Barrier and mechanical properties of modified starches

The study addressed starch-based coatings on paper and fabrics. Coated materials and free starch films containing different amounts of a well-established plasticizer (glycerol) or potential plasticizer (mainly polyols) were tested with respect to water vapour permeance (WVPe), water vapour permeability (WVP), glass transition temperature (T_g), and mechanical strength (tensile tests). Both normal and high- amylose potato starch were used. These starches were modified by (a) oxidation, (b) oxidation and hydroxypropylation or (c) oxidation and hydrophobically modified by reaction with octenyl- or alkenyl-substituted succinic acid anhydride. Free films of hydroxypropylated high-amylose potato starch showed a lower WVP than did the corresponding starches based on regular potato starch. The WVP of the hydrophobically modified regular potato starches was substantially higher than that of films of the corresponding hydroxypropylated starches. The expected hydrophobic effect of the succinic acid anhydrides in terms of a reduced WVP could not be observed. When glycerol was used as a plasticizer, about 30 parts (by wt.) per hundred parts of starch were needed in order to reduce the T_g and to cause observable changes in the mechanical properties of the free films.