The manufacture of food packaging materials from food hydrocolloids has been widely studied during the last decades and multiple alternatives have been investigated, with research mainly focusing on improving the physicochemical and mechanical properties of the different materials. Processing food hydrocolloids by reactive extrusion (REx) for the development of food packaging has, however, been poorly studied. Four film systems were prepared from corn (Zea mays) thermoplastic starch (TPS) containing either cellulose acetate (C) or chromium octanoate (Cat -a potential food grade catalyst), or a blend of both (C + Cat). Processing was done under REx conditions using a twin-screw extruder. An exhaustive study of the resulting materials was carried out in terms of the structural, physicochemical, thermal, surface, mechanical and compostable properties related to their potential use in food packaging applications. The most hydrophobic material was the C-containing film. However, this physicochemical behavior was different on the film surface, thus suggesting molecular rearrangements within the material. The Cat-containing films were darker than the other materials. The mechanical behavior observed in the Cat-containing films was particularly interesting as it suggests that these film systems could be used as shape memory materials for food packaging applications, as long as the following mechanical conditions are not exceeded: 5.02% strain and 0.43 MPa stress. All the films tested were biodegradable. We confirmed that Cat-containing film systems produced non-compostable materials at high concentrations (1 mg/mL), as measured by its effect on lettuce seedlings. This confirms that biodegradable materials are not necessarily compostable.
Several alternatives have been proposed to improve the properties of starch‐based films. However, single step processing and modification procedures such as reactive extrusion (REx) have been little studied in conjunction with carbohydrate polymers. Films were prepared from native and carboxymethylated plantain (Musa ssp., group AAB, sub‐group clone Harton) flour/polystyrene (PS) blends, with glycerol as a plasticizer, by REx using a twin‐screw extruder with chromium octanoate (Cr(Oct)3) as a catalyst (Cat), followed by thermo‐molding. The structural, physicochemical, thermal, surface, mechanical (shape memory) and antimicrobial properties relevant to the potential use of the films in food packaging applications, were then exhaustively characterized. The developed films could be used as shape materials due to their mechanical properties, which featured elastic, creep, and plastic zones, as long as the following mechanical thresholds are not reached: 1.00% strain and 1.14 MPa stress (for the film with the best characteristics). The results of the TGA, mechanical properties tests and antimicrobial activity assay suggest that Maillard reactions can occur simultaneously with the cross‐linking reactions generated by the Cat between the natural and synthetic polymers. The films made with the carboxymethylated flour were less hydrophilic than those prepared using the native flour due to the establishment of a higher dipole moment.
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