The following conclusions can be derived from the aforementioned
experimental results in regard to the photodegradation
by UV-irradiation of the neat PLLA, PDLA, and
PLLA/PDLA films.
1. The PLLA/PDLA blend film was more photodegradation-
resistant than the neat PLLA and PDLA films
when photodegradation was monitored by Mn, Tm, and
WAXS crystalline peak angles. 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.
2. 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.
3. The tensile properties were not sensitive to photodegradation-
inducing chain cleavage, with the exception
of the decreases in tensile strength and elongation at
break of the PLLA/PDLA blend film. However, the
tensile strength and elongation at break of the PLLA/
PDLA blend film retains higher values compared to
those of the neat PLLA and PDLA films during
photodegradation.
4. 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 highly-ordered structural difference
between them, i.e., the three dimensional dry gel
of the former and the spherulites of the latter.