[...]... function of testing direction The size and perfection of spherulites influence certain physical properties II POLYETHYLENE ATTRIBUTES A Intrinsic Properties The various types of polyethylene exhibit a wide range of properties, the specific attributes depending on the molecular and morphological characteristics of the polyethylene resin Each variant of polyethylene has its own characteristics, and within... temperatures of various classes of polyethylene films generally have negligible haze Films are highly resistant to being punctured, cut, or torn Certain types of ionomers can exhibit a noticeable taste and odor 7 Cross-Linked Polyethylene The properties of cross-linked polyethylene depend very much on the base resin and the degree of cross-linking In general they exhibit properties smilar to those of the... distribution, and branching characteristics Manipulation of polyethylene prior to and during crystallization also influences its solid-state properties Polyethylene resins can thus be adapted to many end uses by virtue of both their physical properties and processing characteristics This section briefly outlines some of the relationships between the properties of and principal uses for the various types of polyethylene. .. predictable control of mechanical properties by the variation of polymerization conditions As a matter of course, improved control of the polymerization process led to the tailoring of specific grades of polyethylene to meet particular application needs With the opening of new markets and the improvement of material properties, the demand for polyethylene increased, and production facilities were expanded to meet... representative of the molecular weight and branching distribution The size of a polyethylene molecule is normally described in terms of its molecular weight All polyethylene resins consist of a mixture of molecules with a range of molecular weights The average molecular weight and the distribution of chain lengths comprising a polyethylene resin profoundly affect is properties The molecular weights of molecules... shrink-wrap, vapor barriers, agricultural ground cover, and greenhouse covers Low density polyethylene can be coated onto cardboard to create a waterproof and heat-sealable composite widely used in fruit juice and milk cartons Minor uses include wire and cable insulation and flexible pipe Injection- and blow-molded items made from this resin are flexible and reasonably tough, suiting them for such applications. .. elasticity, and clarity are desirable attributes Outlets for such products include meat packaging and stretch-wrap Ethylene-vinyl acetate is also used for coating cardboard and as wire and cable insulation The other main use of ethylene-vinyl acetate copolymer is as a component of adhesives 2 Commercial Development of Polyethylene I OVERVIEW The development of polyethylene as an integral part of everyday... within each type there is a spectrum of properties There is much overlap between the ranges of properties available for the different variants of polyethylene The relationships linking molecular structure and physical properties are discussed in Chapter 5 A numerical comparison of the different types of polyethylene, highlighting the typical ranges of some key solid-state properties, is presented in Table... the non-cross-linked varieties of polyethylene that are soluble in appropriate solvents at high temperature Cross-links greatly hinder crystallization, limiting the free movement of chains required to organize into crystallites Thus the density of a cross-linked polyethylene is lower than that of the polyethylene resin on which it is based B Molecular Composition Polyethylene resins consist of molecules... distribution may be (and often is) simplistically defined in terms of the ratio of two of the molecular weight averages The breadth and shape of the molecular weight distribution curve can vary greatly; distribution plots can exhibit multiple peaks, shoulders, and tails Molecular weight characteristics have a profound effect on the physical properties of polyethylene resins, affecting such properties as viscosity, . Morphology and Crystallization of Polyethylene 67 5. Properties of Polyethylene 123 6. Characterization and Testing 241 7. The Chemistry of Polyethylene 375 8. Orientation of Polyethylene 415 9. Use and. morphological features and thus with properties and end-use applications. Starting from a molecular de- scription of the principal variants of polyethylene, it constructs a unified picture of polyethylene s. Cross-Linked Polyethylene. Cross-linked polyethylene (XLPE) con- sists of polyethylene that has been chemically modified to covalently link adja- cent chains. A schematic representation of cross-linked