Reactive Compatibilization of Polymer Blends
An increasing number of commercial polymer products is derived from blending two or more polymers to achieve a favorable balance of physical properties. As described in Chapter 2 of this Handbook, from the thermodynamic point of view there are two basic t
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REACTIVE COMPATIBILIZATION OF POLYMER BLENDS
S. Bruce Brown
General Electric Global Research Center, Niskayuna, NY, USA
5.1
Introduction and Purpose
An increasing number of commercial polymer products is derived from blending two or more polymers to achieve a favorable balance of physical properties. As described in Chapter 2 of this Handbook, from the thermodynamic point of view there are two basic types of polymer blends: miscible and immiscible. The vast majority of polymer pairs are immiscible with one another. There are only few commercially important polymer blends based on miscible and partially miscible (i.e., miscible within a low range of concentration) polymer pairs. It is seldom possible to mix two or more polymers and create a blend with useful properties. Instead, when preparing a new polymer blend from immiscible resins, it is necessary to devise a specific strategy for compatibilizing the mixture to provide for optimum physical performance and long-term stability. Although there do exist a very small number of commercial blends of immiscible polymers that are not compatibilized, most commercially available blends of immiscible polymers have been compatibilized by some specific mechanism. The majority of polymer blends containing elastomeric, thermoplastic, and/or liquid crystalline polymers are processed by melt extrusion at some point in their history. After melt extrusion with intensive mixing, the morphology of an immiscible polymer blend on a microscopic scale will often consist of a dispersed phase of the more viscous polymer in a continuous matrix of the less viscous polymer (depending upon the relative amounts and viscosities of the two polymers in the blend). A good analogy from every-day experience is a dispersed mixture of viscous oil in an immiscible water matrix. The formation of optimum dispersed phase particle size and the long-term stabilization of blend morphology are critical if the blend is to have optimum properties and in particular good mechanical properties. If this morphology is not stabilized, then the dispersed phase may coalesce during any subsequent heat and high stress treatment (such as injection molding). Coalescence may result in gross phase segregation and delamination on a macroscopic scale and/or brittleness or poor surface appearance in the final molded part. Good analogies from everyday experience would be the separation on standing of a not stabilized oil-in-water dispersion into two separate liquid phases, or churning butter. Therefore, an important aspect of all compatibilization strategies is the promotion of morphology stabilization. Morphology stabilization L.A. Utracki (Ed.), Polymer Blends Handbook, 339-415. © 2003 Kluwer Academic Publishers. Printed in the Netherlands.
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may be provided by sufficient interfacial adhesion and/or lowered interfacial tension between the two polymer phases. Of the various compatibilization strategies that have been devised, an increasingly common method is either to add a block, graft, or crosslinked copoly
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