Rubber-toughened Polycarbonates

Lazzeri and Bucknall [131] have proposed that the pressure dependence of yield behaviour caused by the presence of microvoids can explain the observation of dilatation bands in rubber-toughened epoxy resins [132], rubber-toughened polycarbonate [133] and styrene butadiene diblock copolymers [134]. These dilatation bands combine in-plane shear with dilatation normal to the shear plane. Whereas true crazes contain interconnecting strands, as described in Section 12.5.1 above, dilatation bands contain discrete voids that, for rubber-toughened polymers, are confined to the rubber phase. 

The different basic mechanisms shown in Figure 19 are valid for other toughened polymers as well. For example, the mechanism in Figure 19 is decisive for rubber-toughened poly(vinyl chloride) (37), polycarbonate, 38, 39), poly(methyl methacrylate) 40, 41), and rubber-toughened epoxies 42, 43). 

Chang and Chou. Rubber-Toughening of Polycarbonate-Nylon Blends 281... 

D. J. Hourston, S. Lane, Toughened polyesters and polycarbonates, in Rubber Toughened Engi-... 

Nylon ("Zytel ST") n. A DuPont rubber-toughened nylon, identified by the initials standing for super-tough, claimed to be the most rugged engineering resin then (1977) available. It is superior to polycarbonate in impact strength, with notched Izod = 9J/ cm (17ft-lb//in.). 

Heterogeneous compatible blends of preformed elastomers and brittle plastics are also an important route for the development of blends of enhanced performance with respect to crack or impact resistance. Polycarbonate blends with preformed rubber particles of different sizes have been used to provide an insight into the impact properties and the fracture modes of these toughened materials. Izod impact strength of the blends having 5-7.5 wt% of rubber particles exhibits best overall product performance over a wide range temperature (RT to -40°C) [151-154]. 

Chung JYJ, Mason JP (1996) Toughened aromatic polycarbonate containing silicone rubber powder as molding composition. US Patent 5556908... 

Two families of transparent polycarbonate-silicone multiblock polymers based on the polycarbonates of bisphenol acetone (BPA) and bisphenol fluorenone (BPF) were synthesized. Incorporation of a 25% silicone block in BPA polycarbonate lowers by 100°C the ductile-brittle transition temperature of notched specimens at all strain rates silicone block incorporation also converts BPF polycarbonate into a ductile plastic. At the ductile-brittle transition two competing failure modes are balanced—shear yielding and craze fracture. The yield stress in each family decreases with silicone content. The ability of rubber to sustain hydrostatic stress appears responsible for the fact that craze resistance is not lowered in proportion to shear resistance. Thus, the shear biasing effects of rubber domains should be a general toughening mechanism applicable to many plastics. 

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