Other Compatibilization Techniques

For blends of polycondensates, the interchange reactions can occur during melt mixing [160] and may lead to miscible systems this situation is undesirable as the amorphous product has lost the beneficial properties of both blend components. Therefore, processing should be led in such a way that only a small amount of block copolymer is formed. This requires relatively low processing temperatures, short residence times in the melt, and only traces of a catalyst (if any). 

block and grafted copolymers can also be produced by solid-state shear pulverization [161], whereby polymer powders are exposed to high shear stresses below their Tg or T, leading to the cleavage of covalent bonds. The polymer radicals then recombine during consequent melt mixing and form compatibilization-effective copolymers. 

Recently, much attention has been paid to the possibility of controlling morphology development in immiscible polymer blends by the addition of interfacially active nanoparticles. In fact, it was found that some nanoparticles could refine and stabilize the morphology, whereas the addition of others leads to an increase in the dispersed particle size [162]. Generally, the optimization of this approach seems to be much more difficult compared to the incorporation of block or graft copolymers. One probable reason for this is that the polymer-filler interactions at the interface are weaker than in the case of copolymers anchored in the respective polymer phases. A critical comprehensive review on this topic was produced by Fenouillot et al. [163]. 

1 Hancock, T. (1857) Personal Narrative of the Origin and Progress of the Caoutchouc or India-rubber Manufacture in England, 

Longman, Brown, Green, Longmans Roberts, London. 

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In comparing the different blends, the specific advantages of each type, as well as any potential overlap in performance with other type of blends have also been discussed. The fundamental advantage of polymer blends viz. their ability to combine cost-effectively the unique features of individual resins, is particularly illustrated in the discussion of crystalline/amorphous polymer blends, such as the polyamide and the polyester blends. Key to the success of many commercial blends, however, is in the selection of intrinsically complementing systems or in the development of effective compatibilization method. The use of reactive compatibilization techniques in commercial polymer blends has also been illustrated under the appropriate sections such as the polyamide blends. 

A compatibilization technique specifically suitable for emulsion polymerization involves the in-situ polymerization of a polymer in the presence of a previously polymerized polymer. As applied to emulsion polymerization, this is typically referred to as core-shell polymerization. The procedure involves the initial polymerization of seed particles. The addition of other monomers can result in two distinct results. One result involves swelling of the monomer in the particles followed by phase separation once a critical molecular weight is achieved (if the two polymers are thermodynamically immiscible). The other result would involve the... 

Despite the incompatibility of silicone towards many polymers, several techniques have been more or less successfully developed to produce silicone containing physical blends. Although compatibilization remains essentially of academic interest only, many industrial applications for IPNs are a testimony to their growing importance. Silicone blends allow researchers to introduce specific properties such as impact resistance or low surface energy to polymers that fundamentally lack these characteristics. On the other hand, it must be acknowledged that silicone blends and related fields of research are still open to further development and will undoubtedly lead to a wide range of future industrial applications. 

Extrusion and impregnation, electrospinning, and multilayer films are other processes applicable for reinforced nanocomposites. Thus, preparation of cellulose whiskers reinforced with polylactic acid nanocomposites (by melt extrusion carried out by pumping the suspension of nanocrystals into the polymer melt during the extrusion process), using polyvinyl alcohol as a compatibilizer for the dispersion of cellulose whiskers within the polylactic acid matrix, was reported (de Menezes et al. 2009) bacterial cellulose whiskers incorporated into poly(oxyethylene) nanofibers by electrospinn to enhance the mechanical properties of electrospun fibers (Peresin et al. 2010) or the use of the layer-by-layer assembly technique, which maximizes the interaction between cellulose whiskers and a polar polymeric matrix (Bruno et al. 2009 Aulin et al. 2010), are some examples of nanocomposites reinforced by the last three methods. 

Future development will see two competing trends. On the one hand, major polymer producers will develop and sell standard grades of compatibilizers for major polyblend markets. On the other hand, with growing understanding and experience in compatibilization, increasing numbers of polyblend processors will develop their own proprietary ingredients and techniques for compatibilizing the polyblends they sell. 

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