Nano-clays processing

Y.H. Lee, T. Kuboki, C.B. Park, and M. Sain. Processing-property behaviors of PP/rice hull and PP/rice hull/nano-clay composites. In The Global Outlook for Natural Fiber Wood Composites, Intertech, Portland, ME, Lake Buena Vista, FL, 2005. 

The oxygen permeability in general decreases by 50 percent in polyamide matrix on nano-clay incorporation. Clay-polyamide nanocomposites can be used for packaging of processed meats, cheese, confectionery, cereals and boil-in-the-bag foods also for extrusion-coating applications in association with paperboard for fruit juice and dairy products, together with co-extrusion processes for the manufacture of beer and carbonated drink bottles (www.tifac.org). The nanocomposite packaging enhances the shelf life of many types of food. 

The primary effect of the nano-clays seems to be related to char formation. The workers at NIST have found that a reduction in mass loss and heat release rate only starts once the surface of the polymer is at least partly covered by char. Beyer reported that, while no char was produced by burning unfilled EVA, the filled composite formed a strong char early in the process [54]. Once the amount of clay is taken into account, final char levels are often similar to unfilled polymer, indicating that while a stronger, more insulating, char may form and retard combustion, it is eventually consumed in this test. 

Figure 10.2 Some processing strategies for making nano-clay polymer composites...

The lack of effect on total heat release, smoke and carbon monoxide, is different from halogenated flame retardants, and is taken to show that the effects are all in the condensed phase. Using gasification equipment, which duplicates the pyrolysis conditions in the cone calorimeter, without flaming taking place, Gilman and co-workers found that the melt that formed on the surface of unfilled polymer was quickly converted to a solid, black char when nano-clays were present [39]. It is postulated that this char is reinforced with nano-particles and slows down the combustion processes. It is,... 

Han, X., Zheng, C., and Lee, L. J. 2002. Processing and cell structure of nano-clay modified microcellular foams. ANTEC 2002. 

Ceramic powders Mica flakes Molybdenum disulfide Nano-clay Polyester fibers Antioxidants Antistatics Preservatives Processing aides Fungicides Smoke suppressants Foaming agents Viscosity modifiers Clarifiers Impact modifiers Odor reducers... 

Over the past decade extensive work has been done to develop a novel extrusion process with the aid of high power ultrasound [18-22], A number of studies on the effect of ultrasound on polymers have been published and reported in various review articles and books. It was shown that ultrasonic oscillations can breakdown the 3-D network in vulcanized rubber within seconds. Ultrasound was found to improve the compatibilization of immiscible plastic blends, plastics/rubber and rubber/rubber blends during extrusion process [23]. In recent years, use of ultrasound to disperse nanofdler in a polymer matrix is gaining attention. Ultrasound helps in rapid exfoliation and intercalation of nano-clay in a polymer matrix [24]. 

This paper investigates the foaming behavior of wood fiber/HDPE composites with small amounts of nano-clay. The nano-clay dispersion was characterized by XRD and TEM. An extrusion foaming experiment blown with N2 was conducted. The cell nucleation and growth of composite foams were studied with varying processing parameters, such as temperature, pressure and clay content. The effect of nano-clay on the final cell morphologies and foam density of wood fiber/clay/HDPE nanocomposite foams were identified. 

The foam density variations of the foamed WPCs with different contents of wood fiber as a function of die temperature are shown in Figure 4. With no gas injection, the density reduction may be due to the volatiles (e.g., moisture or extractives) generated from WF during processing. The addition of 1% exfoliated nano-clay particles decreased slightly the foam density of the composites. This may be because nano-clay particles increase the melt strength and thereby the possibility of gas escape from the extrudate skin decreases. 

Layered materials are of special interest for bio-immobilization due to the accessibility of large internal and external surface areas, potential to confine biomolecules within regularly organized interlayer spaces, and processing of colloidal dispersions for the fabrication of protein-clay films for electrochemical catalysis [83-90], These studies indicate that layered materials can serve as efficient support matrices to maintain the native structure and function of the immobilized biomolecules. Current trends in the synthesis of functional biopolymer nano composites based on layered materials (specifically layered double hydroxides) have been discussed in excellent reviews by Ruiz-Hitzky [5] and Duan [6] herein we focus specifically on the fabrication of bio-inorganic lamellar nanocomposites based on the exfoliation and ordered restacking of aminopropyl-functionalized magnesium phyllosilicate (AMP) in the presence of various biomolecules [91]. 

A series of five nanocomposite elastomer systems were prepared for this study incorporating 0, 1, 2, 4 and 8% (on total resin mass) of the organically modified montmorillonite clay Cloisite 6A. The appropriate level of Cloisite was dispersed in a starting resin blend of OH terminated PDMS (M -77,000 and Mn -550 g mol in a 3 1 ratio) by a combination of mechanical mixing and ultrasonic processing to give a nano-dispersion of clay platelets. The blend was subsequently crosslinked with a stoichiometric level of tetrapropoxysilane (TPOS) in the presence of 5% diphenylmethylsilanol (DPMS) chain terminator and 5% tin(II) 2-ethylhexanoate catalyst, cured in an open mould at 65°C for twenty minutes, then removed from the mould and post cured for a further fifteen hours at 65°C to give an elastomeric mat. 

Abstract The development of polymer-clay nanocomposite materials, in which nano-meter-thick layers of day are dispersed in polymers, was first achieved about 15 years ago. Since then, the materials have gradually become more widely used in applications such as automotive production. The first practical nylon-clay nanocomposite was synthesized by a monomer intercalation technique however, the production process has been further developed and a compound technique is currently widely used. A polyolefin nanocomposite has been produced by the compound method and is now in practical use at small volume levels. In this review, which focuses on njdon- and polyolefin-nanocomposites, detailed explanations of production methods and material properties are described. This article contains mainly the authors work, but aims to provide the reader with a comprehensive review that covers the works of other laboratories too. Lastly, the challenges and directions for future studies are included. 

A nylon 66 clay nanocomposite was produced using the dry-compound method [26]. Co-intercalation organophihc clay was used as the clay base. Na-montmorillonite was first processed using hexadecyl trimethyl ammonium ions and epoxy resin. It was then kneaded using a twin screw extruder to make a clay nano composite. As the amount of clay that was added increased, the amount of y (gamma) phases increased. This is thought to be due to the strong interactions between the nylon 66 chains and the sinface of the clay layers. 

The dispersion of clay platelets (exfoliation and intercalation level of the silicate layers) and surface area of silicate platelets have the potential to alter the rheological behavior of the nanocomposites. In-situ polymerized nano composites exhibit more exfoliated structure than the composites prepared by the melt blending technique. Irrespective of the processing parameter, the nanocomposites show shear thinning behavior at high shear rate (Figure 9.14), whereas the pristine polyamide exhibits Newtonian behavior (i.e., the viscosity remains almost the same). It has also been reported that the polymer nanocomposite possesses higher steady shear viscosity than pristine polyamide at low shear rates. 

Clay size, density and interfacial adhesion may prolong the void initiation process. The fracture energy required to initiate the crack may be increased if the adhesion between the clay and the PP matrix is improved. If the clay particles are dispersed in nano- (or) submicron level, the aspect... 

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