Citric acid cross-linking of starch films

This paper shows that citric acid can cross-link starch and improve the tensile strength, thermal stability and decrease the dissolution of starch films in water and formic acid. The poor mechanical properties and water stability of starch have restricted its industrial applications. Although cross-linking is a common approach to improve the properties of starch products, current starch cross-linking methods are either expensive, toxic or do not impart the desired properties to the cross-linked materials. In this research, the possibility of cross-linking starch films using citric acid to improve their strength and stability was examined. Citric acid cross-linked starch films show about 150% higher strength than non-cross-linked films and have strength better than most cross-linked starch and synthetic polymer blended films previously developed. Films cross-linked with 5% citric acid had only 35% loss in weight after being in formic acid for 5 h at 50 °C whereas the non-cross-linked films dissolved immediately.