HDPE high density polyethylene

Some polyethylenes are supplied as so-called bimodal grades a mix of high- and low-molecular weight components in similar concentrations. They often show quite different processing characteristics compared to normal, monomodal (unmodified) polyethylenes. Bimodal grades PE often have higher die swell. 

Permeability by gases is significantly lower for HDPE compared to that for LDPE. As the permeability (P) for gases is determined as P = D X S, where D = diffusion constant and S = solubility coefficient, the units of permeability are expressed in the amount of gases (cm ) through a film of a unit thickness (mm) per unit area (cm ) per time (s) per pressure difference (cm Hg), that is (cm mm)/(cm s cm Hg). In these units, the permeability of HDPE and LDPE (at 25°G) for nitrogen is 1.4 and 

for helium 11 and 49, for oxygen 4 and 29, for GO2 3.6 and 126, respectively. At 30°G these values are as follows for nitrogen 2.7 and 19, for oxygen 11 and 55, for GO2 35 and 352 [7]. Obviously, a higher rate of penetration for oxygen would lead to a faster oxidative degradation of LDPE compared to HDPE. 

Linear PE (more crystalline) is more stable to oxidation than branched (more amorphous) PE. When the polymer is melted (140°G, or 284°F), oxidation rates are 

COMPOSITION OF WOOD-PLASTIC COMPOSITE DECK BOARDS 

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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. 

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 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). 

With a simple parison, the large-diameter sections of the botde have a thin wall and the small-diameter sections have a thick wad. Certain modifications of the die can control the thickness of the parison wad along its length, which results in a bottle with improved wad thickness distribution and better strength. High density polyethylene (HDPE) is the most common blow mol ding resin used to produce containers ranging in size from 30 cm to 200 L. 

In 1971 a metal-backed polyethylene acetabular cup was introduced. This cup provided an eccentric socket which was replaceable, leaving the metal and replacing only the polyethylene. Because of the success of this component, metal-backed high density polyethylene (HDPE) liner is standard for prosthetic acetabular components. Research confirms that metal-backing reduces the peak stresses in the bone cement, and that HDPE forms a successfiil articulating surface for the prosthetic joint. 

Nor is it tme that poly(ethylene terephthalate) (PET) and high density polyethylene (HDPE) packaging are hsted as 1 and 2 in the Society of the Plastics Industry (SPI) recycling coding system because they are the most recyclable. The numbers assigned to each plastic in the SPI coding system are purely arbitrary and do not redect the material s recyclabihty. 

High Density Polyethylene. High density polyethylene (HDPE), 0.94—0.97 g/cm, is a thermoplastic prepared commercially by two catalytic methods. In one, coordination catalysts are prepared from an aluminum alkyl and titanium tetrachloride in heptane. The other method uses metal oxide catalysts supported on a carrier (see Catalysis). 

Low pressure (0.1 to 20 MPa) and temperatures of 50 to 300°C using heterogeneous catalysts such as molybdenum oxide or chromium oxide supported on inorganic carriers to produce high density polyethylene (HDPE), which is more linear in nature, with densities of 0.94 to 0.97 g/cm. ... 

High Density Polyethylene (HDPE). This material has a density in the range 935-965 kg/m and is more crystalline than LDPE. It is also slightly more... 

High-pressure polymerization of ethylene was introduced in the 1930s. The discovery of a new titanium catalyst hy Karl Ziegler in 1953 revolutionized the production of linear unhranched polyethylene at lower pressures. The two most widely used grades of polyethylene are low-density polyethylene (LDPE) and high-density polyethylene (HDPE). Currently,... 

High-density polyethylene (HDPE) is produced by a low-pressure process in a fluid-bed reactor. Catalysts used for HDPE are either of the Zieglar-type (a complex of A1(C2H5)3 and a-TiCl4) or silica-alumina impregnated with a metal oxide such as chromium oxide or molybdenum oxide. 

See also high density polyethylene (HDPE) low density ... 

FIGURE 11.22 Variation of melt viscosity with shear rate for GR high-density polyethylene (HDPE). (From Yanez-Flores, G., Ramos De-Valle, F.F., and Rodriguez-Femandez, O.S., Proceedings of the Society of Plastics Engineers Annual Technical Conference, 1997, p. 381.)... 

Low-density polyethylene (LDPE) film for food packaging, etc. High-density polyethylene (HDPE) blow molded into bottles and containers... 

In this study, post-synthetic metal grafting was used to incorporate A1 into MCM-41 (Al-MCM-41-P), which was probably the first attempt at the catalytic degradation of waste plastics. The objective of this study was to investigate the kinetic aspect of high-density polyethylene (HDPE) over Al-MCM-41-P. 

The metal catalyzed production of polyolefins such as high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and polypropylene (PP) has grown into an enormous industry. Heterogeneous transition metal catalysts are used for the vast majority of PE and all of the PP production. These catalysts fall generally within two broad classes. Most commercial PP is isotactic and is produced with a catalyst based on a combination of titanium chloride and alkylaluminum chlorides. HDPE and LLDPE are produced with either a titanium catalyst or one based on chromium supported on silica. Most commercial titanium-based PE catalysts are supported on MgCl2. 

Chimassorb 944 Determination in Polypropylene, High Density Polyethylene (HDPE) and Low Density Polyethylene (LDPE) by the Total Nitrogen Content Analytical Method, Code No. KC65/1, Ciba-Geigy, Basel (1980). 

Materials. Low density polyethylene (LDPE) was obtained from Dow Chemical Co., PE 510. High density polyethylene (HDPE) was obtained from Phillips Chemical, Marlex 6001. Polypropylene (PP) was obtained from Exxon Corp., Exxon PP 8216. Di-t.-butylperoxide, 99%, (DtBP) was obtained from Polysciences. Gaseous hexafluoroacetone vras obtained from Nippon Mektron Ltd., Japan. 

When the modification reaction was attempted on high density polyethylene (HDPE), a very low level of incorporation was obtained (sample 9). The diminished reactivity probably results from a low solubility of HDPE in the reaction medium, limiting the reaction to the surface of a solid substrate. 

Figure 14.1 presents the main components of a typical in situ SVE system.910 Vertical extraction wells are installed inside the contaminated zone at appropriate distances from one another. The SVE wells are typically constructed of PVC pipe, with a screened interval, which is placed within the contaminated zone. The wells are connected to blowers or vacuum pumps, which induce a continuous airflow through the pores of the unsaturated zone. The soil surface is sometimes covered with an impermeable seal, made from high density polyethylene (HDPE) or bentonite clay for example, to prevent the vertical influx of air from the surface, which might cause short-circuiting problems, and promote horizontal gas flow through the contaminated area. The airstream, which contains the contaminant vapors, passes initially through an air-water separation unit to remove the entrained moisture and is then directed to the gas treatment unit, where the contaminants are thermally destroyed or removed by adsorption. 

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