Low-density PE

PE produced by a high-pressure polymerization process (pressure 1000-3000 atm) using a free radical initiator is a highly branched material that contains both LCBs and SCBs. The polymer so produced is a low-density material (density up to about 0.925 g/cc) and is known as high-pressure low-density PE (HP LDPE). The LCBs are formed via intermolecular hydrogen transfer [19], whereas SCBs are formed by intramolecular hydrogen abstraction [16]. 

In all the compositions, the DCP-cured blends showed better properties than the corresponding unvulcanized samples. Choudhary et al. [30] further demonstrated the use of EPDM, chlorinated PE, chlorosulfo-nated PE, maleic anhydride modified polyethylene, and blends of epoxidized natural rubber-sulfonated EPDM as compatibilizers in NR-LDPE (low-density PE) blends. 

Geomembrane These liners chiefly provide impermeable barriers. They can be characterized as (1) solid waste containment hazardous landfill, landfill capping, and sanitary landfill (2) liquid containment canal, chemical/brine pond, earthen dam, fish farm, river/coastal bank, waste-water, and recreation (3) mining, leach pad and tailing ponds and (4) specialties floating reservoir caps, secondary containment, tunnel, erosion, vapor barrier, and water purification. Plastics used include medium to very low density PE, PVC, and chlorosulfonated PE (CSPE). (The Romans used in their land and road constructions what we call geomembrane.)... 

In addition to the two-phase TPEs, two new technologies have emerged. They are the metallocene-catalyzed polyolefin plastomers (POPs, the name given to Exxon s EXACT product line) and polyolefin elastomers (POEs, DuPont Dow Elastomer s ENGAGE), and reactor-made thermoplastic polyolefin elastomers (R-TPOs). These new types of TPEs are often called metallocene elastomers-TPEs (MEs-TPEs) [87]. The new POPs and POEs are essentially very low-molecular-weight-Unear low-density PEs (VLMW-LLDPE). These new-generation TPEs exhibit mbber-like properties and can be processed on... 

As part of a multi-technique investigation (see also discussion under mid-infrared spectroscopy later), Corrales et al. [13] plotted the carbonyl index for films prepared from three grades of polyethylenes a high-density PE (HDPE), a linear low-density PE (LLDPE) and a metallocene PE (mPE) (see Figure 5). In this study, the data trend shown in Figure 5 correlated well with activation energies derived from the thermal analysis, which showed that the thermal-oxidative stability followed the order LLDPE > mPE > HDPE, whereas the trend... 

As discussed earlier under Section 2.3, Carbonyl index, in one relatively recent comparison of the photo-oxidative and thermal (oven-aged) degradation behaviour of different polyethylenes, additive free grades of a metallocene (mPE), an HDPE and a linear low-density PE (LLDPE) were analysed by a combination of mid-IR spectroscopy, TGA and CL [13]. The mid-IR... 

Figure 7.11 Scanning electron microscopy (left) and transmission electron microscopy (right) images of low-density PE silica (top) and high-density PE silica (bottom). (Reproduced from ref. 8, with permission.)...

The key to the successful preparation of this new composite is the identification of a surfactant, PE-b-PEG, that is capable of stabilizing the emulsion and promoting the dissolution of the PE. Then submicrometre particles of low-density PE silica and high-density PE silica are synthesized by carrying out a silica sol-gel polycondensation process within emulsion droplets of TEOS-dissolved PE, at elevated temperatures (78 and 130°C for low- and high-density PE, respectively). 

Table 16.3. Permeabilities (in Barrer) for Oxygen andNitrogen Gases Thr0ugh a 70 pm Low-Density PE Film Fluorinated in the Absence (F2/N2) and Presence of a Reactive Gas (Fi/X)"...

High density PE (HDPE) is normally used for high-pressure pipes up to 20 bar for water and up to 7 bar for gas. Low density PE is used for lower pressure applications mainly in agriculture. Examples of applications are potable water up to 20 bar, gas up to 7 bar, surface water drainage systems, storm water drainage, cable ducting. 

Polyethylenes, PE, have been characterized by SEC since the mid-sixties and frequent problems with polystyrene gel columns have been reported ( ). The low density PE, LDPE, because of complexity of the molecular weight and branching distributions,... 

Commercial high density, medium density, low density and linear low density PE s (HDPE, MDPE, LDPE and LLDPE respectively) were used. Their properties are listed in Table III. ... 

Low density PE foam sheets having a thickness of 10 mm were cut from a block produced by compression moulding and their thermal conductivities over the temperature range from 24 to 50C determined. The evolution of the properties along the block was analysed and the cell structure, apparent mean cell diameter, anisotropy, mean cell wall thickness and relative fraction of polymer determined using quantitative image analysis and a previously reported model utilised to predict the thermal conductivity of the foams. 30 refs. 

A realistic RI5 model is used to estimate the relative probabilities of the formation of various types of short branches in ethylene-vinyl acetate copolymers that are rich in ethylene. Butyl is predicted to be the most common short branch in all of the copolymers examined, although it Is less common in the copolymers than in low-density PE. The major factor responsible for the suppression of the Rq4 backbiting intrachain radical transfer is the increased preference for trans states at the main chain bonds flanking the attachment site for an Isolated acetoxy side chain. 

The different available high pressure polymerisation processes of polyethylene (PE) yield LDPE (low density PE), LLDPE (linear low density PE) and copolymer features of the same. The various process variations have been developed during recent decades and introduced a number of well developed steps and devices to achieve safe and economical operating conditions at the very high reaction pressures of 1500 to 3000 bar. 

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