ABSTRACT
The term “plastics” refers to products made from polymers via different processes such as injection molding, extrusion, blow molding, compression molding, rotational molding, thermoforming, injection blow molding, etc. A given polymer can be used in several other product types such as adhesives, coatings, elastomers, fibers, etc. Polymers are referred to as plastic resins in the plastics industry. Polymers [1-4] are large molecular weight compounds or materials made up of recurring monomer or “mer” units. The term “poly” in polymer captures this essence of many or more than one as opposed to “mono” or single in monomers. The terms poly, mono, and mer are derived from Greek roots; mer is associated with “meros” meaning part. For example, the polymer polyethylene, the most popular plastic material in terms of consumption volume, is composed of recurring ethylene (monomer) units connected together primarily via covalent bonds:
n nCH =CH [CH CH ]2 2
polyethyle → − −
ne −
(1.1)
The designation (n) is the number of recurring monomer units in the polymer chain, and is referred to as the degree of polymerization. The degree of polymerization (n) determines the length of a given polymer chain. The weight of the recurring monomer unit or “mer” weight and the degree of polymerization determine the associated weight of the polymer chain. The degree of polymerization (n) for polyethylene is typically more than 10,000 [1,5,6]. A given polymer consists of chains-very long chains of varying lengths. This is a distinct feature or characteristic of thermoplastics and polymers and is referred to as polydispersity. This particular feature or characteristic can be physically visualized as a bowl of worms or spaghetti as per Figure 1.1.
