Compatibilization interphase

The spherulite size is altered by the presence of clay, compatibilizer, etc. Figure 9.13 shows the spherulite size of PP and nanocomposite. In general the size of the spherulite is reduced significantly by the presence of nanoclay. The nucleating effect of clay and the higher nucleation density of clay platelets play the vital role. To some extent, the compatibilizer behaves in a similar manner. But, in the presence of certain compatibilizers like POE-g-MA, the spherulite size increases. It may be due to the indirect contact of clay and PP through POE-g-MA compatibilized interphase. 

We have previously used the term interfacial reaction to describe mixing between two reactive blend components. In reality, as we have seen in the Example 11.2, there is an interphase that is formed on the surface of the dispersed phase where molecules of both components can be found and react (66,67). If the nonfunctionalized blend components have high immiscibility, then the thickness, Si, of the interphase around the droplets, as well as the volume of the interphase, Vh will be small and, thus, the probability of the functional groups to react forming compatibilizing products will be low, giving rise to coarse and not very stable morphologies. Helfand (66) defines Si as... 

Apparently, with a very small interphase thickness the two end-cap groups are too few and not easily accessible to affect compatibilization. On the other hand, when four anhydride (An) groups are attached, randomly on each PDMS chain, then the blend of 20% PDMS/4-An and PA 6/di-amine have a very fine and stable morphology (ca 0.5 pm). Thus, the amount of interfacial reaction product, although diminished by small < / values of the unmodified polymer components, is promoted by the larger number and more accessible functional groups in either or both of the reactive components. Finally, Macosko and co-workers (62) have estimated that the minimum fraction of the interphase that has to be covered by reacted compatibilization products to achieve fine and stable morphologies is about 0.2. 

S. Keszei, Sz. Matko, G. Bertalan, P. Anna, G. Marosi, and A. Toth, Progress in interface modifications From compatibilization to adaptive and smart interphases, Em Polym. J., 2005,41 697-705. 

Enhanced interphase interactions, deduced from thermal and dynamic mechanical properties and morphology observed by SEM, demonstrate the efficient compatibilizing effect of iPS-fo-iPP copolymer on iPS-iPP blends. Each sequence of the iPS-fc-iPP diblock copolymer can probably penetrate or easily anchor its homopolymer phase and provide important entanglements, improving the miscibility and interaction between the iPS and iPP phases. This is in good agreement with what is inferred from the mechanical properties of the iPS-fo-iPP-iPS-iPP polyblends. 

For example, the effects of AN content on miscibility of SAN with PMMA was studied by measuring the thickness of the interphase [Higashida et al., 1995]. The effects of concentration, compatibilization and annealing for PA with either PS or PE (compatibUized by addition of 5 wt% of PP-MA or SMA) were studied by SEM [Chen et al., 1988]. Compatibilization reduced the diameter of dispersed phase by a factor of ten... 

In this chapter, compatibilization of polymer blends by means of addition of a compatibilizer will be discussed. First, the theories will be summarized of the (i) interface, (ii) interphase, and (iii) compatibilization process. This brief summary is to provide a general framework for understanding the phenomena associated with compatibilization, and guidance for optimization of the process to gain maximum performance. 

Let us consider a molten, immiscible, binary blend of polymers A and B, without compatibilizer. Helfand and Tagami [1971], Helfand [1975], Roe [1975], and Helfand and Sapse [1975] have developed a quantitative lattice theory of the interphase that twenty years later still provides good basis for understanding. 

Some polymers have been found miscible with many other resins, or in other words there are many immiscible blends whose components are miscible with the same polymer. Addition of this polymer can be used to partially homogenize the system, i.e., to compatibilize the blend. The added polymer is a co-solvent. Of particular interest are systems in which presence of a co-solvent makes it possible for the two immiscible components to form three-body interactions. In this case, the blend is indeed compatibilized, with the co-solvent being located in the interphase. For the thermodynamic reasons, mostiy copolymers belong to this type of co-solvents. In the left hand side column of Table 4.1 there are polymers that may be used as co-solvents for pairs of resins listed in the other column. Some of the latter resins may show local miscibihty (e.g., PS with styrenic copolymers), but the vast majority is immiscible. 

The interfacial thickness, Al , and the interfacial tension coefficient, v , are both related to the square root of the thermodynamic binary interaction parameter, — Al directly, whereas inversely, thus their product , Al. v , is to be independent of thermodynamic interactions. The latter conclusion may have limited validity, but the general tendency — the reciprocity between the interfacial tension coefficient and the interphase thickness — is correct. The theory correctiy predicted the magnitude of the interphasial thickness, Al = 1-4 nm. Note that the theory is for A/B binary systems, thus extending these predictions to compatibilized systems, where Al < 65 nm may lead to erroneous expectations. For the latter system the reciprocity between v and Al is not to be expected. 

Since the dimensions to be probed are of the order of few nanometers, the most useful microscopic method would be that of the transmission electron microscopy (TEM). Using this technique Fayt et al. [1986] observed location of P(S-b-HB) compatibilizer in a PE/PS blends. The authors inserted a short sequence of isoprene between the styrenic and hydrogenated butadiene blocks. After staining the isoprene double bonds with OsO, the authors were able to observe presence of the copolymer at the interface between the matrix and dispersed phase. Thickness of the interphase could then be measured. The experiments also demonstrated presence of the added compatibilizer as dispersed micelles inside the PE phase. This technique is applicable, however, only when selective staining affects only the compatibilizer. 

In the following part aspects related to morphology of the blends with and without an added compatibilizer (from the nm to the pm scale) will be presented. These include information on the interfacial characteristics (interfacial tension coefficient and thickness of the interphase), morphology, crystallization and performance of the blends. This information will be presented mainly in a tabulated form, summarizing the main feamres from the referenced publications. 

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