Lldpe

Linear structure Many side-chain branches Very short side-chain branches Crystalline structure

Figure 3. Molecular arrangements of HDPE, LDPE, and LLDPE.

A major application for PP is in packaging films. Commercial PP films are available in oriented and unoriented forms. Orientation can be achieved by stretching the film either uniaxially or biaxially during the film-forming process. Oriented PP film (OPP) has improved strength, stiffness, and gas-barrier properties; however, it is not heat sealable. Unoriented PP film has excellent clarity, good dimensional stability, and good heat-seal strength. Beside films, other major applications for PP are containers and closures.

Polystyrene

Polystyrene (PS) is an amorphous polymer that has excellent clarity. Solid PS is a clear, low-gas-barrier, hard, low-impact-strength (unless modified) material. It has a relatively low melting point (88°C) and can be readily thermoformed or injection molded into items such as food containers, cups, closures, and dishware. Because of its excellent clarity, PS film is often used as windows in paper-board boxes to display products (such as baked goods) that do not require a good gas barrier.

Expanded PS (EPS) of various bulk densities are manufactured by adding foaming agents in the extrusion process. EPS is used to make cups, bowls, plates, meat trays, clamshell containers, and egg cartons as well as protective packaging for shipping.

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