Powder recycling

Keywords FRP fine powder, recyclization, lightweight mortar, strengthening... 

Fig. 10.1 Droplet granulation system. (1) Powder, (2) granular product, (3) powder recycle,...

Polishing powders recycling, 200-202 Polycatenar LCs, 7-9, 13-14 Polyoxometalates (POMs), 108-111 Polyoxometalate-srrrfactant complexes for qrratemary arrrmonitrm cation, 109-111... 

NR composites and nanocomposites can be fabricated by three main techniques, namely latex compounding, solution mixing and melt blending. A variety of nanofillers, such as carbon black, silica, carbon nanotubes, graphene, calcium carbonate, organomodified clay, reclaimed rubber powder, recycled poly(ethylene terephthalate) powder, cellulose whiskers, starch nanocrystals, etc. have been used to reinforce NR composites and nanocomposites over the past two decades. In this chapter, we discuss the preparation and properties of NR composites and nanocomposites from the viewpoint of nanofillers. We divide nanofillers into four different types conventional fillers, natural fillers, metal or compound fillers and hybrid fillers, and the following discussion is based on this classification. 

Certain waxes are micro-pulverized to yield particle sizes smaller than a dispersed pigment particle. A micro-pulverized wax is stirred into ink as a powder. Recycled PTFE (Teflon) is supplied in small particle powder form. 

The economics of recycling PET are more favorable than recycling HDPE. To iacrease the recycling of HDPE, the separation of bottles made of these two plastics could be omitted and a mixture processed. Coarse, light-colored powders of the two polymers have been prepared by an experimental soHd state shear extmsion pulverization process (55). The powder has been successfully injection molded without pelletization. 

Triethylaluminum Preparation. Triethyl aluminum [97-93-8], C H Al, can be prepared by a two-step or a one-step process. In the former, aluminum [7429-90-5], Al, powder is added to recycled triethylaluminum and the slurry reacts first with hydrogen [1333-74-0], to produce diethylaluminum hydride [871-27-2], which in the second step reacts with ethylene [74-85-1], to produce triethylaluminum. In the one-step process,... 

Although it would be desirable to recycle laminate scrap, this has been difficult because of its thermoset nature. However, a 1993 patent (18) suggested a means whereby scrap consisting of cellulose, thermoset resins, and partially reacted resins can be ground to a powder which is used as a filler in a thermoplastic resin. The filled thermoplastic resin is then used for mol ding of various articles. 

Recycling. Thermosets are inherently more difficult to recycle than thermoplastics and thermosetting phenoHcs are no exception. However, research in this area has been reported, and molded parts have been pulverized and incorporated at 10—15% in new mol ding powders. Both German and Japanese groups had instituted this type of practice in 1992 (71,72) (see Recycling). 

Recycling. In more recent years, processes that can convert used carbide cutting tools and used tungsten alloy penetrators back into powdered form that can be used directly into new products have been developed. It is estimated that in 1996 ca 25% of cutting inserts used in the United States were recycled in this way. 

Residual traces of zinc are released during vacuum sintering of cemented carbides made with recovered powders. This can be troublesome when a buildup of zinc occurs in the furnace. Teledyne Advanced Materials further developed this process on a commercial basis by achieving zinc levels in the low ppm range (<30 ppm). The fact that the materials were vacuum-sintered in their original form where certain impurities are removed leads to lower impurity levels in the recovered powders. There is a slight oxidation or loss of carbon that must be compensated, otherwise the recycled powder is not in any way inferior to the original. 

The Sbddeutsche Kalkstickstoffwerke process at Trostberg uses powdered calcium carbide along with recycle product and calcium fluoride ia a rotary kiln at 1000—1100°C. The capacity of a unit is 25 t fixed nitrogen per day. The product passes to a rotary cooler and is granular (21). 

The dry powder process has several additional advantages over the wet process. For example, much less waste of enamel occurs because the dry over-spray is airborne and recycled in a closed system. No-pidde ground coats have broadened the apphcation of both wet-process and dry-process systems. These enamels are appHed over cleaned-only metal. Thus the problems of disposing of pickling acid wastes containing iron sulfates and nickel wastes are eliminated (see Metal surface treatments) (7). 

The turbo-tray dryer can handle materials from thick slurries [1 million (N s)/m (100,000 cP) and over] to fine powders. It is not suitable for fibrous materials which mat or for doughy or tacky materials. Thin slurries can often be handled by recycle of dry product. Filter-press cakes are granulated before feeding. Thixotropic materials are red directly from a rotary filter by scoring the cake as it leaves the drum. Pastes can be extruded onto the top shelf and subjected to a hot blast of air to make them firm and free-ffowing after one revolution. 

The economics seem to be better for systems where dry powdered fresh hme plus ground recycled hme is injected along with a relatively coarse spray which impinges on and dries out from the reagent, as described by Stouffer et al. [Hs EC Res., 28(1) 20 (1989)]. Witnum et al. [9th Ann. Pitt. Coal Prep. Util. Euv. Control Contractors Conf. (1993)] describes an advanced version of that system that has been further optimized to the point that it is competitive with wet hme-stone scrubbing for >90 percent flue gas desirffurization. 

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