High Density Polyethylene - HDPE - Chapter

The largest consumers of ethylene are the various types of polyethylene Low Density Polyethylene (LDPE), High Density Polyethylene (HDPE), and Linear Low Density Polyethylene (LLDPE). Chapter 15 gives detailed discussions of preparation of the various types of polyethylene. 

A major example of the second branched polymer type is the polyethylene that is made by free radical polymerization at temperatures of 100-300°C and pressures of 1,000-3,000 atm. The extent of branching varies considerably depending on reaction conditions and may reach as high as 30 branches per 500 monomer units. Branches in polyethylene are mainly short branches (ethyl and butyl) and are believed to result from intramolecular chain transfer during polymerization (described later in Chapter 5). This branched polyethylene, also called low-density polyethylene (LDPE), differs from linear polyethylene (high-density polyethylene, HDPE) of a low-pressure process so much so that the two materials are generally not used for the same application. 

Commercial linear polyethylene, the most commonly used type of plastic, was bom more than half a century ago with the accidental discovery at Phillips Petroleum Company that chromium oxide supported on silica can polymerize a-olefins.1 The same catalyst system, modified and evolved, is used even today by dozens of companies throughout the world, and it accounts for a large share of the world s high-density polyethylene (HDPE) supply, as well as some low-density polymers. The catalyst is now more active and has been tailored in numerous ways for many specialized modem applications. This chapter provides a review of our understanding of the complex chemistry associated with this catalyst system, and it also provides examples of how the chemistry has been exploited commercially. It is written from an industrial perspective, drawing especially on the commercial experience and the research of numerous scientists working at Phillips Petroleum... 

This chapter covers fundamental and applied research on polyester/clay nanocomposites (Section 31.2), which includes polyethylene terephthalate (PET), blends of PET and poly(ethylene 2,6-naphthalene dicarboxy-late) (PEN), and unsaturated polyester resins. Section 31.3 deals with polyethylene (PE) and polypropylene (PP)-montmorillonite (MMT) nanocomposites, including blends of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and high density polyethylene (HDPE). Section 31.4 analyzes the fire-retardant properties of nanocomposites made of high impact polystyrene (HIPS), layered clays, and nonhalogenated additives. Section 31.5 discusses the conductive properties of blends of PET/PMMA (poly (methyl methacrylate)) and PET/HDPE combined with several types of carbon... 

In the United States, about 20 percent or 81,0001 (90,000 tons) of plastic (polyethylene terephthalate PET) soft-drink bottles are being recycled. The high-density polyethylene (HDPE) milk bottles recycled amount to 36,000 t (40,000 tons) per year. See Chapter 12 for more details on the waste problem. 

Clearly, the combinations of resins and fillers and the resulting property variations are endless (see Fig. 6-2). The point is that each combination is in fact a new material with its own trade-offs. Some properties will be improved, others unchanged, and still others diminished from those of the basic unfilled plastic. In this chapter there is no relationship, direct or implied, between any plastic in terms of the space given it and its performance or the size of its market. The largest consumption of these plastics is low-density polyethylene (LDPE) formulations, at about 25 percent weightwise, followed by high-density polyethylene (HDPE), then polypropylene, polyvinyl chloride, and polystyrene. These together total about two-thirds of all plastic consumption. 

Lannders play a very important role in slnrry flows of plants. Cyclone underflow is directed to ball mills then to SAG mills by gravity. Flows in these circuits can cause tremendous wear if provision is not made to control speeds. Launders in plants are typically rnbber lined. Long-distance pipelines are mannfactnred of rubber-lined steel or extra-thick, high-density polyethylene (HDPE). Becanse of the importance of open launders, gravity flows, and drop boxes. Chapter 6 is dedicated to these complex flows. 

A similar study was carried out by Edwards and Shales [30, 31], but in their experiments they used a mixer with a rotor and stator in which the parallel rows of slots were replaced with staggered rows of hemispherical cavities, as described in Chapter 9. The 32 mm extruder with an axially split barrel for opening and screw removal after cooling was fed with 2 mm pellets of high-density polyethylene (HDPE) 50 wt% black and 50 wt% white. Screw speed was 50 rpm and the die pressure was 16 MPa. Photomicrographs of sections removed from the screw channel... 

This introductory chapter starts with the basics, assuming the reader is not famihar with polymers, let alone polyethylene. The chapter provides basic information about polymers in general, describes the structure and composition of polyethylene, and explains how UHMWPE differs from other polymers (including high density polyethylene [HDPE]) and from other materials (e.g., metals and ceramics). The concepts of crystallinity and thermal transitions are introduced at a basic level. Readers familiar with these basic pwlymer concepts may want to consider skipping ahead to the next chapter. 

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