Citation: Gaikwad KK, Ko S (2015) Overview on in Polymer-Nano Clay Composite Paper Coating for Packaging Application. J Material Sci Eng 4: 151. doi:10.4172/2169-0022.1000151
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intergalleries. The in situ polymerization of monomer within the clay interspacing causes the expansion and exfoliation of the nanoclay platelets [24,25]. Although many polymer–nanoclay composites have been developed, it is generally accepted that a strong mechanical force, such as delamination and extrusion, is needed to help polymer molecules penetrating into the nanoclay basal interspacing. Barrier coating is one of the most important properties for paper packaging containers. The conventional barrier boards for water vapor, grease and oxygen-proofing applications have been developed based on the extrusion products of a range of polymers, such as polyethylene (PE), poly (ethyl terephthalate) (PET), or natural wax as well Recently, aqueous-based polymers have come into use in many on-machine or off-machine coatings, due to their environmentally friendly process and easy to use, in comparison with the conventional extruding machine coating processes. There are some challenges in improving barrier coating efficiency using water-based nanoclay composite suspensions. For example, the nanoclay particles must be colloidally stable in the suspension and the clay particles must be exfoliated in the final polymer matrix. The former requires a high hydrophilic surface of the clay so the clay can be well dispersed in water phase but the latter requires a high hydrophobicity so the polymer can diffuse into the intergalleries between clay plates. Furthermore, the nanoclay particles must possess strong affinity to polymer to avoid interior defects formation in hindering the diffusion of permeants through the coating layer. In conventional polymer composites, the micron- sized fillers, for example, kaolin with particle size up to a few microns, are immiscible with polymer matrix, leading to a coarsely blended composite with chemically distinct phases. The poor compatibility causes a poor physical attraction between the organic and inorganic components, resulting in agglomeration, and therefore, weaker mechanical properties, and thus low barrier resistance at the same process conditions [26]. Moisture barrier coatings containing clay Moisture barriers are frequently applied to paper wrappers or paperboard to protect food products and to corrugated paperboard in order to withstand high humidity storage conditions. In the latter case, it is important to prolong the lifetime of the packaging box by resisting creep failure. Barriers can be applied to a substrate such as paperboard by extrusion coating, lamination or dispersion coating techniques. The latter has recently gained much interest as a low cost alternative with many benefits [27-33]. Moisture barrier dispersion coatings have a competitive advantage over wax based coatings, laminates or extruded products in recyclability and higher application speeds as well as fewer processing steps. Barrier dispersion coatings being more readily compostable and repulpable are far more environmentally friendly than extrusion coatings or laminated boards where recovery of the fibres and disposal of polymer film and/or wax represent a significant cost impost. In some food applications, the use of coatings that are free of fluorine containing compounds is also of interest. The two most attractive reasons for using barrier dispersion coatings are lower cost and the ability to use conventional coating techniques. The barrier dispersion coatings studied by C. Kugge based on styrene–butadiene latex and clay, with latex solid ratios of less than one; the coatings are transparent and clay acts as filler in a polymeric matrix. This situation compares with conventional paper coatings where the pigment to latex ratio is greater than one and the latex functions as a binder.
materials. The inorganic particles have at least one dimension in the nanometer (from 1 to 100 nm) range. It means that a uniform dispersion of these particles can lead to ultra-large interfacial area between the constituents. The very large organic/inorganic interface alters the molecular mobility, the relaxation behavior and the consequent thermal and mechanical properties of the resulting nanocomposite material. Various inorganic nano-particles have been recognized as possible additives to enhance the polymer performance. Some examples of these particles are represented by the solid layered, the synthetic polymer nano-fibers, the cellulose nano-whiskers and the carbon nanotube. Among these, up to now only the layered inorganic solids like clay have attracted some attention by the packaging industry. This is not only due to their availability and low cost but also due to their significant enhancements and relative simple process ability. The first successful example of a polymer–clay hybrid, developed at Toyota Central Research Laboratories in 1986 was a nylon–clay hybrid (Figure 1) [9]. Packaging Application Paper and paperboard are coated in order to improve their optical properties and printability. Paper coating formulations generally consist of inorganic pigments such as kaolin and calcium carbonate, binder, soluble co-binders, dispersants, water as carrier and other additives. Pigment is the abundant component in the coating and is naturally the most important factor affecting the properties of the coating materials [10]. The use of mineral pigments in dispersion coating to provide improved barrier properties has recently gaining increased attention [11-16]. Important physical or chemical properties of the pigments which affect the water vapor permeability are their aspect ratio, particle size distribution and hydrophilic/hydrophobic character found that a narrow particle size distribution and a large aspect ratio both had a positive effect on the barrier properties of talc- filled dispersion-coated paper substrates [11-13]. Talc pigments in the polymer coatings were also shown by to give slightly lower water vapor transmission rates (WVTR) than kaolin clays [17,18]. Improving Water and Moisture Barrier in Coating Polymer–clay nanocomposites, with fully-exfoliated platelet structure of nanoclay dispersed within a polymer matrix, provide excellent mechanical and barrier performances due to the high surface- to-volume ratio of the nanofiller and the increased tortuosity of the diffusion path against the permeant [19-23]. The modification of the clay by intercalating cationic surfactants into its interlayer space allows the entry of hydrophobic monomer or polymer into the organophilic
Solid Layered
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Figure 1: Preparation methods of polymer nanocomposites.
J Material Sci Eng ISSN: 2169-0022 JME, an open access journal
Volume 4 • Issue 1 • 1000151
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