Compatibilizing agent, improvement interfacial adhesion

As stated earlier, a copolymer of the two immiscible polymers themselves would seem to be ideally suited to act as a compatibilizing agent for an immiscible blend. If the copolymer is at the interface of the two phases, then the segments of the copolymer dissolve in the respective bulk phases of the same identity. The copolymer acts as emulsifying agent for the blend resulting in reduced interfacial energy and improved interfacial adhesion. 

Blends of immiscible polymers exhibit a coarse and unstable phase morphology with poor interfacial adhesion. The ultimate properties of these blends are often poorer than those of either component. The poor mechanical properties can be improved with a small amount of an interfacial agent that lowers interfacial tension in the melt and enhances interfacial adhesion in the solid. High-strain properties, such as strength, tensile elongation, and impact strength, especially benefit from compatibilization (I, 2). 

One possible way of reducing interfacial tension and improving phase adhesion between PP-based blend phases is to use a selected copolymeric additive that has similar components to the blend, as a compatibilizer in the blend system. Well-chosen diblock copolymers, widely used as compatibilizing agents in PP-based blends, usually enhance interfacial interaction between phases of blends (15, 16), reduce the particle dimensions of the dispersed phase (16, 17), and stabilize phase dispersion against coalescence (16-18) through an emulsification effect, thus improving the mechanical properties (15-19). 

While the reduction of the interfacial tension, v, is relatively easy by introduction of a macromolecular surfactant, the stabilization of morphology and improvement of the interfacial adhesion in the solid state may not be so. One may use either a single compatibilizer that can perform all three compatibilization tasks, or a combination of agents, each playing one or two different roles. For example, stabilization of the desired dispersion (accomplished by addition of surfactant to mechanically mixed compound) may be accomplished by partial cross-linking of one of the three phases matrix, dispersed, and the interphase. In the latter case, the interfacial adhesion in the solid state is also improved. 

Kalf et al. studied the effect of grafting cellulose acetate and methylmethacrylate as compatibilizers on acrylonitrile butadiene rubber (NBR) and styrene-butadiene rubber (SBR) blends. Morphology studies of the samples show an improvement in interfacial adhesion between the NBR and SBR phases in the presence of the prepared compatibilizing agents. The authors also reported the samples with grafted compatibilizers showed superior crosslink density and thermal stability, as compared to the blends without graft copolymers. ... 

In case of sandwich molding of PP and pure PBS as skin and core, sufficient test piece was not obtained due to the lack in interfacial adhesion. In addition, any compatibilizing agent was insufficient to obtain perfect adhesion. Therefore, we tried to add high-flow PP to improve the adhesion. 

The use of copolymers as surfactants is widespread in macromolecular chemistry in order to compatibilize immiscible blends. These additives are sometimes named surfactants , interfacial agents or more usually compatibi-lizers . Their effect on improving different properties is observed interfacial tension and domain size decrease, while there is an increase in adhesion between the two phases and a post-mixing morphology stabilization (coalescence prevention). The aim of the addition of such copolymers is to obtain thermodynamically stable blends, but the influence of kinetic parameters has to be kept in mind as long as they have to be mastered to reach the equilibrium. Introducing a copolymer can be achieved either by addition of a pre-synthesized copolymer or by in-situ surfactant synthesis via a fitted re-... 

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