Nano-clays dispersion

Bandyopadhyay, J., and Sinha Ray, S. The quantitative analysis of nano-clay dispersion in polymer nanocomposites by small angle X-ray scattering combined with electron microscopy. Polymer. 51 no. 6 (2010) 1437-1449. 

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. 

Figure 9.27 shows the TEM micrograph of the cell wall foamed at 100 °C under 28 MPa. Interestingly, the grown cells with a diameter of 200 nm are localized along the dispersed nano-clay particles in the cell wall. In other words, the dispersed nanofiller particles act as nucleating sites for cell formation and the cell growth occurs on... 

It was reported that the compatibilizer normally gets adsorbed on the surface of the clay platelets and alters the interphase [92]. The tensile strength and tensile modulus are always good for CPN compared with PP. The nano-level dispersion of clay in PP plays a vital role in such an improvement. The stiffness of the silicate layers contributes to the presence of immobilized (or) partially immobilized polymer phases [93]. The orientation of the silicate layer and molecular orientation also play a vital role in the improvement of the stiffness. 

The nano-level dispersion of clay in thermoplastic olefin (TPO) polymer has potentially provided a platform for its use in automotive body panels of Volvo cars. The governing factors are light weight, consistent physical and mechanical properties, improved aesthetic appearance, improved wear resistance, and low temperature ductility. Recyclability of nano-clay incorporated thermoplastic olefin nanocomposites has provided an opportunity for their use in step assists and trim and panel in Hummer cars. 

In order to minimize the oxidative degradation of SBR at high temperature. He et al. [112] prepared SBR/clay/carbon black (CB) nanocomposites, then the effects of nano-clay on the properties of SBR nanocomposites were investigated. They found that the two fillers were uniformly dispersed in the SBR matrix at nano-scale. 

Horsch, S. Serhatkulu, G. Gulari, E. Kannan, R. M., Supercritical COj Dispersion of Nano-Clays and Clay/Polymer Nanocomposites. Polymer 2006,47, 7485-7496. 

Nano-clay composites contain very thin, high aspect ratio, alumino-silicate platelets, derived from the stacks present in the parent clay. Two types of stmcture can be recognised, intercalated and delaminated. In the intercalated form, the stacks of platelets are still present, but with polymer chains present between clay platelets, pushing them apart. In the delaminated form, the original stacks are no longer present, and the platelets are fully dispersed. 

Figure 10.6 High resolution electron micrograph of a cross-section of a nano-clay/ polypropylene composite illustrating some intercalated, partly dispersed clay stacks (tactoids) Micrograph kindly supplied by Monica Celotto)...

The same situation exists for nano-clays, but is complicated by the presence of surface-active species used in their preparation. These organic treatments comprise a significant part of most nano-clays, and fulfil a number of very important functions. Thus, they increase the gallery spacing, making it easier for other species, such as monomers or polymers, to intercalate. The increased spacing also makes it easier to disperse, or delaminate the structure. In the simplest cases, these intercalants would also provide the compatibility and interaction with the polymer matrix described previously. It is thus obvious that the nature and amount of intercalant have to be chosen carefully and controlled. For ease of treatment, it is also helpful for the intercalant to be water soluble. 

This is an area where the nanoclays appear to offer very distinct advantages and is already undergoing commercialisation. Thns, as little as 2 wt% of a nano-clay is sufficient to decrease the oxygen transmission rate of a polyamide film by over 40%. Their performance is believed to be due to the creation of a tortuous diffusion path, as shown in Figure 10.8. (Note alignment is necessary for this. Truly random dispersion would not give the same effect). 

Combustion Behavior of Polymeric Nanocomposites Based on Cationic Clays Layered silicates dispersed at a nanoscale in a polymeric matrix reduce the maximum rate of heat release up to 50 to 70% with a clay loading of only 5 wt%. The degree of clay dispersion affects the performance observed. On the one hand, a nano-dispersion is necessary, as no significant improvement in terms of the heat of release rate is observed when layered silicates are dispersed in the polymeric matrix at a micro level. On the other hand, exfoliation of clay is not necessary, and intercalated nanocomposites perform as well as delaminated nanocomposites. ... 

Comparisons were made by Utracki and Sepehr [6] between single and twin screw extruders for compounding nano-clays into polyamide-6 and PP, in which the elongational flow mixer (EFM) described in Chapter 15, was used. The combination of single screw extruder plus EFM produced better dispersions than were achieved with a twin screw extruder with or without an EFM. 

The protein/glycerol/water/Cloisite Na (treated) sample also showed a single Tg at 118.0 °C, 5.5 °C higher than observed in the untreated nanocomposite, due to the further restriction in molecular motion of the protein by the predominantly exfoliated dispersion of the nano-clay. The secondary (or (3) relaxation in the neat protein/glycerol/water/Cloisite Na (untreated) sample was situated at... 

Filled polymer systems of industrial importance, e.g., filled rubber compounds, filled thermoplastics are thus meso or microcomposites, possibly with a structuration (of the dispersed phase) at the nano or meso scale. Whilst no sizeable commercial application yet exist for nanocomposites rubbers or thermoplastics (to the author s knowledge), considerable research has been made since 1984 with so-called ex-foliated layered silicate "nano-clays." Exfoliation means that individual clay sheets, of around 1 nm thickness, have been separated and adequately dispersed in the matrix. Some reinforcement has indeed been demonstrated with such exfoliated nanoparticles but, generally with very specific rubber systems and/or at a cost of preparation that is hardly compatible with reasonable chances of commercialization. 

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]. 

Clays have long been used as fillers in polymer systems because of low cost and the improved mechanical properties of the resulting polymer composites. If all other parameters are equal, the efficiency of a filler to improve the physical and mechanical properties of a polymer system is sensitive to its degree of dispersion in the polymer matrix (Krishnamoorti et ah, 1996). In the early 1990s, Toyota researchers (Okada et ah, 1990) discovered that treatment of montmorillonite (MMT) with amino acids allowed dispersion of the individual 1 nm thick silicate layers of the clay scale in polyamide on a molecular. Their hybrid material showed major improvements in physical and mechanical properties even at very low clay content (1.6 vol %). Since then, many researchers have performed investigations in the new field of polymer nano-composites. This has lead to further developments in the range of materials and synthesizing methods available. 

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