Continuous phase, impact strength

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. 

In HIPS, desirably the PS is the continuous phase including a discontinuous phase of rubber particles. The size and distribution of the rubber particles in the continuous PS phase can affect the properties of the HIPS. In blends of PS with other materials, the distribution of the noncontinuous phase in the continuous poly(styrene) phase is often similarly important (2). The impact strength of HIPS can go up to sevenfold of that of general purpose PS. 

Considering heterogeneous models for the film structure, we realize that if PVC with its low permeability were the continuous phase, there should only be small increases in permeability with the addition of EVA polymer. Such effects have been observed for a system of butadiene-based polymer modifier added to PVC to increase the impact strength (1). Addition of 15% modifier increased the permeability less than 10%. Electron micrographs of this film showed that the butadiene-based modifier was dispersed in the PVC phase. 

If the hard blocks are longer than the soft ones, such as in SBS with a high styrene content, the hard phase will be continuous, and the rubbery phase is present as domains (see Figure 9.6). In such a case SBS behaves as a high-impact PS. Another example of this type is a PP/EP block copolymer tails of EP (random copolymer of ethylene and propylene) on the PP chains segregate into rubbery domains in the PP matrix, which improve the impact strength. 

The Impact Strength of Styrene-Butadiene Block Copolymer and Its Dependence on the Continuous Phase... 

As a means to improve the rubber utilization, a bulk/suspension process evolved, whereby polybutadiene rubber was dissolved in styrene monomer and polymerized in bulk beyond phase inversion before being dropped into suspension. The HIPS produced this way had two distinct advantages over the compounded version styrene to rubber grafting and discrete rubber spheres or particles uniformly dispersed in a polystyrene matrix. This improved the impact strength dramatically per unit of rubber and gave better processing stability, because the rubber phase was dispersed instead of being co-continuous with the polystyrene. 

Internal Phase Composition As with the continuous phase, the internal phase properties also influence the properties of the ELM. Ionic strength, pH, and the presence of organic species will impact on the stability of the ELM. Emulsion liquid membranes work on the basis that the polar substances (usually high concentrations of acid or base) contained in the internal phase are impermeable to the membrane phase. However, the presence of the surfactant can cause the uptake of these compounds by the formation of reverse micelles [97]. 

It is postulated that the morphology of ABA type block copolymers with 20 % or more polyol is that of a continuous rubber network extending through a nylon phase, the deformation behaviour and ultimate strength being determined by the rubber phase. Improvement of impact strength is due to shear flow. 

The first paper in this series describes results of continued research on the effects of molecular weight (M) on FCP response (12). This paper describes and discusses results obtained in a study of the effects of a rubbery phase on the Impact strength and FCP behavior of a series of PVC matrixes comprising a range of different molecular weights. It will be shown that combined effects of M with elastomer content — in this case, a methacrylate-butadiene-styrene (MBS) copolymer— lead to interesting FCP behavior. Additional results will be discussed in future papers, as well as results of current studies on the effects of other structural and compositional factors. 

Impact polystyrene is produced commercially in three steps solid polybutadiene rubber is cut up and dispersed as small particles in styrene monomer mass prepolymerization and completion of the polymerization either in mass or aqueous suspension. During the prepolymerization step, styrene starts to polymerize by itself by forming droplets of polystyrene upon phase separation. When equal phase volumes are attained, phase inversion occurs (15). The droplets of polystyrene become the continuous phase in which the rubber particles are dispersed. Impact strength increases with rubber particle size and concentration, whereas gloss and rigidity decrease. 

Rubber particle size is extremely important to make an optimized impact product. Particles that are both too small and too large cause a loss of impact strength. The ability to form stable particles of optimum size depends on the graft that functions as an oil in oil emulsion. This might better be referred to as an emulsion of two incompatible organic phases. To size the rubber particles, shearing agitation must be provided. If it is not provided, phase inversion does not occur, and a cross-linked continuous phase that produces gel is the result. 

The co-continuity contributes to synergism of properties, e.g., advantageous combination of high modulus and high impact strength in commercial blends. Two expressions for predicting the phase inversion concentration from the viscosity ratio were proposed ... 

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