EP blends

Polarized light—Is used if one of the polymer phases is crystalline or for agglomeration of inorganic filters, (e.g., nylon/EP blends and fillers such as talc. (Figure 4)... 

Solvent etching—When there exists a large solubility difference in a particular solvent of the polymers being studied, e.g., PP/EP blends. 

Figure 4. Light microscopy phase contrast nylon/EP blends.

The band at 1167 cm"1 (with a shoulder at 1156 cm1) corresponding to a CH3 vibration is considered as an internal standard. The method is checked by varying some fitting parameters. The amounts of total (-CH2-CH2) units, isolated ethylene and structural defaults in PP were determined for different iPP/EP blends. 

Using the results of 12 iPP/EP blends, 4 iPP/EP block copolymers and 1 pure EP copolymer [13, 14], the Xe chemical shift of Xe absorbed in EP can be correlated to the chemical composition of EP, i.e., the ethylene fraction. Figure 12.9 shows an approximately linear relationship between the Xe chemical shift and the weight fraction ethylene in the EP copolymer. The values for the pure components PE (ethylene content = 1) and iPP (ethylene content = 0) are included. Of course, this also implies that a linear relationship exists between the Xe chemical shift and the density of the EP copolymer. 

The difference in Tg between iPP and PE also is an important factor in the explanation of the temperature dependence of the Xe spectra. Figure 12.10 shows the Xe spectra between 20 °C and -40 °C of a iPP/EP blend. By spectral simulation of the doublet by two lines the temperature dependence of the line width (Figure 12.11) and of the chemical shift (Figure 12.12) for each line can be determined. 

Figure 12.13 shows the Xe spectra of a iPP/EP blend obtained with single pulse excitation and with => 129Xe cross-polarisation at -33 °C [13]. In the cross-polarisation spectrum only the Xe line from Xe in iPP is observed, because the dipolar interaction between the polymer spins and the 129Xe spins due to the Xe mobility is too weak in EP. Also the cross-polarisation signal of iPP disappears at temperatures higher than the Tg of iPP. 

Figure 12.21 An electron microscope image of the iPP/EP blend investigated by Xe...

In Section 12.3 it was described how, with the help of a two-dimensional exchange spectrum, domain sizes in the iPP/EP blend are estimated. There an estimated value for the Xe diffusion coefficient was used. Now with experimental data from Table 12.2 the average EPDM domain size for the iPP/EPDM blend can be calculated. It was assumed that the structure of the EPDM in the blend is the same as in the pure material, (i.e., the Xe diffusion coefficient in the EPDM domains in the blend is equal to the measured D for pure EPDM and likewise for iPP), then for Xe in the EPDM domain during A = 1.2 seconds is 20 grn. In the same time for Xe in the iPP matrix is approximately 5 grn. These distances for a diffusion time of 1.3 milliseconds, the inverse of the frequency difference 770 Hz of the two lines in the Xe NMR spectrum of the blend, are 0.6 and 0.2 grn, respectively. The average size of the EPDM domains in the iPP/EPDM blend is... 

Furthermore, the friction forces acting in the flow field can induce phase segregation at the mould surface [189]. As pointed out by Cakmak and Cronin [191], in PP/EP blends with a high content of EP particles even shear amplification phenomena may occur due to the presence of the small rubber particles. The shear amplification results from considerable shear fields occurring in small gaps between rubber particles which in turn are subjected to the macroscopic shear field extended over the whole width of the sample. 

Figure 16.2. SEM photographs of PP/EP blends, (a) PP/EP blend (b) PP/EP/talc blend with separated nucrostructure (c) PP/EP/talc blend with core-shell microstructure. [Adapted, by permission, from Shanks R A, Long Y, Polym. Networks Blends, 7, 1997, 87-92.]...

Figure 3.9 Tensile stress-strain curves for LLDPE, LDPE, and LDPE-EP blends.

According to WAXD studies of the iPP and iPP/EP blends, the diffraction patterns of all the blend samples have a broad amorphous background superimposed upon five sharp diffraction lines ascribed to the a-form (monoclinic) (37). These results indicate that the blending of EP copolymers little affects the crystalline region of iPP irrespective of molecular composition in EP copolymers. 

Figure 9.18 Schematic illustration of the lamellar morphology in miscible iPP/EP and immiscible iPP/EP blends. The red line denotes the EP copolymers and the closed dots in the red chains indicate the ethylene units.

EP blends which illustrate a number of the features already discussed and will not be outlined here [151-153]. 

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