Thermoset/clay nanocomposite

Figure 7.6 A flowchart describing the synthesis of a thermoset/clay nanocomposite...

The key question regarding the structure of a thermoset/clay nanocomposite system is whether a true nanocomposite has formed or not. If not, the material is comparable to a conventional filled microcomposite. Generally, wide angle X-ray diffraction (WAXD) analysis and transmission electron microscopy (TEM) are used to elucidate the structure of a nanocomposite. Due to its easiness and availability, WAXD is most commonly used to establish the nanocomposite structure [30, 31]. By monitoring the position, shape, and intensity of the basal reflections from the distributed silicate layers, the nanocomposite structure (intercalated or exfoliated) may be identified. The X-ray technique is often applied to identify nanocomposite structures through Bragg s relation, which is given below ... 

Figure 7.14 A tortuous model for permeability of thermoset/clay nanocomposites...

Thermoset/Clay Nanocomposites. A nmnber of studies have reported the processing and properties of thermoset/clay nanocomposites (26). Nanoclay materials, such as montmorillonite, are layered sihcates, ie they have a lamellar structure. Elementary clay platelets consist of a 1-nm thick layer. Stacking of layers leads to a regular gap called a gallery or interlayer whose rf-spacing can be measured by X-ray diffraction. The interlayer space can be penetrated by... 

Many different polymers have already been used to synthesize polymer-clay nanocomposites. In this section, an overview of the advances that have been made during the last 10 years in the intercalation and the delamination of organoclay in different polymeric media is given. The discussion mainly covers the work involving thermoset nanocomposites along with a brief discussion about thermoplastic-based nanocomposites. 

Incorporation of modified clays into thermosetting resins, and particularly in epoxy35 or unsaturated polyester resins, in order to improve thermal stability or flame retardancy, has been reported.36 A thermogravimetric study of polyester-clay nanocomposites has shown that addition of nanoclays lowers the decomposition temperature and thermal stability of a standard resin up to 600°C. But, above this temperature, the trend is reversed in a region where a charring residue is formed. Char formation seems not as important as compared with other polymer-clay nanocomposite structures. Nazare et al.37 have studied the combination of APP and ammonium-modified MMT (Cloisite 10A, 15A, 25A, and 30B). The diluent used for polyester resin was methyl methacrylate (MMA). The... 

H. Deka and N. Karak, Vegetable oil based hyperbranched thermosetting poly-urethane/clay nanocomposites . Nanoscale Res Lett, 2009, 4,758-65. 

In the last decade, considerable progress was observed in the field of PO/compatibil-izer (predominantly on the base of PO-g-MA)/organo-surface-modified clay nanocomposites. Polyethylene (PE), polypropylene (PP), and ethylene-propylene (EP) rubber are one of the most widely used POs as matrix polymers in the preparation of nanocomposites [3,4,6,30-52]. The PO silicate/silica (other clay minerals, metal oxides, carbon nanotubes, or other nanoparticles) nanocomposite and nanohybrid materials, prepared using intercalation/exfoliation of functionalized polymers in situ processing and reactive extrusion systems, have attracted the interest of many academic and industrial researchers because they frequently exhibit unexpected hybrid properties synergisti-cally derived from the two components [9,12,38-43]. One of most promising composite systems are nanocomposites based on organic polymers (thermoplastics and thermosets). 

There has been a considerable amount of work conducted on thermoset resin/clay nanocomposites. The overall trends seen in thermoplastics concerning engineering, flammability, and barrier properties are also seen in thermosets. Table 33.6... 

Polymer/clay nanocomposites (PCN)are a new class of nanocomposite that makes use of clay materials, which are cheap and well known fillers for polymer materials. The research on polymer-clay intercalation has been reported before 1980s [10]. However, these works were not taken in the history of polymer/clay nanocomposites as these did not result in a dramatic improvement in the physical and engineering properties of the polymers. The researchers at Toyota, Japan demonstrated for the first time that clay (so called filler) can do miracles in 1993 [11,12]. While searching for a lightweight material for automotive applications they successfully developed a nylon-6/clay nanocomposite, which resnlts in a dramatic improvement in properties compared to the pristine polymer. Subseqnently, the technique was extended to thermoset resins leading to the formation of thermoset nanocomposites. 

The two decades have witnessed an extensive research and development in the field of thermoset nanocomposites. The physics and chemistry of intercalation of clay (layered silicate) in thermoset resin have been understood to a great extent though synthesis of fully exfoliated thermoset-based nanocomposites still remains as a challenge. More research is necessary to study the feasibility of integrating the nanoreinforced thermoset resins into the fibre-reinforced plastics to develop composite structure not... 

Storage modnlus of PP-wood composites [80], basalt fibre-reinforced PP [88], ethylene-propylene-diene terpolymer [89], polyvinyl fluoride-clay nanocomposites [90], thermosetting resins [91], and water-based adhesives [81, 82]. 

Liu Ying-Ling, Wang Yao-Hsuan, and Chen Hsueh-Shih. Novel thermosetting resins based on 4-(N-maleimido) phenylglycidylether, 4 preparation and properties of polymer-clay nanocomposites. Macromol. Chem. Phys. 206 no. 5 (2005) 600-606. 

The comprehensive flame retardation of polymer-clay nanocomposite materials was reported by Dr. Jeff Gilman and others at NIST [7]. They disclosed that both delaminated and intercalated nanoclays improve the flammability properties of polymer-layered silicate (clay) nanocomposites. In the study of the flame retardant effect of the nanodispersed clays, XRD and TEM analysis identified a nanoreinforced protective silicate/carbon-like high-performance char from the combustion residue that provided a physical mechanism of flammability control. The report also disclosed that The nanocomposite structure of the char appears to enhance the performance of the char layer. This char may act as an insulation and mass transport barrier showing the escape of the volatile products generated as the polymer decomposes. Cone calorimetry was used to study the flame retardation. The HRRs (heat release rates) of thermoplastic and thermoset polymer-layered silicate nanocomposites are reduced by 40% to 60% in delaminated or intercalated nanocomposites containing a silicate mass fraction of only 2% to 6%. On the basis of their expertise and experience in plastic flammability, they concluded that polymer-clay nanocomposites are very promising new flame-retarding polymers. In addition, they predict that the addition... 

Triantafillidis, C.S. LeBaron, P.C. Pinnavaia, T.J. Thermoset epoxy-clay nanocomposites the dual role of alpha.omega-diamines as clay surface modifiers and pol3mer curing agents. J. Solid State Chem. 2002, 167, 354-362. 

With both thermoset and thermoplastic in situ polymerization techniques, there are some fundamentals of polymer nanocomposite synthesis that are weU understood. One fundamental to consider is the interface between polymer and nanoparticle in the final application without a well-designed interface between nanoparticle and polymer, no synthetic technique will yield a good polymer nanocomposite. For in situ polymerization, the focus is on clay nanocomposites, as this field has a wealth of information on structure-property relationships between clay and polymer. Some factors that must be considered include ... 

Solvent Blending Solvent blending for production of polymer-clay nanocomposites has been perceived as a process to be used only on a research scale, but in reality it may be more industrially friendly than the in situ process, at least for primary polymer producers rather than the downstream users. Although aspects of solvent blending are used in processing thermoset nanocomposites, this technique is really limited to thermoplastics or to polymers that can swell extensively in solvent, allowing polymer chains and clay to mix freely. 

To achieve improved dispersibUity of nanoclay fillers within polymer systems, three familiar methods are commonly used, namely, melt intercalation, solution intercalation, and in situ polymerization. The melt-intercalation method is based on the melting point of polymer matrices and is applied by annealing above the melting point of the polymer (Reddy et al., 2013). This method has been chosen by industrial sectors to produce polymer/clay nanocomposites. However, it is not apphcable to the fabrication of biobased polymer/clay nanocomposites based on thermosetting materials such as epoxy and polyester due to their high viscosities (Wypych and Satyanarayana, 2005 Wang et al., 2014). Therefore, the fabrication of biobased thermosetting polymer/clay nanocomposites is mainly based on solution intercalation or in sim polymerization. 

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