High impact polystyrene fracture

Fracture Behavior of High-Impact Polystyrene and Acrylonitrile-Butadiene-Styrene... 

Craze formation is a dominant mechanism in the toughening of glassy polymers by elastomers in polyblends. Examples are high-impact polystyrene (HIPS), impact poly(vinyl chloride), and ABS (acrylonitrile-butadiene-styrene) polymers. Polystyrene and styrene-acrylonitrile (SAN) copolymers fracture at strains of 10 , whereas rubber-modified grades of these polymers (e.g., HIPS and ABS) form many crazes before breaking at strains around 0.5. Rubbery particles in... 

Although the toughening mechanisms may be different in RTPMMA, the transitions in fracture behavior observed here at high rates are qualitatively similar to those described by Bucknall (20) for the impact of high-impact polystyrene containing different fractions of modifier. Here, the main result is that all the transitions are shifted simultaneously when the 2 L rubber content is increased. 

Vu-Khanh T. Fracture behaviour of high-impact polystyrene and acrylonitrile-butadiene-styrene, Chapter 27. In Scheirs J, Priddy DB, editors. Modem Styrenic Polymers Polystyrenes and Styrenic Polymers. Hoboken (NJ) John Wiley and Sons 2003. 

Figure 3.27. Scanning electron micrographs of fracture surfaces of high-impact polystyrene subjected to cyclic loading (10 Hz). (a,b) Crack propagation rate 2.5 x lO"" cm/cycle X 2300. (c) Crack propagation rate -2.5 x 10" cm/cycle x 1830. (d) Crack propagation rate — 2.5 X 10" cm/cycle x 8000. (Manson and Hertzberg, 1973b.)...

Bucknall and Smith [128] remarked on the connection between crazing and stress whitening. It was observed that the fracture of high-impact polystyrene, which incorporates rubber particles into the polystyrene, is usually preceded by opaque whitening of the stress area. Figure 12.11 shows a stress-whitened... 

Yang, H.H. and Bucknall, C.B. (April 1997) Evidence for particle cavitation as the precursor to crazing in high impact polystyrene, 10th International Conference on Deformation, Yield Fracture of Polymers, Churchill College, Cambridge, Institute of Materials, London, p. 458. 

The incorporation of rubber particles into a brittle polymer has a profound effect upon the mechanical properties as shown from the stress-strain curves in Fig. 5.66. This can be seen in Fig. 5.66(a) for high-impact polystyrene (HIPS) which is a blend of polystyrene and polybutadiene. The stress-strain curve for polystyrene shows brittle behaviour, whereas the inclusion of the rubbery phase causes the material to undergo yield and the sample to deform plastically to about 40% strain before eventually fracturing. The plastic deformation is accompanied by stress-whitening whereby the necked region becomes white in appearance during deformation. As will be explained later, this is due to the formation of a large number of crazes around the rubber particles in the material. 

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