Polyethylene commercial aspects

Economic Aspects. Trimesic acid being a smaH-volume chemical, availabiUty is in polyethylene-lined fiber dmms in 34- and 136-kg quantities. Mesitylene [108-67-8] the raw material, is readily available, and oxidation to trimesic acid presents no problems. The market size is dictated by commercial uses. 

The best known aspect, and the first one to find commercialization in the direct fluorination area, was the fluorination of polymer surfaces. This Lagow-Margrave invention, trademarked Fluorokote, involved many types of polymeric materials in various forms e.g., polyethylene bottles, polypropylene objects, and rubber gloves. Polyethylene bottles are easily given fluorocarbon surfaces (>0.1 mm), and this has been commercialized. Air Products has at least 20 licenses for what is known as their Aeropak process and Union Carbide has a Linde Fluorination process as well. Applications in chemical, pharmaceutical, and cosmetic storage are widespread. 

The sheer size and value of the polyethylene industry ensure that there is continued research, progress, and development in catalysis, for their potential commercial impact. Although this whole subject is not within the scope of this chapter, we mention a couple of aspects of the progress, which offer the potential to impact this industry. In 1995, DuPont introduced work, carried out with them at the University of North Carolina—via the largest patent applicafion ever in the USA. They disclosed what are described as post-metallocene catalysts. These are transition and late transition metal complexes with di-imine ligands, which form part of the DuPont Versipol technology. Such catalysts create highly branched to exceptionally linear ethylene homopolymers and linear alpha-olefins. Late transition metals offer not only the potential for the incorporation of polar comonomers, which until now has only been possible in LDPE reactors, but also their controlled sequence distribution, compared to the random composition of free radical LDPE copolymers. Such copolymers account for over 1 million tons per annum [20]. Versipol has so far only been cross-licensed and used commercially by DuPont Dow Elastomers (a former joint venture, now dissolved) in an EPDM plant. 

Despite their versatility, both polyethylene and polypropylene are made only of carbon and hydrogen atoms. We are so used to these remarkable plastics that we do not often stop to ask how materials made out of such simple building blocks can have this extraordinary range of properties and applications. The answer to this question lies on how the carbon and hydrogen atoms are connected to define the molecular architecture or microstructure of polyolefins. Because microstructure plays such a relevant role in polyolefin properties, several characterization techniques have been specifically developed to measure different aspects of their molecular architectures. Section 2.1 classifies the different types of commercial polyolefins according to their microstructures, discusses several microstructural characterization techniques developed for these polymers, and demonstrates how they are essential to understand polyolefins. 

A more positive aspect of the chemical functionality of PHB is that the polymer can act as a processing acid for other polymers such as PVC and polyacrylonitrile. Both PHB homopolymer and the HB-HV copolymers reduce the gelation time and improve the surface finish of extrudates when blended with unplasticized PVC at the 1% level prior to processing. They function in much the same way as high molecular weight polyacrylates and chlorinated polyethylene, which are already used commercially in this application. In addition, the power required to melt-extrude polyacrylonitrile-based resins, such as the Barex range from Lonza AG, is much reduced by the addition of 1% PHB to the polymer. 

One of the most important aspects of any commercial polyethylene reactor is the time it takes to transition to a new product without producing off-grade polyethylene or keeping off-grade material to a minimum. 

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