Agro-proteins are an attractive alternative to synthetic plastic
made from non-renewable resources that can be a hazard to the
environment [24] at least in some applications. Protein films
generally exhibit excellent barrier properties against oxygen,
lipids, and aroma, poor mechanical properties and high water
vapor permeability [25–27]. This behavior should be attributed to
the inherent hydrophilic nature of proteins, and to the presence of
plasticizers (e.g. glycerol) in the formulation that are usually added
to avoid chipping or cracking of the film during subsequent
handling and storage [28]. These properties along with their
biodegradability makes these materials interesting for their use
in short-lived products such as food packaging.
Among proteins, those from soybeans have been extensively
studied in order to develop films that are biodegradable, and even
edible, because soy proteins are among the most abundant and
economical and furthermore can be recovered as a recyclable
by-product of the vegetable-oil industry [29].
Numerous studies have been reported and reviewed by Song
et al. [30] considering different alternatives to improve the
mechanical properties and to decrease the water sensibility of
soy proteins based materials thus extending their usefulness. They
included physical chemical and/or enzymatic treatments on proteins
and film forming dispersions, the preparation of materials
from blends of proteins with other biopolymers, the addition of
lipids, fibers, nanoreinforcements and other compounds that could
activate films with other properties, such us antimicrobial or
antioxidant ones.
Because of the hydrophilic nature of both the soy proteins and
natural sodium MMT, the dispersion of both materials in water and
subsequent generation of nanocomposites through the process of
casting becomes possible.
The aim of this work was therefore to study the effect of
MMT addition to soy-protein-based films on the physicochemical
properties of the resulting nanocomposites and to analyze the
structure–function relationship of these materials and the changes
in phase structures due to different interaction between the
material components (proteins, montmorillonite, glycerol and