Blends phase domains

Els and McGill [48] reported the action of maleic anhydride on polypropylene-polyisoprene blends. A graft copolymer was found in situ through the modifier, which later enhanced the overall performance of the blend. Scott and Macosko [49] studied the reactive and nonreactive compatibilization of nylon-ethylene-propylene rubber blends. The nonreactive polyamide-ethylene propylene blends showed poor interfacial adhesion between the phases. The reactive polyamide-ethylene propylene-maleic anhydride modified blends showed excellent adhesion and much smaller dispersed phase domain size. 

FIGURE 20.12 (a) Top part shows variations of elastic modulus profile measured in different locations of the polypropylene (PP)-ethylene-propylene-diene terpolymer (EPDM) blend. The locations are shown by white dots in the blend phase image placed at the bottom. Vertical white dashed lines show the components borders and the elastic modulus value for this location. Vertical black dotted lines indicate the locations where elastic modulus E gradually changes between PP (E ) and EPDM (E )- These values are indicated with black arrows on the E axis, (b) LvP curves for PP-matrix, EPDM-domains, and one of interface locations. The approach curves are seen as solid black lines and the retract curves as gray lines. 

It is the intent of this doeument to define the terms most commonly encountered in the field of polymer blends and eomposites. The scope has been limited to mixtures in which the eomponents differ in ehemical composition or molar mass or both and in which the continuous phase is polymeric. Many of the materials described by the term multiphase are two-phase systems that may show a multitude of finely dispersed phase domains. Hence, incidental thermodynamic descriptions are mainly limited to binary mixtures, although they can be and, in the scientific literature, have been generalized to multicomponent mixtures. Crystalline polymers and liquid-crystal polymers have been considered in other documents [1,2] and are not discussed here. 

Melt-processable polymer blend or copolymer in which a continuous elastomeric phase domain is reinforced by dispersed hard (glassy or crystalline) phase domains that act as junction points over a limited range of temperature, or... 

Note 2 The interfacial interaction between hard and soft phase domains in a thermoplastic elastomer is often the result of covalent bonds between the phases and is sufficient to prevent the flow of the elastomeric phase domains under conditions of use. Note 3 Examples of thermoplastic elastomers include block copolymers and blends of plastics and rubbers. 

Shape, optical appearance, or form of phase domains in substances, such as high polymers, polymer blends, composites, and crystals. 

Note For a polymer blend or composite, the morphology describes the structures and shapes observed, often by microscopy or scattering techniques, of the different phase domains present within the mixture. 

Region between phase domains in an immiscible polymer blend in which a gradient in composition exists [3]. 

Note In a polymer blend, the continuous phase domain is sometimes referred to as the host polymer, bulk substance, or matrix. 

Dynamic viscoelastic and stress-optical measurements are reported for blends of crosslinked random copolymers of butadiene and styrene prepared by anionic polymerization. Binary blends in which the components differ in composition by at least 20 percentage units give 2 resolvable loss maxima, indicative of a two-phase domain structure. Multiple transitions are also observed in multicomponent blends. AU blends display an elevation of the stress-optical coefficient relative to simple copolymers of equivalent over-all composition. This elevation is shown to be consistent with a multiphase structure in which the domains have different elastic moduli. The different moduli arise from increased reactivity of the peroxide crosslinking agent used toward components of higher butadiene content. 

It would often be desirable to create submicron particles containing two or more polymers. These could be in the form of a blend or in the form of a graft copolymer. In a simple blend, the two polymers may or may not be compatible. If they are compatible, the particle will be homogenous. If the polymers are not compatible, then microphase separation is likely. However, if the phase separation occurs in submicron particles, the phase domains will be small, and decent dispersion of the two polymers will occur. Homogenous, grafted, or phase-separated morphologies might conceivably be of practical value. 

For partially miscible and immiscible blends, various domain/phase structures can be invoked. Unfortunately, the resonance position of a particular spin in each domain is not appreciably affected by its respective domain structure (see Section 10.2.2.1). Therefore, we cannot expect to observe highly resolved NMR resonances for different domains. Since relaxation times are different for each domain, a relaxation curve is observed to be a featureless multiexponential one and, in most of the cases, is too monotonous to include interdomain spin diffusion. Therefore, most of the experimental results have been explained by using the simplified picture of no interdomain spin diffusion and the observed multiexponential decay is fitted to a sum of exponential functions. Practically three exponentials are enough to realize the observed decay. Each relaxation time represents one domain, thus, only a few domains can be distinguished by one resonance line. Inevitably, the heterogeneous structures deduced from NMR relaxation experiments become simple. 

Much additional work is still needed, however, to develop reliable rules for predicting (even at a merely qualitative level) the phase structure (the continuities and sizes of phase domains) in immiscible blends from a knowledge of the composition, the component properties and the flow field in a mixing or processing device [47],... 

The phenomenological blend and composite modulus and strength models developed by Pukanczky et al [17-19], which also attempt to account for the effects of the strengths of the interfaces between phase domains, are also useful in correlating and explaining existing data. 

PP-MA (0-20) dispersed phase domain size vs. vol. fraction of compatibilizer / also blends containing EP rubber Rosch, 1995 Rosch and Miilhaupt, 1995 1993... 

Figure 15.7a shows that the two phases are with irregular domain sizes and shapes. This indicates that the NR/EPDM blends were completely immiscible, large EPDM domains being dispersed in the NR matrix. The average domain size of the dispersed phase was 4.1 pm. The compatibility of the NR/EPDM system was improved by the addition of a compatibilizer, as can be seen in Fig. 15.7b-g the treatment resulted in noticeable surface hardening, and the physical changes in the surface were expected to influence physically both the deformation and adhesion of the two mbbers, that is, the compatibilizers improved both the morphology and compatibility of the blends because of the reduction in the interfacial tension between EPDM and NR rubbers. The size of the dispersed phase (EPDM) domain decreased with the addition of compatibilizers, and no gross phase separation was present in the blends (Fig. 15.7). For NR/BR/EPDM, the domain size was approximately 3.8-1.26 pm NR/PVC/EPDM, 2.7-0.75 pm NR/chlorosulfonated PE/EPDM, 2-0.75 pm NR/p-radiation/EPDM 4-1.5 pm and NR/MAH/EPDM. 1-0.25 pm. These results are in agreement with the observations of Anastasiadas and Koberstein (58) and Meier (59), who reported that compatibilizers reduced the phase domain size.

---