High-impact polystyrene rubber-toughened

An important class of copolymers made by chain copolymerisation is graft copolymers, synthesized in order to toughen brittle materials through inclusion of a rubber phase. Examples are the cases of styrenic copolymers called "HIPS" for High-Impact Polystyrene and ABS for Acrylonitrile-Butadiene-Styrene. Both are synthesized in two steps. 

D. Li, H. Xia, J. Peng, M. Zhai, G. Wei, J. Li, and J. Qiao, Radiation preparation of nano-powdered styrene-butadiene rubber (SBR) and its toughening effect for polystyrene and high-impact polystyrene, Radiat. Phys. Chem., 76(11-12) 1732-1735, November-December 2007. 

The technical and commercial success of high impact polystyrene (HIPS) and acrylonitrile-butadiene-styrene (ABS) has led to a widespread research program on the use of rubbers as toughening agents for plastics. There is now an impressive 11st of rubber-toughened polymers including both amorphous and... 

There are some additional applications of the theory which are presently under investigation. These are the effects of drawing on fibers for which the three-dimensional theory with transverse symmetry is applicable and the toughening mechanism in high impact polystyrene for which the flaw spectrum may be viewed as caused by the size, orientation, and spacing distributions of the rubber particles. 

Bucknall and Smith (17) concluded that crazing is the dominant mechanism to toughen high impact polystyrene and related polymers. One important function of the rubber particles is to serve as craze initiators and stabilizers in the glassy matrix. However Newman and Strella (18) concluded from optical microscope studies that cold drawing is responsible for toughness in ABS. 

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... 

Phase-separated polymers are of practical importance. An example is the way that a brittle polymer such as polystyrene may be toughened by the addition of an incompatible rubber that undergoes phase separation. Provided that this is done with attention to the interface between the two phases, a rubber-toughened high-impact polystyrene (HIPS) will result. 

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. 

The polystyrene/styrene/polybutadiene (PS/S/PBD) system occurs in the production of high impact polystyrene. The process for making toughened polystyrene as described by Moulau and Keskkula (1) starts with a rubber in styrene solution. As S is polymerized to PS, phase separation results in immediate formation of droplets of a PS phase. With further polymerization, the PS phase increases in volume until phase volumes are equal. At this point, phase inversion occurs—the dispersed PS phase becomes the continuous phase and the PBD phase becomes the disperse droplets. Complete conversion of S to PS yields the commercially important high impact polystyrene. 

In rubber-modified polymers like high impact polystyrene or acrylonitrile-butadiene-styrene (ABS) resins, the toughening effect of the dispersed rubber particles appears only in the presence of block or graft copolymers. These copolymers regulate the particle size of the rubber dispersion and achieve adhesion of the two phases. Hence, graft copolymers are of practical importance in polymer alloys. 

Kuboky and co-workers [40] used transmission electron microscopy (TEM) to study block and white crazes in high impact polystyrene (PS). They examined the mechanism of block craze formation and found that the rubber molecules were not necessarily diffused into the entire crazes. The length of the block crazes varied before they turned to white and in some cases only white crazes were generated from the rubber particles. TEM should thus be used with caution in examining stained rubber-toughened polymers to ensure that all crazes, including the white crazes, were considered for evaluation of the extent of the deformation behaviour [41]. 

These structures are illustrated in Figure 1.3. Through the leadership of Amos and others, polymer blends and grafts found uses as rubber-toughened plastics, which include high-impact polystyrene (HiPS) and acrylonitrile-butadiene-styrene (ABS) plastics. As further illustrated in Table 1.1, block copolymers containing a water-soluble block and an oil soluble block became important as surfactants through the work of Lunsted, while other block copolymers, composed of elastomer and plastic blocks, were useful as thermoplastic elastomers. 

The high-impact polystyrene shown in the upper left has polystyrene (a hard, glassy plastic) as the continuous phase, and so would be expected to be hard. The rubber domains have an occluded polystyrene cellular structure, which is really a phase-within-a-phase-within-a-phase. This complexity makes for excellent toughening and impact resistance. By contrast, the... 

HaU R A (1992) Computer modelUng of rubber-toughened plastics Part II Geometric models of high-impact polystyrene and calculation of interparticle distance parameters, J Mater Sci 27 6029-6035. 

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