Polyolefin high-density polyethylene

Table I shows the production of different kinds of polyolefins [high-density polyethylene (HDPE), low-density polyethylene (LDPE), isotactic polypropylene (PP), and linear low-density polyethylene (LLDPE)] (6). Apart from LDPE (discovered by workers at ICI), which has a highly branched structure and is produced in free radical reactions at ethylene pressures of 1000-3000 bar (1 bar = 105 Pa), the other polyolefins are synthesized at far lower pressures and in the presence of catalysts (7).

BLENDS OF POLYOLEFINS (HIGH DENSITY POLYETHYLENE AND ISOTACTIC POLYPROPYLENE) WITH A SEMIFLEXIBLE LIQUID CRYSTALLINE POLYMER... 

Polyolefin blends are of critical importance to the success of the material. Ethylene propylene diene rubber (EPDM) immiscibly blends with PP as an impact modifier. It is the most common and most commercially utilised blend of polyolefins. High-density polyethylene (HOPE) can be added to this blend to achieve maximum toughness [11-13]. Applications include wire and cable insulation, automotive... 

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. 

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). ... 

In the mid-1950s a number of new thermoplastics with some very valuable properties beeame available. High-density polyethylenes produced by the Phillips process and the Ziegler process were marketed and these were shortly followed by the discovery and rapid exploitation of polypropylene. These polyolefins soon became large tonnage thermoplastics. Somewhat more specialised materials were the acetal resins, first introduced by Du Pont, and the polycarbonates, developed simultaneously but independently in the United States and Germany. Further developments in high-impact polystyrenes led to the development of ABS polymers. 

A somewhat different approach to the production of thermoplastic polyolefin rubbers has been adopted by Allied Chemical with their ET polymers. With these materials butyl rubber is grafted on to polyethylene chains using a phenolic material such as brominated hydroxymethyl phenol. The initial grades of these polymers, which were introduced commercially towards the end of the 1970s, had polyethylene butyl rubber ratios of 50 50 and 75 25. Both low-density and high-density polyethylene-based varieties were produced. 

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. 

Low- and high-density polyethylene, polypropene, and polymers of other alkene (olefin) monomers constitute the polyolefin family of polymers. All except LDPE are produced by coordination catalysts. Coordination catalysts are also used to produce linear low-density polyethylene (LLDPE), which is essentially equivalent to LDPE in structure, properties, and applications (Sec. 8-1 lc). The production figures given above for LDPE do not include LLDPE. The production of LLDPE now exceeds that of LDPE, with about 10 billion pounds produced in 2001 in the United States. (Copolymers constitute about one-quarter of all low density polyethylenes see Sec. 6-8b.)... 

The principal polyolefins are low-density polyethylene (ldpe), high-density polyethylene (hope), linear low-density polyethylene (lldpe), polypropylene (PP), polyisobutylene (PIB), poly-1-butene (PB), copolymers of ethylene and propylene (EP), and proprietary copolymers of ethylene and alpha olefins. Since all these polymers are aliphatic hydrocarbons, the amorphous polymers are soluble in aliphatic hydrocarbon solvents with similar solubility parameters. Like other alkanes, they are resistant to attack by most ionic and most polar chemicals their usual reactions are limited to combustion, chemical oxidation, chlorination, nitration, and free-radical reactions. 

PIB exhibits a comparatively low gas permeation (56). In Table 6.5, gas permeation coefficients of some polyolefins are given. Oppanol B 200 is compared with natural rubber, high density polyethylene) and low density poly(ethylene). Certain other Oppanol types have roughly the same permeability to gases as Oppanol B 200. 

Random ethylene copolymers with small amounts (4-10 wt-%) of 7-olefins, e.g. 1-butene, 1-hexene, 1-octene and 4-methyl- 1-pentene, are referred to as linear low-density polyethylene, which is a commercially relevant class of polyolefins. Such copolymers are prepared by essentially the same catalysts used for the synthesis of high-density polyethylene [241]. Small amounts of a-olefin units incorporated in an ethylene copolymer have the effect of producing side chains at points where the 7-olefin is inserted into the linear polyethylene backbone. Thus, the copolymerisation produces short alkyl branches, which disrupt the crystallinity of high-density polyethylene and lower the density of the polymer so that it simulates many of the properties of low-density polyethylene manufactured by high-pressure radical polymerisation of ethylene [448] (Figure 2.3). 

When other polyolefins (such as high-density polyethylene, polypropylene, and the ethylene copolymers) were introduced into commercial use they also were found to be unreceptive to inks and adhesives, but it became apparent that many of the techniques that were in use for treating low-density polyethylene could be applied also to these newer materials. 

The polyolefins are high-molecular-weight hydrocarbons. They include low-density, linear low-density, and high-density polyethylene, polyallomer, polypropylene, and polymethylpentene. All are break-resistant, nontoxic, and... 

In addition to the polyolefin blends designed for thermoplastic elastomer applications, a great deal of interest also has centered on other kinds of blends of polyolefins as has been reviewed recently (see chapter 21 of Ref. 10 by Plochocki). In a recent paper (84), we showed that blends involving polypropylene-high density polyethylene-low density polyethylene in various proportions and combinations exhibit additivity of tensile strength however, there are serious losses in ductility in some cases such that the blends are less ductile than either pure component. It is interesting to note, however, that these losses in ductility can largely be restored by addition of rather small amounts of an amorphous ethylene-propylene rubber (84). 

Polypropylene and polyethylene are perhaps the two most important polyolefin fibers. Polyethylene has a simple, linear chain structure consisting of a carbon backbone and small hydrogen side groups. Such a structure makes it easy to crystallize. There are three common grades of polyethylene low density polyethylene (LDPE), high density polyethylene (HDPE), and ultra-high molecular... 

It is well known from diffusion theory that different types of polymers have different diffusion behaviours. For example, the polyester type polymers like poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN) and polycarbonate (PC) as well as rigid poly(vinyl chloride) (PVC), which have a high glass transition temperature, are low diffusive polymers. The migration of potential contaminants in these polymers will result in low migration values. In contrast, polyolefins like high density polyethylene (HDPE), polypropylene (PP) or low density polyethylene (LDPE), which... 

A great proportion of plastics end its lifetime as a part of the overall solid waste stream where they represent roughly 10 wt%. The typical distribution of plastics in household wastes is shown in Figure 3.1 [3]. The main components are polyolefins low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE) and polypropylene (PP), accounting for about 67% of the total amount of plastic wastes. Other important components in plastic wastes are polystyrene (PS), poly (vinyl chloride) (PVC) and poly (ethylene terephthalate) (PET). 

When a block copolymer is blended with a homopolymer that differs in composition from either block the usual result is a three-phase structure. Miscibility of the various components is not necessarily desirable. Thus styrene-butadiene-styrene block copolymers are recommended for blending with high density polyethylene to produce mixtures that combine the relative high melting behavior of the polyolefin with the good low temperature properties of the elastomeric midsections of the block polymers. 

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