Different characterization methods spanning length scales from molecular to micron scale were applied to inspect the microstructures and mechanical/hydrophilic features of agar/konjac glucomannan (KGM) films prepared under different drying temperatures (40 and 60 °C). Note that the lower preparation temperature (40 °C) could increase the strength and elongation of agar/KGM films at high KGM levels (18:82 wt/wt KGM-agar, or higher). This was related to the variations in the film multi-scale structures with the increment of KGM content: the reduced crystallinity, the increased perfection of nanoscale orders at some KGM amounts, and the negligibly-changed morphology and molecular chemical structure under 40 °C preparation temperature. These structural changes initially decreased the film tensile strength, and subsequently increased the film strength and elongation with increasing KGM content. Moreover, under the higher drying temperature (60 °C), the increased KGM content could concurrently reduce the strength and elongation for the films, associated with probable phase separations on nano and smaller scales. In addition, the increased KGM amount tended to make the film more hydrophilic, whereas the changes in the film structures did not dominantly affect the changing trend of hydrophilicity.
Keywords: agar-based film; konjac glucomannan; structural features.