Handbook Of Polyethylene Structures Properties And Applications Pdf
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- LDPE vs HDPE: Properties, Production and Applications
ISBN 13: 9780824795467
It is a polymer, primarily used for packaging plastic bags , plastic films , geomembranes , containers including bottles , etc. Many kinds of polyethylene are known, with most having the chemical formula C 2 H 4 n. PE is usually a mixture of similar polymers of ethylene , with various values of n. It can be low density or high density : low density polyethylene is extruded [ verification needed ] using high pressure — atm and high temperature Kelvin , while high density polyethylene is extruded [ verification needed ] using low pressure 6—7 atm and low temperature — K.
Polyethylene is usually thermoplastic , but it can be modified to become thermosetting instead, for example in cross-linked polyethylene. Polyethylene was first synthesized by the German chemist Hans von Pechmann , who prepared it by accident in while investigating diazomethane.
The first industrially practical polyethylene synthesis diazomethane is a notoriously unstable substance that is generally avoided in industrial application was again accidentally discovered in by Eric Fawcett and Reginald Gibson at the Imperial Chemical Industries ICI works in Northwich , England. Because the reaction had been initiated by trace oxygen contamination in their apparatus, the experiment was difficult to reproduce at first.
It was not until that another ICI chemist, Michael Perrin , developed this accident into a reproducible high-pressure synthesis for polyethylene that became the basis for industrial low-density polyethylene LDPE production beginning in The landmark breakthrough in the commercial production of polyethylene began with the development of catalysts that promoted the Polymerization at mild temperatures and pressures.
The first of these was a chromium trioxide —based catalyst discovered in by Robert Banks and J. Paul Hogan at Phillips Petroleum. The Phillips catalyst is less expensive and easier to work with, however, and both methods are heavily used industrially. By the end of the s both the Phillips- and Ziegler -type catalysts were being used for high-density polyethylene HDPE production. In the s, the Ziegler system was improved by the incorporation of magnesium chloride.
The Ziegler- and metallocene-based catalysts families have proven to be very flexible at copolymerizing ethylene with other olefins and have become the basis for the wide range of polyethylene resins available today, including very low density polyethylene and linear low-density polyethylene.
Such resins, in the form of UHMWPE fibers , have as of begun to replace aramids in many high-strength applications. The properties of polyethylene can be divided into mechanical, chemical, electrical, optical, and thermal properties. Polyethylene is of low strength, hardness and rigidity, but has a high ductility and impact strength as well as low friction. It shows strong creep under persistent force, which can be reduced by addition of short fibers.
It feels waxy when touched. The commercial applicability of polyethylene is limited by its low melting point compared to other thermoplastics. Polyethylene consists of nonpolar, saturated, high molecular weight hydrocarbons. Therefore, its chemical behavior is similar to paraffin. The individual macromolecules are not covalently linked. Because of their symmetric molecular structure, they tend to crystallize; overall polyethylene is partially crystalline.
Higher crystallinity increases density and mechanical and chemical stability. Crystalline samples do not dissolve at room temperature. Polyethylene other than cross-linked polyethylene usually can be dissolved at elevated temperatures in aromatic hydrocarbons such as toluene or xylene , or in chlorinated solvents such as trichloroethane or trichlorobenzene. Polyethylene absorbs almost no water. The gas and water vapour permeability only polar gases is lower than for most plastics; oxygen , carbon dioxide and flavorings on the other hand can pass it easily.
PE can become brittle when exposed to sunlight, carbon black is usually used as a UV stabilizer. Polyethylene burns slowly with a blue flame having a yellow tip and gives off an odour of paraffin similar to candle flame. The material continues burning on removal of the flame source and produces a drip. Polyethylene cannot be imprinted or bonded with adhesives without pretreatment.
High strength joints are readily achieved with plastic welding. Polyethylene is a good electrical insulator. It offers good electrical treeing resistance; however, it becomes easily electrostatically charged which can be reduced by additions of graphite , carbon black or antistatic agents. Depending on thermal history and film thickness PE can vary between almost clear transparent , milky-opaque translucent or opaque. Transparency is reduced by crystallites if they are larger than the wavelength of visible light.
The ingredient or monomer is ethylene IUPAC name ethene , a gaseous hydrocarbon with the formula C 2 H 4 , which can be viewed as a pair of methylene groups — CH 2 — connected to each other. Acceptable contaminants include N 2 , ethane common precursor to ethylene , and methane.
Ethylene is usually produced from petrochemical sources, but also is generated by dehydration of ethanol. Polymerization of ethylene to polyethylene is described by the following chemical equation :. Ethylene is a stable molecule that polymerizes only upon contact with catalysts. The conversion is highly exothermic. Coordination polymerization is the most pervasive technology, which means that metal chlorides or metal oxides are used.
Another common catalyst is the Phillips catalyst , prepared by depositing chromium VI oxide on silica. Commonly used methods for joining polyethylene parts together include: .
Adhesives and solvents are rarely used because polyethylene is nonpolar and has a high resistance to solvents. Pressure-sensitive adhesives PSA are feasible if the surface chemistry or charge is modified with plasma activation , flame treatment , or corona treatment. Polyethylene is classified by its density and branching. Its mechanical properties depend significantly on variables such as the extent and type of branching, the crystal structure, and the molecular weight.
There are several types of polyethylene:. Because of its outstanding toughness and its cut, wear, and excellent chemical resistance, UHMWPE is used in a diverse range of applications. These include can- and bottle -handling machine parts, moving parts on weaving machines, bearings, gears, artificial joints, edge protection on ice rinks, steel cable replacements on ships, and butchers' chopping boards.
It is commonly used for the construction of articular portions of implants used for hip and knee replacements. As fiber , it competes with aramid in bulletproof vests. HDPE is defined by a density of greater or equal to 0. HDPE has a low degree of branching. The mostly linear molecules pack together well, so intermolecular forces are stronger than in highly branched polymers.
These catalysts prefer the formation of free radicals at the ends of the growing polyethylene molecules. They cause new ethylene monomers to add to the ends of the molecules, rather than along the middle, causing the growth of a linear chain. HDPE has high tensile strength. It is used in products and packaging such as milk jugs, detergent bottles, butter tubs, garbage containers, and water pipes. One-third of all toys are manufactured from HDPE.
In , the global HDPE consumption reached a volume of more than 30 million tons. PEX is a medium- to high-density polyethylene containing cross-link bonds introduced into the polymer structure, changing the thermoplastic into a thermoset. The high-temperature properties of the polymer are improved, its flow is reduced, and its chemical resistance is enhanced.
PEX is used in some potable-water plumbing systems because tubes made of the material can be expanded to fit over a metal nipple and it will slowly return to its original shape, forming a permanent, water-tight connection. MDPE is defined by a density range of 0. MDPE has good shock and drop resistance properties.
MDPE is typically used in gas pipes and fittings, sacks, shrink film, packaging film, carrier bags, and screw closures. LLDPE is defined by a density range of 0. LLDPE is a substantially linear polymer with significant numbers of short branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins for example, 1-butene , 1-hexene , and 1-octene.
Lower-thickness gauge films can be blown, compared with LDPE, with better environmental stress cracking resistance, but they are not as easy to process. LLDPE is used in packaging, particularly film for bags and sheets. Lower thickness may be used compared to LDPE. It is used for cable coverings, toys, lids, buckets, containers, and pipe. While other applications are available, LLDPE is used predominantly in film applications due to its toughness, flexibility, and relative transparency.
Product examples range from agricultural films, Saran wrap, and bubble wrap to multilayer and composite films. LDPE is defined by a density range of 0. LDPE has a high degree of short- and long-chain branching, which means that the chains do not pack into the crystal structure as well.
It has, therefore, less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. This results in a lower tensile strength and increased ductility.
LDPE is created by free-radical polymerization. The high degree of branching with long chains gives molten LDPE unique and desirable flow properties. LDPE is used for both rigid containers and plastic film applications such as plastic bags and film wrap.
The radical polymerization process used to make LDPE does not include a catalyst that "supervises" the radical sites on the growing PE chains. In HDPE synthesis, the radical sites are at the ends of the PE chains, because the catalyst stabilizes their formation at the ends.
Secondary radicals in the middle of a chain are more stable than primary radicals at the end of the chain , and tertiary radicals at a branch point are more stable yet.
Each time an ethylene monomer is added, it creates a primary radical, but often these will rearrange to form more stable secondary or tertiary radicals.
Addition of ethylene monomers to the secondary or tertiary sites creates branching. VLDPE is defined by a density range of 0. VLDPE is a substantially linear polymer with high levels of short-chain branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins for example, 1-butene, 1-hexene and 1-octene. VLDPE is most commonly produced using metallocene catalysts due to the greater co-monomer incorporation exhibited by these catalysts.
VLDPEs are used for hose and tubing, ice and frozen food bags, food packaging and stretch wrap as well as impact modifiers when blended with other polymers. Recently, much research activity has focused on the nature and distribution of long chain branches in polyethylene. In HDPE, a relatively small number of these branches, perhaps one in or 1, branches per backbone carbon, can significantly affect the rheological properties of the polymer.
Applicability and Fundamentals. A practical reference for all plastics engineers who are seeking to answer a question, solve a problem, reduce a cost, improve a design or fabrication process, or even venture into a new market. Applied Plastics Engineering Handbook covers both polymer basics — helpful to bring readers quickly up to speed if they are not familiar with a particular area of plastics processing — and recent developments — enabling practitioners to discover which options best fit their requirements. Each chapter is an authoritative source of practical advice for engineers, providing authoritative guidance from experts that will lead to cost savings and process improvements. Throughout the book, the focus is on the engineering aspects of producing and using plastics. The properties of plastics are explained along with techniques for testing, measuring, enhancing and analyzing them.
It is a polymer, primarily used for packaging plastic bags , plastic films , geomembranes , containers including bottles , etc. Many kinds of polyethylene are known, with most having the chemical formula C 2 H 4 n. PE is usually a mixture of similar polymers of ethylene , with various values of n. It can be low density or high density : low density polyethylene is extruded [ verification needed ] using high pressure — atm and high temperature Kelvin , while high density polyethylene is extruded [ verification needed ] using low pressure 6—7 atm and low temperature — K. Polyethylene is usually thermoplastic , but it can be modified to become thermosetting instead, for example in cross-linked polyethylene.
Descriptions: This text provides the basic history, molecular structure and intrinsic properties, practical applications and future developments of polyethylene.
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This text provides the basic history, molecular structure and intrinsic properties, practical applications and future developments of polyethylene production and marketing - including recycling systems and metallocene technology. It describes commercial processing techniques used to convert raw polyethylene to finished products, emphasizing special properties and end-use applications. The author is a leading scientist. The page chapter on characterization and testing is a book in itself, with good sense explanations of the underlying theory, test methodology, interpretation and precautions. Many clear diagramsaccompany the text.
LDPE vs HDPE: Properties, Production and Applications
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Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. Ujianto Published Materials Science. Polyethylene PE is the highest volume commodity polymer. The largest volume applications are flexible and rigid packaging. Key properties for packaging application materials include barrier, mechanical, and thermal properties. Material, energy and capit.
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Descriptions : This text provides the basic history, molecular structure and intrinsic properties, practical applications and future developments of polyethylene production and marketing - including recycling systems and metallocene technology. It describes commercial processing techniques used to convert raw polyethylene to finished products, emphasizing special properties and end-use applications. Thank you Structures : Properties , and Applications. H and book of Polyethylene : Structures : Properties , and Applications. This text provides the basic history, molecular structure and intrinsic properties, practical.
Classified as: Polymers and Plastics.
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