Gas Barrier Properties of Biopolymerbased Nanocomposites: Application in Food Packaging - Advanced Materials for Agriculture, Food and Environmental Safety - page 368

13.1 Introduction
A nanocomposite is a multiphase material derived from the combination
of two or more components, including a matrix (continuous phase) and a
discontinuous nanodimensional phase with at least one nanosized dimen-
sion (i.e., with less than 100 nm). h e nanodimensional phase can be
divided into three categories according to the number of nanosized dimen-
sions. Nanospheres or nanoparticles have the three dimensions on the
nanoscale. Both nanowhiskers (nanorods) and nanotubes have two nano-
metric dimensions, with the dif erence that nanotubes are hollow, while
nanowhiskers are solid. Finally, nanosheets or nanoplatelets have only one
nanosized dimension. Most nanosized phases have a structural role, act-
ing as reinforcements to improve the mechanical properties of the matrix
(usually a polymer), since the matrix transfers the tension to the nanore-
inforcement through the interface. Nanoreinforcements are especially
useful for biopolymers, because of their usually poor performance when
compared to conventional petroleum-based polymers. h e incorporation
of nanosized reinforcements into biopolymers may open new possibilities
for improving not only their properties but also their cost-price ei ciency.
Nowadays, most materials used for packaging are practically undegrad-
able, representing a serious global environmental problem. New bio-based
materials have been exploited to develop edible and biodegradable ilms
in a big ef ort to extend shelf life and improve quality of food while reduc-
ing packaging waste [1]. However, the use of edible and biodegradable
polymers has been limited because of problems related to performance,
processing and cost. Starch, for example, has received considerable atten-
tion as a biodegradable thermoplastic polymer. However, it has a poor per-
formance by itself because of its water sensitivity and limited mechanical
properties with high brittleness, which is related to the anarchical growth
of amylase crystals with time [2]. h e application of nanotechnology to
these polymers may open new possibilities for improving not only the
properties but also the cost-price ei ciency. h e main advantage of plas-
tics compared with other packaging materials is that they are lightweight,
can be processed quickly and easily and of er design and printing l exibil-
ity. However, petroleum resources are i nite and fuel prices have recently
been escalating. In addition, the end-of-life management of plastics has
also depleted the world's rights for sustainability. Hence, the emergence of
biopolymers as an alternative material option has been promising.
h e majority of materials currently used for packaging are nondegrad-
able, creating environmental problems. Several biopolymers and proteins