Blends continued polymer

Melting point alone cannot uniquely identify an OBC. For example, blends of high and low density polyolefins also exhibit an elevated melting point at equivalent density. Sample 3 in Fig. 17 (small circle) is a 70 30 physical blend of 0.86 and 0.94 g cm-3 ethylene-octene copolymers, and the melting point is similar to the OBCs. Physical blends of polymers of such disparate densities are not phase-continuous, however, and segregate into domains of the high and low density polymers. Figure 18 reveals differences in appearance of pressed plaques of the polymer samples... 

Kolarik J, Lednicky F, Locati G, Fambri L (1997) Ultimate properties of polycarbonate blends effects of inclusion plastic deformation and of matrix phase continuity. Polym Eng Sd 37 128-137... 

Willemse RC (1999) Co-continuous morphologies in polymer blends stability. Polymer 40 2175-2178... 

Miles IS, ZurekA (1988) Preparation, structure, and properties of two-phase co-continuous polymer blends. Poly Eng Sci 28 796... 

Polymer Blends. Blending of polymers with each other accounts for approximately 40 percent of the present plastics market, and the practice is growing continually, because it permits the development of improved properties without the cost of inventing new polymers. When polymers are fairly miscible, as in the polyethylenes, and in polyphenylene ether plus polystyrene, blending can be used to produce intermediate properties and balance of properties. Most polymer blends... 

Specific Interactions Induced Controlled Dispersion of Multi wall Carbon Nanotubes in Co-Continuous Polymer Blends... 

Co-continuous polymer blends of 50/50 polyamide6/acrylonitrile-butadiene-styrene copolymer (PA6/ABS) involving multiwall carbon nanotubes (MWNTs) were prepared by melt mixing technique in order to develop conducting composites utilizing the concept of double-percolation. To control the dispersion and to selectively restrict MWNTs in the PA6 phase of the blends, MWNTs were pre-treated with two modifiers which differ in their molecular length scales and... 

Figure 11 shows the theoretical permeabilities that are expected for a two-phase blend of polymers. The two solid curves represent calculations based upon Maxwell s equation (24) for an aspect ratio of 1 for the discontinuous phase. The dotted line is a prediction of the permeability using Nielsen s model (25) when a barrier polymer with an aspect ratio of 8 is discontinuous in a nonbarrier matrix. Figure 12 shows the expected result of a phase inversion for a two-polymer blend. The discontinuous phase is assumed to have an aspect ratio of 1. At some critical composition, the composite switches from being continuous in one polymer to being continuous in the other. Figure 12 is really a special case of Figure 11. Selar RB is a blend of polyethylene and nylon-6. Polyethylene is the majority constituent and forms the continuous phase. The product has its best barrier when it can be used in processes that impart orientation to the product. This gives a high aspect ratio to the nylon-6 and enhanced barrier to the article. Blends of polyethylene and EVOH are being developed.

For PP/PE blends with polymer component ratios of 50 50 and 25 75, both components most likely formed the continuous phase in the blend and, as a result, the apparent viscosity was observed to rise sharply (MFI decreased). These blends have MFIs close to the values for the neat PP and PE. 

The film produced from a blend of 5 and 6 was cut with a scalpel the separated edges were then placed in close proximity and heated to approximately 90 °C. Visual observation of the material over this temperature ramp showed that the surface remained homogeneous. After cooling back to room temperature, the broken edges had re-engaged, and the material could again be peeled like a continuous polymer film (Fig. 10). 

In the continuous method of extrusion, CO2 is fed into the polymer melt and nu-cleation (and hence foaming) is initiated at the exit die. Pressure and temperature conditions at the exit die are controlled to result in supersaturation of the polymer. The inter-relationships between the key variables to control cell nucleation and growth in the continuous extrusion foaming process were summarized by Tomas-ko et al. [19]. Extrusion of polymers under CO2 pressure enables operation to occur at reduced temperatures, facilitates the blending of polymer blends, and provides an environment for reactions to occur (reactive extrusion) [105]. 

Although miscible blends of polymers exist, most blends of high-molecular-weight polymers exist as two-phase materials. Control of the morphology of these two-phase systems is critical to achieve the desired properties. A variety of morphologies exisL such as dispersed spheres of one polymer in another, lamellar structures, and co-continuous phases. As a resnlL the properties depend in a complex maimer on the types of polymers in the blend, the morphology of the blend, and the effects of processing, which may orient the phases by shear. 

Nanocomposites consist of a nanometer-scale phase in combination with another phase. While this section focuses on polymer nanocomposites, it is worth noting that other important materials can also be classed as nanocomposites—super-alloy turbine blades, for instance, and many sandwich structures in microelectronics. Dimensionality is one of the most basic classifications of a (nano)composite (Fig. 6.1). A nanoparticle-reinforced system exemplifies a zero-dimensional nanocomposite, while macroscopic particles produce a traditional filled polymer. Nanoflbers or nanowhiskers in a matrix constitute a one-dimensional nanocomposite, while large fibers give us the usual fiber composites. The two-dimensional case is based on individual layers of nanoscopic thickness embedded in a matrix, with larger layers giving rise to conventional flake-filled composites. Finally, an interpenetrating network is an example of a three-dimensional nanocomposite, while co-continuous polymer blends serve as an example of a macroscale counterpart. 

Willemse et al. (1999) studied the influence of interfacial tension on the composition range within which fully co-continuous polymer blend structures can exist for different blends with selected matrix viscosities and viscosity ratios. The critical composition for full co-continuity was found to increase with increasing interfacial tension, narrowing the composition range. The effect of the interfacial tension on the critical composition was found to be composed of two counteracting effects the stability of the co-continuous morphology and the phase dimensions. The latter effect was smaller than the former. 

In immiscible polymer blends, one polymer is dispersed in the form of domains in the continuous phase of the other. The degree of dispersion depends upon the mixing ability of the polymers, which decreases with an increase in concentration of the other polymer in the blend. Therefore, the quantity of domains and the degree of dispersion in PVC/CPE blends determine the progress of the degradatimi. The evolved HCl partially lags in the bulk sample, due to inefficient diffusion and, consequentially, has a catalytic effect on dehydorchlorination at low level of dehydrochlorination, as well as on the secondary reactions of polyene residues (Mahmood and Quadeer 1994). 

Polymer blend manufacturers continue to identify new application areas for polymer blends by working closely with the customers to identify the niche opportunities. Hence, engineering design and application developments are currently the major thrust areas in polymer blends. Engineering polymer blends tend to be more expensive than commodity polymers, due to higher processing and material costs. Hence, for high-volume applications like automotive, there is... 

Historically, any material containing two or more polymers, each in network form, without induced cross-links between the individual polymers, usually produced by polymerizing and/or cross-linking at least one component in the immediate presence of the other, thus thermoset in character. Currently, the term IPN encompasses the thermoplastic co-continuous polymer blends, as well as ionomers and block and graft... 

G.H. Fredrickson, F.S. Bates, Stabilizing co-continuous polymer blend morphologies with ABC block copolymers, European Physical Journal B 1 (1) (1998) 71-76. 

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