Compatibility of Polymer Blends

Compatibility of Polymer Blends

Compatibilization:
Process of modification of the interphase in immiscible polymer blends, resulting in reduction of the interfacial energy, development and stabilization of the desired morphology, leading to the creation of a polymer alloys with enhanced performance
Interphase:
Third phase in binary polymer alloys, engendered by interdiffusion or compatibilization. Its thickness ?l = 2 to 60 nm depends on polymers’ miscibility and compatibilization


Figure 1: (a) Ideal configuration of a block copolymer at the interface between polymer phases A and B. (b) Formation of an interphase between phases A and B promoted by a compatibilizer .
To improve performance of immiscible blends, usually they need to be compatibilized. There are three aspects of compatibilization:
(1) Reduction of the interfacial tension that facilitates fi ne dispersion,
(2) Stabilization of morphology against its destructive modifi cation during the subsequent high stress and strain processing
(e.g., during the injection molding), and
(3) Enhancement of adhesion between phases in the solid state, facilitating the stress transfer, hence improving the mechanical
properties of the product.
Compatibilizer:
It is a polymer or copolymer that helps bond the two phases to each other more tightly. Use of Compatibilizer is one of the most interesting ways to make immiscible blends stronger. Often times, a compatiblizer is a block of graft copolymer of the two components of immiscible blend of polymer A and polymer B.

Compatibilization Methods:
Compatibilization methods are employed to improve the morphology of the blend:
1- Addition of linear or star shaped AB block copolymer for blends of A and B.
2- Addition of linear random copolymer.
3- IPN technology : An interpenetrating polymer network, IPN, is defined as a blend of two or more polymers in a network form, at least one of which is synthesized and/or crosslinked in the immediate presence of the other(s). An IPN can be distinguished from polymer blends, blocks, or grafts in two ways: (1) an IPN swells, but does not dissolve in solvents, and (2) creep and fl ow are suppressed
4-.Co-reaction in blend, e.g. transesterification. It has the disadvantage that it is difficult to control and can lead to completely different (co)polymers.
5-Crosslinking of blend ingredients .This is similar to the IPN technology since it also involve the use of crosslinked polymers to maintain an initially formed morphology.
6-Interaction between the constituent polymers after modification by ionic interactions or hydrogen bonds.
7-Addition of a co-solvent. Two immiscible polymers may dissolve in a common solvent. After evaporation of the solvent, the interfacial area is so large that even weak polymer-polymer interactions will stabilize the system.
8-High stress shearing may result in mechanical interlocking of the two phases.
Strategies for Compatibilization of Polymer Blends
? Fundamentals
Most of the reports in the literature deal with novel methods for compatibilization of polymer blends, mainly focused on the modification of the interface and studying the effect of such modifications on the phase morphology and the mechanical properties.
Compatibility of polymer blends can be achieved by reducing the interfacial tension or increasing the interfacial adhesion through the addition of interfacial active agents, for instance block or graft copolymers.
Another way is to create in situ copolymers in the melt. The copolymer, either added or created in situ by the melt coupling reaction at the interface, is believed to play a dual role in promoting mixing of blend components:
1- Reduce the interfacial tension by accumulating at the interface, as shown in figure bellow and consequently to promote droplet break-up when melt mixing in a shear field.