Effect of moisture content on the heat-sealing property of starch films from different botanical sources

In this study, we investigated the differences in the crystallinity of starch films (mung bean, water chestnut, sweet potato, and cassava starches) with different moisture contents stored in different humidity conditions (11%, 22%, 33%, 43%, 54%, 75%, and 84%) and evaluated their thermal adhesion and sealing properties. X-ray diffraction analysis revealed an association between the degree of crystallinity and the moisture content in starch films: crystallinity decreased with an increase in the moisture content. Field Emission Scanning Electron Microscopy (FE-SEM) analysis showed that films with low moisture content failed to completely adhere, but films with a high moisture content and lower crystallinity showed good adherence, with two films perfectly adhered at the same temperature because water molecules acted as a mobility enhancer. The peeling test demonstrated the failure modes of the heat-bound films. The cassava starch film, which had a low amylose content and crystallinity, showed better adhesion compared to other starch films.