Polystyrene stress-strain

Proportion of Hard Segments. As expected, the modulus of styrenic block copolymers increases with the proportion of the hard polystyrene segments. The tensile behavior of otherwise similar block copolymers with a wide range of polystyrene contents shows a family of stress—strain curves (4,7,8). As the styrene content is increased, the products change from very weak, soft, mbbedike materials to strong elastomers, then to leathery materials, and finally to hard glassy thermoplastics. The latter have been commercialized as clear, high impact polystyrenes under the trade name K-Resin (39) (Phillips Petroleum Co.). Other types of thermoplastic elastomers show similar behavior that is, as the ratio of the hard to soft phase is increased, the product in turn becomes harder. 

Mechanical data like stress/strain behavior, impact resistance in comparison to polystyrene... 

Figure 5.84 Stress-strain curves for polystyrene (PS) and high-impact polystyrene (HIPS). Reprinted, by permission, from N. G. McCrum, C. P. Buckley, and C. B. Bucknall, Principles of Polymer Engineering, 2nd ed., p. 200. Copyright 1997 by Oxford University Press.

Figure 3.3 shows representative stress-strain curves for a variety of polymeric materials. At normal use temperatures, such as room temperature, rigid polymers such as polystyrene (PS) exhibit a rapid increase in stress with increasing strain until sample failure. This behavior is typical of brittle polymers with weak interchain secondary bonding. As shown in the top curve in Figure 3.3, the initial stress-strain relation in such polymers is approximately linear and can be described in terms of Hooke s law, i.e., S = Ee, where E is Young s modulus, typically defined as the slope of the stress-strain plot. At higher stresses, the plot becomes nonlinear. The point at which this occurs is called the proportional limit. 

Fig. 3 Percentage of gauche conformations along the stress-strain curve of atactic polystyrene. The dashed curve is the stress-strain curve (From [11])...

Figure 8.8 Stress-strain isotherms for PDMS-polystyrene (PS) composites.50 Each curve is labeled with the wt % PS present in the composite, and the dashed fines locate the relatively linear portions of the curves useful for quantitative interpretations.129...

Some plastic materials have different tensile and compressive characteristics. For example, polystyrene is tough under compressive load but very brittle in tension. However, for most elastoplastic materials, the stress-strain curves in compression are the same as in tension. Hence, the deformation properties of these materials in tension may also be applied to those in compression, which is of great interest to gas-solid flows. 

Fisher124,125 has studied the stress-strain and optical properties of three SBS block copolymers containing, respectively, 31,40 and 49% polystyrene as a function of temperature. He has shown that these materials are two phase systems in which the polybutadiene chains form an elastomeric phase and the polystyrene chains a glassy phase acting as physical crosslinks. Fisher126 has also obtained electron micro-... 

The mechanical properties of a macrolattice of SBS has been investigated (65). The sample consists of a hexagonal array of polystyrene cylinders embedded in the polybutadiene matrix. The stress-strain curves... 

Figure 2. Cyclic tensile stress-strain behavior of TR-41-1649 and its blend with polystyrene (M 20,400) at room temperature at a constant rate of tensile strain, 50%/min. Curves (1) and (2) refer to the first and second stretching half-cycles, respectively, and the tensile stress is expressed in terms of nominal stress (29).

Morphology, Viscoelastic Properties, and Stress-Strain Behavior of Blends of Polycarbonate of Bisphenol-A (PC) and Atactic Polystyrene (PST)... 

It follows that for a constant refractive index the craze strain is also constant. Our observations on polystyrene indicate that neither the craze refractive index nor the ratios kB/kc and kB/kh are constant along the length of the craze (Figure 6). The values of A calculated from Equation 4 are shown in Figure 7. That the craze strain is not constant does not preclude the possibility that the craze stress is still constant, as might be the case for an ideal plastic material. However, the experiments on craze stress-strain properties by Kambour (10) and Hoare and Hull (11) indicate that this is not the case. 

If we look at Figure 21.3, we can see that there is an upper limit to the overall styrene content in the polymer if making a polymer to have rubbery properties is the desired outcome [66]. As the styrene content increases, the stress-strain response changes dramatically for these neat SBS polymers. At 53 and 65% styrene content, the polystyrene endblocks form the continuous phase in the phase-separated block copolymer, and these polymers behave more like polystyrene than a rubber at low strain. This low strain behavior is also shown at 39% styrene content, but a rubbery plateau begins to show at lower stress. 

Fig. 1-2. Stress-strain curves, (a) Synthetic fiber, like nylon 66. (b) Rigid, britile plastic, like polystyrene, (c) Tough plastic, like nylon 66. (d) Elastomer, like vulcanized natural rubber.

The tensile stress-strain response of the homopolymer, and of two rubber modified grades of polystyrene, is shown in Fig. 1. The principal mode of deformation is crazing and all three materials exhibit a craze yield stress. However, there is no evidence of localized necking in any of the three materials. The craze yield stress decreases and the elongation to fracture, and the toughness, increase significantly with increase in rubber content. 

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