Polyethylene basic characteristics

The majority of spunbonded fabrics are based on isotactic polypropylene and polyester (Table 1). Small quantities are made from nylon-6,6 and a growing percentage from high density polyethylene. Table 3 illustrates the basic characteristics of fibers made from different base polymers. Although some interest has been seen in the use of linear low density polyethylene (LLDPE) as a base polymer, largely because of potential increases in the softness of the final fabric (9), economic factors continue to favor polypropylene (see OlefinPOLYMERS, POLYPROPYLENE). 

PESA can be blended with various thermoplastics to alter or enhance their basic characteristics. Depending on the nature of thermoplastic, whether it is compatible with the polyamide block or with the soft ether or ester segments, the product is hard, nontacky or sticky, soft, and flexible. A small amount of PESA can be blended to engineering thermoplastics, e.g., polyethylene terepthalate (PET), polybutylene terepthalate (PBT), polypropylene oxide (PPO), polyphenylene sulfide (PPS), or poly-ether amide (PEI) for impact modification of the thermoplastic, whereas small amount of thermoplastic, e.g., nylon or PBT, can increase the hardness and flex modulus of PESA or PEE A [247]. 

The relationship between chemical structures and their physical performance is one of the central topics of polymer physics. lUPAC has recommended a whole set of names to describe the detailed chemical structures of polymer chains and their derivatives. However, in our daily communication, people prefer to use the popular names of polymers reflecting their characteristic physical performances, such as high-density polyethylene (HOPE), foamed polystyrene, thermoplastic elastomers, liquid crystal polymers, conductive polymers, and polyelectrolyte. Such terminology allows us to comprehend quickly the basic characteristics of chemical structures responsible for their specific physical properties. 

Double bonds characterize the basic building blocks of the petrochemical business. Ethylene, for example, is the chemical compound used to make vinyl chloride, ethylene oxide, acetaldehyde, ethyl alcohol, styrene, alpha olefins, and polyethylene, to name only a few. Propylene and benzene, the other big-volume building blocks, also have the characteristic double bonds. 

This chapter introduces basic features of polyethylene, a product that touches everyday life in countless ways. However, polyethylene is not monolithic. The various types, their nomenclatures, and how they differ will be discussed. Key characteristics and classification methods will be briefly surveyed. An overview of transition metal catalysts has been included in this introductory chapter (see section 1.5) because these are the most important types of catalysts currently used in the manufacture of polyethylene. Additional details on transition metal catalysts will be addressed in subsequent chapters. 

Polyethylene foams are used extensively in buoyancy applications because of their excellent water-resistant properties. These basically closed-cell foams absorb less than 0.5% by voliune of water after being immersed for 24 hours. The low density of the foams also contribute to their buoyancy. The excellent dielectric characteristics of polyethylene are retained when it is expanded into foams. Polyethylene foam is a candidate for many electrical-material uses requiring good properties of dielectric strength, dielectric constant, dissipation factor, and volume resistivity (6). 

As a rigid thermoplastic, PLA has basic properties comparable with those of PET and PS (Table 3), but rather different from those of polyethylene (PE) and polypropylene (PP). PLA has many unique beneficial characteristics (Table 4), such as superb transparency, glossy appearance, high rigidity (which allows downgauging of thermoforming parts), printing effects, and twist retention. These special characteristics make PLA a perfect fit for some market sectors, such as fibers, disposable... 

The primary characteristics of a plastic material are largely determined by the original monomer. The name of the high-polymer is, therefore, used for the basic designation of plastics, such as polyethylene, polystyrene. 

Polyethylene data are shown in Fig. 2.23. At the equilibrium melting temperature of 416.4 K, the heat of fusion and entropy of fusion are indicated as a step increase. The free enthalpy shows only a change in slopes, characteristic of a first-order transition. Actual measurements are available to 600 K. The further data are extrapolated. This summary allows a close connection between quantitative DSC measurement and the derivation of thermodynamic data for the limiting phases, as well as a connection to the molecular motion. In Chaps. 5 to 7 it will be shown that this information is basic to undertake the final quantitative step, the analysis of nonequilibrium states as are common in polymeric systems. 

We must conclude from this set of typical data that the crystallite properties of the gel and that of the lamellae formed in dilute solution are the same. Hence, barring an unusual set of coincidences the basic crystallite characteristic of the gel should be of lamellar form for the linear polyethylenes when crystallized from homogeneous solutions. Thus we have at least one system where the crystaUization elation phenomenon does not involve a fringed micellar structure. 

In medical applications, it is of basic significance that the radiation absorption characteristics of the medium to be irradiated and that of the calorimetric absorber should be similar. Thus, calorimeters to that purpose have been constructed of water (Domen 1982), graphite (Petree and Lamperti 1967), polystyrene, polyethylene-carbon mixture (Milwy et al. 1958), and A-150 tissue-equivalent plastic (McDonald et al. 1976 Smathers et al. 1977). 

One of the basic operational characteristics of polymeric materials is shock durability in this connection structures on the basis of polyethylene of high density (PEHD) are investigated by a technique of shock tests on Sharpy. 

The volatile decomposition products of all the investigatedpolyolefins,as canbeseenfrom Table 5,possesspractically the same qualitative composition. Only the quantitative ratio varies for various pol5rmers. Thus, in four hours of oxidation of polypropylene at 150°C, 15 times as much acid is formed as in the oxidation of low-pressure polyethylene, 13 times as much formaldehyde, and 6 times as much aldehyde. Increasing the temperature leads to an increase in the yield of volatile products, the content of acids and carbonyl compounds mainly increasing. It is characteristic that the basic volatile destruction product is water. 

The films prepared by the electrophoretic sol-gel deposition are basically composed of monodispersed spherical particles, and have a lot of open spaces among these particles. If the open spaces are filled with some organic polymers, new type of inorganic-organic composite films with unique characteristics are expected to be obtained (Hasegawa, 1999). Silica particles are modified with 3-aminopropyltriethoxysilane (APS) and vinyltriethoxysilane (VTES). Smooth and crack-free films ca. 15 fim thick are obtainable when ASP-modified silica particles are used for cathodic deposition with addition of PEI. Thick films with reduced open spaces are obtained when VTES modified silica particles are co-deposited with polyethylene maleate. 

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