Elastomers, morphology

Xiaoyan, M., Guozheng, L., Haijun, L., Hailin, L., and Yun, H. 2005. Novel intercalated nanocomposites of polypropylene, organic rectorite, and poly(ethylene octene) elastomer Morphology and mechanical properties. Journal of Applied Polymer Science 97 1907-1914. 

The effect of MMT content and PP molecular weight on the elastomer morphology in PP/PP-g-MA/MMT/EOR nanocomposites is shown in Fig. 17.11. The elastomer particles are large with a mixture of spherical and elongated shapes in L-PP/EOR blend or mostly spherical shapes in the H-PP/EOR blend without MMT and become small and mostly elongated in the presence of MMT in both L-PP- and H-PP-based nanocomposites. The nonspherical nature of elastomer particles is... 

H., Vancso, G.J., van der Does, L., Noordermeer, J.M.W., and Janssen, P.J.P. (1999) Atomic force microscopy of elastomers morphology, distribution of filler partides, and adhesion using chemically modified tips. Rubber Chem. Techn., 71 (5), 862-875. 

M. Ono, K. Nakajima, T. Nishi, Nano-physical properties in polyolefin and elastomer blend consisting of different elastomer morphologies. Polymer Preprints, Japan 55 (2) (2006) 3598. 

Figure 4.16 Idealized triblock copolymer thermoplastic elastomer morphology.

The above discussion mainly concentrated on the understanding of the polyurethane elastomer morphology. A significant number of studies were also devoted to the relationship between the morphology and mechanical properties. Ryan et al [12-15] demonstrated that for several model PUU copolymers, sheai-modulus, G, as a function of HSF can be qualitatively described by Davies [35-37] equation, (where G, G, and (l) are... 

The strength of the interfacial adhesion, for example, may be improved through the addition of compatibilizers, which decrease interfacial tension between the two phases, reduce elastomer domain size and improve the stability of elastomer morphology [7]. The use of compatibilizers, however, may not be practical for some TPO blends due to unfavorable cost versus performance issues. It has also... 

Unfortunately, injection molders typically run then-processes at temperatures between 190-240°C in order to improve flow and processability of the material and to shorten cycle time. Molding at these higher temperatures may have a negative impact on the elastomer morphology and thus affect the physical properties of the TPO blend. 

Additional information on elastomer and SAN microstmcture is provided by C-nmr analysis (100). Rubber particle composition may be inferred from glass-transition data provided by thermal or mechanochemical analysis. Rubber particle morphology as obtained by transmission or scanning electron microscopy (101) is indicative of the ABS manufacturing process (77). (See Figs. 1 and 2.)... 

Pig. 1. Interpenetrating network morphology of thermoplastic elastomer where A = the crystalline domain, B = the junction of crystalline lamellae, and... 

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyUithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibiHty (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

Rubber-Modified Copolymers. Acrylonitrile—butadiene—styrene polymers have become important commercial products since the mid-1950s. The development and properties of ABS polymers have been discussed in detail (76) (see Acrylonitrile polymers). ABS polymers, like HIPS, are two-phase systems in which the elastomer component is dispersed in the rigid SAN copolymer matrix. The electron photomicrographs in Figure 6 show the difference in morphology of mass vs emulsion ABS polymers. The differences in stmcture of the dispersed phases are primarily a result of differences in production processes, types of mbber used, and variation in mbber concentrations. 

Thermoplastic Elastomers. These represent a whole class of synthetic elastomers, developed siace the 1960s, that ate permanently and reversibly thermoplastic, but behave as cross-linked networks at ambient temperature. One of the first was the triblock copolymer of the polystyrene—polybutadiene—polystyrene type (SheU s Kraton) prepared by anionic polymerization with organoHthium initiator. The stmcture and morphology is shown schematically in Figure 3. The incompatibiHty of the polystyrene and polybutadiene blocks leads to a dispersion of the spherical polystyrene domains (ca 20—30 nm) in the mbbery matrix of polybutadiene. Since each polybutadiene chain is anchored at both ends to a polystyrene domain, a network results. However, at elevated temperatures where the polystyrene softens, the elastomer can be molded like any thermoplastic, yet behaves much like a vulcanized mbber on cooling (see Elastomers, synthetic-thermoplastic elastomers). 

Properties such as low permanent set, low creep and low hysteresis are really measures of the efficiency of the heat fugitive network system. This is a complex function of the morphology. As a very general statement, the problem would seem to be less important with the harder grades of thermoplastic elastomer. 

Unlike incompatible heterogeneous blends of elastomer-elastomer, elastomer-plastic, and plastic-plastic, the reactively processed heterogeneous blends are expected to develop a variable extent of chemical interaction. For this reason the material properties, interfacial properties, and phase morphology of reactively processed blends would differ significantly from heterogeneous mixtures. 

As shown in Fig. IIB, dispersion morphology for the nylon 6/Vectra B/SA-g-EPDM blend was totally different from that of the PBT-Vectra A-SA-g-EPDM blend. TLCP phases were very uniformly and finely dispersed in the nylon 6-Vectra B-SA-g-EPDM blend and a large fibril shape observed in the PBT-Vectra A-SA-g-EPDM blend could not be seen under polarized microscope. It should be noted that the size of the dispersed TLCP phase is very small (submicron size). This small size of the TLCP phase in the nylon 6/elastomer matrix was not observed by any others [4,54,55,58]. A closer look by SEM more clearly revealed the dispersion of Vectra B in the matrix (Fig. 12B). TLCP phases are very... 

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