Melt intercalation method

In this method, the nanofillers are mixed with the polymer matrix in the molten state. This method has great advantages over either in-situ intercalative polymerization or solution intercalation. First, this method is environmentally benign due to the absence of organic solvents. Second, it is compatible with current industrial processes such as extrusion and injection molding. The melt intercalation allows the use of polymers, which are not suitable for in-situ polymerization or the solution intercalation method. A wide range of silicone rubber nanocomposites have been prepared by this method [143,144]. 

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SCHEME 2.1 The melt-intercalation method for nanocomposite preparation. 

This is the most widely used naturally occurring rubber. The literature search shows that many research groups have prepared nanocomposites based on this rubber [29-32]. Varghese and Karger-Kocsis have prepared natural rubber (NR)-based nanocomposites by melt-intercalation method, which is very useful for practical application. In their study, they have found increase in stiffness, elongation, mechanical strength, and storage modulus. Various minerals like MMT, bentonite, and hectorite have been used. 

This is a highly polar polymer and crystalline due to the presence of amide linkages. To achieve effective intercalation and exfoliation, the nanoclay has to be modified with some functional polar group. Most commonly, amino acid treatment is done for the nanoclays. Nanocomposites have been prepared using in situ polymerization [85] and melt-intercalation methods [113-117]. Crystallization behavior [118-122], mechanical [123,124], thermal, and barrier properties, and kinetic study [125,126] have been carried out. Nylon-based nanocomposites are now being produced commercially. 

Layered siUcate/polypropylene nanocomposites were prepared by melt intercalation method. Homopolymers PP alone and maleic anhydride-grafted polypropylene (PPgMA) as a compatibiUzer were used as the matrix. Clay (Na montmorillonite, MMT) particles were used to obtain silicate nano-layers within the PP matrix. Structural modification of MMT... 

Figure 6.7 (a) Schematic representation of the melt intercalation method, (b) Stepwise representation of the melt intercalation method [20,21],... 

Recently, Ahmadi et al. [320] prepared EPDM/clay nanocomposites with organoclay that was intercalated with MA-grafted EPDM (MA-g-EPDM) and EPDM-clay composites with pristine clay via indirect melt intercalation method. Authors characterized the dispersion of the silicate layers in the EPDM matrix by XRD and TEM analysis methods. They showed that the particles of organoclay were completely exfoliated in EPDM matrix, and the mechanical, thermal, and chemical properties of nanocomposites were significantly improved compared with conventional composites. 

Other methods to prepare nanocomposites include a solvent-assisted process, whereby a cosolvent is employed to help carry the monomer into the galleries and is subsequently removed from the polymer system, and direct polymer melt intercalation methods, which involve the direct addition of nanoclays to a polymer melt under shear conditions atelevated temperatures, allowing their direct exfoliationintothepolymer[5]. 

A number of methods have frequently been employed in the production of nanocomposite materials. These include solution intercalation, melt intercalation, polymerization, sol-gel, deposition, magnetron sput-tering, laser, ultrasonication, supercritical fluid, etc. In PHA nanocomposite fabrication, solution intercalation and melt intercalation methods are the most widely explored procedures. However, use of in situ intercalative polymerization, supercritical fluids and electrospinning are shown to be promising and emerging techniques. The performance and quality of a nanocomposite depends on how well the nanofillers disperse or blend into the matrix. Therefore, these methods constitute different strategies to improve the composites thermo-mechanical and physico-chemical properties by enhancing efficient interactions between the nanofiller and the polymer matrices. 

M. Abdollahi et al. prepared NR/BR blend/clay nanocomposites via a combined latex/melt intercalation method. The TGA results indicated an improvement in main and end decomposition by increasing the elay loading. ... 

The melt intercalation method for preparation of bio-polymers can leads to better dispersion of fillers at large extent, which finds their space in manufacture of nanobiocomposite based packaging, however, there processing activity is limited at elevated temperature. 

Nanocomposite membranes have been tested as a barrier of methanol fuel. Jung et al. [99] studied nanocomposite membranes with layered structure of inorganic materials. In this work, they made a nanocomposite membrane with various contents of mont-morillonite (MMT), and modified montmorillonite (m-MMT) by the melt intercalation method using an internal mixer. Nanocomposite membranes were characterized by XRD and intercalation or exfoliation of layered structures was checked. Ionic conductivity of composite membranes was measured to be 8.9-6.7 x 10" Scm at 110°C. They confirmed that nanocomposite membranes have lower melhanol aossover than Nafion membranes in MEA performance at high temperature. 

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. 

Figure 20.8 Mechanical properties of SPS nanocomposites prepared by direct melt intercalation method (a) tensile strength, (b) tensile modulus, and (c) flexural modulus. Reprinted with permission from Reference 15. Copyright Wiley-VCH Verlag GmbH Co. KGaA.

Shafiee M, Ramazani SAA, Danaei M. Investigation of the gas barrier properties of PP/clay nanocomposite films with EVA as a compatibiliser prepared by the melt intercalation method. Polym-Plast Technol Eng 2010 49 991-995. 

From the above discussion, it can be seen that the method adopted to prepare nanocomposites is highly dependent on the nature of the polymer. When the polymers or monomers are water soluble, they can be incorporated into the pristine LDH without any organo-modification due to their good affinity with the LDH. Additionally, the aqueous environment is compatible with the condition for the synthesis of LDH materials. Therefore, water-soluble polymer-LDH nanocomposites can be prepared using some special methods such as in situ synthesis, ion exchange and reconstruction. In the case of water-insoluble polymers and monomers, their nanocomposites are usually prepared in orga-nosolvent (solution intercalation method, exfoliation-absorption method and in situ polymerization method) or molten polymer (melt intercalation method). However, emulsion polymerization and suspension polymerization are methods that allow the incorporation of a water insoluble polymer into an LDH in water. The following sections are devoted to polymer-LDH nanocomposites obtained via emulsion polymerization and suspension polymerization. 

PHB is a naturally occurring polyester produced by numerous bacteria in nature as intracellular reserve of carbon or energy. Maiti et al.° reported the first preparation of PHB/OMLS nanocomposites (PHBCNs) by melt intercalation method. They used three different kinds of OMLS for the preparation of nanocomposites. Nanocomposites were prepared by using a twin-screw extruder operated at 180°C. The extruded strands were palletized and then dried under... 

Melt rheological properties of PCL-based nanocomposites were first reported by Krishnamoorti and Giannelis in the case of delaminated structures prepared by in-situ intercalative polymerization. Recently, Lepoittevin et a/. reported the detail melt rheology properties of PCL-based nanocomposites prepared by melt intercalation method. The rheological behaviour of the PCL filled with 3wt.% of MMT-AIk and MMT-(OH)2 was significantly different compared to the unfilled PCL and PCL/MMT-Na nanocomposites, for which the power law observed at low frequencies agrees with expectation for thermoplastics. The frequency dependence of G and G" was, however, perturbed by organically modified MMT. The effect was dramatic in the case of G which drops from 2 to 0.14 and 0.24 for MMT-(OH)2 and MMT-AIk, respectively. 

As mentioned in the Introduction, the further property improvement of PBT can be done by the PLS technique, especially by the polymer melt intercalation method. In this session, we discuss on the preparation and characterization of PBT/organic montmorillonite (MMT) (PBT/organoclay) nanocomposites using three kinds of organoclays, each possessing different ammonium cations, in order to see their effects on the morphology of the PBT hybrids. Table 9.2 shows the related structure information of three typical kinds of commercial organoclays produced by Southern Clay, Texas, USA (whose trade names are Cloisite 6A, Cloisite lOA and Cloisite 30B). 

EVA/organic layered silicate nanocomposites can be also prepared by melt intercalation method. Alexandre and Dubois" found that nanocomposites were only formed when EVA was melt-blended at 1S0 C with nonfunctionalized organoclay, such as MMT exchanged with dimethyldioctadecyl ammonium. Zanetti et prepared EVA nanocomposites with fluorohectorite-like synthetic silicate exchanged with octadecylammonium and studied their thermal behaviors. 

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