Uncompatibilized

Blends of Saturated Hydrocarbon Elastomers (Uncompatibilized Blends)... 

Evidence of chemical interaction between the mbbers and compatibUizers was demonstrated by extracting the blends with chloroform at room temperamre and examining both soluble and insoluble fractions with Fourier transform infrared (ETIR) spectrometry. The weight of the insoluble fraction of the compatibilized melt blend was more than that in the uncompatibilized blend indicating the formation of (EP-g-MA)-g-CR due to reaction between MA and allylic chlorine of CR. The compounds containing epoxidized EPDM additive were examined by both optical and... 

O Uncompatibilized 128 layers Uncompatibilized 256 layers Compatibilized 128 layers 0 Compatibilized 256 layers... 

Examination of the fracture by SEM shows that although there is no interphase adhesion in uncompatibilized blends, adhesion between the phases increased and dispersed domains decreased... 

This drawback can be at least partially eliminated by blending PLLA with other polymers (26-29). In addition, ABS has been used for blending (30). The blends were prepared laboratory mill equipped with a twin-screw. It turned out that uncompatibilized blends of PLLA and ABS have a morphology with big phase size and a weak interface. The blends exhibit poor mechanical properties with low elongation at break and decreased impact strength. 

The solubility of carbon dioxide at the selected saturation conditions of 5 MPa and 40°C, is shown in Table 1. Both the uncompatibilized and the compatibilized PPE/SAN blends absorb similarly high amounts of carbon dioxide in the range of 100, mgg-1. However, in contrast to one-phase systems, the solubility data of the overall multiphase blend is not sufficient to describe the system, but the content of carbon dioxide in each blend phases needs to be considered. In the case of PPE/SAN blends compatibilized by the SBM triblock terpolymers, one can distinguish three distinct phases, when neglecting interfacial concentration gradients (idealized case) (1) the PPE phase intimately mixed with the PS block, (2) the SAN phase mixed with the PMMA block, and (3) the PB phase located at the interface between PPE/PS and SAN/PMMA. 

As a next step, the effect of compatibilization on the foaming behavior will be discussed. While the density can only be slightly reduced by SBM, and remains at a rather high level, the foam structure reveals distinct differences, exemplarily shown for a foaming temperature of 160°C and at a foaming time of 10 s (Fig. 18). As mentioned earlier, the uncompatibilized blend reveals a highly inhomogeneous structure,... 

For evaluating the efficiency of the nanostructured interface for cell nucleation, the particle density of PPE, as a measure for the number of nucleating sites available for nucleation, is plotted versus the nucleation density observed for the foam (Fig. 21). For comparison, the previously found values of the uncompatibilized PPE/SAN blend are added. For PPE/SAN, even the relatively high number of PPE particles of around 5 x 10ncm-3 only leads to nucleation of approximately 2.5 x 1010 cells cm-3, i.e., only 1/20 of the potentially available PPE particles act as cell nucleating agents. Via compatibilization, however, not only the particle density of PPE and the nucleation density can be increased, but also the efficiency is strongly enhanced. While the number of cells directly scales with particle density, more than two foam cells are nucleated by one PPE particle. 

Fig. 21 Nucleation density vs particle density of PPE/SAN blends compatibilized by SMB triblock terpolymers, in comparison to uncompatibilized PPE/SAN blends...

Figure 1 shows SEM micrographs of the uncompatibilized and compatibilized PC-PA (30/70) blends after etching away of the PC phase with dilute KOH so-... 

Figure 1. SEM images of uncompatibilized and compatibilized blends (A) PC/PA = 30/70 and (B) PCVPA/compatibilizer = 70/30/5.

Tensile deformation of the uncompatibilized blend with 50% PS was characterized by the appearance of several regions of localized stress-whitening in the gauge section without global necking. Fracture occurred at one of these regions at a relatively low strain, about 3.2%. This behavior is characterized as quasi-brittle rather than brittle, because some level of plastic deformation precedes fracture even though the fracture strain is low (Chapter 21). 

Fracture Stress and Strain. Yielding and plastic deformation in the schematic representation of tensile deformation were associated with microfibrillation at the interface and stretching of the microfibrils. Because this representation was assumed to apply to both the core-shell and interconnected-interface models of compatibilization, the constrained-yielding approach was used without specific reference to the microstructure of the interface. In extending the discussion to fracture, however, it is useful to consider the interfacial-deformation mechanisms. Tensile deformation culminated in catastrophic fracture when the microfibrillated interface failed. This was inferred from the quasi-brittle fracture behavior of the uncompatibilized blend with VPS of 0.5, which indicated that the reduced load-bearing cross section after interfacial debonding could not support plastic deformation. Accordingly, the ultimate properties of the compatibilized blend depended on interfacial char-... 

Blends of PP/PEST are at an early stage of development. PP is antagonistically immiscible with PEST, and when the concentration of the dispersed phase exceeds 5-10 wt% compatibiliza-tion is necessary. Initially, the uncompatibilized... 

The goal of combining two or more polymers such as pairs from those categories described above e.g., an engineering thermoplastic plus a commodity polyolefin) is to achieve in the blend a combination of favorable properties from each polymer. Figure 5.1 shows idealized expected property combinations from blending two polymers that are either miscible (solid center line), immiscible and uncompatibilized (bottom line), or immiscible and compatibilized (top line). In the case of polymers that are miscible in all propor-... 

The formation of optimum dispersed phase particle size and the stabilization of the resulting blend morphology are critical if the blend is to have optimum properties and in particular good mechanical properties. Eigure 5.2 shows a morphology generated by processing an uncompatibilized... 

Table 5.2 shows further examples of dispersed phase coalescence in blends of PA dispersed phase in a less viscous PE or PS matrix. The data show that the mean PA particle size increases dramatically with simple heating under static conditions in the absence of any mechanism for morphology stabilization. The same coalescence can occur in molded parts of uncompatibilized polymer blends subjected to further thermal treatment after molding (fi.g., in a paint drying oven). The mechanical properties of these blends are quite poor. 

Table 5.2. Change of dispersed phase dimensions in uncompatibilized polymer blends upon annealing [adapted from White and Min, 1989]...

Table 5.3 shows dramatic examples of the stabilization of dispersed phase morphology in the presence of a compatibilizing copolymer. In all examples essentially no change in dispersed phase particle size occurs after annealing under static conditions for up to 90 min. The data shown in this Table 5.3 should be compared with those presented in Table 5.2, where the dispersed phase mean dimensions were presented for similar, uncompatibilized blends. 

Figure 15.7. Instrumented Impact behavior of ABS/PA-6 (50/50) blends top — uncompatibilized blend, bottom — compatibilized blend [Akkapeddi et al., 1993].

Figure 15.8. Morphology of ABS/PA-6 blends (TEM, phosphotungstic acid) top — Uncompatibilized blend (5000X), bottom — Compatibilized blend (10,000X) lAkkapeddi, 1993],...

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