High density polyethylene ,

The extremely high molecular weight of HOPE combined with its very low coefficient of friction produces an excellent abrasion-resistant product which is resistant to gouging, scuffing, and scraping. 

Unival HDPE resins have been developed for blow-moulded bottles, drums, and other industrial containers. These resins have excellent rigidity, superior stress crack resistance, high impact and melt strength, and moderate swell. Unival resins are used to produce bottles up to 20 gallons in size used to contain household industrial chemicals, toiletries and cosmetics, health and medicinal aids, food products, and milk, juice, and water. 

High-density polyethylene (HDPE) bottles in multi-serve and single-serve sizes are used for juice drinks that appeal- mainly in the chill cabinet (short shelf-life distribution) section. This is probably more to do with the product process 

High density polyethylene (HDPE) is defined by ASTM D1248-84 as a product of ethylene polymerisation with a density of 0.940 g/cm or higher. This range includes both homopolymers of ethylene and its copolymers with small amounts of a-olefins. The first commercial processes for HDPE manufacture were developed in the early 1950s and utilised a variety of transition-metal polymerisation catalysts based on molybdenum (1), chromium (2,3), and titanium (4). Commercial production of HDPE was started in 1956 in the United States by Phillips Petroleum Company and in Europe by Hoechst (5). HDPE is one of the largest volume commodity plastics produced in the world, with a worldwide capacity in 1994 of over 14 x 10 t/yr and a 32% share of the total polyethylene production. 

The term HDPE embraces a large variety of products differing predominandy in molecular weight, molecular weight distribution (MWD), and crystallinity. 

Crystallinity and Density. Crystallinity and density of HDPE resins are derivative parameters both depend primarily on the extent of short-chain branching in polymer chains and, to a lesser degree, on molecular weight. The density range for HDPE resins is between 0.960 and 0.941 g/cm. In spite of the fact that UHMWPE is a completely nonbranched ethylene homopolymer, due to its very high molecular weight, it crystallines poorly and has a density of 0.93 g/cm.  

The number of branches in HDPE resins is low, at most 5 to 10 branches per 1000 carbon atoms in the chain. Even ethylene homopolymers produced with some transition-metal based catalysts are slightly branched they contain 0.5—3 branches per 1000 carbon atoms. Most of these branches are short, methyl, ethyl, and -butyl (6—8), and their presence is often related to traces of a-olefins in ethylene. The branching degree is one of the important stmctural features of HDPE. Along with molecular weight, it influences most physical and mechanical properties of HDPE resins. 

As with nearly all other polymers, HDPE resin is a collection of polymer chains of different lengths, varying from short, with molecular weights of 500—1000, to very long, with molecular weights of over 10 million. Relative contents of chains with different lengths (ie, the shape and width of MWD) depend mostly on production technology and on the type of catalyst used for polymerization. The MWD width of HDPE resins can be tailored to specific apphcations. 

High density polyethylene, shown in Fig. 18.2 a), consists primarily of linear hydrocarbon chains of the type shown in Fig. 18.1. We commonly abbreviate its name to HDPE. As with all other polymers, high density polyethylenes contain a distribution of molecular weights. The molecules have few, if any, branches. 

The initial published reports on high density polyethylene were dynamic mechanical studies, but before considering them it is necessary to compare the mechanical relaxations in isotropic material with those observed in unoriented low density polyethylene. From the schematic curve of tan S v. temperature f Fig. 7(b)] it can be seen that the p relaxation, which was ascribed to branch point mobility, is not present, and that the high temperature relaxation is frequently resolvable into a and a peaks. 

McCrum and Morris also compared torsion data for samples originally with an oriented surface layer and then with the layer removed. They did resolve the a peak, which they found diminished by removal of the oriented layer. Interpretation was made in terms of a two phase model of Iwayanagi involving lamellar boundary slip. It was concluded that the relaxation was caused by an inter-lamellar shear process. 

In the same year Takayanagi et reported measurements of complex Young s moduli in the 0 and 90 directions in both cold drawn and 

The absence of a crossover in cold drawn material was considered as caused by anisotropy of modulus in the amorphous regions, due to tension in intercrystalline tie molecules. 

The static measurements of Hadley et al. using a grade of Rigidex polymer showed considerable differences compared with low density material. Apart from shallow minima in 0 and G at low draw ratios the behaviour at room temperature appeared rather straightforward (Fig. 11). With increase of draw ratio Eq increased steeply, the torsion modulus increased slightly and 90 varied only a little V12 and vjs were generally not inconsistent with a value of 0-50, and seemed insensitive to the 

There are two main types of processes used for the production of high density polyethylene (HDPE) and both type 1 (narrow molecular weight distribution) and type 2 (broad molecular weight distribution) HDPE can be produced by these processes  

Besides these two processes, HDPE type 1 can also be produced by a solution process. 

The loop reactor processes and the gas phase reactor processes normally have only one reactor, while the STR processes typically have two or more reactors to reach a reasonable plant capacity and to have the flexibility to produce type 2 HDPE (broad molecular weight distribution) using a Ziegler catalyst. 

An overview of HDPE processes and parameters is shown in Table 3.5. 

Process type Reactor type Number of reactors Diluent Catalyst HDPE typel HDPE type 2 

Two distinct processes were developed almost simultaneously in the mid-1950s, based on Ziegler catalysts and on mixed oxide catalysts the Phillips process is the most widely employed of the latter. 

Reference has been made to injection moulding, which is a fair market for HDPE. Extruded pipe from HDPE and a tougher variant of lower density is widely used for natural gas distribution, particularly in cold climates where some failures of PVC (Chapter 8) have been encountered. HDPE has also been formed into mudguards for commercial vehicles, where the non-corroding 

and more recently, modified polyethylene of lower density, are used in gas distribution systems for many important reasons, including economic shaping, ability to withstand both the internal and external loads, good low-temperature impact properties and relative impermeability to the gases 

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United States The Ziegler route to polyethylene is even more important because it occurs at modest temperatures and pressures and gives high density polyethylene which has properties superior to the low density material formed by the free radical polymerization described m Section 6 21... 

Branching occurs to some extent and can be controlled. Minimum branching results in a high-density polyethylene because of its closely packed molecular chains. More branching gives a less compact solid known as low-density polyethylene. 

OLEFIN POLYTffiRS - POLYETHYLENE - HIGH DENSITY POLYETHYLENE] (Vol 17)... 

PH)PE [OLEFIN POLYTffiRS - POLYETHYLENE - HIGH DENSITY POLYETHYLENE] (Vol 17) -as paper contamnants [RECYCLING - PAPER] (Vol 21)... 

HDPE, high density polyethylene PP, polypropylene EVA, ethylene—vinyl alcohol SMC, sheet-molding compound ERP, fiber-reinforced plastic LDPE, low density polyethylene PE, polyethylene BMC, bulk mol ding compound TPE, thermoplastic elastomer. 

Table 6 shows the sales estimates for principal film and sheet products for the year 1990 (14). Low density polyethylene films dominate the market in volume, followed by polystyrene and the vinyls. High density polyethylene, poly(ethylene terephthalate), and polypropylene are close in market share and complete the primary products. A number of specialty resins are used to produce 25,000—100,000 t of film or sheet, and then there are a large number of high priced, high performance materials that serve niche markets. The original clear film product, ceUophane, has faUen to about 25,000 t in the United States, with only one domestic producer. Table 7 Hsts some of the principal film and sheet material manufacturers in the United States.

Structural Components. In most appHcations stmctural foam parts are used as direct replacements for wood, metals, or soHd plastics and find wide acceptance in appHances, automobUes, furniture, materials-handling equipment, and in constmction. Use in the huil ding and constmction industry account for more than one-half of the total volume of stmctural foam appHcations. High impact polystyrene is the most widely used stmctural foam, foUowed by polypropylene, high density polyethylene, and poly(vinyl chloride). The constmction industry offers the greatest growth potential for ceUular plastics. 

There are three basic types of polyethylene foams of importance (/) extmded foams from low density polyethylene (LPDE) (2) foam products from high density polyethylene (HDPE) and (J) cross-linked polyethylene foams. Other polyolefin foams have an insignificant volume as compared to polyethylene foams and most of their uses are as resia extenders. 

Plastic materials represent less than 10% by weight of all packagiag materials. They have a value of over 7 biUion including composite flexible packagiag about half is for film and half for botties, jars, cups, tubs, and trays. The principal materials used are high density polyethylene (HDPE) for botties, low density polyethylene for film, polypropylene (PP) for film, and polyester for both botties and films. Plastic resias are manufactured by petrochemical companies, eg. Union Carbide and Mobil Chemical for low density polyethylene (LDPE), Solvay for high density polyethylene, Himont for polypropylene, and Shell and Eastman for polyester. 

Formic acid is commonly shipped in road or raH tankers or dmms. For storage of the 85% acid at lower temperatures, containers of stainless steel (ASTM grades 304, 316, or 321), high density polyethylene, polypropylene, or mbber-lined carbon steels can be used (34). For higher concentrations. Austenitic stainless steels (ASTM 316) are recommended. 

The majority of spunbonded fabrics are based on isotactic polypropylene and polyester (Table 1). Small quantities are made from nylon-6,6 and a growing percentage from high density polyethylene. Table 3 illustrates the basic characteristics of fibers made from different base polymers. Although some interest has been seen in the use of linear low density polyethylene (LLDPE) as a base polymer, largely because of potential increases in the softness of the final fabric (9), economic factors continue to favor polypropylene (see OlefinPOLYMERS, POLYPROPYLENE). 

Flashspun high density polyethylene fabrics have been commercial since the 1960s however, this is a proprietary and radically different process of manufacturing a spunbonded fabric, more technically challenging to produce, and highly capital intensive. 

High density polyethylene. Linear low density polyethylene. 

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