SIDE-CHAIN-SUBSTITUTED VINYL THERMOPLASTICS

Oleh Designer3dmax 09 Apr, 2011 Posting Komentar

Polystyrene (PS, IPS, HIPS)

The catalytic or thermal polymerization of styrene yields general-purpose or crystal polystyrene (PS).19,20 The designation of ‘‘crystal’’ refers to its high clarity. PS is an amorphous polymer (atactic geometric configuration) and exhibits high stiffness, good dimensional stability,

moderately high heat deflection temperature, and excellent electrical insulating properties.However, it is brittle under impact and exhibits very poor resistance to surfactants and a wide range of solvents.

The three main categories of commercial PS resins are crystal PS, impact PS, and expanded PS foam.

Copolymerization of styrene with a rubber, polybutadiene, results in the rubber being grafted onto the PS. This impact-modified PS has increased impact strength, which is accompanied by a decrease in rigidity and heat deflection temperature. Depending on the levels of rubber, impact polystyrene (IPS) or high-impact polystyrene (HIPS) can be prepared. These materials are translucent to opaque and generally exhibit poor weathering characteristics.

PS finds wide use in styrofoam. Typically styrofoam is produced from expandable styrene (EPS) beads, which contain a blowing agent. When heated, the blowing agent vaporizes and expands the PS and forms a low-density foam. The density of the foam is controlled by the amount of blowing agent. Typical properties for PS, IPS, and HIPS appear in Table 5.

Uses. Ease of processing, rigidity, clarity, and low cost combine to support applications in toys, displays, consumer goods (television housings), medical (labware, tissue culture flasks), and house wares such as food packaging, audio/video consumer electronics, office equipment, and medical devices.

EPS can readily be prepared and is characterized by excellent low thermal conductivity, high strength to-weight ratio, low water absorption, and excellent energy absorption. These attributes have made EPS of special interest as insulation boards for construction (structural foam sections for insulating walls), protective packaging materials (foamed containers for meat and produce), insulated drinking cups and plates, and flotation devices.

Edward N. Peters

General Electric Company

Selkirk, New York

Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.

Edited by Myer Kutz