Semicrystalline polymer blends

Binary composite membranes constitute the chief example of membranes classified under (b) in the introductory section. They include binary polymer blends or block or graft copolymers exhibiting a distinct domain structure, filled or semicrystalline polymers and the like. 

Qian et al. (18) have recently studied the evolution of melting of polymer blends composed of an amorphous high modulus (PS) component and a semicrystalline low modulus (LLDPE) component in Co-TSE full kneading elements. They observed that over a concentration range of 10-50%, the weaker modulus LLDPE melts faster than the higher modulus PS. Furthermore, when the semicrystalline component has a low melt... 

The first group are the semicrystalline homopolymers, while a second group would include a diverse collection of block polymers, blends, and segmented elastomers. The latter systems were emphasized at a symposium on "Multicomponent Polymer Systems organized as part of the 175th National Meeting of the American Chemical Society in Anaheim, March 13-17, 1978. 

Gaymans RJ (2000) Toughening semicrystalline thermoplastics. In Paul DR and Bucknall CB (eds) Polymer Blends, Vol 2. Wiley, New York p 177... 

The phase angle shift can be used to obtain contrast due to local differences in energy dissipation as a consequence of different surface characteristics related to materials properties. These different properties allow one to differentiate materials with different adhesion [110] or widely different Young s moduli, if these differences are related to differences in energy dissipation [111-115]. Hence the amorphous and crystalline phases in semicrystalline polymers can be clearly differentiated, as discussed in Sect. 3.2, as well as different phases in polymer blends or filled systems (see below). As an example, we show in Fig. 3.52 an intermittent contact AFM phase image of a block copolymer thin film on silicon [116]. 

In spin-diffusion studies it is possible to detect not only two but three domain sizes. The third domain can be considered the interface (i) between the other two domains, which can be different chemical species in a polymer blend or rigid crystalline (r) and mobile amorphous (m) material in a semicrystalline polymer. To illustrate this point, a mobility timescale is depicted in Fig. 7.2.25(a) and the simplified ID domain structure of PE underneath in (b). Rigid crystalline and mobile amorphous materials exhibit motion of chain segments with different correlation times Tc. The chains at the interface between both domains exhibit intermediate mobility. The exact ranges of correlation times in the individual domains depend on the particular choice of filters. Therefore, the values of domain sizes derived through spin-diffusion NMR also depend on the type of filters used. In particular, the interface is defined solely by the NMR experiment and can only be detected if the filters are properly chosen. 

Enhancement of mechanical properties is of interest only if it is not accompanied by a loss of other important properties of the blend. Of particular concern for such polymer blends is stiffness, because most means of increasing impact strength also reduce stiffness (14-19). But this is not the case for the iPS-fc-iPP-iPS-iPP blends studied here as seen in Table II. It is clear that the enhancement in toughness just described is not accompanied by a loss of stiffness, but it is essentially unaffected by the compatibilizer. And the stiffness of iPS-fc-iPP-iPS-iPP is higher than that of iPP and HIPS. The impact-modulus behavior seems to be due to the tough (or rigid) characteristics, morphologies of phases, and semicrystalline isotactic structure of each block in the iPS-b-iPP diblock copolymer. 

When the sample is a ternary system, analysis of the scattering data is in general much more difficult than has been discussed in this and previous chapters, but the need to investigate a ternary system is encountered often. Examples of such ternary systems are a diblock copolymer in a common solvent, a suspension of latex particles having a core-shell structure, and an incompatible binary polymer blend in which one of the polymers is semicrystalline. By employing the technique of contrast matching... 

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). 

The morphology of a semicrystalline polymer blend is largely determined by the type of segregation of the amorphous component (section... 

From a commercial point of view, semicrystalline polymers are of prime importance. Among the four mostly used commodity plastics (PE, PS, PVC and PP), only PS is completely amorphous. The three semicrystalhne polymers account for the largest volume of the commercial polymer blends. A majority of the polymer blends contains at least one crystalline component. Most polymer blends are immiscible. 

The immiscible semicrystalline polymer blends may be classified in terms of crystalline/crystalline systems in which both components are crystalliz-able, and crystalline/amorphous systems in which... 

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. 

Table 3.17. Influence of compatibiUzers on the nucleation behavior of the semicrystalline matrix in crystaUine/amorphous polymer blends... 

The addition of a second non-crystallizable component to a crystallizable matrix can cause drastic variations of important morphological and structural parameters of the semicrystalline phase, such as the shape, size, regularity of sphemlites and intersphemlitic boundary regions, lateral dimensions of the lamellae, etc. These factors may greatly influence the mechanical behavior and, in particular, the fracture mechanisms, and thus are of great importance, especially when the toughening of semicrystalline polymer blends is considered. 

Table 3.23. Overview of literature in which the final semicrystalline morphology in immiscible crystaUine/amorphous polymer blends has been studied...

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. 

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