Polyolefins polyethylene, high-density

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... 

Polyethylene high density HOPE, medium density MDPE, low density LDPE, linear low density LLDPE, ultra high molecular weight UHMWPE Polyolefines II... 

The world production of polymers is about 260 million tons per year and half of the production is made of polyolefins (induding low-density polyethylene, high-density... 

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. 

This polymer is typical of the aliphatic polyolefins in its good electrical insulation and chemical resistance. It has a melting point and stiffness intermediate between high-density and low-density polyethylene and a thermal stability intermediate between polyethylene and polypropylene. 

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. 

The hyperbranched grafting chemistry used with polyolefin films and wafers was also extended to modification of 200 p.m diameter high density PE powder substrates [19]. However, because of the relatively high surface area of the 200 pm-diameter polyethylene powder (the measured BET surface area was... 

You should be somewhat familiar with the general production totals. More plastics are made each year, about 72 billion lb, than fibers or elastomers. The largest volume plastic is polyethylene, with combined low-, linear low-, and high-density types amounting to 30 billion lb. Linear low-density polyethylene is the rising star. These three polyethylenes serve different applications because of their different properties. The largest fiber market is polyester at 3.9 billion lb, but polyolefin is a close second and has had a rapid rise in production. The largest synthetic elastomer is styrene-butadiene at 1.9 billion lb. 

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.)... 

There are two types of polyethylene and polypropylene, called low density and high density. High-density polyolefins are made on a catalyst, while low-density polyolefins are made by free-radical polymerization. Characteristics of these polyolefins are summarized in Table 11-2. 

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. 

G. Polyolefins. The thermoplastic hydrocarbons polyethylene and polypropylene are flexible, inexpensive materials with good chemical resistance. Two types of polyethylene are available low density and high density. The former contains branched polymer chains which impart flexibility. The maximum usa-... 

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). 

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).

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... 

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