General-purpose polystyrene brittleness

Rubber-modified polystyrene was the next logical evolution after general-purpose polystyrene. Very early on it was apparent that the Achilles heel of polystyrene was its inherent brittleness. Rubber-modified polystyrene is a two-phase system consisting of a dispersed rubber phase and a continuous polystyrene phase (or matrix). Impact-modified polystyrene was invented as early as 1927 by Ostromislensky [15] by addition of natural rubber either polymerized with styrene or blended in polystyrene. 

Polystyrene is a linear polymer that, in principle, can be produced in isotactic, syndiotactic, and atactic forms. The commercial product or general-purpose polystyrene is atactic and as such amorphous isotactic polystyrene is more brittle and more difficult to process than atactic polystyrene. It is therefore not of commercial interest. 

In practice, three different types of polystyrene are distinguished. The transparent and brittle polymer is called general purpose polystyrene (GPPS), the white, non-shiny but relatively flexible, rubber modified polystyrene is called (high) impact polyst5Tene (IPS or HIPS). Expandable or foam polystyrene (EPS) is ihe third group to distinguish here due to its different production techniques. 

There have been several examples of the unsatisfactory use of PS, because of the brittle nature of the material the application in toys is typical. Children frequently abuse their toys and thus a good impact performance is essential. General-purpose polystyrene (GPPS) breaks and exposes a sharp edge as an additional hazard. The advent of HIPS allowed the good features of PS to be retained, with the additional benefit of toughness at room temperature (the toughness falls dramatically below — 20°C), for only a small increase in... 

Brittle Fracture. In this type of failure the part fractures extensively without yielding. A catastrophic mechanical failure such as the one in the case of general-purpose polystyrene is observed. 

Toughened or rubber modified polystyrene blends are prepared by incorporating up to 10 percent by weight of poly butadiene or styrene-butadiene copolymer rubbers into the resin. The dispersed rubber particles decrease the plastic s brittleness by interrupting the crack propagation process. Unlike the unblended polymer, rubber modified polystyrene is translucent. The volume of rubber modified polystyrene made is roughly the same as that of general purpose polystyrene. 

Polystyrene homopolymer A clear, colorless, and brittle amorphous polymer (often called crystal polystyrene or general-purpose polystyrene )... 

The brittleness of polyvinyl chloride and polystyrene was decreased by blending with plasticizers or impact modifying polymers. The flammability of polystyrene and polyolefins was decreased by the addition of flame retardants and the Instability of polyvinyl chloride and polypropylene was reduced by the addition of stabilizers. — The strength and heat resistance of all of the general purpose plastics were Improved by reinforcing with fiberglass or graphite fibers. 

Copolymerization, which, in its objective, may be compared to alloying in metallurgy, is very useful for synthesizing polymer with the required combination of properties. For example, polystyrene is brittle, and polybutadiene is flexible therefore copolymers of styrene and butadiene should be more flexible than polystyrene but tougher than polybutadiene. The general purpose rubber SBR (styrene-butadiene rubber), the first practical synthetic rubber, is a copolymer of styrene and butadiene. 

The first step in the identification of polymers is a critical visual examination. While the appearance of the sample may indicate whether it is essentially a raw polymer or a compounded and processed item, learning about its form, feel, odor, color, transparency or opacity, softness, stiffiiess, brittleness, bounce, and surface texture may be important in the process of the identification of the polymer. For example, polystyrene, the general purpose polymer, is transparent and brittle, and produces a characteristic metallic tinkle when objects molded from it are dropped or struck. 

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