Polymer resin is considered a raw material, but sometimes a resin can be shaped into a finished product, such as polystyrene, or used as a coating, such as epoxy. Polymer resin that will be used to fabricate plastic products is formed into pellets or granules, which can be made into a variety of objects and products by heating, shaping, and cooling. Thermoplastic materials are heat set so they retain their shape. Plastic products may be finished by printing and embossing, such as for vinyl wallcovering; or coating with a wear layer of plastic, such as for vinyl flooring; or impregnating with resin, such as for plastic laminate. However, most plastics have pigment added in the solution phase and the resulting products do not require additional finish.
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The methods and forms most often used to shape plastic products used in buildings and interiors are discussed next.
Extrusions are used to make continuous elements such as moldings, sheets, or fibers.
Plastic resin pellets or granules are fed through a hopper into a heated barrel or chamber.
The pellets are melted into a solution and forced through the chamber by a rotating screw and exit through a die that creates the desired shape and size. For instance, plastics to be made into fiber will be extruded through a device that has small holes, resembling a shower head, to create filaments. When the solution is forced through a thin, narrow opening, the result is a polymer ribbon that can be stretched into a thin film or sheet. The extruded plastics are cooled by air or water.
Injection molding is used for plastic parts that have complex shapes. Plastic granules, chips, or pellets are melted in a separate container, and then injected or forced under external pressure into the cavity of a hollow cooled mold that is split when the plastic solidifies.
Rotational molding is used for objects with heavy walls and/or complex shapes. Melted plastic disperses over the inner surface of a rotating mold. The mold rotates, evenly distributing the plastic solution along the walls of the mold.