Tham khảo tài liệu 'fundamentals of polymer engineering part 16', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 15 Polymer Processing INTRODUCTION Thus far we have talked about how polymers are synthesized how they are characterized and how they behave as solids melts or in the form of solutions. Ultimately however it is necessary to convert the polymer into useful products. Typically these may be rods pipes films fibers or molded articles. Most frequently these materials are made from a single polymer. Increasingly though blends filled polymers and composite materials are used. It should be noted that even when a single polymer is used it is rarely a chemically pure material. Almost invariably it contains additives that act as dyes plasticizers antioxidants and so on. A variety of physical structures can result depending on the kind of polymer and additives used and also on how these materials are processed. Because the final structure obtained determines the physical properties of the product the process used has to be chosen with care. For inexpensive high-volume disposable items such as beverage containers or toys the most inexpensive process is used. The manufacture of high-value-added sophisticated items such as compact disks or optical lenses on the other hand requires a great deal of engineering and an intimate knowledge of the fundamentals of polymer behavior. In this chapter we discuss just three of the most common polymer processing operations-extrusion injection molding and fiber spinning. Because 630 Copyright 2003 Marcel Dekker Inc. Polymer Processing 631 most polymers are sold in the form of pellets an extruder is required to melt homogenize and pump the thermoplastic material. Although articles such as tubes rods and flat sheets can be made by extrusion an extruder is often coupled with other polymer processing machinery. A knowledge of extrusion is therefore a prerequisite for studying other polymer processing operations. Note that extrusion is a continuous operation. As opposed to this injection molding is a cyclic operation used to make a very wide .
