Compatibilization Methods

In many articles on polymer blends the term compatibility is often used with different and, sometimes, controversial meanings it is frequently used as synonymous with miscibility, referring to systems that are 

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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Third phase in binary polymer alloys, enhanced by inter-diffusion or compatibilization. Thickness of this layer varies with the blend components and compatibilization method from 2 to 60 nm. 

The references in this review are strictly limited to journal articles. Although the majority of Reactive Compatibilization examples are found in industrial research, these are documented mostly in patents. The majority of patents have so few details that often only an educated guess is possible concerning the compatibilization strategy employed. Numerous examples of industrial compatibilization methods have been provided in a recent book based on the patent literature [Utracki, 1998]. 

Miscellaneous compatibilization methods belonging to this category are listed in Table 5.11. Park et al. [1997] have claimed that PA blends with PO may be compatibilized by copolymer... 

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. 

Blend Component Reasons for blending Compatibilization method... 

Nowadays, the most popular is the reactive compatibilization method — it is used in preparation of over 90% of commercial alloys. The process can be conducted either in a single step, in two, or in three steps. The later method is the oldest, simples, and least economic ... 

In the following text examples of recycled polymer blends will be given, first for the commodity, then for the engineering and specialty resin blends. Whenever possible, the methods of compatibilization and re-compatibilization should be the same. In particular, when recycling is to reproduce the original blends performance, the same compatibilization method is essential. For this reason, support of the blends manufacturer should be ascertained. 

Application of the compatibilization method by means of melt blending is not decided as yet because of inadequate understanding of and difficulty in realization of real technologies, which require complex apparatus. 

When the blends are immiscible in the molten state, the crystallinity is an even more complex function of the ingredients properties, compatibilization method, processing parameters, and post-processing treatments. The following factors have been identified to play a major role (i) the molecular constitution and of the components (ii) composition (iii) the type of phase morphology and the degree of dispersion (iv) the interphase, thus interactions between the phases, nature of the interface, migration of nuclei from one phase to the other, etc. ... 

Recycling of Commingled Plastics 20.3.1 With a Compatibilizing Method... 

Initially, the addition of a third polymeric component to a polymer blend was the most common compatibilization method. It was assumed that the compatibilizer would migrate to the interface, broadening the segmental concentration profile. However, it remains to be demonstrated that most of the copolymer added actually proceeds to the interface. Also, there is evidence that the addition of a block or graft copolymer reduces the interfacial tension and alters the molecular structure at the interface, but rarely increases the interphase thickness. Moreover, the actual preparation of the copolymer requires specific chemical routes and reaction conditions. 

Amongst the above mentioned compatibilization methods, the obtaining of IPNs and SIPNs often proved to be a promising and very efficient route. An IPN is a polymer alloy comprised of two or more chemically crosslinked polymers. The difference between polymer blends and IPNs is that the latter ones swell instead of dissolving in solvents and do not creep or flow. Types of IPNs include sequential, simultaneous, latex and gradient IPNs and may also be thermoplastic (i.e. when physical crosslinks are imphed). Thermoplastic IPNs behave as thermosets at ambient temperature, but usually flow when heated at certain temperatures, possess IPN properties and often exhibit dual phase behavior [1]. 

The performance of polymer blends largely depend on the degree of dispersion. For example, mixtures of PO and PS are antagonistically immiscible. Their blends have coarse phase morphology and poor mechanical properties [8]. However, the morphology and performance can be enhanced by a judicious selection of the compatibilization method. 

A modification of the interface between immiscible blends components. As noted above, the weak interfadal adhesion can be enhanced hy using so-called compatibilization methods, and these will be discussed later in the chapter. 

Neither of the two base polymers (A and B) contain reactive groups. Most hydrocarbon polymers, such as polyethylene PE, PP, PS and copolymers thereof, are in this situation. In such cases, different compatibilization methods can be envisioned. The first one is to add two reactive polymers (C and D) which are mutually reactive and are miscible with A and B, respectively. The resulting copolymer will be of type C-D. The second one is to hmctionalize polymers A and B with different functional groups, which are mutually reactive. Take PE/PS blends as an example. When PE is functionalized with a carboxylic group and PS with an oxazoline group, they will be able to react with each other and form a desired compatibilizer [6]. 

A compatibilizer must be located at the interfaces to play its roles. This determines, to a great extent, the pros and cons of physical and reactive compatibilization methods. However, direct comparisons are scarce because of experimental difficulties. By direct comparisons it is meant that at least the molecular architectures and the concentrations of the interfacial agents employed in both compatibilization methods are the same or very similar. Unfortunately, these two minimum requirements can hardly be met in practice. Nevertheless, one would expect that an in-situ generated interfacial agent (reactive compatibilization) would be more efficient than an externally added one (physical compatibilization) provided their molecular architectures and concentrations are the same. Nakayama et al. [30] confirmed this expectation by comparing PS/PMMA (70/... 

Materials development. In such cases, what matters the most is the properties of polymer blends at the die exit. For this reason, virtually all polymer blends studied are compatibilized. Much effort is directed towards the development of compatibilization methods, especially routes to synthesizing interfacial agents. 

The vector fluid concept was first suggested for a polyethylene (PE)/polyamide (PA) reactive blending system [12], as mentioned earlier in this chapter. This concept is interesting because it has the potential to provide a compatibilization method for polymers that have no chemical functionalities suitable for copolymer formation during melt blending (e.g. the case of polyolefin and polystyrene). It has been seen that the blends of polyolefin/polystyrene are difficult to compatibilize in situ by simply adding a free radical initiator into the blending process. Usually, flie pre-made block or reactive polymers or copolymers, which can be expensive, are needed for polyolefin/polystyrene compatibilization [15-17]. If a suitable vector fluid can be found for the polyolefin/ polystyrene/peroxide in situ compatibilization, the process could become more controllable and more cost efficient. 

Figure 3.1 Generalized illustration of effect of compatibilizer methods on particle size...

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