ABSTRACT
Polymers are shaped into useful objects using a variety of forming processes. In Chapters 13 and 14, we will study engineering aspects of polymer manufacturing in several of these processes, including calendering, compression molding, extrusion, fiber spinning, film blowing, injection molding, and spin coating, all of which are used to fashion polymers into objects with defined size, shape, and surface finishes. In many of these processes, a liquid or molten polymer is forced through channels under the action of external forces to transport a specified amount of the flowing material to one or more specially shaped molds. In the mold, the polymer must flow into even smaller openings to imprint a desired shape. Subsequent cooling of the mold or molten polymer exiting the mold solidifies the material and produces solid articles in specified shapes [1,2]. An important recent extension of this approach involves the use of printing technology to create intricate three-dimensional objects [3]. This so-called 3D printing methodology builds up a macroscopic object layer by printed layer. By using liquid polymer and colloidal suspension inks in a variety of chemistries, it is able to create objects with well-defined, spatially resolved material compositions not possible with conventional polymer forming processes. As with conventional polymer processing, however, the method takes advantage of the ability of polymers to flow in a specified manner under an applied load to control the thickness, spatial distribution, and chemical makeup of the finished article. The force required to fill a mold in a preset time or to achieve a specified flow rate in a print head nozzle or channel with known dimensions influences capacity and production rates in all polymer forming processes. It is therefore important to understand the fundamental physical variables that govern polymer resistance to flow.
