Rubber domain size

The morphology and structure of PP/rubber blends have been studied by a nmnber of researchers [4-10]. It is also known that the rubber domain size is critical for the impact toughness of PP/mbber blends [11-14]. However, correlations among stmcture, morphology and fracture behavior have not been systematically investigated. 

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. 

The reactive extrusion of polypropylene-natural rubber blends in the presence of a peroxide (1,3-bis(/-butyl per-oxy benzene) and a coagent (trimethylol propane triacrylate) was reported by Yoon et al. [64]. The effect of the concentration of the peroxide and the coagent was evaiuated in terms of thermal, morphological, melt, and mechanical properties. The low shear viscosity of the blends increased with the increase in peroxide content initially, and beyond 0.02 phr the viscosity decreased with peroxide content (Fig. 9). The melt viscosity increased with coagent concentration at a fixed peroxide content. The morphology of the samples indicated a decrease in domain size of the dispersed NR phase with a lower content of the peroxide, while at a higher content the domain size increases. The reduction in domain size... 

In order to obtain a finely sized dispersed phase in the PET matrix, the use of reactive compatibilization has been found to be important. Small dispersed rubber particles and a small interparticle distance are necessary to induce high toughness. For effective rubber toughening of PET, it is important that the rubber domains be less than 3 im in diameter (and preferably less than 1 xm) and that the interparticle distance be between 50-300 nm. 

Figure 14.10 Electron micrograph of PET + 20% E-EA-GMA (reactive tough-ener - Lotader AX8900) showing the size and distribution of the rubber particles (note the 5 im scale bar). The rubber domains have been selectively etched out by solvent to provide contrast enhancement...

A twin-screw extruder is generally preferred for producing rubber-toughened, glass-filled PET compounds for injection moulding applications. The PET and impact modifier are added at the throat while the glass reinforcement is added downstream. The size of the rubber domains will depend on the amount of energy and the capability of the equipment used for dispersion. 

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. 

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. 

Fig. 2. Transmission electron micrograph of ABS produced by a mass process. The rubber domains are typically larger in size and contain higher...

When ABS was first commercialized, there was much confusion in the plastics industry referring to it as a terpolymer. The system is not a terpolymer as butadiene is added to the reactor as a polymer along with styrene and acrylonitrile monomers. Polymerization causes SAN to be grafted to the rubber to produce a dispersible domain. It is indeed a requirement that the polybutadiene regions exist as a separate phase of a specified size. Since the domain size is critical to its impact properties, it is important that it is stable through compounding and processing steps [20]. 

Copoly(ester ester)s belong to the family of thermoplastic elastomers (TPEs) and consist in general of thermo-reversible hard and elastic soft domains [11]. The copoly(ester ester) used here consists of 60% poly(butylene terephthalate), 35% poly(butylene adipate) and 5% 4,4 -methylenebis(phenyl isocyanate), and shows domain sizes of about 20 nm [12]. The material possesses a rubber plateau between the glass transition temperature of the mixed amorphous PBA/PBT phase (the PBT phase is semi-crystalline) at about -30°C and the melting point of the PBT at about 220°C. Due to the vulnerability of the amorphous PBA/PBT soft domains towards water attack [13] the PBT/PBA copoly(ester ester) is used here to study the existence of ESC of a chemical rather than a physical nature. For the sake of clarity it should be emphasized that no additives have been used in the copoly(ester ester) described here. 

Interpenetrating polymer networks are important because their crosslinks offer a novel method of controlling domain size and shape many mechanical properties such as impact strength depend on the size of the rubber domain. Thus, small, nearly uniform domains can be generated. 

Transmission electron microscopy (TEM) was used to study the morphology of the cross-linked matrix and to determine the size of the rubber domains. Specimens were microtomed and exposed to osmium tetroxide vapor to stain the rubber-rich portions of the network. The fracture surfaces of specimens were coated with gold and examined with a scanning electron microscope (SEM). 

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