Polyethylene physical

Polyetiiylene (PE) is one of the lowest-cost polymers. There are various types of polyethylene denoted by their molecular weight. This ranges from low-density polyethylene (LDPE) through uTtrahigh-molecular-weight (UHMW) polyethylene. Physical properties, processability, and other characteristics of the polyethylene vary greatly with the molecular weight. 

An example of the dependence of polymer properties on catalyst activation temperature is shown in Table 5. Polymers of various MW were made with a Cr/silica catalyst activated at various temperatures. The polymers were then tested for environmental stress crack resistance (ESCR), a measure of their ability to resist chemical attack when polymer strips are placed under stress (bent). The test is conducted in the presence of hot surfactant, and the time to failure is monitored. Like most other polyethylene physical properties, ESCR is usually improved when the MW is increased. Therefore, comparisons of catalysts are usually made at similar melt indices (a surrogate for MW). A broader MW distribution... 

The identification of both short chain and long chain branches in polyethylene at concentrations of 1 per 10,000 carbon atoms has become feasible with the availability of improved probes and improved computer hardware/ software capabilities. Reviewed in this chapter are the methods and computations as well as the basic requirements for sound quantitative analyses namely, correct choice of solvent, a consideration of concentration effect on line widths and satisfying nuclear Overhauser effects and spin lattice relaxation time requirements. Finally, the NMR generated structural information is put to use in correlations with polyethylene physical properties and measurements of number average molecular weight. 

The development of the concepts of run number, average sequence lengths and triad distributions would be of little more than academic interest if they could not be usefully applied. The concept of run number is most valuable in a consideration of the effect of comonomer content versus branch length in affecting polyethylene density. The following section utilizes the run number in a correlation with a number of polyethylene physical properties. 

This is a long essay question which can be answered using any of the major modification techniques listed in the chapter on polyethylene modification. All information needed to compare and contrast two modification techniques, the changes in polyethylene physical and chemical properties, and an example of real world applications for that modified polyethylene are to be found for each ofthe techniques Sulphochlorination, Chlorination, Plasma Modification, Crosslinking - Chemical and E-Beam, and Graft Modification with Maleic Anhydride. 

Composition Acrylic acid modified high density polyethylene Physical Form Pellets... 

Coaposition Acrylic acid aodified high density polyethylene Physical Fora Pellets... 

Many of the tests described as useful in identification are also run routinely as quality controls on known polymers. Although infrared (IR) spectroscopy is extremely helpful as an identification tool, it is also applied to the measurement of crystallinity and branching in some polymers (notably polyethylene). Physical testing, molecnlar weight determination, and electrical testing have been discussed previously. The larger polymer producers perform almost all of these tests routinely. The smaller, more specialized laboratories of many fabricators and consumers may not possess all of the instruments needed for these tests. Independent laboratories will perform them on a consulting basis. Where the instruments are expensive or the test method is quite involved, recourse to independent laboratories may be wise. 

Although each production process yields ash that is essentially chemically equivalent, the various products differ ia physical properties and ia contaminants as shown ia Table 6. Hopper cars, pneumatic tmcks, supersacks, and multiwaH kraft bags with polyethylene liners are the usual shipping containers. 

The film tube is collapsed within a V-shaped frame of rollers and is nipped at the end of the frame to trap the air within the bubble. The nip roUs also draw the film away from the die. The draw rate is controlled to balance the physical properties with the transverse properties achieved by the blow draw ratio. The tube may be wound as such or may be sHt and wound as a single-film layer onto one or more roUs. The tube may also be direcdy processed into bags. The blown film method is used principally to produce polyethylene film. It has occasionally been used for polypropylene, poly(ethylene terephthalate), vinyls, nylon, and other polymers. 

Physical Stabilization Process. Cellulai polystyrene [9003-53-6] the outstanding example poly(vinyl chloride) [9002-86-2] copolymers of styrene and acrylonitrile (SAN copolymers [9003-54-7]) and polyethylene [9002-88-4] can be manufactured by this process. 

Extmsion of polyethylene and some polypropylenes is usually through a circular die into a tubular form, which is cut and collapsed into flat film. Extmsion through a linear slot onto chilled rollers is called casting and is often used for polypropylene, polyester, and other resins. Cast, as well as some blown, films may be further heated and stretched in the machine or in transverse directions to orient the polymer within the film and improve physical properties such as tensile strength, stiffness, and low temperature resistance. 

Cables are available in a variety of constmctions and materials, in order to meet the requirements of industry specifications and the physical environment. For indoor usage, such as for Local Area Networks (LAN), the codes require that the cables should pass very strict fire and smoke release specifications. In these cases, highly dame retardant and low smoke materials are used, based on halogenated polymers such as duorinated ethylene—propylene polymers (like PTFE or FEP) or poly(vinyl chloride) (PVC). Eor outdoor usage, where fire retardancy is not an issue, polyethylene can be used at a lower cost. 

Polyethylene. Traditional melt spun methods have not utilized polyethylene as the base polymer because the physical properties obtained have been lower compared to those obtained with polypropylene. Advances in polyethylene technology may result in the commercialization of new spunbonded stmctures having characteristics not attainable with polypropylene. Although fiber-grade polyethylene resin was announced in late 1986 (11,12), it has seen limited acceptance because of higher costs and continuing improvements in polypropylene resin technology (see Olefin POLYMERS, POLYETHYLENE). 

The prime installation method is mechanically fastened but fully adhered and ballasted appHcations can also be used. CSPE exhibits strong resistance not only to weathering but also to a broad range of chemicals and pollutants it is also inherently ozone-resistant. It can be produced in many colors and the sheet widths are typically 5—6.5 ft (1.5—1.65 m). The physical characteristics of a CSPE sheet have been described (17) (see Elastomers, SYNTHETIC-Cm OROSULFONATED POLYETHYLENE). 

Chlorinated Polyethylene. Chlorinating polyethylene under pressure results in a polymer having a chlorine content varying from 25 to 42%. The polymer requires the incorporation of carbon black and minerals for achieving good physical properties. The polymers handle like conventional polymers and can be mixed and processed on conventional mbber equipment. 

Table 17. Physical Properties of a Multilayer Barrier Film and a Polyethylene Film ...

Functional polyethylene waxes provide both the physical properties obtained by the high molecular weight polyethylene wax and the chemical properties of an oxidised product, or one derived from a fatty alcohol or acid. The functional groups improve adhesion to polar substrates, compatibHity with polar materials, and dispersibHity into water. Uses include additives for inks and coatings, pigment dispersions, plastics, cosmetics, toners, and adhesives. 

Nearly all polymeric materials require the addition of antioxidants to retain physical properties and to ensure an adequate service life. The selection of an antioxidant or system of antioxidants is dependent upon the polymer and the anticipated end use. A product that will not be exposed to the elements for a long period of time such as polyethylene grocery bags does not need a long term stabilizer polyethylenes used to iasulate communication cable must be stabilized for many years of service. 

Ozonc-rcsjstant elastomers which have no unsaturation are an exceUent choice when their physical properties suit the appHcation, for example, polyacrylates, polysulfides, siHcones, polyesters, and chlorosulfonated polyethylene (38). Such polymers are also used where high ozone concentrations are encountered. Elastomers with pendant, but not backbone, unsaturation are likewise ozone-resistant. Elastomers of this type are the ethylene—propylene—diene (EPDM) mbbers, which possess a weathering resistance that is not dependent on environmentally sensitive stabilizers. Other elastomers, such as butyl mbber (HR) with low double-bond content, are fairly resistant to ozone. As unsaturation increases, ozone resistance decreases. Chloroprene mbber (CR) is also quite ozone-resistant. 

These conclusions are further suppo] ted by expected physical properties of dried film of chlorosulfonated polyethylene from the different types of ... 

In order to improve the physical properties of HDPE and LDPE, copolymers of ethylene and small amounts of other monomers such as higher olefins, ethyl acrylate, maleic anhydride, vinyl acetate, or acryUc acid are added to the polyethylene. Eor example, linear low density polyethylene (LLDPE), although linear, has a significant number of branches introduced by using comonomers such as 1-butene or 1-octene. The linearity provides strength, whereas branching provides toughness. 

Although plastics materials may in principle be processed in a variety of physical states (in solution, in emulsion, as a paste or as a melt), melt processing is used almost exclusively with polyethylene. The main features to be borne in mind when processing the polymers are ... 

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