ABSTRACT
Development of innovative products starts from the raw materials. Packaging industry relies heavily on oil-based materials in certain applications. Replacing the oil-based material with bio-based products might give a competitive advantage due to more sustainable and greener image. In addition, nanotechnology in food packaging is expected to grow strongly over the next 5 years as the increased globalization sets demands for shelf life enhancing packaging. Recently, a lot of effort has been aimed at developing new bio-based polymer containing films and nanocomposites which can act as for example barriers in packaging materials (Arora and Padua, 2010; Lagarón and Fendler, 2009; Vartiainen et al., 2010a, 2010b). Unlike synthetic plastics, in dry conditions, the films and coatings from natural polymers exhibit good barrier properties against oxygen and grease due to the high amount of hydrogen bonds in their structure. However, natural polymers are hydrophilic in nature, thus films and coatings produced from these materials are often hygroscopic, resulting in partial loss of their barrier properties at high humidity (Hansen and Plackett, 2008). A major challenge for the packaging developers is to overcome the inherent hydrophilic behavior of biomaterials. Among the potential fillers for nanocomposites, clay platelets have attracted a particular interest due to their high performance at low filler loadings, rich intercalation chemistry, high surface area, high strength and stiffness, high aspect ratio of individual platelets, abundance in nature, and low cost (Blumstein, 1965). Clays are naturally occurring materials composed primarily of fine-grained minerals. Nanoclays (or nanolayered silicates) such as hectorite, saponite, and montmorillonite are promising materials with high aspect ratio and surface area (Lan et al., 1994; Messersmith and Giannelis, 1995; Yano et al., 1997). Because of their unique platelet-like structure nanoclays have been widely studied regarding the barrier properties. Such nanoclays can be very effective at increasing the tortuosity of the diffusion path of the diffusing molecules, thus significant improvement in barrier properties can be achieved with the addition of relatively small amounts of clays (Pavlidou and Papaspyrides, 2008). When the nanoclay layers are completely and uniformly dispersed in a continuous polymer matrix, an exfoliated or delaminated structure is obtained. Full exfoliation (single platelet dispersion) of nanoclay by using existing/traditional compounding techniques is very difficult due to the large lateral dimensions of the layers, high intrinsic viscosity of the polymer and a strong tendency of clay platelets to agglomerate (Hussain et al., 2006). Most of the clays are hydrophilic, thus mixing in water with water-soluble polymers
results good dispersion, especially when the sufficient amount of mixing energy is used. The degree of exfoliation can be improved by the use of conventional shear devices such as extruders, mixers, ultrasonicators, ball milling, fluidizators, and so on.
MATERIALS AND METHODS
