Many materials found in nature are polymers. In fact, the basic molecular structure of all plant and animal life is similar to that of a synthetic polymer. Natural polymers include such materials as silk, shellac, bitumen, rubber, and cellulose. However, the majority of polymers or plastics used for engineering design are synthetic and often they are specifically formulated or “designed” by chemists or chemical engineers to serve a specific purpose. Other engineers (mechanical, civil, electrical, etc.) typically design engineering components from the available materials or, sometimes, work directly with chemists or chemical engineers to synthesize a polymer with particular characteristics. Some of the useful properties of various engineering polymers are high strength or modulus to weight ratios (light weight but comparatively stiff and strong), toughness, resilience, resistance to corrosion, lack of conductivity (heat and electrical), color, transparency, processing, and low cost. Many of the useful properties of polymers are in fact unique to polymers and are due to their long chain molecular structure. These issues will be discussed at length in the next chapter. In this chapter, focus will be on general characteristics, applications and an introduction to the mechanical behavior including elementary concepts of their inherent time dependent or viscoelastic nature.
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