We aimed to achieve wide area rapid monitoring of
the crystallinity change in poly(lactic acid) (PLA) during
photodegradation caused by ultraviolet (UV) light by using a
newly developed near-infrared (NIR) camera (Compovison).
Several kinds of PLAsamples with different crystallinities and
their blends with poly[(3)-(R)-hydroxybutyrate] were prepared.
Their two-dimensional NIR spectra in the 1,000–
2,350-nm region were measured by Compovision at a 5-min
interval during photolysis. An intensity decrease of the band
in the 1,900-1,925-nm region due to the second overtone of
the C = O stretching vibration of PLA was observed during
photolysis. This suggests that an anhydride carbonyl is produced
during photolysis. The NIR image of the crystallinity
change monitored by the band at 1,917 nm in the standard
normal variate spectra clearly shows the inhomogeneity of
crystal evolution. A logarithmic increase was observed for all
identified areas in the PLAfilm; however, the time to reach the
maximum crystallinity was slightly different according to the
initial crystallinity of the sample. It is likely that the initial
crystallinity of the sample influences the degradation speed
more than the degradation amount. These imaging results
have provided fundamental chemical insights into the photolytic
process for PLA, and at the same time they have demonstrated
that the two-dimensional spectral data obtained by
Compovision are useful for process monitoring of polymers.