Shape, rubber phase domain

Rubber Phase Domain Size and Shape. Phase domain size seems to be controlled in part by the time of phase separation in relationship to the gel time of the reaction. Smaller phases are generally produced when phase separation is delayed until near or after the gel point of the total reaction. It is possible to tell if phase separation has occurred near the gel point by the clarity of the mix. If phase separation has occurred, the mix is cloudy or milky. In addition the bimodal distribution of phase domain sizes found in some samples is evidence that the reactions are truly simultaneous because the larger domains are probably formed before gelation and smaller domains by continued phase separation after gelation. 

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.

It is somewhat difficult conceptually to explain the recoverable high elasticity of these materials in terms of flexible polymer chains cross-linked into an open network structure as commonly envisaged for conventionally vulcanised rubbers. It is probably better to consider the deformation behaviour on a macro, rather than molecular, scale. One such model would envisage a three-dimensional mesh of polypropylene with elastomeric domains embedded within. On application of a stress both the open network of the hard phase and the elastomeric domains will be capable of deformation. On release of the stress, the cross-linked rubbery domains will try to recover their original shape and hence result in recovery from deformation of the blended object. 

Atomic force microscopy and attenuated total reflection infrared spectroscopy were used to study the changes occurring in the micromorphology of a single strut of flexible polyurethane foam. A mathematical model of the deformation and orientation in the rubbery phase, but which takes account of the harder domains, is presented which may be successfully used to predict the shapes of the stress-strain curves for solid polyurethane elastomers with different hard phase contents. It may also be used for low density polyethylene at different temperatures. Yield and rubber crosslink density are given as explanations of departure from ideal elastic behaviour. 17 refs. 

In rubber-plastic blends, clay reportedly disrupted the ordered crystallization of isotactic polypropylene (iPP) and had a key role in shaping the distribution of iPP and ethylene propylene rubber (EPR) phases larger filler contents brought about smaller, less coalesced and more homogeneous rubber domains [22]. Clays, by virtue of their selective residence in the continuous phase and not in the rubber domains, exhibited a significant effect on mechanical properties by controlling the size of rubber domains in the heterophasic matrix. This resulted in nanocomposites with increased stiffness, impact strength, and thermal stability. 

Formulations have been developed where small rubber domains of a definite size and shape are formed in situ during cure of the epoxy matrix. The domains cease growing at gelation. After cure is complete, the adhesive consists of an epoxy matrix with embedded rubber particles. The formation of a fully dispersed phase depends on a delicate balance between the miscibility of the elastomer, or its adduct with the resin, with the resin-hardener mixture and appropriate precipitation during the crosslinking reaction. 

Extruded films of PP/rubber blends [89] showed that the CO2 concentration is higher in the rubber domains than in the PP matrix. In addition, as expected, the rubber domains were the only place where the porous phase can develop according to different CO2 solubility and viscoelastic behavior of both phases. Nanostructured PP/TPS blends were foamed with a saturation stage performed at 20 MPa and 25°C during 1 h, followed by a pressure release at a rate of 1 MPa/s and a foaming stage at 120°C. In this study the 80-PP/20-HSIS blend presented the best results, with pore sizes of approximately 200-400nm but low porosities below 25% (Fig. 9.19). Another remarkable output from this study is the perfect relationship found between the sizes of the rubber domains of the precursor and the pores of the foam as well as between the shape and orientation of the nanostructure of the precursor and the porous structure of the foam. 

ABS matrix (black rubber particles in SAN, white) contains irregularly shaped PA 6 particles with semicrystalline structure (bright lamellae and dark amorphous parts) and small SAN domains (white) a five-phase morphology is visible [12] ... 

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