Nanocomposites melt mixing method

Achillas et al. [55] have prepared, by the melt mixing method, and characterized PHB/organically modified clay nanocomposites. 

In the melt mixing method, nanoclays are incorporated into the polymer in the molten state. This technique has considerable advantages over either the in situ intercalative polymerization or polymer solution intercalation techniques. Firstly, this method is environmentally benign due to the absence of organic solvents. Secondly, melt processing is compatible with current industrial processes, such as extrusion and injection moulding. The melt intercalation method allows the use of biopolymers that were not suitable for in situ polymerization. This has been the most widely used method in the literature for obtaining PLA/clay nanocomposites. " ... 

Nanocomposites based on starch/PVOH/silicate clay are not widely studied (Dean and others 2008 Vasile and others 2008 Majdzadeh-Ardakani and Nazari 2010). Dean and others (2008) produced a series of thermoplastic starch/PVOH/montmoril-lonite (MMT) micro and nanocomposites which exhibit intercalated and exfoliated structures through extrusion processing. A small amormt of PVOH (up to 7 wt%) and MMT (up to 5 wt%) were used and the improvement of tensile strength (up to 67% increase) and tensile modulus (up to 85% increase) were reported. Vasile and others (2008) prepared starch/PVOH/MMT composites by the melt mixing method. They revealed the morphology and thermal behavior changes for the nanocomposites and reported a slight increase in thermal stability for starch. 

Fabrication methods have overwhelmingly focused on improving nanotube dispersion because better nanotube dispersion in polyurethane matrix has been found to improve the properties of the nanocomposites. The dispersion extent of CNTs in the polyurethane matrix plays an important role in the properties of the polymer nanocomposites. Similar to the case of nanotube/solvent suspensions, pristine nanotubes have not yet been shown to be soluble in polymers, illustrating the extreme difficulty of overcoming the inherent thermodynamic drive of nanotubes to bundle. Therefore, CNTs need to be surface modified before the composite fabrication process to improve the load transfer from the polyurethane matrix to the nanotubes. Usually, the polyurethane/CNT nanocomposites can be fabricated by using four techniques melt-mixing (15), solution casting (16-18), in-situ polymerization (19-21), and sol gel process (22). 

Many studies have used these methods for processing of both thermosetting and thermoplastic polymers. Y. Liao (53) dissolved epoxy in a well-dispersed, ultra-sonicated CNT suspension. The solvent was evaporated, and the epoxy was subsequently cured to form a nanocomposite in which the good CNT dispersion was achieved. Jin et al. (54) produced various types of polymer-coated and polymer-grafted MWNT solutions, in some cases evaporating the solvent and subsequently melt-mixing with another polymer. Yudasaka et al. (55) used a mixture of SWNTs and PMMA in monochlorobenzene (MCB) for dispersion, purification and subsequent spin-casting of the material. 

A modified melt blending method has been developed for preparing exfoliated nanocomposites of poly(m-xylylene adipamide) with sodium montmoril-lonite [100]. There, an aqueous solution of sodium montmorillonite was blended with the polymer in a twin-screw extruder. This kind of mixing ensures that the silica nanoparticles are exfoliated in the polymer matrix through fixing the nanoparticles within the polymer matrix just as they are in water. Oxygen permeation data show enhanced the barrier properties of the nanocomposites. 

To obtain a homogeneous and thermodynamically stable dispersion of nanomaterials in the polymer matrix, a variety of techniques are used in vegetable oil-based polymer nanocomposites. The state of dispersion of nanomaterials in the polymer matrix is the main governing factor in obtaining the required nanocomposites. However, depending on the suitability, end-use applications and cost, the three most widely used methods for the preparation of polymer nanocomposites are (i) the solution technique, (ii) in situ polymerisation and (hi) the melt mixing technique. ... 

Three methods are generally used to fabricate PP/CNT nanocomposites solution mixing, in situ polymerization, and melt mixing. For solution mixing, CNTs are suspended in a solvent by mechanical stirring or ultrasonication. The suspension is then mixed with polymer solution. The nanocomposites are obtained by evaporating off the solvent or by precipitation in... 

However, the simple melt mixing of polyolefins with natural clays, does not guarantee a sufficient level of dispersion of the nanoparticles, which are often present in the form of micron-size agglomerates. In order to overcome this problem, two main strategies have been followed surface functionalization of needle-like clays (usually by alkyl-silanes) or addition of a third polymeric phase (usually maleic anhydrite modified PP PP-g-MA), which acts as a compatibilizer between the matrix and nanofiller. Both methods tend to modify the surface energies of the nanocomposite system, in order to reduce the interparticle interaction and improve the dispersion. In the case of a reactive surface treatment only, the polymer-day interaction is expected to be enhanced, along with better nanoclay dispersion, which is very important for the final mechanical properties. 

To obtain a uniform dispersion in the rubbery matrix, different processing methods like solution casting, latex blending, two-roll mill mixing, melt mixing etc. have been attempted. However, two methods are popularly used to prepare nanocomposites of NR and have been discussed in detail in a recent review on chitin whiskers. 

When obtaining PLA/clay nanocomposites, three main techniques are frequently used to produce nanocomposites of this material, namely in situ intercalative polymerization, solution-casting and melt mixing. Of the three, the in situ intercalative polymerization method exhibits the highest performance, since it is the one that results in a higher degree of interaction... 

Generally, there are three preparative methods for synthesizing polymer/metal oxide nanocomposites (Fig. 1). The first is direct mixing or blending of a polymer and metal oxide NPs, either as discrete phases (known as melt mixing) or in solution (solution mixing). The second is a sol-gel process, which starts with a molecular precursor at ambient temperature and then forms a metal oxide framework by hydrolysis and condensation. The third is in-situ polymerization of monomers in the presence of metal oxide NPs. 

Radhakrishnan V K, Davis E W and Davis V A (2010) Influence of initial mixing methods on melt-extruded single-walled carbon nanotube-polypropylene nanocomposites, Polym Eng Sci 50 1831-1842. 

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