R)-3HB] were prepared with amorphous P(CL-co-LA) ranging from 30 to 100 mol % LA. The spherulites of P[(R)-3HB] in the miscible P[(R)-3HB]/P(CL-co-LA) blends were volume-filled, and the spherulitic growth rate decreased with an increase in the content of the P(CL-co-LA) component. The enzymatic hydrolysis of P[(R)-3HB]/P(CL-co-LA) blend films was carried out at 37 degrees C and pH 7.4 in a potassium phosphate buffer with an extracellular PHB depolymerase from Alcaligenes faecalis. The rates of enzymatic hydrolysis on the films of P[(R)-3HB]/P(CL-co-LA) blends decreased with an increase in the P(CL-co-LA) content.