Immiscible polymer blends crystallization behavior

Eor the discussion of the crystallization and melting behavior in immiscible polymer blends, a division into 3 main classes is proposed. 

This chapter, related to the crystallization, morphological structure and melting of polymer blends has been divided into two main parts. The first part (section 3.1) deals with the crystallization kinetics, semicrystalline morphology and melting behavior of miscible polymer blends. The crystallization, morphological strucmre and melting properties of immiscible polymer blends are described in the second part of this chapter (section 3.4). 

In the following part, a discussion on the crystallization behavior in immiscible polymer blends is given, including the nucleation behavior, spheiuhte growth, overall crystallization kinetics, and final semicrystalline morphology. Each topic is illustrated with several examples from the literature, to allow the reader to find enough references on the discussed subject for further information. 

The discussion on the crystallization behavior of neat polymers would be expected to be applicable to immiscible polymer blends, where the crystallization takes place within domains of nearly neat component, largely unaffected by the presence of other polymers. However, although both phases are physically separated, they can exert a profound influence on each other. The presence of the second component can disturb the normal crystallization process, thus influencing crystallization kinetics, spherulite growth rate, semicrystalline morphology, etc. 

Some general principles governing the crystallization behavior of homopolymers also remain vahd for immiscible polymer blends in which the crystallizable component forms the continuous phase. 

Nucleating Activity of the Interface The second phenomenon found to influence the crystallization behavior in immiscible polymer blends is the nucleating activity of the interface [Bartczak et al., 1987 Wenig et al., 1990 Wei-Berk, 1993]. 

In immiscible polymer blends with a high degree of immiscibility such as PP/PS, it has been shown that nucleation at the interface affects the crystallization behavior. Wenig et al. [1990] showed that, with increasing the amount of PS in a blend with PP, the nucleation shifted from preferentially thermal (related to the degree of undercooling) to more athermal. This was... 

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... 

Crystallization, Morphological Structure, and Melting Behavior of Immiscible Polymer Blends... 

The properties of the finished articles made from immiscible blends are governed by the morphology created as a result of the interplay of processing conditions and inherent polymer characteristics, including crystallizability. Therefore, a scientific understanding of the crystallization behavior in immiscible polymer blends is necessary for the effective manipulation and control of properties by compounding and processing of these blends. 

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. 

Since the phases are physically separated in immiscible blends, the same heterogeneities that nucleate the pure polymer in the blend at T j. Therefore, the crystallization temperature T of the blend during cooling from melt will generally not differ much from that of the T of the component. Hence, the general principles governing the crystallization behavior of homopolymers remain valid too for immiscible polymer blends in which the crystallization polymer forms a continuous phase. 

A large number of polymer blends contain one or two crystallizable components. The crystallization behavior of a polymer component in a blend is expected to be altered by the presence of the second blend component, whether both are completely miscible, partially miscible or totally immiscible. Therefore, a profound scien-... 

In the following overview, a survey of the most important topics concerning crystallization behavior in immiscible crystalline/crystalline polymer blends is given. Because the physical state of the second phase affects the crystallization mode of the phase under consideration, a distinction has been made for blends crystallizing in a melt environment and those crystallizing when the second phase has solidified. 

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. 

Conclusions on the Crystallization Behavior of Immiscible Crystalline/crystalline Polymer Blends... 

The immiscible semicrystalline polymer blends may be classified in terms of crystalline/crystalline systems in which both components are crystallizable and crystalline/amorphous systems in which only one component can crystallize, being either the matrix or the dispersed phase (Utracki 1989). Numerous authors have been investigating the crystallization behavior of immiscible blends. In Tables 3.14 and 3.15, an overview is given of a number of important immiscible crystallizable blend systems. 

The scientific literature on crystallization in polymer blends clearly indicates that the crystallization behavior and the semicrystalline morphology of a polymer are significantly modified by the presence of the second component even when both phases are physically separated due to their immiscibility. The presence of the second component, either in the molten or solid state, can affect both nucleation and crystal growth of the crystallizing polymer. The effect of blending on the overall crystallization rate is the net combined effect on nucleation and growth. 

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