Compatibilized polymer blends crystallization behavior

Table 3.26. Influence of compatibilization on the crystallization behavior of the dispersed phase in amorphous /crystalline polymer blends...

Effect of Compatibilization on the Crystallization Behavior in Crystalline/Crystalline Polymer Blends... 

The general influence of a compatibilizer on the crystallization behavior of an immiscible polymer blend system is stiU far from being well understood. However, abstract can be made between two main classes. A first class consists of compatibilizers that form a kind of immiscible interlayer between the two phases. Examples are given by Holsti-Miettinen et al. [1992], and... 

When two crystallizable components are blended, a more complex behavior due to the influence of both phases on each other is expected. In general, the discussion for matrix crystallization and droplet crystallization can be combined. However, crystallization of one of the phases can sometimes directly induce crystallization in the second phase. As a consequence, the discussion of blends of this type has been subdivided with respect to the physical state of the second phase during crystallization. The special case of coincident crystallization , in which the two phases crystallize at the same time, is discussed. Finally, the effect of compatibilization of crystalline/crystalline polymer blends is briefly reviewed. 

Blending offers an interesting means of tailoring product properties to specific applications. However, in the case of immiscible polymer pairs, the desired properties are not achieved readily without a compatibilizer, which enhances the phase dispersion and stability, as well as a good adhesion between the phases. This can be effectuated by physical or reactive methods [Folkes and Hope, 1993]. Compatibilization strongly affects the blend phase morphology and as such, it also may influence the crystallization behavior of the blend [Flaris et al., 1993]. Because both factors are related to the final properties of the blend, it is worth paying attention to these phenomena. 

Several authors have investigated the influence of compatibilization on the global blend morphology. However, only a few authors really tried to understand the effect of compatibilization in crystalline/crystalline polymer blends on the crystallization kinetics, melting behavior and semicrystalline morphology of the components. In Table 3.29 some recent results on this topic are summarized. 

Concerning compatibilized blends, the interfacial behavior of the compatibilizer has an important effect upon the crystallization of the blended components as it was shown for crystaHine/crystalline polymer blends (60,65-67) and for crystalline polymer/LCP blends (32,37,38,68). For the latter blends, the enhanced phase interactions and improved interfacial adhesion could increase the above-mentioned nucleation activity of the LCP toward the crystallizable matrices. In the particular case of using polyolefin-g-LCP copolymer compatibilizer, the crystallization of the two blend phases might have a reverse effect upon the compatibilizing activity. Moreover, the miscibility (69,70) and/or cocrystallization (60) between the bulk homopolymers and corresponding segments of the copolymer could strongly influence the crystallization behavior of the blends. 

Table 3.26 Inflijence of compatibilization in amoiphous/dystalline polymer blends (Hi the crystallization behavior of the dispersed phase ...

Chap. 2, Thermodynamics of Polymer Blends Chaps. 3, Crystallization, Micro- and Nano-structure, and Melting Behavior of Polymer Blends and 8, Morphology of Polymer Blends Chap. 4, Interphase and Compatibilization by Addition of a Compatibilizer Chap. 5, Reactive Compatibilization ... 

Reactive blending is an important technique which is very frequently used for control of the phase morphology, phase stabilization and interfacial adhesion in multiphase immiscible polymer blends. Recently a lot of attention has been focused on the reactive blending process in order to understand how phase morphology develops in reactively compatibilized blends. The stability of the in situ formed copol3aner at the interface and its influence on phase morphology generation, phase co-continuity and on the crystallization behavior of the ciystallizable component(s) are crucial aspects with respect to the blend material properties. 

The presence of nanomaterial influences the crystaltization process as it acts as additional heterogeneity creating more interfaces [29]. In some cases, the presence of a nanofiller alters the crystaltization temperature and thus the thermal properties. In the dispersed phase, the presence of nanoparticles increases the occurrence of fractionated crystaltization [17,23,27,29,53-55,61-63,93-95]. Also, the extent of compatibilization effect from the nanomaterial can alter the whole process of crystaltization in the polymer blend. When a nanofiller is organically modified, using compounds with a similar chemical structure to one or both polymers present in the blend, the influence of the nanofillers here on the crystallization behavior is complex. This is because several factors have to be taken in consideration, such as the nucleating effect of the matrix on the dispersed phase or vice-versa, the nucleating effect of the nanofiller compatibitizer on both phases. There are reported cases where modified nanofillers have impeded the crystaltization process and thus retarded crystaltization in the overall material. 

The compatibilization largely affects the phase morphology of the blends and the interfacial properties, thus it may significantly influence the crystallization behavior of the polymer components and the structure of crystalline phases. In the next paragraphs some examples of blends compatibilized by means of different methods will be presented, with focus on the morphological aspects, phase interaction phenomena, and crystallization behavior. 

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