Polyethylene powder

In 1954 the surface fluorination of polyethylene sheets by using a soHd CO2 cooled heat sink was patented (44). Later patents covered the fluorination of PVC (45) and polyethylene bottles (46). Studies of surface fluorination of polymer films have been reported (47). The fluorination of polyethylene powder was described (48) as a fiery intense reaction, which was finally controlled by dilution with an inert gas at reduced pressures. Direct fluorination of polymers was achieved in 1970 (8,49). More recently, surface fluorinations of poly(vinyl fluoride), polycarbonates, polystyrene, and poly(methyl methacrylate), and the surface fluorination of containers have been described (50,51). Partially fluorinated poly(ethylene terephthalate) and polyamides such as nylon have excellent soil release properties as well as high wettabiUty (52,53). The most advanced direct fluorination technology in the area of single-compound synthesis and synthesis of high performance fluids is currently practiced by 3M Co. of St. Paul, Minnesota, and by Exfluor Research Corp. of Austin, Texas. 

Rotational Molding. Hodow articles and large, complex shapes are made by rotational mol ding, usuady from polyethylene powder of relatively low viscosity (57—59). The resin is in the form of a fine powder. A measured quantity is placed inside an aluminum mold and the mold is heated in an oven and rotated at low speed. The resin sinters and fuses, coating the inside of the mold. The mold is then cooled by water spray and the part solidifies, dupHcating the inside of the mold. 

Although the above applications consume over 90% of the polyethylene produced there are a number of other important end-uses. Filament for ropes, fishing nets and fabrics are an important outlet for high-density polyethylene powdered polymers are used for dip coating, flame spraying, rotational moulding and other outlets, whilst fabricated sheet is important in chemical plant. 

The process was originally developed in the 1940s for use with vinyl plas-tisols in liquid form. It was not until the 1950s that polyethylene powders were successfully moulded in this way. Nowadays a range of materials such as nylon, polycarbonate, ABS, high impact polystyrene and polypropylene can be moulded but by far the most common material is polyethylene. 

Because plants present chlorophylls and carotenoids simultaneously, it may be useful to separate both groups from each other in a laboratory or preparative scale in order to avoid contamination in further purification steps, mainly when they are prepared in large amounts. Clean-up procedures using an open column packed with absorbents such as alumina, magnesia, polyethylene powder, powdered sucrose, DEAE-Sepharose, starch, cellulose, or MgO HyfloSupercel are good approaches. MgO HyfloSupercel in a proportion of 1 1 or 1 2 is the usual adsorbent. Sucrose and cellulose are interesting as they do not alter the chlorophylls, but they are tedious to work with. 

Bridgwater, J., Attrition of High-Density Polyethylenes, Powder Tech., 50 243 (1987)... 

If for a given material, Vmf > 50 mm s1 (i.e., above the boundary shown in Fig. 5) andX< 0.001 m3 s kg-1 (i.e., below the boundary shown in Fig. 6), then dense-phase low-velocity slug-flow (Wypych, 1995a) is possible (e.g., mustard seed, polyethylene powder, 1000 pm sand, polyethylene pellets and granulated sugar). Note that dilute-phase also is possible. 

Fig. 2 Progress of hyperbranched poly(acrylic acid) graft formation on smooth gold films as measured by ellipsometry ( ) or on polyethylene powders as measured by titration ( ) of the supported - CO2H groups...

Scheme 4 Chemistry used to prepare hyperbranched polyfacrylic acid) grafts on polyethylene film, polyethylene powder or polypropylene wafers...

The hyperbranched grafting chemistry used with polyolefin films and wafers was also extended to modification of 200 p.m diameter high density PE powder substrates [19]. However, because of the relatively high surface area of the 200 pm-diameter polyethylene powder (the measured BET surface area was... 

Because SEM-AIA is often used to explain behavior under specific processing conditions, samples are prepared in the same size in which they are received. Coal samples with their included mineral matter are prepared for image analysis by mixing samples. of the dry coal with polyethylene powder (as a diluent) and molten carnauba wax in a volume ratio of 1 2 2. Pellets are then cut along the cylindrical axis to expose a vertical cross section of coal and mineral matter and polished using standard petrographic procedures. The surfaces are coated with 150 A of carbon to provide a conductive surface for SEM examination. 

Polyethylene powder, 118 Polyglutamates, tee Pteroyl-oligo-y-gluta-mates... 

MPa was obtained. The temperature was further elevated to 85°C and maintained at this temperature for 2 hours. At the end of polymerization the ethylene feed was stopped and the reactor quickly cooled, vented, and polyethylene powder isolated from hexane. Polymerization scoping reactions studies are provided in Table 1. 

Interest in the direct fluorination of polymers in Japan was established about the same time the initial work on direct fluorination from Rice University was announced. The Japanese workers Okada and Makuuchi(19) studied the fluorination of polyethylene powder and described the reaction as a fiery intense reaction, but were finally able to control it by dilution with nitrogen or helium and use of evacuated reaction vessels. The focus of their study was the rate of reaction. 

Figure 3. Polyethylene powder Figure 4. Suspension PVC (Solvic (Microthene FN 500) 229)...

Into a 5-liter autoclave, continuously stirred at a speed of 450 rpm, water, a dispersing agent, and polyethylene (powder or pellets) are introduced in the proportions set forth in Table II. After introduction of the initiator, the vinyl chloride is injected in such a quantity that, at the polymerization temperature, the vinyl chlorides partial pressure is lower than the vapor pressure of pure vinyl chloride at the same temperature. The vinyl chloride quantities compatible with this condition are easily determined by the absorption isotherms. When the pressure has dropped to at least half of its maximum value, the nontransformed vinyl chloride is removed. After filtering, washing, and drying, the product is collected. 

Amorphous polyimide powders prepared by dissolution/precipitation processes, can be used to toughen thermosetting polymers. Polyethylene powders are frequently used in low-shrink unsaturated polyester formulations. 

Figure 3.74 presents the air temperature inside the mold in a typical rotational molding cycle for polyethylene powders [7],... 

This development started with an observation of Pennings and Kiel (1965) that, when dilute solutions of polyethylene were cooled under conditions of continuous stirring, very fine fibres were precipitated on the stirrer. These fibres had a remarkable morphology a fine central core of extended CH2-chains, with an outer sheath of folded chain material. Electron microscopy revealed a beautiful "shish kebab" structure (see Fig. 19.16). Shish kebabs have also been observed in experiments without any stirring. For example, by washing polyethylene powder with xylene (Jamet and Perret, 1973) and by crystallising nylon 4 from a glycerol/water mixture (Sakaoku et al., 1968). 

Fig. 13 shows an example of how important it is to avoid contamination, and its influence on the final result of the analysis. The analytical procedure was a pre-concentration of aluminum by adsorption of its complex with an organic reagent (chrome azurol S) onto a polymeric material (polyethylene powder) packed into a column. Standard solutions were prepared and the procedure carried out after adopting stepwise precautions to avoid contamination. It can be seen that, only after adopting all steps, was the contamination controlled. The graph also shows that the lower the aluminum content in the sample the higher is the contribution of the contamination sources. 

Table 10. Aluminum extracted from polyethylene powder by action of different washing solutions by shaking 0.1 g PE in 10 mL solution for 24 h (blank discounted)...

Example 20.2 An approximation for the exothermic reaction that takes place during the explosion of polyethylene powder is (Hertzberg and Cashdollar, 1987)... 

Ethylene, isobutane, comonomer and catalyst are continuously fed to the loop reactor where polymerization occurs at temperatures lower than 100°C and pressures of approximately 40 kg/cm2 and residence times of approximately one hour. Ethylene conversion exceeds 97% per pass. Reactor effluent is flashed to separate the solid resin from the gaseous stream (3). Polyethylene powder is purged (4) with nitrogen to remove traces of hydrocarbons and pneumatically conveyed to the extrusion area for stabilization and pelletizing. The gaseous stream is compressed, purified and recycled back to the reactor. 

As shown in Fig. (8), fluorination reactions of polyethylene powders in the fluidized bed were slower compared to those of films in the plasma. This may be related to the greater surface area involved in the treatment of powders ( 0.15 m /g for powder compared to 0.03 m /g for film). Further, for treatment of powders, the overall extent of fluorination is lower compared to that of films - 52% F as opposed to 60% for films (Fig. 8). This is also supported by the C, spectra (Fig. 9) in which residual... 

High-density polyethylene powders for the coating of shirt interlinings. 

Catalysts prepared by supporting TiCl on silica or polyethylene powder and activated by organoaluminium compounds before polymerization have an activity which is 10 times as high as that of bulk d-TiCls x 0.3 AICI3 (Table 1). This increase is due to the increase of the number of ACj. As it has been shown the dispersed surface phase of TiCls is an active component of these supported catalysts. 

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