ATR FTIR (attenuated total reflectance Fourier transform infrared) spectroscopy was
applied for direct evaluation of the crystallinity of poly(3- hydroxybutyrate -co- 4-
hydroxybutyrate) (P(3HB-co-4HB) polymers. At low 4HB content, this is believed to be a
much more accurate method compared to the crystallinity calculated by differential
scanning calorimetry (DSC). The FTIR method is also simpler and easier to interpret
compared to x-ray diffraction or scattering. As the crystallinity of semi-crystalline P(3HBco-
4HB) polymers reduces with increased 4HB content, it could be used in composition
analysis of copolymers. ATR FTIR spectroscopy also provides good insight into the
morphological changes of the P(3HB-co-4HB) molecules due to orientation (e.g. fiber
drawing, filaments or film orientation, post draw, etc). As the percent fraction of the
mobile amorphous phase is shown to reduce with aging in P(3HB) homopolymer and in its
semi-crystalline copolymers with 4HB, easy monitoring of aging could also be offered
based on this technique. The biodegradation specifics, e.g. morphological changes caused
by the biodegradation in soil and compost, would be difficult to measure by transmission
FTIR due to high absorbance of films, but quite possible with surface ATR FTIR. Among
other factors, e.g. glass transition temperature and crystal size, the biodegradation rates in
P(3HB) copolymers have been reported to decrease with an increase in crystallinity, e.g. in
[1,2]. For the purposes of providing materials with controlled biodegradation rates, multi
layer coextruded films are industrially offered and ATR FTIR could be very useful in
monitoring the morphological changes of these films over time.We present the calculation
of the crystallinity indicator of P(3HB-co-4HB) polymers as a ratio of crystalline phase
specific absorption at 1227 cm1 to amorphous phase specific absorption at 1184 cm1,
which is shown to correlate well with crystallinity calculated from DSC measurements. The
developed method could be used in water based PHA latexes as water does not absorb at
the selected wavelengths.