Influence of Alkali Treatment on the Physicochemical and Mechanical Properties of Starch Chitosan Films

Treating starch‐chitosan films with mild alkali makes them insoluble in water and common solvents, required for converting chitosan‐starch blends into value added products. Chitosan has good antibacterial properties but has poor resistance to aqueous conditions. Although chemical and physical modification helps to improve properties of chitosan and starch, most of these modifications are expensive. Previous studies have shown that alkali treatment can affect the structure and properties of chitosan and starch. Hence, the objective of present work is to study the effect of alkali treatment on the physicochemical and mechanical properties of chitosan starch blends. Various ratios of chitosan are blended with starch and made into films using the solution casting process. Films formed are immersed in a 0.5 N NaOH solution for 10 min which resulted in substantial transformation of the polymers, particularly chitosan. Mechanical properties, swelling, and sorption in water and physical characteristics of the pure and blend films are investigated. Chitosan starch blend film after alkali treatment in neutral and alkaline medium showed decrease in water sorption from 800 to 100% whereas strength of the chitosan starch blend films increased with increasing starch percentage. The 50/50 blend film had strength of 9 MPa and the alkali treatment helps in increasing the flexibility of the films by nearly 50%. The films are resistant to common solvents and even boiling water after the alkali treatment. The extent of changes in water sorption and mechanical properties were dependent on the proportion of starch/chitosan. Pure and blend films after alkali treatment could be considered for packaging, medical, and other applications. Starch and chitosan are natural biopolymers extensively used for non‐food industrial applications. However, both starch and chitosan are hydrophilic and do not have necessary stability in aqueous conditions and also lack good mechanical properties. The authors demonstrate a simple approach of increasing the water stability and mechanical properties of starch‐chitosan blend films.