Influence of plasticizers in pectin films: Microstructural changes

This study investigated the effect of two plasticizers, i.e. glycerol (GLY) and polyethylene glycol (PEG), on pectin film structure. The results reveal that glycerol acts as an internal plasticizer. GLY increased the predominant amorphous character of the plasticized films because of decreased intermolecular attraction, resulting in low temperature degradation and allowing the conformational transformation of the galacturonan ring via a boat conformation. Glycerol produced more deformable and weaker films. Also, glycerol led to films with a greater Swelling Index (SI) and Water Vapor Permeability (WVP) value. When PEG was used as the plasticizer, films were also weaker and a lower Young's modulus was obtained compared to the neat pectin film. However, with increasing PEG MW, more compacted films were obtained, resulting in less deformable films. The WAXD spectra and DSC thermograms indicate that PEG existed as a separate phase in the pectin matrix. Moreover, the pectin phase became more compacted and less permeable to water vapor as the PEG MW is increased. These results show that PEG acts as an external plasticizer.