Elastomer domain

In the time interval between phase inversion and gelation of the polystyrene continuous phase, the final morphological features such as size average and size distribution of elastomer domains become fixed. Since these morphological changes affect properties such as modulus and impact resistance, the characteristics of the system at and just after phase inversion and before gelation demand the closest scrutiny. The open time interval was found to decrease as the polyester prepolymer content increases, probably because higher polystyrene conversions are required for the system to reach suitable phase inversion conditions. 

Opacity. Specimens prepared from the VC/EPR graft copolymers are opaque. This seems to be because of the two-phase structure of the system, the large difference between the refractive indexes of the two phases, and the fact that the elastomer domains are large enough. 

The last experiment discussed here, shows that the mobility of Xe in the iPP matrix is much lower than in the elastomer domains. 

The simplest method of polyblending involves equipment such as rolls or extruders, which can effect the mechanical blending of the two polymeric components in the molten state (Matsuo, 1968). High-impact polystyrene (HiPS) is an important example of a polyblend made by this technique. Such materials commonly contain 5-20 % of rubber, usually polybutadiene, dispersed in a polystyrene matrix. As shown in Figure 3.1, electron microscopy studies on specimens stained with osmium tetroxide reveal well-defined, irregular rubber particles (1-10 fim in diameter) dispersed in the polystyrene matrix. The elastomer domains appear dark because the osmium tetroxide stains the elastomer preferentially (see Section 2.4). 

Because of their high shear-thinning and melt elasticity, plastomers and POEs disperse well in the PP matrix yielding fine elastomer domain dispersions leading to the better properties. POEs are easier to handle as they are available in pellet form, whereas EPDM is typically baled and needs additional equipment for feeding into the extruder compounding process. POEs also offer improved melt flow in TPO blends compared to EP copolymer-type elastomers. Currently, POEs account for about a third of the elastomer volume used in the compounded TPOs. 

Applications showing the range of microscopy techniques and specimen preparation methods used on commercial impact polymers will be described. Changes in polymer morphology are expected upon addition of an elastomer for instance, such addition is expected to cause a decrease in the spherulite size as the elastomer domains can act as nucleating sites [274]. This has been observed for many polymers including... 

In addition to the two mechanisms of comminution and stretching, elastomer and carbon black have to be compacted.Compaction, or massing, is the displacement of entrapped air in the machine by applied compressive force. This requires deformation of elastomer domains to match the shape of the carbon black, followed by relaxation of the elastomer in the deformed state. In another case study, Nakajima and Harrell estimated that about 6% of the energy used in incorporation was required for compaction. 

SINs, phase inversion has taken place so that the elastomer phase is discontinuous (A-E). While the elastomer domains do not differ greatly in size (Table 2), their shape does vary depending on the oil used. Also, the morphology of the elastomer phase depends on the mode of pol3rmerization. With a 10/90 SIN in which the styrene was mixed with the oil prior to polymerization of the oil phase, no cellular domains of PS were observed within the elastomer domain. 

In the elastomer domain, zinc oxide is important and a fatty acid such as stearic is generally included in the formulation. Solubilization of the zinc oxide and subsequent reaction of the metal with resorcinol and accelerators appear to be preliminary steps to the actual R-F condensation. Lack of kinetic response through the silica suggests that it may contribute to pre-adsorbing the rubber-insoluble reactants and by uniformly distributing them without actually migrating or carrying them. ... 

An HISPS is a multicomponent blend comprising SPS, PPO, SEES triblock copolymer, and MA-g-SEBS. Controlling the morphology of HISPS is a key point to enhance the mechanical properties. There are a lot of structural factors that should be controlled, for example, the size and the orientation of elastomer domains and the degree of crystallinity in the SPS matrix, and also the interfacial thickness between the domain and the matrix. 

The enhancement of the partial miscibility of the elastomer domains and the SPS matrix causes the reduction of the domain size and the thickening of the interface (compatibilizer effect). 

Figure 3.2 Elastomer domains and well-dispersed carbon black aggregates.

In addition to these two mechanisms, a mixture of elastomer and carbon black have to be compacted. Compaction is the elimination of free spaces between carbon black particles and elastomer domains by an externally applied force. The importance of the compaction step may be illustrated by the following example. 

The nature of physical and chemical interactions between the elastomer and the surface of carbon black has been a subject of interest for many years. A prerequisite to such surface interactions is the wetting of the surface with elastomer molecules. However, the elastomer molecules do not spontaneously flow to the surface of carbon black. The elastomer domains must be deformed to conform with the topology of the carbon black and made to relax in the deformed state. This mechanism may constitute the essence of the theory of compaction, which is examined in this study. 

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... 

As depicted on micrographs in Figure 1, TPO A and TPO B blends show similar elastomer domain sizes for the unmelted pellets. The maximum size of the elliptically-shaped elastomer domains ranged from 2-2.5 ocm for TPO A and 1-2 ocm for TPO B, with many smaller domain sizes also present. 

However, secondary processes such as injection molding are rarely able to achieve shear rates comparable to the rates during initial processing and are, therefore, unable to positively affect the elastomer domain size for a high viscosity ratio TPO blend (i.e., TPO A). TPO B, however, shows that it is possible to overcome the negative effects of secondary processing conditions. 

At high temperatures (Conditions 4-6), the elastomer domain sizes remained between 4-5 ocm, suggesting that, under these conditions, temperature had a dominant effect on domain size and that additional mixing was uable to prevent coalescence. At lower temperatures, a slight decrease in domain size was observed with increase of... 

Condition TPO A elastomer domain size [ocm] TPO B elastomer domain size r m]... 

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