COMPLEXES OF STARCH POLYSACCHARIDES AND POLY(ETHYLENE COACRYLIC ACID) - STRUCTURAL CHARACTERIZATION IN THE SOLID-STATE

The structural characterization of model complexes of amylose (AM) and amylopectin (AP) with poly(ethylene-co-acrylic acid) (EAA) was undertaken in order to better understand the interactions that occur between the polysaccharides and EAA in starch-EAA-polyethylene films. X-ray diffraction and CP/MAS C-13-NMR studies showed that precipitates from solution mixtures of AM and EAA form crystalline, helical V-type inclusion complexes. The proportion of AM forming the V-type complex in the EAA/AM blends, estimated from shifts in the C1 resonance of AM, increased with increasing EAA/AM ratio, reaching a value of about 80% at EAA/AM = 0.5 (w/w). Similar measurements for EAA/AP complexes showed < 10% V structure. Approximately 80% of the AM and 4% of the AP in these blends was resistant to amylase digestion, in good agreement with their V-structure contents as determined above. Resonances at 184 and 181 ppm were observed for the carboxyl carbon of EAA in the EAA/AM and EAA/AP complexes. The resonance at 181 ppm, which was not observed in pure EAA, probably reflects greater shielding of the carboxyl inside the polysaccharide helix as well as changes in hydrogen bonding. The intensity of this peak was 2-3 times larger for the EAA/AM than for the EAA/AP complexes. FTIR experiments suggest that most (> 50%) of the EAA carboxyl groups were hydrogen bonded to polysaccharide hydroxyl groups in both AM and AP complexes when EAA/polysaccharide < 1.