Polymer high-density polyethylene

Second, in the early 1950s, Hogan and Bank at Phillips Petroleum Company, discovered (3,4) that ethylene could be catalyticaHy polymerized into a sohd plastic under more moderate conditions at a pressure of 3—4 MPa (435—580 psi) and temperature of 70—100°C, with a catalyst containing chromium oxide supported on siUca (Phillips catalysts). PE resins prepared with these catalysts are linear, highly crystalline polymers of a much higher density of 0.960—0.970 g/cnr (as opposed to 0.920—0.930 g/cnf for LDPE). These resins, or HDPE, are currentiy produced on a large scale, (see Olefin polymers, HIGH DENSITY POLYETHYLENE). 

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. 

Olefin polymers -high density polyethylene [OLEFIN POLYMERS - POLYETHYLENE - HIGH DENSITY POLYETHYLENE] (Vol 17) -m hydraulicfluids [HYDRAULIC FLUIDS] (Vol 13) -linear low density polyethylene [OLEFIN POLYMERS - POLYETHYLENE - LINEAR LOW DENSITY POLYETHYLENE] (Vol 17) -low density polyethylene [OLEFIN POLYMERS - POLYETHYLENE - LOW DENSITY POLYETHYLENE] (Vol 17) -polyethylene [OLEFIN POLYMERS - POLYETHYLENE - INTRODUCTION] (Vol 17) -polymers of higher olefins [OLEFIN POLYMERS - POLYMERS OF HIGHER OLEFINS] (Vol 17) -polypropylene [OLEFIN POLYMERS - POLYPROPYLENE] (Vol 17)... 

Yury V. Kissin, Mobil Chemical Company. Edison. NJ. htlp/Acwu. csxonmobilchcmical.com/. Polyethylene (under Olefin Polymers) High Density Polyethylene (under Olefin Polymers) Linear Low Density Polyethylene (under Olefin Polymers) and Polymers of Higher Olefins (under Olefin Polymers)... 

Figure 2.13 Examples of crystalline polymers high-density polyethylene (EIDPE), isotactic polypropylene (PP) and polyamide-6 (Nylon-6).

Figure 3-29. Effect of Glass Fiber Content on Deflection Temperature Under Load (DTUL) for Two Amorphous Polymers (Polycarbonate and Polystyrene) and Two Crystalline Polymers (High-Density Polyethylene and Nylon 6/6) (Typically, the optimum effect is reached at 20% glass fiber content, with the exception of nylons where 30% is the optimum.)...

Properties of semicrystalline thermoplastics are normally enhanced via reinforcing filler. However, the type and amount of such fillers would complicate any comparison. Hence, properties of various unfilled semicrystalline resins are compared shown in Tables 1.1-1.3. For comparison two commodity semicrystalline polymers, high density polyethylene (HDPE) and polypropylene (PP), are included in Table 1.1. Table 1.1 summarizes properties of HDPE, PP, POM, and polyesters. Table 1.2 contains properties of polyamides and SPS. Table 1.3 lists properties of the highly aromatic, semicrystalline polymers. Clearly, semicrystalline ETPs exhibit very broad performance enhancements over commodity semicrys-talhne polymers. 

HDPE [OLEFIN POLYMERS - POLYETHYLENE - HIGH DENSITY POLYETHYLENE] (Vol 17)... 

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). 

An independent development of a high pressure polymerization technology has led to the use of molten polymer as a medium for catalytic ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization at a high pressure (see Olefin polymers, low density polyethylene) have been converted to accommodate catalytic polymerization, both stirred-tank and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C (57,83,84). CdF Chimie uses a three-zone high pressure autoclave at zone temperatures of 215, 250, and 260°C (85). Residence times in all these reactors are short, typically less than one minute. 

The chemical iadustry manufactures a large variety of semicrystalline ethylene copolymers containing small amounts of a-olefins. These copolymers are produced ia catalytic polymerisation reactions and have densities lower than those of ethylene homopolymers known as high density polyethylene (HDPE). Ethylene copolymers produced ia catalytic polymerisation reactions are usually described as linear ethylene polymers, to distiaguish them from ethylene polymers containing long branches which are produced ia radical polymerisation reactions at high pressures (see Olefin POLYMERS, LOWDENSITY polyethylene). 

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene—propylene mbbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance (see Elastomers, ETHYLENE-PROPYLENE rubber). This is done by sequential polymerisation of homopolymer polypropylene and ethylene—propylene mbber in a multistage reactor process or by the extmsion compounding of ethylene—propylene mbber with a homopolymer. Addition of high density polyethylene, by polymerisation or compounding, is sometimes used to reduce stress whitening. In all cases, a superior balance of properties is obtained when the sise of the discrete mbber phase is approximately one micrometer. Examples of these polymers and their properties are shown in Table 2. Mineral fillers, such as talc or calcium carbonate, can be added to polypropylene to increase stiffness and high temperature properties, as shown in Table 3. 

HDPE melts at about 135°C, is over 90% crystalline, and is quite linear, with more than 100 ethylene units per side chain. It is harder and more rigid than low density polyethylene and has a higher melting point, tensile strength, and heat-defiection temperature. The molecular weight distribution can be varied considerably with consequent changes in properties. Typically, polymers of high density polyethylene are more difficult to process than those of low density polyethylene. 

Blends of isobutylene polymers with thermoplastic resins are used for toughening these compounds. High density polyethylene and isotactic polypropylene are often modified with 5 to 30 wt % polyisobutylene. At higher elastomer concentration the blends of butyl-type polymers with polyolefins become more mbbery in nature, and these compositions are used as thermoplastic elastomers (98). In some cases, a halobutyl phase is cross-linked as it is dispersed in the polyolefin to produce a highly elastic compound that is processible in thermoplastic mol ding equipment (99) (see Elastomers, synthetic-thermoplastic). ... 

The distribution of chlorine atoms along the polymer chain has been studied in great detail. The distribution in various functional types is shown in Table 4 (18). High density polyethylene chlorosulfonated to 35% G1 and 1% S has been found to contain only 1.7% highly active chlorines, ie, reactive to weak bases. AH of these are attributed to the chlorine in the sulfonyl chloride group and those in beta position to SO2GI. No vicinal chlorides groups were found (19). 

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