Morphology Development During Melt Processing

28) t]m is the matrix viscosity, y the shear rate, d the particle diameter, 

If the hydrodynamic stress is sufficiently high, Ca exceeds a certain value known as the critical capillary number, CacR. Under these conditions no stable shape can persist in the flow, and the droplet deforms continually until it breaks into daughter droplets. These can undergo consequent deformations and breakups until the droplets are so small that the interfadal stress overrules the hydro-dynamic stress. At Ca Cocr the droplets are deformed into a shape which is stable in the flow and can be also predicted by the theory of Maffetone and Minale [76]. On the other hand, at very high values of Ca (Ca CacR), a quick affine deformation of the droplets occurs and long cylindrical threads are formed which are rather stable in the flow and decay only at very high deformations or even just after the cessation of flow [77,78]. 

The final break-up mechanism is specific, as it does not require deformation of the mother droplet. Lin et al. [97] observed a release of thin ribbons and streams of droplets from the surface of the mother droplet, and termed the mechanism surface erosion. Surprisingly, this type of break-up was confirmed also in blends with p 4 - that is, in systems where Taylor theory and many experimental studies have claimed that droplet break-up under shear is not possible. 

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Fig. 14.5 Morphological model of structures developed in as-spun HDPE. Take-up velocities are (a) very low (b) low (c) medium and (d) high. [Reprinted by permission from J. E. Spruiell and J. L. White, Structure Development during Polymer Processing Studies of the Melt Spinning of Polyethylene and Polypropylene Fibers, Polym. Eng. Set, 15, 660 (1975).]...

Bhardwaj and Mohanty [8] proposed and demonstrated a new industrially relevant methodology to develop a polylactide (PLA)-based nano blend having outstanding stiffness-toughness balance. In this approach, a hydroxyl functional hyper branched polymer (HBP) was in situ cross-linked with a polyanhydride (PA) in the PLA matrix during melt processing. There was formation of new HBP-based cross-linked particles in the PLA matrix. TEM and AFM revealed the sea-island morphology of... 

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