Production and characterization of fully biobased foamed films based on gelatin

The objective of this study was to produce and characterize gelatin foamed films using extrusion. Three “optimum” formulations containing tannic acid, nanoclays (Cloisite Na+), glycerol, water, and gelatin, as well as three “controls” without tannic acid and nanoclays were prepared by calendering. Furthermore, the three “optimum” formulations were produced by extrusion film blowing only, since no stable processing conditions could be obtained for the controls. A complete set of sample characterization was performed, including morphological, mechanical, physical, and thermal properties. The results showed that besides the processing method, the thickness was also controlled by the glycerol and water content, leading to density slightly above unity, with higher values for the optimum materials. The calendered films from the optimum formulations showed overall a higher number of cells and cell density than the controls. Higher elastic moduli and tensile strengths were obtained for the films from the optimum formulations made by either method because of the reinforcing effect of the tannic acid and nanoclays, but this led to lower strain at break. The thermal profiles were similar for all films, with higher stability for the optimum formulations. The results were also explained via chemical interactions between the components as observed by Fourier transform infrared spectroscopy. Overall, the optimum formulations not only produced better foamed films in terms of general properties but were much easier to process by both methods (calendering and blowing).