Business and Technology of the Global Polyethylene Industry: An In-depth Look at the History, Technology, Catalysts, and Modern Commercial Manufacture of Polyethylene and Its Products

Chapter 5

Commercial Manufacture of Polyethylene

5.1 Introduction

Polyethylene is a semicrystalline, thermoplastic material classified as a synthetic organic polymer. Depending on manufacturing process conditions, polyethylene melts between approximately 110–135°C to form a non-Newtonian liquid that may be molded into a wide variety of shapes utilizing various fabrication techniques. One of the first questions many scientists and engineers ask when beginning a career in the polyethylene industry is: How can such a simple polymer, represented by the formula -(CH₂-CH₂)_n-, result in such a complex business? The answer lies in the enormous variety of molecular structures that are possible in the polymerization and, more importantly, copolymerization of ethylene with a wide variety of other 1-olefins.

Polyethylene is manufactured by either a high-pressure process or a low-pressure process and each process is discussed in detail in this chapter. However, the two methods may be briefly summarized as follows:

(a) Low-pressure process: There are a wide variety of low-pressure manufacturing processes with two common features, (1) all low-pressure methods require a transition metal catalyst in which ethylene is inserted into a transition metal-carbon bond to produce a polyethylene molecule, and (2) each transition metal active site undergoes a chain termination step that provides a continuous active site that produces additional polyethylene molecules. The low-pressure method was discovered ...