Melts miscibility

When a melt-miscible polymer system is analyzed at temperatures lower than the crystallization temperature of one constituent, a phase-separated or single crystalline phase structure might result. When the T% of the noncrystalline component is lower than the crystallization temperature, the component phase separates as it is rejected from the crystal structure. The extent of phase separation may be easily visualized... 

These PE polymers offer a broad spectrum of structures, properties, and applications. However, the blending of different types of PEs (HDPE, LDPE, LLDPE, and UHMWPE) has attracted growing interest because of the potential for obtaining low cost materials with improved mechanical properties and better processabilities, as compared to those of the pure constituents (1-34). Nowadays, 70% of PEs in the market are blends (24). The processability and properties of PE blends are dependent on the melt miscibility. Moreover, the properties are also dependent on the morphological structure of the blend, which is basically a combination of the crystallization behavior and melt miscibility. Therefore, the miscibility and crystallization behavior of PE blends have been prevalent research topics over the last two decades. 

In blends of amorphous glycol-modified PET and semi-crystalline PEN, a melt miscibility is observed. The diluent effect of the glycol-modified PET severely retards the crystallization of the PEN component within the blends. However, after an isothermal stretching at 120 °C, a crystallization may occur [54]. 

Akpalu and Ping Peng (Akpalu et al. 2005) studied the melt miscibility of a commercial linear polyethylene and LLDPE system using SANS. 

Y.A. Akpalu, P. Peng, Probing the melt miscibility of a commercial polyethylene blend by small-angle light scattering. Mater. Manuf. Process. 23, 269-276 (2008)... 

F.C. Stehling, G.D. Wignall, Small angle neutnm scatbaing investigatimis of melt miscibility and phase segregation in blends of linear and branched polyethylenes as a function of the branch content. Macromolecules 30(3), 561-566 (1997)... 

T. Hameed, LA Hussein, Melt miscibility and solid-state properties of metallocene LLDPE blends with HOPE influence of MM of LLDPE, J. Cent. South Univ. Technol. si—0183 —05 (2007)... 

Figure 6.7a depicts the IDF profile from different compositions of melt-miscible crystalline/amorphous blends of PCL/PVC (i.e., polycaprolactone (PCL)/poly(vinyl chloride). The maxima and minima in the obtained IDF profile, and their deconvolution, provides an estimate of the long period, I (negative peak) and the thickness of crystalline (Ic) and amorphous layers (y as either li and (2 or vice-versa, as shown in Figure 6.7b. The entire IDF profile has been fitted to the superimposition of three peak contributions two positive peaks (corresponding to Ic and la) and one negative peak (L), assuming their Gaussian distribution.

Schultz JM. The crystallization and morphology of melt-miscible polymer blends. Front Chem China 2010 5 262-276. 

PLLA-fe-PCL linear diblock copolymers were found to be either melt miscible or weakly segregated in the melt. This means that upon cooling the material will be able to form spherulites (see details in Refs [50,51,66,95]). 

Examples of crystallizable systems with full melt miscibility over the whole composition range have been pointedoutforpoly(ethyleneterephthalate)/poly(butylene terephthalate) (PET/PBT), poly (hydroxy butyrate)/ poly (ethylene oxide) (PHB/PEO), and polycarbonate/ poly(e-caprolactone) (PC/PCL) blends [29]. 

For shape memory applications, crystals formed upon cooling of the semicrystalline polymer act as physical crosslinks by which a permanent or equilibrium shape can be set. In a complementary fashion, the miscible amorphous phase governs temporary shape fixing. In turn, crystallization kinetics, crystallite size, and degree of crystallinity collectively determine kinetics of permanent shape setting and shape memory performance characteristics. Thus, it is possible to tailor the shape memory properties of a system by varying the composition and the thermal history of such blends[9], leading us to the present study focused on crystallization kinetics from melt-miscible crystalline-amorphous blends. 

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