PHYSICAL PROPERTIES OF HYDROGEL FILM BASED ON ACETYLATED POTATO STARCH/CHITOSAN/TANNIC ACID REINFORCED WITH MONTMORILLONITE NANOPARTICLES

The development of biopolymer-based hydrogels for food packaging applications has gained particular relevance in recent years. In this work, the effect of montmorillonite nanoparticles (MMT-NP) concentration on the mechanical properties and the swelling of hydrogel films based on acetylated starch/chitosan/tannic acid was studied. Potato starch was acetylated using acetic anhydride (3 g acetic anhydride /100 g starch) and 4% NaOH solution (w/v) at pH 8.0-8.4 for 75 min. The MMT-NP were dispersed in distilled water (1g/100 g) using a mechanical homogenizer (20,000 rpm/ 30 min) and an ultrasonic processor (60% amplitude/15 min). Hydrogel films were prepared using acetylated potato starch (degree of substitution= 0.09±0.01) and chitosan (3 g biopolymers/100 g de film forming solution) at 3:1 ratio (starch/chitosan) by the casting method, and montmorillonite nanoparticles (0, 1, 3, and 5 g montmorillonite/100 g polymers), glycerol (30 g glycerol/100 g starch) and tannic acid (5 g tannic acid/ 100 g biopolymers) as crosslinking agent. Film thickness was measured using a digital micrometer. The mechanical properties were determined by uniaxial tensile tests (ASTM method D882-10). The swelling ratio was determined by the gravimetric method using distilled water at 25 °C for 24 h. The MMT-NP presented a hydrodynamic diameter of 315.7±0.15 nm with a polydispersity index of 0.24±0.02. The thickness of the hydrogel films was approximately 110 µm and was not affected by MMT-NP presence (0-5%). The increase of MMT-NP concentration (0-5%) did not influence the tensile strength of the films, which varied from 9.5±1.9 to 12.7±1.9 MPa. Meanwhile, the elongation at break of the films increased by 51% at 5% MMT-NP, suggesting a better dispersion of the nanoparticles at this concentration. The swelling ratio of the films varied from 1402.2±226.6 to 673.4±23.9% with the addition of MMT-NP (0-5%), showing a decrease at 5% concentration, probably due to the formation of hydrogen bonds between the nanoparticles and the hydrogel matrix. The incorporation of MMT-NP into the hydrogels can enhance their elongation at break and tune the swelling ratio. These findings provide valuable insights into the effects of nanoparticle concentration on the properties of a hydrogel matrix for food packaging systems.