Immiscible blends, interfacial polarization

Polymer blends can be divided into two groups miscible and immiscible blends. Miscible blends are homogeneous and stable. Their properties tend to be intermediate. However, they are relatively few. Most polymer blends are immiscible. Their properties are strongly affected by their phase morphologies, which are decided by their viscosity, interfacial tension, and processing methods. In this review we will describe polyolefin blends. Many of these blends involve polar polymers with polyolefins. 

Interfacial polarization or MaxwelVWagner/SUlars (MWS) polarization (Wagner 1914 SUlars 1937) is a phenomenon that is characteristic for phase-separated or multiphase systems like immiscible polymer blends. Precondition for the observation of a MWS polarization is that the different phases have nonidentical properties. As a result of this, for instance, accumulation of charges takes place at the interfaces of the different phases. Steeman and van Tumhout (2003) published a compilation concerning polymeric materials including polymer blends. 

Because of their highly polar and hydrogen bonded structure of the backbone, as a general rule polyamides are immiscible with most of the commercially known polymer systems. In addition, the high degree of interfacial tension [Wu, 1989] between polyamides and other classes of polymers leads to highly phase separated blends with poor delamination resistance. Hence simple blends of PA with other commercial polymers generally do not have any practical value. 

Block copolymers, formed by transesterification of blend components or otherwise, will act as interfacial agents in blends of immiscible polymers which are identical to or compatible with the components of the block copolymer. A recent patent application for a system of this type refers to the use of triblock copolymers of polymer A-polysiloxane-polymer B as interfacial agents in blends of polymers A and B which have different polarity or hydrophilicity [6]. In this case the intermediate polysiloxane blocks, strongly immiscible with either polymer A or polymer B, helps to drive the copolymer to the A-B interface and reduce the possibility of dissolution of the copolymer in either blend phase. In the example quoted polymer B is PCL (or a non-polar polyether) and polymer A is a polar polyether or other polar polymer. 

Unfortunately, PA-6 and rPE are incompatible due to the different polarity and different crystalline stmcture, which are thermodynamically immiscible, leading to incompatible blends with low mechanical properties. Nonetheless, one technical problem associated with plastics waste such as PA-6 and rPE is its heterogeneous composition, immiscibility and poor interfacial adhesion between dispersed phase and matrix, resulting in poor physical-mechanical... 

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