Polyblends properties

The commercial success of ABS polymers has led to the investigation of many other polyblend materials. In some cases properties are exhibited which are superior to those of ABS and some of the materials are commercially available. For example, the opacity of ABS has led to the development of blends in which the glassy phase is modified to give transparent polymers whilst the limited light aging has been countered by the use of rubbers other than polybutadiene. 

Certain polymers have come to be considered standard building blocks of the polyblends. For example, impact strength may be improved by using polycarbonate, ABS and polyurethanes. Heat resistance is improved by using polyphenylene oxide, polysulphone, PVC, polyester (PET and PBT) and acrylic. Barrier properties are improved by using plastics such as ethylene vinyl alchol (EVA). Some modem plastic alloys and their main characteristics are given in Table 1.2. 

Dianippon Ink Chemical Company (DIC) manufactures the Pandex series of TPUs that are used to make polymeric blends with PVC. These polyblends show comparable mechanical properties to others. Germany s Beyer Chemical Company also has similar products. The related information about these commercial products can be obtained from the manufacturers. 

Flow behavior of the polymer blends is determined by their structure, which is governed by the degree of dispersion of the component and by the mode of their distribution. For blends having identical compositions, it is possible to produce systems in which one and the same component may be either a dispersion medium or a dispersed phase [1]. This behavior of the polyblend systems depends on various parameters, the most important of which is the blending sequence. It is, therefore, difficult to obtain a uniform composition property relationship for the polymer blends even though the composition remains identical. 

The mechanical properties of two-phase polymeric systems, such as block and graft polymers and polyblends, are discussed in detail in Chapter 7. However, the creep and stress-relaxation behavior of these materials will be examined at this point. Most of the systems of practical interest consist of a combination of a rubbery phase and a rigid phase. In many cases the rigid phase is polystyrene since such materials are tough, yet low in price. 

However, from a commercial standpoint, modifying the polymer mainly for improved flame retardancy is usually done reluctantly, since other properties usually suffer and cost is generally increased. The present trend for developing improved polymers is to utilize polyblending. Can a polyblending approach achieve efficient flame retardancy ... 

Evidently, the homogeneous complex phase is an equilibrium property for copolymers. Any effects resulting from the history of specimen preparation (cf., photomicrographs and dashed lines in Figures 9 and 10) are eliminated by annealing. In contrast, for polyblends the compatible phase is a metastable state. 

Matsuo, Nozaki, and Jyo (20) showed that heterogeneity at 100 A scale and under can be detected readily. Thus, microscopy can offer a measure of heterogeneity down to 0.01 p scale which is much smaller than the domain size of most polyblends. Results of microscopy have established convincingly that nearly all polyblends are heterogeneous two-phase systems. How does one describe the results Obviously, heterogeneity as revealed by microscopy is a relative property. If compatibility is used in a qualitative sense, a polyblend with a finer domain size will be more compatible than one with a larger size, provided equilibrium size distribution has been attained in both cases. 

In practical terms, very good durability can be achieved by increasing the Mw of the PMMA component. Since PVdF plasticizes the PMMA, the melt viscosity of the blend was not appreciably changed by increasing the Mw of the PMMA component from 100,000 to 200,000. This change did, however, effectively double the exposure lifetime through which the maximum tensile properties of the polyblend were maintained. 

Dynamic and Stress-Optical Properties of Polyblends of Butadiene—Styrene Copolymers Differing in Composition... 

VVThen two chemically different polymers are mixed, the usual result is a two-phase polyblend. This is true also when the compositional moities are part of the same polymer chain such as, for instance, in a block polymer. The criterion for the formation of a single phase is a negative free energy of mixing, but this condition is rarely realized because the small entropy of mixing is usually insufficient to overcome the positive enthalpy of mixing. The incompatibility of polymers in blends has important effects on their physical properties, which may be desirable or not, depending on the contemplated application. 

Using these techniques to prepare the resin and rubber components of polyblends, transparent impact polymer blends can be obtained which exhibit mechanical properties comparable with ABS materials. Like ABS, they have a fairly flat modulus curve, which varies gradually over a wide temperature range (Figure 4). Impact properties are outstanding for these transparent impact polymers even at temperatures as low as —40°C. 

Table III. The Effect of Graft Resin on Polyblend Mechanical Properties (Resin—Backbone Rubber Ratio = 2.5—1.0)...

The importance of the graft handle on a 62/38 butadiene-methyl methacrylate rubber can be illustrated by its effect on the optical properties of the polyblend. From Table II it can be seen that the reduction in percent haze is dramatic for an increase of methyl methacrylate graft from 0 to 27% by weight, while there is no apparent change in the light transmission. The blend resin in this polyblend system was an 88-12 methyl methacrylate-styrene copolymer, and the total resin to backbone rubber ratio was kept at 2.5-1.0. The measured refractive indices are included for each component (the graft rubber and the blend resin). The difference in refractive index amounts to no more than 0.004 unit for any of the components. 

The effect of the graft resin on the polyblend mechanical properties for this same system (2.5-1.0 resin-backbone rubber) can be seen in Table III. 

Typical mechanical properties for transparent injection-molded polymers, designated MBAS, having a compositional range of from 11-18%, 1,3-butadiene, 34-39% styrene, and 23-25% each of acrylonitrile and methyl methacrylate are given in Table IV. This polymer is closely akin to the polyblend described previously, differing by containing a butadiene-styrene elastomer backbone, with a terpolymer resin graft consist-... 

Typical physical properties for an injection-molded transparent acrylic polyblend resin are given in Table II. The injection molding conditions used are given in Table III. Tensile, flexural, and impact properties are within the range reported for typical ABS and high impact polystyrene resins. Optical properties approach those of the acrylics [i.e., poly (methyl methacrylate)]. The strength properties are on the low side of those reported in the first paper for the transparent diene... 

A variety of comonomers (2) could be used to produce saturated rubber-resin polyblends having optical properties approaching homopolymers and physical properties similar to ABS but with improved resistance to photoxidation. 

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