Preparation and characterization of soy protein films reinforced with cellulose nanofibers obtained from soybean by-products

In this paper, we report the preparation of nanofibers obtained from low-cost agro-industrial by-products (soybean hulls and pods) and their use as nano reinforcers of soy protein films. From hulls, we obtained white and stable in-time aqueous dispersions of cellulose nanofibers of about 20 nm wide and 500 nm long and a hydrodynamic diameter of 269 nm, with a marked increase in the crystalline index as compared to raw material. Filmogenic solutions of soy proteins were prepared using glycerol as a plasticizer and different amounts of cellulose nanofibers (0; 10; 20 and 40% in relation to the amount of soy protein). The rheological behavior of filmogenic solutions containing nanofibers suggests an interaction between matrix and reinforcements. Films were prepared by casting of filmogenic solutions. As a result, we obtained films with a homogeneous surface having a large number of nanofibers, showing increasing opacity in samples with larger amounts of cellulose nanofibers. The addition of nanofibers decreases the film's susceptibility to water, by which a significant decrease in the total soluble matter and swelling in water was observed with an increase in contact angle. In addition, mechanical properties were also improved, obtaining more rigid films as the number of nanofibers increased.