Fracture of polystyrene

The effects of orientation on the mechanical properties of polymers at both small and large deformations depend on the mode of orientation, which determines the preferred average chain alignment. For example, the mechanical properties obtained after uniaxial orientation (which biases the chain end-to-end vectors in one favored direction) differ from those obtained by biaxial orientation (which biases these vectors in two favored direction). Furthermore, the mechanical properties obtained after simultaneous equibiaxial orientation (where orientation in the two favored directions is imposed simultaneously, at equal rates, and to equal extents) often differ from those obtained after sequential orientation in the two favored directions, as well as after orientation by different amounts and/or at different rates in those two directions. See Seitz [35] for a review of the effects of uniaxial and biaxial orientation on the fracture of polystyrene, which fails by brittle fracture or crazing, under uniaxial tension and impact. 

Knudsen KD, Cifre JGH, dela Torre JG (1996) Conformation and fracture of polystyrene chains in extensional flow studied by numerical simulation. Macromolecules 29 3603-3610... 

Anh, T.H. and Vu-Khanh, T. Fracture and Yielding Behaviors of Polystyrene/Ethylene-Propylene Rubber Blends Effects of Interfacial Agents, Polym. Eng. Set 41(12), 2073-2081, December 2001. 

Looking at the melt fracture of specific polymers, we see many similarities and a few differences. Polystyrene extrudates begin to spiral from smooth at t 105 N/m2, and at higher shear stresses, they are grossly distorted. Visual observations show a wine glass entrance pattern with vortices that are stable at low stress values and spiral into the capillary and subsequently break down, as t is increased. Clearly, melt fracture is an entrance instability phenomenon for this polymer. 

FIG. 2 Two-dimensional colloidal crystal formed by a single layer of polystyrene spheres of diameter 3 /mi. The particles are initially suspended in water. The crystal is formed by confining the suspension between two glass plates and reducing the separation until it equals the diameter of particles. Here, one can see some typical features of crystals such as defects, fractures and vacancies. 

Fracture Surface Morphology and Phase Relationships of Polystyrene/Poly(methyl Methacrylate) Systems... 

Another important property - wettability was followed by SEM analysis on PS/MWCNTs nanocomposite prepared by in-situ bulk-suspension polymerization (54). Figure 8.7 presents a micrograph of fracture surface of the prepared nanocomposite. The picture very clearly evidences that the nanotubes are covered by a thick layer of polystyrene. Parts of original nanotubes can be identified at the end of the fracture noteworthy is also the smaller diameter at the end of tubes. 

The Fracture Energy of Low Molecular Weight Fractions of Polystyrene... 

The fracture energy of polystyrene is a combination of the plastic energy needed to form crazed material from uncrazed material, the energy to create the exposed surface in the craze, the elastic strain energy stored in the craze, and the energy to create new surface when the craze ruptures (5, 9). As the molecular weight decreases, the amount of crazing and... 

Formation in Polystyrene, paper presented at British Plastics Institute, Research Meeting on the Effect of Structure on the Fracture of Plastics— The Role of Craze in Fracture, Univ. of Liverpool, Liverpool, England (April 14, 1972). 

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. 

Figure 18.7. Calculated shear yield stress under uniaxial tension (solid line) and brittle fracture stress (dashed line) of polystyrene below the glass transition temperature. Note that the shear yield stress has a much stronger temperature dependence than the brittle fracture stress. 

Kramer and co-workers (7) reported that acoustic emission occurred in polystyrene immersed in diflFerent swelling liquids only when the crazes ruptured but not during their formation and growth. As long as the bridging by filamental elements is still intact, the deformation at the craze tip and in the craze is still so slow that no acoustic bursts are generated. It is the final fracture of these elements which is abrupt enough to cause the emission of a detectable acoustic burst. 

Murray, J. and Hull, D. (1970) Fracture surface of polystyrene mackerel pattern, J. Polymer Sci., Polymer Phys., 8, 583-594. 

Fracture energy of polystyrene at 23 C after drawing above the glass transition at s, showing effect of molecular orientatioi direction (after L J. Broutman and F. J. McGany). 

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