Neat poly(L-lactic acid) (PLLA) and poly
(D-lactic acid) (PDLA) films and PLLA/PDLA blend films
were prepared by solution casting, and their photodegradation
by UV-irradiation was investigated using wideangle
X-ray scattering (WAXS), gel permeation chromatography,
differential scanning calorimetry, tensile testing,
and polarized optical microscopy. The PLLA/PDLA blend
film was more photodegradation-resistant than the neat
PLLA and PDLA films when photodegradation was monitored
by molecular weight, melting temperature, and
WAXS crystalline peak positions. This indicates that the
chains in both amorphous and crystalline regions of the
PLLA/PDLA blend film were photo-cleavage-resistant
compared to those of the neat PLLA and PDLA films. The
changes in melting temperature and WAXS crystalline
peak positions before and after photodegradation respectively
indicated the increased crystalline lattice disorder
and the decreased crystalline lattice sizes of the neat PLLA
and PDLA films, whereas these changes were insignificant
for the blend films. Photodegradation caused no significant
change in tensile properties, with the exception of
significant decreases in the tensile strength and elongation
at break of PLLA/PDLA blend film. However, the tensile
strength and elongation at break of the PLLA/PDLA blend
film retained higher values compared to those of the neat
PLLA and PDLA films during photodegradation. In spite
of the slower photodegradation of the PLLA/PDLA blend
film traced by Mn, Tm, and WAXS crystalline peak positions
than that of neat PLLA and PDLA films, the rapid
decrease in tensile strength and elongation at break of the
former than that of the latter should be due to the highlyordered
structural difference between them, i.e., the three
dimensional dry gel of the former and the spherulites of the
latter.