High-density polyethylene Ziegler

Ethene HOPE, high-density polyethylene Ziegler-Natta, metallocene catalysis Piping, containers, plastic bags... 

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... 

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. 

Following the considerable commercial success of Ziegler-Natta polymerisation systems which made possible high density polyethylene, polypropylene, ethylene-propylene rubbers and a number of speciality materials, a considerable... 

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 produced by a low-pressure low-temperature process involving Ziegler-Natta catalysts. This creates low levels of branching and hence a high degree of crystallinity. 

A small number of companies use metal oxide catalysts, such as the example shown in Fig. 18.6, to make high density polyethylene. The polyethylene made with this catalyst generally has a narrower molecular weight distribution than high density polyethylene made with Ziegler-Natta catalysts. 

CP [Continuous polymerization] A continuous process for making high-density polyethylene, based on the Ziegler process but using a much more active catalyst so that de-ashing (catalyst removal) is not required. Developed by Mitsui Petrochemical Industries and upgraded into its CX process, which was first licensed in 1976. 

High-density polyethylene (HDPE) is a commodity chemical that is produced on a very large scale in one of two catalytic processes the Ziegler-Natta and the Phillips process. The latter accounts for about one third of all polyethylene. It uses a catalyst consisting of small amounts of chromium (0.2-1.0 wt% Cr) on a silica support, developed by Hogan and Banks at the Phillips Petroleum Company in the early 1950s [84,85]. 

In 1953, Ziegler in Germany, Phillips Petroleum Co. (USA) and Standard Oil Co. (USA) were able to discover the process of manufacturing polyethylene by avoiding the use of high pressure. The polyethylene so obtained is termed as the high density polyethylene. 

High density polyethylene was made by Ziegler in 1953 by using low pressure (2-4 atm) and temperature in the range of... 

Ziegler-Natta polymerization leads to linear unbranched polyethylene, the so-called high density polyethylene (HDPE), which is denser, tougher and more crystalline. By copolymerization with other alkenes it is possible to obtain linear low density polyethylene (LEDPE) with better mechanical properties than LDPE. Blends of LLDPE and LDPE are used to combine the good final mechanical properties of LLDPE and the strength of LDPE in the molten state. 

Sometimes a lower density polyethylene is made with both this type of catalysis or Ziegler-Natta. Branching is controlled by the addition of small amounts of 1-alkenes added to the ethylene. 1-Hexene would give a C4 branch, 1-octene a Ce branch, etc. If enough 1-alkene is used the polymer is called linear low-density polyethylene (LLDPE). It is made by a high-density polyethylene process but branching gives a lower density. 

In 1953 K. Ziegler and coworkers discovered a class of heterogeneous catalysts that allowed ethylene to be polymerized at low pressures and low temperatures (low-pressure polyethylene=high-density polyethylene=PEHD). 

Karl Ziegler, Max Planck Institute High density polyethylene... 

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