Blends of aliphatic polyesters. IV. Morphology, swelling behavior, and surface and bulk properties of blends from hydrophobic poly(L-lactide) and hydrophilic poly(vinyl alcohol)

Blend films were prepared from hydrophobic poly(L-lactide) (PLLA) and hydrophilic poly(vinyl alcohol) (PVA) with different PLLA contents [X-PLLA (w/w) = PLLA(PVA + PLLA)] by solution casting and melt quenching. Their morphology, swelling behavior, and surface and bulk properties were investigated. Polarizing optical microscopy, scanning electron microscopy, differential scanning calorimetry, X-ray diffractometry, and tensile testing revealed that PLLA and PVA were phase separated in these blend films and the PLLA-rich and PVA-rich phases both formed a continuous domain in the blend film of X-PLLA = 0.5. The water absorption of the blend films was higher for the blend films of low X-PLLA values when compared at the same immersion time, and it was larger than expected from those of nonblended PLLA and PVA films. The dynamic contact angles of the blend films were linearly increased with an increase in X-PLLA. The tensile strength and Young's modulus of the dry blend films decreased with a rise in X-PLLA but this dependence was reversed because of the large decreases in tensile strength and Young's modulus for the blend films having high X-PLLA values after immersion in water. The elongation at break was higher for the wet blend film than for the dry blend film when compared at the same X-PLLA and that of the dry and wet blend films decreased with an increase in X-PLLA. (C) 2001 John Wiley & Sons, Inc.