PEO-PU blends

Figure 4.41 T s for PEO-PU blends plotted versus overall blend composition (filled circles) and versus calculated amorphous phase composition (open circles). The full curve is as predicted by the Fox equation, [equation (4.44) ...

Figure 4.42 shows the application of the Hoffman-Weeks procedure [17] to separate the morphological effect on melting point depression and to determine the equilibrium melting point of PEO in the blend and in the pure state. The observed melting temperature (T. ) of PEO and the PEO-PU blends increases linearly with increase in crystallization temperature for a wide range of undercooling. A depression of T, for the same T, is observed for blends. The analysis is based on the relationship... 

Figure 4.43 Melting point depression analysis to obtain the interaction energy density B for PEO-PU blends. The slope gives B = -14 J cm" ...

The negative values found for B in the case of PEO-PU blends support the idea that these polymers are miscible in the molten state and the fact that the intercept of the Nishi-Wang plot is close to zero indicates that entropic effects contribute little to B. 

Figure 4.42 Hoffman-Weeks plot to obtain the equilibrium melting point for PEO in blends with PU. All samples were quenched from 100 "C to T,. and crystallized at for 24 h...

The authors used high-resolution XPS to fiilly deconvolute the Cls spectra into C—C, C—O, NHCOO (urethane carbonyl), and NHCONH (urea carbonyl). On the surface of matrix PU, the majority of carbon were from the carbons in the C—C bond (Figure 2.12(a)). The fresh polymer blend with 20% copolymer 2 in the PU showed more carbon from the C—O ether bond (note that all the ether bonds are from the PEO groups) (Figure 2.12(b)). It was noted that after a prolonged aging process, predominant carbons were those from C—O ether bonds, suggesting that the surface was covered by copolymer 2. 

The degree of surface enrichment of PEO groups depends on not only the aging time but also the MW of the triblock copolymer. When the low MW copolymer 1 was blended with matrix PU, the surface of the blended polymer film had the same ether carbon content as that of copolymer 2 after just 3 days of aging... 

Another modified spinneret was designed with multiple single jets in order to enhance nanofibers spinning rate of PEO (Theron et al. 2005) or to prepare nanofibrous mats composed of two different and immiscible polymers such as PVA and cellulose acetate. A multiple jet composed of four tips was used in order to blend PVA and cellulose acetate nanofibers in different ratios (Pham et al. 2006). In another study, a collector moving transversely was used in front of a multiple jet composed of two tips in order to produce a mixture of electrospun PEO and polyurethane (PU) nanofibers and a uniform distribution of this mixture was achieved due to the motion of the collector (Kidoaki et al. 2005). 

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