PE polyethylene

Polyethylenes are probably among the best-known thermoplasts. Polyethylene is produced in various grades that differ in molecular structure, crystallinity, molecular weight, and molecular distribution. They are a member of the olefin family. The basic chemical structure is  

PE is produced by polymerizing ethylene gas obtained from petroleum hydrocarbons. Changes in the polymerizing conditions are responsible for the various types of PE. 

Physical and mechanical properties differ in density and molecular weight. The three main classifications of density are low, medium, and high. These specific gravity ranges are 0.91-0.925, 0.925-0.940, and 0.940-0.965. These grades are sometimes referred to as Type I, II, and III. 

All polyethylenes are relatively soft, and hardness increases as density increases. Generally, the higher the density, the better the dimensional stability and physical properties, particularly as a function of temperature. The thermal stability of polyethylenes ranges from 190T (SS C) for the low-density material up to 250°F/121°C for the high-density material. 

Industry practice breaks the molecular weight of polyethylene into four distinct classifications that are  

Polyethylene (PE) is the simplest polymer from a chemical standpoint. It is polymerized from ethylene monomer and consists of a carbon chain backbone with two hydrogen atoms bonded to each carbon atom (Fig. 1.1). Individual molecules, or chains, may be as long as hundreds to tens of thousands of carbon atoms. PE chains maybe very linear or may be branched, depending on how the polymer was synthesized. There are many synthesis techniques for polyethylene [1]. 

Polyethylene also named polythene (PE) with the basic ethylene molecule [—H C—CH, 

In the high pressure process, the high purity ethylene is compressed under pressures ranging from 150 to 300 MPa at 300°C in the presence of traces of oxygen acting as a catalyst. The polymerization reaction is very simple and can be written as follows  

Polyethylene is a thermoplastic material which varies from type to type according to the particular molecular structure of each type. Actually, several products can be made by varying the molecular weight (i.e., the chain length), the crystallinity (i.e., the chain orientation), and the branching characteristics (i.e., chemical bonds between adjacent chains). Polyethylene can be prepared in four commercial grades  

High-density polyethylene (HOPE) prepared with Ziegler-based catalysts have predominantly n-alkyl or saturated end groups. Those prepared with chromium-based catalysts have a propensity towards more olefinic end groups. The ratio of olefinic to saturated end groups for PE prepared with chromium-based catalysts is approximately unity. 

Hammond and co-workers [46] conducted an IR study of bond rupture of carbonyl and vinyl groups formed during plastic deformation of HDPE. 

The effects of minor proportions of PVC and PS in the polyolefins are quite dramatic. As little as 5% of PVC or PS in LDPE reduces the impact strength (toughness) of the latter by about 65%. This results from their presence as separate phases in the polyolefin matrix which leads to rapid crack propagation on impact. The effect of PP is very much less 10% of PP in LDPE reduced the energy absorbing capacity (toughness) of the matrix by only 1 % and 20% of PP reduced it by only 5%. The addition of block copolymers which act as compatibilisers or more correctly solid-phase dispersants (SPDs) for a second incompatible phase reduces the size of the heterogeneous domains and improves impact resistance. However, a considerable concentration ( 20%) of SPD is required, which unacceptably increases the cost in most cases. 

This problem can be partially overcome by high-shear mixing of a number of polymers by some of the procedures discussed in the next section. High shear mixing of polymers leads to the breaking and reformation of chemical bonds in the polymer backbone and to the in situ formation of block copolymers that act as SPDs. 

However, as a result of side-reactions of the above macroradicals with oxygen (Chapter 3, page 47 et seq.) the durability of polyblends made from recycled plastics is generally inferior to virgin polymers and they are normally used in downgraded, secondary apphcations. 

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A recent innovation in IR sample preparation is the use of disposable sample cards made from thin sheets of either polyethylene (PE) or polytetrafluoroethylene (PTFE). 

HDPE, high density polyethylene PP, polypropylene EVA, ethylene—vinyl alcohol SMC, sheet-molding compound ERP, fiber-reinforced plastic LDPE, low density polyethylene PE, polyethylene BMC, bulk mol ding compound TPE, thermoplastic elastomer. 

Polyethylene (PE) is a genetic name for a large family of semicrystalline polymers used mostiy as commodity plastics. PE resins are linear polymers with ethylene molecules as the main building block they are produced either in radical polymerization reactions at high pressures or in catalytic polymerization reactions. Most PE molecules contain branches in thek chains. In very general terms, PE stmcture can be represented by the following formula ... 

Succinic acid and succinic anhydride are sold in 25-kg net polyethylene (PE) bags having cardboard box protection for the anhydride, in 70-liter (50-kg net) fiber dmms, and in 55-gaHon (275-lb 125-kg net) dmms. The two products must be stored in a fresh, dry, ventilated area. Succinic anhydride must be carefully protected from moisture during transportation and storage to avoid hydrolysis to succinic acid. 

List the monomers of polyethylene (PE), polyvinyl chloride (PVC), and polystyrene (PS). 

Thin coatings consist of paints and varnishes, which are applied as liquids or powdered resin with a thickness of about 0.5 mm [e.g., epoxy resin (EP) [2]]. Typical thick coatings are bituminous materials [3] and polyolefins [e.g., polyethylene (PE) [4]], thick coating resin combinations [e.g., EP tar and polyurethane (PUR) tar [2]] as well as heat-shrinkable sleeves and tape systems [5]. 

Fig. 15. Dynamic stiffness images of alternating layers of polyethylene (PE) of two molecular weights at (a) 105 Hz and (b) 200 Hz. The contrast is due to changes in contact compliance (1/stiffness) of the nanoindenter probe in contact with each of the two polymers. The probe-sample respon.se (1/stiffness) as a function of frequency shown in (c) is consistent with the dynamic stiffness images.

In studying contact between films of polyethylene (PE) and polyethylene terephthalate (PET) bonded to quartz cylinders, they observed an increase in adhesion energy with contact time for a PE/PE pair, but not for PE/PET or PET/PET combinations. They interpreted this as evidence for the development of nanoscale roughness due to the interdiffusion of chains across the PE/PE interface [84],... 

The actual experimental moduli of the polymer materials are usually about only % of their theoretical values [1], while the calculated theoretical moduli of many polymer materials are comparable to that of metal or fiber reinforced composites, for instance, the crystalline polyethylene (PE) and polyvinyl alcohol have their calculated Young s moduli in the range of 200-300 GPa, surpassing the normal steel modulus of 200 GPa. This has been attributed to the limitations of the folded-chain structures, the disordered alignment of molecular chains, and other defects existing in crystalline polymers under normal processing conditions. 

Electron beam-initiated modification of polymers is a relatively new technique with certain advantages over conventional processes. Absence of catalyst residue, complete control of the temperature, a solvent-free system, and a source of an enormous amount of radicals and ions are some of the reasons why this technique has gained commercial importance in recent years. The modification of polyethylene (PE) for heat-shrinkable products using this technique has been recently reported [30,31]. Such modification is expected to alter the surface properties of PE and lead to improved adhesion and dyeability. 

TPEs from blends of rubber and plastics constitute an important category of TPEs. These can be prepared either by the melt mixing of plastics and rubbers in an internal mixer or by solvent casting from a suitable solvent. The commonly used plastics and rubbers include polypropylene (PP), polyethylene (PE), polystyrene (PS), nylon, ethylene propylene diene monomer rubber (EPDM), natural rubber (NR), butyl rubber, nitrile rubber, etc. TPEs from blends of rubbers and plastics have certain typical advantages over the other TPEs. In this case, the required properties can easily be achieved by the proper selection of rubbers and plastics and by the proper change in their ratios. The overall performance of the resultant TPEs can be improved by changing the phase structure and crystallinity of plastics and also by the proper incorporation of suitable fillers, crosslinkers, and interfacial agents. 

As a safety specialty, polyethylene separators are used to shut down run-away (shorting) Li cells by simply melting and creating a high-resistance barrier. The speed of resistance gains increases, approaching the melting point. Bilayers of polyethylene (PE) and polypropylene (PP) are even faster (Hoechst) (see also Chapter III, Sec. 10). 

V2O5-P205 (95 5, molar ratio) cathode and a lithium anode (Li/a-V205 cell) [1]. In this section, we describe safety test results for AA Li/a- V2Os cells. The AA cell we fabricated has a pressure vent, a Polyswitch (PS, Raychem Co., thermal and current fuse) and is composed of a spirally wound cathode sheet, a metallic Li-based anode sheet and a polyethylene (PE) separator [87]. 

Polyolefins Plastics such as polyethylene (PE), polypropylene (PP), and polybutylene (PB) that are derived from unsaturated hydrocarbons (also called olefins). 

PE. See polyethylene (PE) pendulum test method perfonnance of product design affecting predicting process and penneability of plastic PET. See polyethylene terephthalate (PET)... 

One modification of polyethylene (PE), which appears to be stable at high temperatures and pressures (see Sect. 3.2), also presents a pseudohexagonal packing and a disorderd chain conformation [59],... 

The present review is devoted to recent advances, mainly concerning the characterization of semicrystalline polymers, specifically polyethylene (PE) by means of microindentation hardness. The author has chosen to organize the chapter as follows ... 

The extrapolation of the MH values for g = 1 and g = 0.86 g/cm3 yields the limiting values for an ideal polyethylene (PE) crystal (Hc 150-180 MN m-2) and ideally PE amorphous matrix (Ha 1 MN m-2) respectively. It is noteworthy that the extrapolated value obtained for Hc in PE practically coincides with the theoretical value of S0 given in Table I. The experimental MH values given in the literature evidently correspond to materials with g largely deviating from unity. 

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