Effects of the geometry of reinforcement on physical properties of sodium caseinate/TiO2 nanocomposite films for applications in food packaging.

Plastic materials for food packaging are being replaced by biodegradable films based on biopolymers due to the adverse effects they have had on animal life and the environment. In this study, nanocomposite films containing 2.5 wt% sodium caseinate and 2 wt% glycerol were reinforced with 0.1 or 0.2 wt% nano TiO2 prepared in two forms: spheres (P25) and tubes. The effects of nanoreinforcement geometry on mechanical, tensile, barrier, thermogravimetric, and optical properties, and distribution of nanoparticles were described. The interactions among film components were analyzed by Fourier transform infrared spectroscopy (FTIR). Addition of nanotubes significantly increased E' (341 wt%) and E" (395 wt%) moduli, the Young modulus E (660 wt%), the residual mass at 500°C (38 wt%), and color change (6.78) compared to control film. The compositional mapping studies showed that P25 nanoparticles were homogeneously distributed between the surfaces of the film while nanotubes were found on the bottom surface. The changes in position of the FTIR spectra signals as compared to pure protein signals indicated strong matrix/reinforcement interactions. In addition, the changes in intensity in 1100, 1033, and 1638 cm-1 FTIR signals suggested formation of a protein/Tween 20 ester. The geometry of reinforcement was highly relevant regarding physical properties, showing nanotubes as being very successful for enhancing tensile properties.

Nanoreinforcement as a strategy to improve physical properties of biodegradable composite films based on biopolymers.

Food packaging is evolving from inert plastic to renewable biopolymer film that acts as barrier against gases, light radiation, and microorganisms, reducing food waste without environmental damage. Distinct starting systems were selected to prepare films: single polymer matrix, blend of polymers, cross-linked polymers, and emulsion-based matrix. The blend of polymers was one of the best approaches to improve mechanical and barrier properties of films, especially when one of the polymers was pectin, gelatin or xanthan gum. These polymers can form a gel and increase the viscosity of the starting systems leading to a more elastic matrix. Although some of these films showed potential to replace plastic materials, their physical properties were poor compared to plastics. Thus, several strategies were used to strengthen matrix building block connections or interactions between nanoreiforcement and matrix compounds with the aim of improving physical properties. Among metal oxides, TiO2, ZnO, CaO, and MgO were the most studied, alone or in combinations with other reinforcements. Natural fillers, like chitosan and cellulose nanofibers were also added to improve the biopolymer's performance. Several of these systems successfully extended the shelf life of food systems by retarding spoilage, showing great potential to improve food quality and reduce waste. However, most of the studies were carried out on a laboratory scale and it would be necessary to explore the feasibility of producing these films on an industrial scale.