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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Clay and Polymer Matrix Varieties on the Barrier Properties The mechanism to increase the barrier properties of materials from nanoclay is based on the increase in the tortuous length of the diffusion path through a polymer matrix. Because nanoclay has much greater specific surface area than micron-sized clay particles, higher barrier resistance will be expected for nanoclay-polymer composite than micron-clay-polymer complex. This also suggests that the barrier properties of the polymer/claynanocomposite will strongly depend on the degree of the dispersion of the nanoclay in thepolymer matrix, or obviously on the exfoliation degree of nano-clay layers. Therefore, the change of the barrier properties of the composite reflects indirectly the dispersion state of the nanoclay in polymer matrix, if other conditions Fillers can be added to a barrier polymer to reduce the price of the coating, to enhance the opacity or for mechanical reinforcement. The addition of fillers to polymer matrices can either increase or decrease the permeability, depending on the compatibility and adhesive properties between the polymer and the filler and also on their relative concentrations. Dispersion polymers are readily compatible with conventional coating pigments such as clay. The barrier properties are improved by increasing the diffusion path length of the permeating species (Figure 2). The critical pigment volume concentration CPVC is an important factor concerning filler addition. The CPVC concept refers to the point where the binder concentration is just large enough to fill in the interstitial voids between pigment particles for conventional paper coating, the addition of fillers is usually done at concentrations considerably higher than the CPVC. In barrier dispersions, on the other hand, pigments are added at a concentration well below the CPVC. The reason is that an increased number of filler particles will lead to an increase in voids, thus leading to an increase in permeability a higher binder concentration gives a more flexible coating, and the optimum pigment volume concentration becomes a compromise between barrier properties and flexibility. The CPVC of dispersions is affected by the immobilization volumes (i.e. the packing volume of the wet coating, which is dependent on particle shape, size, size distribution of pigment and binders, colloidal, chemical and rheological properties), the consolidation power of the binders, the type of substrate and the drying conditions. The most important factors concerning filler addition to barrier dispersions are the adhesion of the binder to the pigment particles, the particle shape and the chemical nature of the pigments. The CPVC value of a polymer/pigment system depends on are maintained the same. Filler Reinforcement
CPVC
Polymer
Filler
Void
Figure 3: Critical pigment volume concentration (CPCV).
the latex particle size and its size distribution [34]. Increased particle size decreases the CPVC as does an increased value of the glass transition temperature. In contrast, in dispersions where strong deformation of the latex particles occurs, a higher CPVC is obtained due to the more dense packing of polymer (Figure 3). Nanoparticulate Materials Montmorillonite is a naturally abundant clay material with a layered aluminosilicate structure that is often used in nanocomposite technology due to its high surface area and large aspect ratio. Dispersion of layered silicates in a polymer matrix can result in a number of different states, leading to micro composites, intercalated or exfoliated nanocomposites. It is believed that complete and homogeneous dispersion in which the clay platelets are arranged in a non-parallel manner (exfoliation) will give the highest performance improvements in coatings. The aluminosilicates can be dispersed into individual layers only 10 Å thick. The distance between the platelets, the basal spacing, is defined as the distance from a certain plane in one layer to the corresponding plane in a parallel layer. Montmorillonite is hydrophilic but can be made organophilic by exchanging the naturally occurring Na + ions in the galleries of the clay with organic cations, e.g. alkyl ammonium surfactants, making them more compatible with organic polymers. The relationship between surface diameter and thickness of the nanoclay particles is defined as the aspect ratio. Typically, commercial nanoclays have aspect ratios between 50 and 1000, which is much larger than for typical clay pigments (10–30) used in paperboard coating. The large aspect ratio of nanoclays makes them effective for barrier improvement even at very low (≤5% by weight) concentrations [35-37]. Higher weight additions may be difficult from a processing perspective, because the viscosity of the dispersions increases significantly at increased loads of clay. The use of nanoparticles in paper and board coating is thus advantageous, particularly given that less material is required (thinner coating layers) to reach the desired barrier or mechanical properties. Less material use leads to reduced costs and reduced amounts of waste [38]. Southern Clay Products and Nanocor are among the biggest suppliers of montmorillonite clays for nanocomposite applications. The addition of a nano filler is made to reinforce the polymer, i.e. to increase the strength and toughness of the material [39]. Other issues are to enhance the optical, thermal or barrier properties. The mechanism of barrier improvement relies on increasing the path length that the molecules have to traverse while diffusing through the film, i.e. forcing them to take a tortuous path, which leads to significantly prolonged transmission rates The barrier properties of a nanocomposite material depend on the relative orientation of the silicate layers and on the state of aggregation and dispersion. The plate- like structure of clay increases the path for diffusing molecules, thus decreasing the permeability of molecules through the material [40] . Porous nanoparticles into which the diffusing molecules can penetrate
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J Material Sci Eng ISSN: 2169-0022 JME, an open access journal
Volume 4 • Issue 1 • 1000151
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