Morphology of Immiscible Blends

The structure and morphology of immiscible blends depends on many factors among which the flow history and the interfacial properties are the most important. At high dilution, and at low flow rates the morphology of polymer blends is controlled by three dimensionless microrheologi-cal parameters (i) the viscosity ratio, where r j is the viscosity of the dispersed liquid and r 2 that of the matrix (ii) the capillarity number, k = d / Vj2, where d... 

In most cases, some mode of sample preparation has to be used after the blend formation, viz., staining, swelling, fracturing, or etching. These are very appropriate for and have been extensively used to characterize morphology of immiscible blends, but they have obvious severe shortcomings in miscible or partially miscible... 

To improve the compatibility properties of the nanoparticles, the surface chemistry can be modified and organically modified nanoparticles have been found to have good dispersion in polymer phases. The kinetic conditions like the processing condition and mixing protocol can be altered to get the best compatibiUzation effect. However, the manner in which these nanoparticles help stabilize the phase morphology of immiscible blend is still far from being understood properly. 

Creation of reproducible morphology of immiscible blends is notoriously difficult. The task is simpler when the system comprises a block copolymer... 

A new mixer, the Minibatch mixer, has been developed for small-scale blending of specialty polymers and nanoscale composites. This mixer is a 1 20 scale down of the standard 60mL internal batch mixer and maintains general geometric similarity. Morphology of immiscible blends showed a spherical dispersed phase stracture and uniform distribution throughout the blend however, particle size of blends made in the Minibatch appeared... 

The effect of viscosity ratio on the morphology of immiscible polymer blends has been studied by several researchers. Studies with blends of LCPs and thermoplastics have shown indications that for good fibrillation to be achieved the viscosity of the dispersed LCP phase should be lower than that of the matrix [22,38-44]. 

Since the processing conditions and mixing equipment have a crucial effect on the morphology of immiscible polymer blends [45], experiments were carried out in four different types of extruders to find optimal conditions for blend preparation and fibrillation. Nevertheless, the morphologies of PP-LCP blends produced by... 

The properties of immiscible polymers blends are strongly dependent on the morphology of the blend, with optimal mechanical properties only being obtained at a critical particle size for the dispersed phase. As the size of the dispersed phase is directly proportional to the interfacial tension between the components of the blend, there is much interest in interfacial tension modification. Copolymers, either preformed or formed in situ, can localize at the interface and effectively modify the interfacial tension of polymer blends. The incorporation of PDMS phases is desirable as a method to improve properties such as impact resistance, toughness, tensile strength, elongation at break, thermal stability and lubrication. 

Goldel A, Ruckdaschel H, Muller AHE, Potschke P, Altstadt V (2008) Controlling the phase morphology of immiscible poly(2,6-dimethyl-l,4-phenylene ether)/poly(styrene-coacrylonitrile) blends via addition of polystyrene. e-Polymers 151... 

Immiscibility of polymers in the melt is a common phenomenon, typically leading to a two-phase random morphology. If the phase separation occurs by a spinodal decomposition process, it is possible to control the kinetics in a manner that leads to multiphase polymeric materials with a variety of co-continuous structures. Common morphologies of polymer blends include droplet, fiber, lamellar (layered) and co-continuous microstructures. The distinguishing feature of co-continuous morphologies is the mutual interpenetration of the two phases and an image analysis technique using TEM has been described for co-continuous evaluation.25... 

Fig. 11.17 The melting mechanism of immiscible blends, showing in cartoon form the evolution of blend morphology during and following melting in twin rotor devices. [Reprinted by permission from C. E. Scott and C. W. Macosko, Morphology Development During the Initial Stages of Polymer-polymer Blending, Polymer, 36, 461-470, (1995).]...

B. D. Favis, Factors Influencing the Morphology of Immiscible Polymer Blends in melt Processing, in Polymer Blends, Vol. I, D. R. Paul and C. B. Bucknall, Eds., Wiley-Interscience, New York, 1999. 

There are a number of important factors governing the change of the crystallization rate and semicrystalline stracture of a polymer in blend systems. Those include the degree of miscibility of the constituent polymers, their concentration, their glass-transition and melting temperamre, the phase morphology and the interface structure in the case of immiscible blends, etc. 

Meijer et al. [1988] and Elemans et al. [1988] investigated the potential of electron irradiation to stabilize the morphology of immiscible polymer blends. Their concept was that selective crosslinking of a dispersed phase in a matrix that remains unaffected, or degrades, should help fix the morphology of the blend. 

Because of the high interfacial tension, the morphology of the blends is not stable. Coalescence readily occurs in the molten state. As suggested by Macosko et al. (121), in melt mixing of immiscible polymer blends, the disperse phase is first stretched into threads and then breaks into droplets, which can coalesce together into larger droplets. The balance of these processes determines the final dispersed particle sizes. With increase of disperse phase fraction (usually more than 5 wt%), the coalescence speed increases and the dispersed phase sizes increase (121-123). 

The morphology of PP/PS blends was studied following the emulsification behavior as explained in Section 20.3.1.2. Figure 20.10 shows that the emulsification curve follows a typical trace, which was frequently reported for compatibilization of immiscible blends (28-30). It is clear that after a significant drop in particle size, an equilibrium value is reached at about 0.7% AICI3. This value has been taken as the cmc condition. It has to be remarked that the particle size decreases to one third of its initial value, reaching an equilibrium diameter of about 0.5 pm. Also, the particle size homogeneity increases with the catalyst content. It is shown by the decrease in error bars in Fig. 20.10. From these results, it is foreseen that the copolymer formed by the F-C reaction behaves as an efficient in situ compatibi-lizer for the PP/PS blend. 

F. Xiang, Y. Shi, X. Li, T. Huang, C. Chen, Y. Peng, Y. Wang, Cocontinuous morphology of immiscible high density polyethylene/polyamide 6 blend induced by multiwalled carbon nanotubes network. Eur. Polymer J. 48, 350-361 (2012)... 

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